Mechanisms Shizuo
of soluble
Akira and Tadamitsu Osaka University,
A two
chain
model,
composed
subunits,
first indentified
revealed
in several
shared
by several
characteristic
other
Current
systems.
systems The
is now becoming cloning
Osaka, Japan
interleukin-6
cytokine
receptor
Common
may explain
signaling clearer
and signal transducing
receptor
system,
from
redundancy
the
due to the successful
in Immunology
has been
signal transducers
a functional
pathway
of several transcription
Opinion
Kishimoto
of ligand-binding
in the
of cytokines.
gene activation
mediators
receptor
to
molecular
factors.
1992, 4:307-313
rived growth factor and colony stimulating factor (CSF)-1. Molecular analysis of the c-kit gene in Wmutant mice has demonstrated deletions within the gene, or point muta tions in the tyrosine kinase domain.
Introduction
Growth and differentiation of hematopoietic and lym phoid cells are regulated by various kinds of soluble mediators called cytokines. Cytokines convey their sigThe complementary nature of the Wand SI mutations has nals into the cell nucleus through high affinity cell-surled to the hypothesis that the SZlocus encodes a ligand face receptors. Recently, many cytokine receptors have for c-kit. Using different approaches, three groups have been cloned and characterized, revealing the existence -defined-a new hematopoietic growth factor with a broad of a large family of cytokine receptors. Several transcript , tion factors, that may be nuclear targets in the complex- ’ range of biological activities [3*-8*]. Several lines of evdence have suggested that this factor is a l&and for c-kit. signal transduction cascade, have also been molecularly Zsebo et al. [5*] purified stem-cell factor (SCF) from the cloned. Although the pathways transmitting signals from supernatant of a buffalo rat liver-cell line, using an assay cytokine receptors to genes responsible for cell prolifersystem that measures high proliferative potential colonyation, growth inhibition, and cell differentiation are still a forming cells in post 5-FU bone marrow. Using a conmystery, during the past year several important findings tinuous mast-cell line as a target, and supernatant from a have provided insight into this black box. murine bone marrow stromal-cell ljner~jlliams et a!. [ 3.1 defined a new m‘ast-cell growth factor (MGF). Huang et al [7*] also used a mast-cell assay to define a factor they call KL (kit ligand). To unify nomenclature Witty renamed Novel growth factors involved in early this novel factor Steel factor (SIP) in his review ‘[91. Punhematopoiesis fied SLF binds to the c-kit receptor specifically, as shown by the binding of radiolabeled SLF to cells expressing a Steel factor: a ligand for c-&it functional c-kit receptor and the formation of a stable Mice with mutations at the dominant white spotting complex between SLF and the c-kit receptor. The gene ( W) and Steel (Sl) loci are characterized by a reduced encoding SLF maps near the Sl locus on mouse chromonumber of pluripotent hemopoietic stem cells, anemia, some 10 and is deleted or altered in the SZalleles of SZ a deficiency of mast cells, and defects in gametogenesis mutant mice [4*]. and pigmentation. Several experiments, including in vivo Although the isolated natural protein is soluble, the cell transplantation and in vitro co-culture between the SLF amino acid sequence has the features of a transtwo strains, have shown that the defect in Wmutant mice membrane protein: an amino-terminal signal peptide, is intrinsic in the hematopoietic stem cells, whereas the defect in SI mice is in the marrow stromal-cell environan extracellular domain, a transmembrane domain, and ment. Furthermore, it has been demonstrated that c-kit is a carboxy-terminal intracellular segment. Tissue-specific the product of the Wlocus [ 1,2]. The c-kit proto-oncoalternative splicing produces two types of SLF mRNA gene encodes a transmembrane tyrosine kinase receptor, [lo*]. Both encode a protein with a transmembrane domain, but one is synthesized as a membrane-bound closely related structurally to the receptors for platelet-deAbbreviations CIEBP-CCAATienhancer binding protein; CSF-colony-stimulating factor; G-CSF-granulocyte colony-stimulating factor; GM-CSF-granulocyte-macrophage colony-stimulating factor; IFN-interferon; IL-interleukin; KL-kit ligand; LIF-leukemia inhibitory factor; M-CSF-macrophage colony-stimulating factor; MCF-mast-cell growth factor; NK-natural killer; NKSF-natural killer cell stimulatory factor; SCF-stem-cell factor; S/-Steel; SLF-Steel factor; TNF-tumor necrosis factor; W--dominant white spotting. @ Current
Biology
Ltd ISSN 0952-7915
307
308
Lymphocyte
activation
and effector
functions
growth factor that can also be cleaved from the cell membrane by an unidentified protease to yield a soluble form, and the other preferentially produces the cell surface form as the sequence around this cleavage site is deleted. Soluble SLF is physiologically active and promotes the proliferation of purified hematopoietic stem cells, T-cell precursors, and B-lymphoid precursors. Soluble SLF by itself has modest effects on early myeloid and lymphoid cells but it synergizes dramatically with other factors such as granulocyte-macrophage colonystimulating factor (GM-CSF) and interleukin (IL)-7. In 1~iz10administration of soluble SLF effectively reverses the anemia and mast-cell deficiency of SUSP mice. However, it has been shown that soluble SLF has little ability to fulfil the normal biological functions of this growth factor in the intact organism. Some Sl mutant mice, in which the sequences encoding the transmembrane and intracellular domains of SLF are deleted, still produce a bioactive form of soluble SLF, implying that SLF expression on the cell surface has a critical biological role in processes of normal development [lo*]. In fact, in situ analysis of SLF during embryogenesis has shown that SLF is expressed in cells associated with both the migrating pathway and homing sites of melanoblasts, germ cells, and hematopoietic stem cells [11**,12. 1. These observations suggest that the kit-SLF system may have a role in cell migration and homing.
Interleukin-II
Another novel hematopoietic growth factor has been cloned from a bone marrow stromal-cell line [ 13.1. A pnmate bone marrow derived stromal-cell line, designated PU-34, supports long-term hematopoiesis by normal human or primate progenitor cells in culture. In addition to known growth factors including IL-~, IL-7, GM-CSF, macrophage colony-stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF), and leukemia inhibitory factor (LIF), the ILlcr stimulated PU-34 conditioned medium contained a novel factor that stimulated the proliferation of a mouse plasmacytoma-cell line, even in the presence of a neutralizing antiserum against human IL-~. A cDNA clone encoding the novel growth factor activity was isolated by expression cloning, on the basis of its ability to stimulate the proliferation of an 1~6 dependent mouse plasmacytoma-cell line. The cDNA contained a single long reading frame of 598 nucleotides encoding a predicted 199 amino acid polypeptide. The sequence of this cDNA was shown to have no homology with known cytokines and the product was designated IL-11. This cy tokine can also stimulate the T cell dependent development of Ig-producing B cells and act synergistically with IL-3 to shorten the GO period of early B-cell progenitors. Because IL-1 1 has many biological properties in common with IL-~, it is possible that these two cytokines may use a similar signal transduction pathway or may even share a common signal transducer.
Expression of cytokines
during
embryonic
development The potential role of cytokines during embryonic development and particularly their possible function in the development of pluripotent hemopoietic-stem cells were studied by several investigators. Murray et al. [14*] examined the expression of IL-3, IL-~, LIF and GM-CSF in the blastocyst prior to developmental commitment. Using polymerase chain reaction analysis, they detected mRNA transcripts for IL-~ and LIF, but not for GM-CSF or IL-3, in mouse blastocysts after 3.5 days of gestation, suggesting that IL-~ and LIF may regulate the growth and development of trophoblasts or embryonic stem cells, IJsing the embryonic stem-cell system, Schmitt et al. [ 15.1 correlated the expression of cytokines, their receptors, the P-globins, and the hematopoietic cell-surface markers throughout the time course of embryonic stem-cell differentiation with hematopoietic development. Of the genes analyzed, only SLF and c-kit were expressed throughout the time course, and were even found in undifferentiated embryonic stem cells. Genes encoding the majority of the other cytokines (Epo, CSF-1, IL-4, and IL-~) and their receptors underwent considerable transcriptional activation during embryonic stem-cell development. In most cases, the receptor genes were transcribed before the corresponding growth factors. However, IL-3 and GMCSF were not expressed during the first 24 days of embryonic stem-cell differendation, strongly suggesting that IL-3 and GM-CSF are not critical to early hematopoiesis. A similar conclusion was presented by recent studies from Burkert et al. [I6].
A model
for cytokine-receptor
interaction
Recent molecular cloning of cytokine receptors has shown that they belong to the superfamily characterized by a single hydrophobic membrane spanning region, an intracellular domain without kinase activity and an extracellular domain with four cysteine residues located in the amino terminal half and the Trp-Ser-X-TrpSer (where X is any amino acid), motif located close to the transmembrane domain. These features are shared by the receptors for IL-2 (p70), IL-3, IL-4, IL-5, IL-~, IL-7, G-CSF, GM-CSF, growth hormone, prolactin and erythropoietin and distinguish them from other types of cytokine receptors such as those belonging to Ig superfamily receptors or the tumor necrosis factor (TNF) receptor fam ily. Bazan [17**,18*] proposed a provocative structural model for cytokine-receptor interaction. A detailed analysis of receptor folds has revealed that the shared - 200 amino acid binding segments containing the four cysteine residues and the TrpSer-X-Trp-Ser box are composed of two structurally similar (j3 strand rich) - 100 residue domains. In addition, the individual domain is distantly related to a common -90 amino acid structure known
Mechanisms
as fibronectin type III domain. A predictive analysis of the generic domain fold in turn proposes that seven consensus P-strands form an antiparallel P-sandwich with a topology analogous to an Ig constant domain (Fig. 1). A binding crevice for cytokines is predicted between the linked Ig-like domains. This link between primitive adhesive structures and sophisticated binding receptors is analogous to the structural kinship between primitive Iglike adhesive molecules and antibddy frameworks. These Iindings have strong implications for the evolutionary emergence of an important class of regulatotv molecules from primitive adhesive modules,
of soluble
mediators
Akira
and
Kishimoto
intracytoplasmic portions, still associates with gp130 in the presence of IL-~, and mediates IL-~ function (Fig. 2). Thus, the IL-~ receptor system consists of two functionally different polypeptide chains: a ligand-binding chain, and a non ligand binding, but signal-transducing chain. might work as Taga et al. [19] predicted that -130 a signal transducer for other unknown ligand-receptor systems. It is also a member of the cytokine receptor family and was recently molecularly cloned [20-i]. In fact, the novel mechanism discovered in the IL-~ receptor system has been demonstrated in several other receptor systems. Interestingly, the recent cloning of the receptor for ciliaty neurotrophic factor [21-l has shown that it has a high degree of homology with the IL-~ receptor Together with its lack of a cytoplasmic domain, this suggests that this system may also use a signal transducer resembling gp130.
IL-6
gpl30
Fig. 2. IL-6 induced
association
of IL-6 receptor
and gp130.
Fig. 1. Predicted
tertiary structure of cytokine receptors. Two -100 residues domains are proposed to be related to a common -90 amino acid fibronectin type III domain. Seven consensus p-strands form an antiparallel p-sandwich with a topology analogous to an Ig constant domain. A binding crevice for cytokines forms between these linked Ig-like domains. c, cysteine; Type III, fibronectin type Ill.
A two-chain
system in cytokine
receptors
The IL-~ receptor has a relatively short intracellular domain that was shown not to be important for signal transduction. Taga et al [19] demonstrated that the IL6 signal is mediated through a membrane glycoprotein, gp130, associating with the receptor. These proteins become associated only after the receptor is stimulated by IL-6. This association takes place extracellularly, as the soluble IL-~ receptor, lacking the transmembrane and
A common GM-CSF,
associate
molecule
for 11-3,
and IL-5 receptors
The ability of IL-3 and GM-CSF to cross-compete for binding on cell types expressing both receptors suggests that they could share a common associate molecule. Using monoclonal antibodies raised against a murine multi-factor responsive immature mast-cell line (IC2), the genes encoding the low affinity mouse IL-3 receptor (AIC2A) and another protein (AIC2B) have been cloned [22,23]. Both proteins possess characteristics of the cy tokine receptor family but despite its 95% homology with AIC2A, AIC2B does not bind IL-3. Using the mouse IL-3 receptor cDNA as a probe, the human homolog KH97 was isolated [24*]. KII97 encodes a transmembrane protein of 120kD that has 56% homology with
309
310
lymphocyte
activation and effector functions
its murine counterpart. This protein alone does not bind any of the cytokines tested. However, when cells were cotransfected with the genes for low-aIhnity human GM-CSF receptor, a high-a&&y receptor for GM-CSF was formed. The human IL-3 and GM-CSF receptors may also share a common associate molecule because reciprocal inhibition of receptor binding by IL-3 and GM-CSF has been observed in human cells responsive to these two ligands [25]. In addition, recent data [26] suggest that the molecule shared by the human IL-3 and GM-CSF receptors could also be shared by the human IL-5 receptor. Taken together, these results suggest that KH97 may be a common associate molecule for the human IL-3, GM-CSF, and IL-5 receptors. Furthermore, co-expression of the human GM-CSF receptor with mouse AIC2B, but not AK%, resulted in human GM-CSF-dependent growth in a mouse IL2 dependent T-cell line CTLL2 that previously did not proliferate at all in response to human GM-CSF. This suggests that the protein encoded by the AIC2B cDNA is an associate molecule of the mouse GM-CSF receptor [ 27.1. It has also been shown that the low-affinity mouse IL-5binding protein forms a high-afhnity IL-5 receptor with AIC2B [ 28’1. Thus, it is likely that the high-affinity receptors for GM-CSF, IL-3, and IL-5 share a common associate molecule (KH97) in the human whereas the GM-CSF and IL-5 receptors share a common associate molecule (AIC2B) in the mouse.
Natural receptor
killer
cell stimulatory
factor W-12)
system
Natural killer (NK) cell stirnulatoxy factor (NKSF) is a B cell derived, heterodimeric cytokine that has pleiotropic activities, which include induction of interferon (IFN)-y secretion from NK and T cells, costimulation of peripheral blood lymphocyte proliferation and enhancement of the cytotoxicity of NK cells. The functional NKSF molecule (~75) consists of two subunits, p35 and ~40, that are inactive when expressed separately. The NKSF molecule binds to a cellular receptor of Mr 180000. Gearing and Cosman [29=] have reported that NKSF p40 shares extensive amino acid sequence homology to the entire extracellular domain of the human IL-~ receptor. In contrast, the amino acid sequence of the p35 subunit reveals no obvious similarity to other cytokines or receptors but secondary structure predictions showed a strong a-helical content, as has been found for many ligands of the cytokine receptor family. These data show an interesting analogy to the IL-GIL-~ receptor system depicted in Fig. 2. The p75 complex of NKSF might act in a similar fashion to the complex of IL&soluble IL-~ receptor and the cellular NKSF receptor might be functionally equivalent to gp130.
Tyrosine
phosphorylation
in cytokine
signaling
Although very little is known about intracytoplasmic signaling mechanisms of cytokines, tyrosine phosphotylation is thought to be involved in signal transduction
from several cytokines, including IL-2, IL-3, IL-4 and GMCSF. Tyrosine residues on a set of proteins are rapidly phosphorylated after the addition of these growth factors. Recently, a lymphocyte-specific tyrosine kinase, lck was reported to be involved in the IL-2 signaling pathway [ 30.1. The IL-2 receptor P-chain and p56lck formed a complex through specific association between the cytoplasmic domain of the IL-2 receptor P-chain and the tyrosine kinase catalytic domain of lck. Furthermore, IL-2 stimulation activated p56lck kinase activity. It is not clear, however, whether the IL-2 receptor p-chain itself is a critical substrate for p561$ or whether p56[$ once linked to the receptor, can activate other metabolic processes. Other members of the newly growing cytokine receptor family may also interact directly with a certain tyrosine kinase(s).
Cytokines
and transcription
factors
NF-xB
Cytokines convey signals to the interior of cells for cellular proliferation, differentiation, and other activities. The cell responds to such external stimuli by turning on a plethora of transcription factors, which may in turn intluence the transcription of many genes. Recent studies have revealed that IWxB is involved in transcriptional regulation of many genes encoding cytokines and their receptors (Fig. 3) [31]. The NF-XB was originally characterized as a kappa Ig enhancer DNA-binding protein. Binding sites for NI-xB are present in the regulatory regions of certain cytokine genes (including TNF-a, lymphotoxin, IL-~, IL-8 and IFN-P genes), the IL-2 receptor gene, class I and II histocompatibility antigen genes, several acute phase response genes, and several viral enhancers including human immunodeficiency virus. NF-xB is a complex of two proteins of 50 and 65kD. It pre-exists in the cytoplasm of most cells in an inactive form, complexed to an inhibitor, termed IxB. Stimulation by a number of agents such as phorbol my&ate acetate, lipopolysaccharide, and TNF-a results in the dissociation of the IxB-NFxB complex, probably by phosphorylation of IxB. Subsequently, the NI-xB heterodimer migrates to the nucleus where it binds to its cognate DNA-binding sites and activates transcription, The genes encoding the p50 and the p65 subunits of NI-xB were recently cloned and found to have a high level of homology to the proto-oncogene c-rel and the Drosophila maternal. effect gene dorm1 within a large domain required for DNA binding and dimerization [32**,33**,34*]. The product of the full-length cDNA-encoding p50 is 105 kD. ~105 shows no DNA-binding capacity and contains six repeats of the ankyrin consensus sequence in its carboxy terminus. Ankyrins are known to constitute a family of proteins that regulate interactions between a variety of membrane structures and the cytoskeleton. p50 is produced from the ~105 precursor by an unidentilied proteolytic mechanism, which removes the ankyrin repeat domain from the DNA-binding subunit. The p50 homodimer and p50-p65 heterodimer specifically bind
Mechanisms
NF-kB
of soluble
mediators
Akira
and Kishimoto
ing al-acid glycoprotein, angiotensinogen, complement C3 and serum amyloid A as well as several cytokines including IL-2, IL-8 and G-CSF. Poli et al. [38*] have cloned and characterized a cDNA coding for IL6 dependent DNA binding protein, which is responsible for IL6 mediated induction in several acute-phase proteins. The IL6 dependent DNA binding protein exhibited a very high level of homology with human NF-1~6, suggesting that it.is the rat homolog of NI-IL6. Furthermore, their observation that both the DNA-binding activity and the transactivating capacity of IL6 dependent DNA binding protein are induced in hepatoma cells by treatment with IL-~, implicates the gene encoding the IL6 dependent DNA binding protein (NI-1~6) as a nuclear target of IL-~ and its product as a mediator of the IL6 dependent transcriptional activation. The characterization of the mechanisms through which NI-IL6 is activated will help to elucidate the nuclear events in the IL-~ signal transduction pathway.
Conclusion Many cytokines and their corresponding receptors have been cloned. Comparison of the primary structures of these cytokine receptors has revealed the existence of the Fig.3. From cytokine receptors to activation of transcription facnew cytokine receptor family, suggesting that members tors. may have evolved from a common ancestral adhesive to DNA, whereas p65 cannot bind by itself. An IxB-like!? , ’molqztie. A two-chain model (ligand-binding and signal transducing subunits), first identified in the IL-~ recepmolecule has also been cloned [ 35.1. The cDNA encodes. tor system, has been found in several other cytokine a protein of 317 amino acids with one domain containreceptor systems and several transcription factors that ing five tandem repeats of the ankyrin motif, similar to may be nuclear targets in cytopne signaling pathways the precursor of the p50 subunit. The presence of these have recently been identified. Despite recent progress repeats in IxB may indicate that IxB keeps NF-xB in the in the cytokine field, signal transduction by cytokine cytoplasm by linking the complex to cytoplasmic strucreceptors is still poorly understood. However, research tures through these ankyrin repeats. concentrated on identification of kipa6es or molecules as Recently the gene encoding the xB binding subunit sociated with cyt&ne receptors or transcription factors, (plOO), and also p49 by altemativee splicing was cloned will soon provide a better understanding of this area. [36*]. ~100 is most closely related to the ~105 subunit of NK)cB. p49 can form a heterodimer with p65 and act in synergy to simulate the xB-binding genes. c- relalso binds Note added in proof to the xB site and forms a heterodimer with the p50 subunit. A functional distinction between rebp50, p4’+p65 Recent work has reinforced the hypothesis that the highand p50-p65 heterodimers awaits further investigation. affinity receptors for GM-CSF, IL-3, and IL-5 share a com-
NF-IL6
A recently cloned transcription factor, termed NI-Iti may also be a pleiotropic mediator of many inducible genes (Fig. 3). NI-IL6 was initially identified as a nuclear factor binding to the IL-1 responsive element of the IL-~ gene. Direct cloning of human NF-IL6 revealed its homology with CCAAT/enhancer binding protein (C/EBP), a liver enriched transcription factor [37*]. C/EBP and W-IL6 recognize the same nucleotide sequence, but exhibit distinct patterns of expression. C/EBP is expressed in liver and adipose tissues, whereas NF-IL6 is produced in many cell types in response to a variety of stimuli including lipopolysaccharide, IL-l, TNF and IL-~. Recently, several studies showed that C/EBP-like factors may be involved in the expression of several acute-phase proteins includ-
mon associate molecule (KH97) in the human, whereas the GM-CSF and IL-5 receptors share a common associate molecule (AIC2B) in the mouse [3!+41]. Gearing et al. [42] cloned the receptor for LIF, which is highly similar to gp130. Also the Iinding that the high-affinity receptor for LIF and oncostatin M share gp130, a signal transducer for IL-~, has been recently presented [43].
References
and recommended
reading
Papers of particular interest, published within the annual period of review, have been highlighted as: . of special interest .. of outstanding interest 1.
EN, F&IN M4 HOUSMANDE: The Dominant-white Spotting (W) Locus of the Mouse Encodes the c-kit Protooncogene. Cell 1988, 553185-192.
GEISSLER
311
312
LvmDhocvte activation and effector functions 2.
CHABOT B, STEPHENSONDA, CAHPMANVM, BESMERP, BERNSTEIN A: The Proto-oncogene c-kit Encoding a Transmembrane
Tyrosine Kinase Receptor Nature 1988, 355:m9.
Maps to the Mouse W Locus.
WILUAMSDE, EISENMANJ, BAIRD A, RAUCH C, NESS KV, MARCH CJ, PARK IS, MARTIN U, M~CHLZUKIDY, BOSWELLHS, ET AL: Identllication of a Ligand for the c-kit Proto-Oncogene. Cell 1990, 63:167-174. Reports the purification and biological activities of a novel MGF. 3. .
4. .
COPEIAM) NG, GILBERTDJ, CHO BC, DONOVAN PJ, JENKINSNA, COSMAN D, ANDERSON D, LYMANSD, WILLIAMS DE: Mast CeU
Growth Factor Maps Near the Steel Locus on Mouse Chromosome 10 and is Deleted In a Number of Steel Alleles. Cell 1990, 63:175-183. This paper documents that the MGF gene maps near S1 in the distal region of mouse chromosome 10 and is deleted in a number of Slalleles. 5. .
ZSEBO KM, WYWCH J, MCNIECE IK, Lu HS, SMITH DA, KARKARE SB, SACHDEVRK, YUSCHENKOFFVN, BIRKETT NC, WILUAMS LR, ET AL: Identification, Purification and Biological Characterl-
zation of Hematopoietic Stem Cell Factor from Buffalo Rat Liver-conditioned Medium. Cell 1990, 63:195-201. Describes the purification and biological characterization of a novel growth factor, SCF. 6. .
.
PAUL SR, BENNET F, CALVETI’JA, I KELIEHERK, WOOD CR, DA, YANG O’HARARM, LFARY AC, SISLEY B, CWUCSC, WILLIAMS Y-C: Molecular Cloning of a cDNA Encoding Interleukin 11, a Stromal Cell-derived Lymphopoietic and Hematopoietic Cytokine. Proc Natl Acad Sci U S A 1990, 87:7512-7516. Reports molecular cloning of a novel interleukin derived from a stromal cell line.
13. .
14. .
MURRAY R, LEE F, CHIU CP: The Genes for Leukemia Inhibitory Factor and Interleukin-6 are Expressed in Mouse Blastocysts Prior to the Onset of Hemopoiesis. Mol Cell Biol 1990, 10:4953-4956. This paper documents that both IL-~ and LIF genes, but not IL-3 or GM-CSF genes, are expressed in blastocysts in vivo.
SCHM~ RM, BR~NNSE, SNODGRASSHR: Hematopoietic Development of Embryonic Stem Cells in Vitro: Cytokine and Receptor Gene Expression. Genes Dev 1991, 5:72%740. These authors suggest that IL-3 and GM-CSF are not critical to early in vitro hematopoietic development and that the expression of SLF, Epo, IL-4 and IL-~ may be important during the early stages of embryonic stem-cell differentiation. 15. .
16.
ZSEBO KM, WILLL~MSDA, GEISSIER EN, BROUDY VC, MARTIN FH, A%INS HL, HSU R-Y, BIRKETT NC, OKINO KH, MURIXXK
DC, ET AL: Stem Cell Factor is of the Mouse and its Ligand for Receptor. Cell 1990, 63:21%224. Reports the molecular cloning of mouse vide biological and physical evidence that receptor. 7.
Matsui et al. [ ll**] and also suggest involvement of SLF and c-kit in the organization of the neural tube and brain.
Encoded at the Sl Locus the c-kit Tyrosine Kinase SCF. The authors also proSCF is a l&and for the c-kit
HUANGE, NOCKAK, BEIER DR, CHU T-Y, BUCK J, IAHM H-W, WELLNERD, LEDERP, BESMERP: The Hematopoietic Growth
Factor KL is Encoded by the SZ Locus and is the Ligand of the c-kii Receptor, the Gene Product of the W Locus. Cell 1990, 63~225235. A description of the molecular cloning of a mouse hemopoietic growth factor, KL
BAZANJF: Structural Design and Molecular Evolution of a Cytukine Receptor Superfamily. Proc Nat1 Acud Sci USA 1990, 87~6934-6938. This paper describes the predictive tertiary structure of a cytokine receptor superfamily, and presents implications for the evolutionary emergence of the cytokine receptor superfamily from primitive adhesive modules. 17. ..
18. BAZANJF: Haemopoietic Receptors and Helical Cytokines. . Immunol To&y 1990, 11:350-354. ReporS a structural model for cytoine-receptor interaction. 19.
8.
ANDERSON DM, LVMANSD, BAIRD A, WIGNALL JM, EISENMAN J, RAUCHC, MARCHCJ, BO~WEXLS, GIMPELSD, COSMAND, WILLIAMS DE: Molecular Cloning of Mast CeU Growth Factor, a Hematopoietin that is Active in Both Membrane Bound and Soluble Forms. Cell 1990, 63:23>243. Reports the molecular cloning of a mouse mast cell growth factor. .
Wm ON: Steel Locus Defines New Multiple Growth Factor. Cell 1990, 63:4-6. &is is a mini-review summarizing a remarkable series of papers concerning a ligand for the c-kit receptor.
9.
10. .
FLANACANJG, CHAN DC, LEDER P: Transmembrane
Form of the Kit Llgand Growth Factor is Determined by Altemative Splicing and is Missing in the S@ Mutant. Cell 1991, 64:10251035. Tissue-specI!ic alternative splicing gives rise to a transmembrane form and a soluble form of SLF. Sl mutants have no transmembrane form,
12. .
KESHETE, LVMANSD, WILLIAMS DE, ANDERSON DM, JENKINSNA, COPELAND NG, PARADA LF: Embryonic RNA Expression Pat-
terns of the c-kit Receptor and its Cognate Ligand Suggest Multiple Functional Roles in Mouse Development. EMBOJ 1991, 10:24252435. The authors performed in situ hybridization analysis to compare the expression proliles of SLF and c-kit transcripts during mouse embryogenesis. The results are in agreement with the data reported by
TAGA T, HIL%I M, HIRATAY, YAMA.SAKI K, YASUKAWA K, MATSUDA T, HIRANOT, KISHIMOTOT: Interleukin-6 Triggers the Association of its Receptor with a Possible Signal Transducer, gp130. Cell 1989, 58:573581.
M, Spsro M, HIRANOT, TAGAT, KISHIMOTO T: HIBI M, MKJRAKAM~ Molecular Cloning and Expression of an IL-6 Signal Transducer, gp130. Cell 1990, 63:114%1157. Molecular cloning of a non l&and binding but signal transducing subunit of the IL-6 receptor, gp130, revealed that it also belongs to a member of the qtokine receptor family. 20. ..
21. .
DAMS S, ALDRICH TH, VALENZUELADM, WONG V, FURTH ME, SQUINTO SP, YANCOPOULOS GD: The Receptor for Ciliaty
Neurotrophic Factor. Science 1991, 253:5’+63. Molecular cloning of the receptor for ciliary neurotrophic factor. The absence of a cytoplasmic domain in the ciliary neurotropic receptor and its high degree of homology with the IL-~ receptor suggest that it may use a signal transducer resembling the IL-~ signal transducer, gp130. 22.
11. ..
MATSUIY, BEI KM, HOGANBLM: Embryonic Expression of a Hematopoietic Growth Factor Encoded by the SZ Locus and the Ligand for c-kit. Nature 1990, 34766749. In situ hybridization analysis reveals that SCF, the l&and for c-kit, is expressed during embryogenesis in cells associated with both the migratory pathways and homing sites of melanoblasts, germ cells and hematopoietic stem cells, This indicates that the c-kit receptor-SCF ligand system may have an important role in ceU migration.
BURKERTU, VONRUDENT, WAGNEREF: Early Fetal Hematopietic Development from In Vitro Differentiated Embryonic Stem Cells. New Biologist 1991, 3:69%708.
23.
ITOH N, YONEHARA S, SCHREURSJ, GORMANDM, MARWAMA K, ISHII A, YAHARA I, ARAl K-I, MIYAJIMA A: Cloning of an Interleukin-3 Receptor Gene: A Member of a Distinct Receptor Gene Family. Science 1990, 247:324327.
* GORMAN DM,
ITOH N, KITAMURA T, SCHREUR~J, YONEHARA S, YAHARA I, ARAI K-I, MIYAJIMAA: Cloning and Expressing of
a Gene Encoding an Interleukin 3 Receptor like Proteik Indetification of Another Member of the Cytokine Receptor Gene Family. Proc Nat1 Acud Sci U S A 1990, 87~54595463. 24. .
HAYAsHmA K, KITAMLJRA T, GORMANDM, ARABK-I, YOKOTA T, MNAJIMA AZ Molecular Cloning of a Second Subunit of the
Receptor for Human Granulocyte-Macrophage Colony-stimulating Factor (GM-CSF): Reconstitution of a High-atlinity GM-CSF Receptor. Prcc Nat1 Acud Sci .!I S A 1990, 87~96559659. This paper indicates that the IL-3 receptor-like cDNA (KH97) encodes a second subunit of the high-affinity human GM-CSF receptor.
Mechanisms 25.
26.
LOPEZ AF, EG~ON JM, GILUS D, PARK Is, CLARK S, VAD.U MA: Reciprocal Inhibition of Sinding Between Interleukin 3 and Granulocyte-macrophage Colony-stimulating Factor to Human Eosinophils. Proc Nat1 Acad Sci U S A 1989, 867022. IQPEZ AF, EG~ON
JM, LYONSB, TAPLF( PM, To LB, PARKLS,
CLARKSC, VADASMA: Human Interleukin-3 Inhibits the Binding of Granulocyte-macrophage Colony-stimulating Factor and Interleukin-5 to BasophiIs and Strongly Enhances their Functional Activation. J Cell P&i01 1990, 1456977.
of soluble
mediators
Akira and Kishimoto
Molecular cloning of the p65 subunit of NFxB is described. It is also reported that the p65 subunit is related to rel, like ~50. 35.
HAXILL S, BEG AA, TOMPKINSSM, MOIUUSJS, YUR~CHKO AD,
.
SAMPSON-J•
A, MONDAL K, RALPH P, BALDWIN AS: Char-
acterization of an Immediate-early Gene Induced in Adherent Monocytes that Encodes IxB-like Activity. Cell 1991, 65:1281-1289. Keports molecular cloning of a putative IxB molecule. .SCHMD RM, PERKINS ND, DUCKFZTI CS, ANDREWS PC, NABEL GJ: Cloning of an NK-xB Subunit Which Stimulates
27. .
KIT~URA T, HAYA~HIDA K, SAKAMAKI K, YOKOTA T, ARAI K~ I, MNAJIMAA: Reconstitution of Functional Receptors for Human Granulocyte/Macrophage Colony-stimulating Factor (GM-CSF): Evidence that the Protein Encoded by the AIC2B cDNA is a Subunit of the Murine GM-CSF Receptor. Proc Nat1 Acud Sci CTS A 1991, 88:5082-5086. This paper indicates that the IL-3 receptor-like cDNA (AlC2B) encodes a second subunit of the high-affinity mouse GM~CSF receptor.
36.
28. .
DEVOS R, PLAETINCK J, VAN DER HEYDEN J, CORNEUS S, VANDEKERCKHOVE J, FIERS W, TAVERNERJ: Molecular Basis of a High Allinity Murine Interleukir-5 Receptor. EMBO J 1991, 8:2133-2137. This paper documents that a high-affinity mouse IL-5 receptor is composed of the low-affinity mouse IL-5 receptor and the mouse IL-3 receptor-like protein.
37.
GEXRINGDP, COSMAND: Homology of the p40 Subunit of Natural Killer Cell Stlmulatory Factor (NKSF) with the Extracellular Domain of the Interleukin-6 Receptor. Cell 1991, 66+10. The authors show that NKSF ~40 shares extensive amino acid sequence homology with the entire extracellular domain of the human IL-~ receptor, and present the possibility that NKSF ~75, a complex of soluble receptor-like ~40 and ~35, transduces its signal through the NKSF receptor in a similar fashion to the IL-&soluble 1~~6receptor. -
Pou V, MANCINIFP, CORTESE R: IL-6DBP, a Nuclear Protein Involved in Interleukin-6 Signal Transduction, Defines a New Family of Leucine Zipper Proteins Related to C/EBP. Cell, 1990, 63643453. Molecular cloning of IL6 dependent DNA binding protein, a nuclear factor binding to the IL6 responsive elements of several acute phase proteins,It was demonstrated that IL6 stimulation increased the binding activltieti as well as the transcriptional activities in hepatocytes.
29. .
30. .
HATAKEYAMAM, KONO T, KOBAYA~HI N, KAWAHARA A, LEVIN SD, PERUUTER RM, TANICUCHI T: Interaction of the IL-
2 Receptor with the SYC-Family Kinase p5Wck: Identilication of Novel Intermolecular Association. Science 1991, 252315251528. This paper documents a physical association between a cytokine receptor family member and a tyrosine kinase. 31.
MJ, BALTIMORE D: NF-xb: A Pleiotropic of Inducible and Tissue-specitic Gene Control. 581227-229.
32.
KIERANM, BU\NKV, LLXEAT F, VANDEKERCKHO~E J, ~~SPEICH
..
F, Ix BAIL 0, URBAN MB, KOURIISKV P, BAEUERLEPA, ISRAAELA: Subunit of NF-xB is Identical to Factor The DNA Siding
LENARE
..
GHOSH S, GWORD AM, RMERE I& TEMPST P, NOLAN GP, BAL~MORE D: Cloning of the ~50 DNA Binding Subunit of
NF-xB: Homology to rel and dorsal. Cell 1990, 62:101%1029. Reports molecular cloning of the ~50 subunit of the transcription factor NF-xB. ~50 shows remarkable homology, at the amino-terminal end, with the onogene v-rel 34. .
HIV Transcription in Synergy with p65. Nature 1991, 352~733-736. Molecular cloning of a novel subunit of the NFxB complex is described. Thls subunit is most related to the ~105 (~50 precursor). The complex of this subunit and ~65 is found to be more potent transcriptionally than the ~5~~65 heterodimer.
.
NOL%NGP, GHOSH S, LIOU H-C, TEMPST P, BAL~MORE D: DNA binding and IlcB Inhibition of the Cloned p65 Subunit of NF-xB, a rel-Related Polypeptide. Cell 1991, 64961-969.
AKIRAS, ISSHW H, SUGITA T, TANABE0, KINOSHXA S, NISHIO Y, NAKAJIMAT, HIRANO T, KISHIMOTO T: A Nuclear Factor for
IL-6 Expression (NF-IL6) is a Member of a C/EBP Family. EMBO J 1990, 9:1897-1906. Molecular cloning of a transcription factor involved in IL-~ expression is documented. This revealed the existence of a new family with leuclne zipper structure related to C/EBP. 38. .
39.
KITAMURAT, SATO N, ARAI K-I, MNAJIMAA: Expression Cloning of the Human IL-3 Receptor cDNA Reveals a Shared p Subunit for the Human IL-3 and GM-CSF Receptors. Cell 1991, 66:1165-1174.
40.
TAKAKIS, MITA S, KITAMURA T, YONEHARAS, YAMAGUCHI N, TOMINAGA 4 M~AJIMA A, TAKATSU K: Identification of the Second Subunit of the Murlne Interleuldn-5 Receptor: Interleukin-3 Receptor-like Protein, AICZB is a Component of the High-affinity Interleukin-5 Receptor. EMBO J 1991, 10:2833-2838.
Mediator Cell 1989,
KBF-1 and Homologous to the rel Oncogene Product. Cell 1990, 62:1007-1018. Describes molecular cloning of the transcription factor KBFl invoked in the expression of the class I MHC antigen. KBFl is identical to the 50 kD DNA-binding subunit of NF-xB. KBF also displays extensive amino-acid homology with the v-rel oncogene. 33.
.
41.
TAVENIERJ, DEVOS R, CORNELISS, TLJY~ENST, \(Am DER -EN J, FIERYW, PIAETINCK G: A Human High&in@ Interleukin-5
Receptor (ILSR) is Composed of and IL5-Specific a Chain and a !.3Chain Shared with the Receptor for GM-CSF. Cell 1991, 66:1175-1184 42.
GEARING DP, THUT CJ, VAN DEN BOS T, GIMPEL SD, DEIANEY PB, KING J, PRICE V, COSMAN D ANDBECKMAN MP: Leukemia
Inhibitory Factor Receptor is Structurally Related to the IL-6 Signal Transducer, gp130. EMBO J 1991, 10:283’+2848. 43.
GF,ARINGDP, COMEAU MR, FRIEND DJ, GIMPEL SD, THUT CJ, MCCOURTY J, BRASHERKK, KING-J4 GILLISS, MOSLF~ B, ZIEGLER SF AND COSMAN D: The IL-~ Signal Transducer, gp130: An
Oncostadn M Receptor and tin&y Converter Receptor. Science 1992, 255:1434-1437. S Akira and T Klshimoto, Suita, Osaka 565, Japan.
Division of Immunology
l-3,
for the LIF
Yamadaoka
313
of soluble
Akira and Tadamitsu Osaka University,
A two
chain
model,
composed
subunits,
first indentified
revealed
in several
shared
by several
characteristic
other
Current
systems.
systems The
is now becoming cloning
Osaka, Japan
interleukin-6
cytokine
receptor
Common
may explain
signaling clearer
and signal transducing
receptor
system,
from
redundancy
the
due to the successful
in Immunology
has been
signal transducers
a functional
pathway
of several transcription
Opinion
Kishimoto
of ligand-binding
in the
of cytokines.
gene activation
mediators
receptor
to
molecular
factors.
1992, 4:307-313
rived growth factor and colony stimulating factor (CSF)-1. Molecular analysis of the c-kit gene in Wmutant mice has demonstrated deletions within the gene, or point muta tions in the tyrosine kinase domain.
Introduction
Growth and differentiation of hematopoietic and lym phoid cells are regulated by various kinds of soluble mediators called cytokines. Cytokines convey their sigThe complementary nature of the Wand SI mutations has nals into the cell nucleus through high affinity cell-surled to the hypothesis that the SZlocus encodes a ligand face receptors. Recently, many cytokine receptors have for c-kit. Using different approaches, three groups have been cloned and characterized, revealing the existence -defined-a new hematopoietic growth factor with a broad of a large family of cytokine receptors. Several transcript , tion factors, that may be nuclear targets in the complex- ’ range of biological activities [3*-8*]. Several lines of evdence have suggested that this factor is a l&and for c-kit. signal transduction cascade, have also been molecularly Zsebo et al. [5*] purified stem-cell factor (SCF) from the cloned. Although the pathways transmitting signals from supernatant of a buffalo rat liver-cell line, using an assay cytokine receptors to genes responsible for cell prolifersystem that measures high proliferative potential colonyation, growth inhibition, and cell differentiation are still a forming cells in post 5-FU bone marrow. Using a conmystery, during the past year several important findings tinuous mast-cell line as a target, and supernatant from a have provided insight into this black box. murine bone marrow stromal-cell ljner~jlliams et a!. [ 3.1 defined a new m‘ast-cell growth factor (MGF). Huang et al [7*] also used a mast-cell assay to define a factor they call KL (kit ligand). To unify nomenclature Witty renamed Novel growth factors involved in early this novel factor Steel factor (SIP) in his review ‘[91. Punhematopoiesis fied SLF binds to the c-kit receptor specifically, as shown by the binding of radiolabeled SLF to cells expressing a Steel factor: a ligand for c-&it functional c-kit receptor and the formation of a stable Mice with mutations at the dominant white spotting complex between SLF and the c-kit receptor. The gene ( W) and Steel (Sl) loci are characterized by a reduced encoding SLF maps near the Sl locus on mouse chromonumber of pluripotent hemopoietic stem cells, anemia, some 10 and is deleted or altered in the SZalleles of SZ a deficiency of mast cells, and defects in gametogenesis mutant mice [4*]. and pigmentation. Several experiments, including in vivo Although the isolated natural protein is soluble, the cell transplantation and in vitro co-culture between the SLF amino acid sequence has the features of a transtwo strains, have shown that the defect in Wmutant mice membrane protein: an amino-terminal signal peptide, is intrinsic in the hematopoietic stem cells, whereas the defect in SI mice is in the marrow stromal-cell environan extracellular domain, a transmembrane domain, and ment. Furthermore, it has been demonstrated that c-kit is a carboxy-terminal intracellular segment. Tissue-specific the product of the Wlocus [ 1,2]. The c-kit proto-oncoalternative splicing produces two types of SLF mRNA gene encodes a transmembrane tyrosine kinase receptor, [lo*]. Both encode a protein with a transmembrane domain, but one is synthesized as a membrane-bound closely related structurally to the receptors for platelet-deAbbreviations CIEBP-CCAATienhancer binding protein; CSF-colony-stimulating factor; G-CSF-granulocyte colony-stimulating factor; GM-CSF-granulocyte-macrophage colony-stimulating factor; IFN-interferon; IL-interleukin; KL-kit ligand; LIF-leukemia inhibitory factor; M-CSF-macrophage colony-stimulating factor; MCF-mast-cell growth factor; NK-natural killer; NKSF-natural killer cell stimulatory factor; SCF-stem-cell factor; S/-Steel; SLF-Steel factor; TNF-tumor necrosis factor; W--dominant white spotting. @ Current
Biology
Ltd ISSN 0952-7915
307
308
Lymphocyte
activation
and effector
functions
growth factor that can also be cleaved from the cell membrane by an unidentified protease to yield a soluble form, and the other preferentially produces the cell surface form as the sequence around this cleavage site is deleted. Soluble SLF is physiologically active and promotes the proliferation of purified hematopoietic stem cells, T-cell precursors, and B-lymphoid precursors. Soluble SLF by itself has modest effects on early myeloid and lymphoid cells but it synergizes dramatically with other factors such as granulocyte-macrophage colonystimulating factor (GM-CSF) and interleukin (IL)-7. In 1~iz10administration of soluble SLF effectively reverses the anemia and mast-cell deficiency of SUSP mice. However, it has been shown that soluble SLF has little ability to fulfil the normal biological functions of this growth factor in the intact organism. Some Sl mutant mice, in which the sequences encoding the transmembrane and intracellular domains of SLF are deleted, still produce a bioactive form of soluble SLF, implying that SLF expression on the cell surface has a critical biological role in processes of normal development [lo*]. In fact, in situ analysis of SLF during embryogenesis has shown that SLF is expressed in cells associated with both the migrating pathway and homing sites of melanoblasts, germ cells, and hematopoietic stem cells [11**,12. 1. These observations suggest that the kit-SLF system may have a role in cell migration and homing.
Interleukin-II
Another novel hematopoietic growth factor has been cloned from a bone marrow stromal-cell line [ 13.1. A pnmate bone marrow derived stromal-cell line, designated PU-34, supports long-term hematopoiesis by normal human or primate progenitor cells in culture. In addition to known growth factors including IL-~, IL-7, GM-CSF, macrophage colony-stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF), and leukemia inhibitory factor (LIF), the ILlcr stimulated PU-34 conditioned medium contained a novel factor that stimulated the proliferation of a mouse plasmacytoma-cell line, even in the presence of a neutralizing antiserum against human IL-~. A cDNA clone encoding the novel growth factor activity was isolated by expression cloning, on the basis of its ability to stimulate the proliferation of an 1~6 dependent mouse plasmacytoma-cell line. The cDNA contained a single long reading frame of 598 nucleotides encoding a predicted 199 amino acid polypeptide. The sequence of this cDNA was shown to have no homology with known cytokines and the product was designated IL-11. This cy tokine can also stimulate the T cell dependent development of Ig-producing B cells and act synergistically with IL-3 to shorten the GO period of early B-cell progenitors. Because IL-1 1 has many biological properties in common with IL-~, it is possible that these two cytokines may use a similar signal transduction pathway or may even share a common signal transducer.
Expression of cytokines
during
embryonic
development The potential role of cytokines during embryonic development and particularly their possible function in the development of pluripotent hemopoietic-stem cells were studied by several investigators. Murray et al. [14*] examined the expression of IL-3, IL-~, LIF and GM-CSF in the blastocyst prior to developmental commitment. Using polymerase chain reaction analysis, they detected mRNA transcripts for IL-~ and LIF, but not for GM-CSF or IL-3, in mouse blastocysts after 3.5 days of gestation, suggesting that IL-~ and LIF may regulate the growth and development of trophoblasts or embryonic stem cells, IJsing the embryonic stem-cell system, Schmitt et al. [ 15.1 correlated the expression of cytokines, their receptors, the P-globins, and the hematopoietic cell-surface markers throughout the time course of embryonic stem-cell differentiation with hematopoietic development. Of the genes analyzed, only SLF and c-kit were expressed throughout the time course, and were even found in undifferentiated embryonic stem cells. Genes encoding the majority of the other cytokines (Epo, CSF-1, IL-4, and IL-~) and their receptors underwent considerable transcriptional activation during embryonic stem-cell development. In most cases, the receptor genes were transcribed before the corresponding growth factors. However, IL-3 and GMCSF were not expressed during the first 24 days of embryonic stem-cell differendation, strongly suggesting that IL-3 and GM-CSF are not critical to early hematopoiesis. A similar conclusion was presented by recent studies from Burkert et al. [I6].
A model
for cytokine-receptor
interaction
Recent molecular cloning of cytokine receptors has shown that they belong to the superfamily characterized by a single hydrophobic membrane spanning region, an intracellular domain without kinase activity and an extracellular domain with four cysteine residues located in the amino terminal half and the Trp-Ser-X-TrpSer (where X is any amino acid), motif located close to the transmembrane domain. These features are shared by the receptors for IL-2 (p70), IL-3, IL-4, IL-5, IL-~, IL-7, G-CSF, GM-CSF, growth hormone, prolactin and erythropoietin and distinguish them from other types of cytokine receptors such as those belonging to Ig superfamily receptors or the tumor necrosis factor (TNF) receptor fam ily. Bazan [17**,18*] proposed a provocative structural model for cytokine-receptor interaction. A detailed analysis of receptor folds has revealed that the shared - 200 amino acid binding segments containing the four cysteine residues and the TrpSer-X-Trp-Ser box are composed of two structurally similar (j3 strand rich) - 100 residue domains. In addition, the individual domain is distantly related to a common -90 amino acid structure known
Mechanisms
as fibronectin type III domain. A predictive analysis of the generic domain fold in turn proposes that seven consensus P-strands form an antiparallel P-sandwich with a topology analogous to an Ig constant domain (Fig. 1). A binding crevice for cytokines is predicted between the linked Ig-like domains. This link between primitive adhesive structures and sophisticated binding receptors is analogous to the structural kinship between primitive Iglike adhesive molecules and antibddy frameworks. These Iindings have strong implications for the evolutionary emergence of an important class of regulatotv molecules from primitive adhesive modules,
of soluble
mediators
Akira
and
Kishimoto
intracytoplasmic portions, still associates with gp130 in the presence of IL-~, and mediates IL-~ function (Fig. 2). Thus, the IL-~ receptor system consists of two functionally different polypeptide chains: a ligand-binding chain, and a non ligand binding, but signal-transducing chain. might work as Taga et al. [19] predicted that -130 a signal transducer for other unknown ligand-receptor systems. It is also a member of the cytokine receptor family and was recently molecularly cloned [20-i]. In fact, the novel mechanism discovered in the IL-~ receptor system has been demonstrated in several other receptor systems. Interestingly, the recent cloning of the receptor for ciliaty neurotrophic factor [21-l has shown that it has a high degree of homology with the IL-~ receptor Together with its lack of a cytoplasmic domain, this suggests that this system may also use a signal transducer resembling gp130.
IL-6
gpl30
Fig. 2. IL-6 induced
association
of IL-6 receptor
and gp130.
Fig. 1. Predicted
tertiary structure of cytokine receptors. Two -100 residues domains are proposed to be related to a common -90 amino acid fibronectin type III domain. Seven consensus p-strands form an antiparallel p-sandwich with a topology analogous to an Ig constant domain. A binding crevice for cytokines forms between these linked Ig-like domains. c, cysteine; Type III, fibronectin type Ill.
A two-chain
system in cytokine
receptors
The IL-~ receptor has a relatively short intracellular domain that was shown not to be important for signal transduction. Taga et al [19] demonstrated that the IL6 signal is mediated through a membrane glycoprotein, gp130, associating with the receptor. These proteins become associated only after the receptor is stimulated by IL-6. This association takes place extracellularly, as the soluble IL-~ receptor, lacking the transmembrane and
A common GM-CSF,
associate
molecule
for 11-3,
and IL-5 receptors
The ability of IL-3 and GM-CSF to cross-compete for binding on cell types expressing both receptors suggests that they could share a common associate molecule. Using monoclonal antibodies raised against a murine multi-factor responsive immature mast-cell line (IC2), the genes encoding the low affinity mouse IL-3 receptor (AIC2A) and another protein (AIC2B) have been cloned [22,23]. Both proteins possess characteristics of the cy tokine receptor family but despite its 95% homology with AIC2A, AIC2B does not bind IL-3. Using the mouse IL-3 receptor cDNA as a probe, the human homolog KH97 was isolated [24*]. KII97 encodes a transmembrane protein of 120kD that has 56% homology with
309
310
lymphocyte
activation and effector functions
its murine counterpart. This protein alone does not bind any of the cytokines tested. However, when cells were cotransfected with the genes for low-aIhnity human GM-CSF receptor, a high-a&&y receptor for GM-CSF was formed. The human IL-3 and GM-CSF receptors may also share a common associate molecule because reciprocal inhibition of receptor binding by IL-3 and GM-CSF has been observed in human cells responsive to these two ligands [25]. In addition, recent data [26] suggest that the molecule shared by the human IL-3 and GM-CSF receptors could also be shared by the human IL-5 receptor. Taken together, these results suggest that KH97 may be a common associate molecule for the human IL-3, GM-CSF, and IL-5 receptors. Furthermore, co-expression of the human GM-CSF receptor with mouse AIC2B, but not AK%, resulted in human GM-CSF-dependent growth in a mouse IL2 dependent T-cell line CTLL2 that previously did not proliferate at all in response to human GM-CSF. This suggests that the protein encoded by the AIC2B cDNA is an associate molecule of the mouse GM-CSF receptor [ 27.1. It has also been shown that the low-affinity mouse IL-5binding protein forms a high-afhnity IL-5 receptor with AIC2B [ 28’1. Thus, it is likely that the high-affinity receptors for GM-CSF, IL-3, and IL-5 share a common associate molecule (KH97) in the human whereas the GM-CSF and IL-5 receptors share a common associate molecule (AIC2B) in the mouse.
Natural receptor
killer
cell stimulatory
factor W-12)
system
Natural killer (NK) cell stirnulatoxy factor (NKSF) is a B cell derived, heterodimeric cytokine that has pleiotropic activities, which include induction of interferon (IFN)-y secretion from NK and T cells, costimulation of peripheral blood lymphocyte proliferation and enhancement of the cytotoxicity of NK cells. The functional NKSF molecule (~75) consists of two subunits, p35 and ~40, that are inactive when expressed separately. The NKSF molecule binds to a cellular receptor of Mr 180000. Gearing and Cosman [29=] have reported that NKSF p40 shares extensive amino acid sequence homology to the entire extracellular domain of the human IL-~ receptor. In contrast, the amino acid sequence of the p35 subunit reveals no obvious similarity to other cytokines or receptors but secondary structure predictions showed a strong a-helical content, as has been found for many ligands of the cytokine receptor family. These data show an interesting analogy to the IL-GIL-~ receptor system depicted in Fig. 2. The p75 complex of NKSF might act in a similar fashion to the complex of IL&soluble IL-~ receptor and the cellular NKSF receptor might be functionally equivalent to gp130.
Tyrosine
phosphorylation
in cytokine
signaling
Although very little is known about intracytoplasmic signaling mechanisms of cytokines, tyrosine phosphotylation is thought to be involved in signal transduction
from several cytokines, including IL-2, IL-3, IL-4 and GMCSF. Tyrosine residues on a set of proteins are rapidly phosphorylated after the addition of these growth factors. Recently, a lymphocyte-specific tyrosine kinase, lck was reported to be involved in the IL-2 signaling pathway [ 30.1. The IL-2 receptor P-chain and p56lck formed a complex through specific association between the cytoplasmic domain of the IL-2 receptor P-chain and the tyrosine kinase catalytic domain of lck. Furthermore, IL-2 stimulation activated p56lck kinase activity. It is not clear, however, whether the IL-2 receptor p-chain itself is a critical substrate for p561$ or whether p56[$ once linked to the receptor, can activate other metabolic processes. Other members of the newly growing cytokine receptor family may also interact directly with a certain tyrosine kinase(s).
Cytokines
and transcription
factors
NF-xB
Cytokines convey signals to the interior of cells for cellular proliferation, differentiation, and other activities. The cell responds to such external stimuli by turning on a plethora of transcription factors, which may in turn intluence the transcription of many genes. Recent studies have revealed that IWxB is involved in transcriptional regulation of many genes encoding cytokines and their receptors (Fig. 3) [31]. The NF-XB was originally characterized as a kappa Ig enhancer DNA-binding protein. Binding sites for NI-xB are present in the regulatory regions of certain cytokine genes (including TNF-a, lymphotoxin, IL-~, IL-8 and IFN-P genes), the IL-2 receptor gene, class I and II histocompatibility antigen genes, several acute phase response genes, and several viral enhancers including human immunodeficiency virus. NF-xB is a complex of two proteins of 50 and 65kD. It pre-exists in the cytoplasm of most cells in an inactive form, complexed to an inhibitor, termed IxB. Stimulation by a number of agents such as phorbol my&ate acetate, lipopolysaccharide, and TNF-a results in the dissociation of the IxB-NFxB complex, probably by phosphorylation of IxB. Subsequently, the NI-xB heterodimer migrates to the nucleus where it binds to its cognate DNA-binding sites and activates transcription, The genes encoding the p50 and the p65 subunits of NI-xB were recently cloned and found to have a high level of homology to the proto-oncogene c-rel and the Drosophila maternal. effect gene dorm1 within a large domain required for DNA binding and dimerization [32**,33**,34*]. The product of the full-length cDNA-encoding p50 is 105 kD. ~105 shows no DNA-binding capacity and contains six repeats of the ankyrin consensus sequence in its carboxy terminus. Ankyrins are known to constitute a family of proteins that regulate interactions between a variety of membrane structures and the cytoskeleton. p50 is produced from the ~105 precursor by an unidentilied proteolytic mechanism, which removes the ankyrin repeat domain from the DNA-binding subunit. The p50 homodimer and p50-p65 heterodimer specifically bind
Mechanisms
NF-kB
of soluble
mediators
Akira
and Kishimoto
ing al-acid glycoprotein, angiotensinogen, complement C3 and serum amyloid A as well as several cytokines including IL-2, IL-8 and G-CSF. Poli et al. [38*] have cloned and characterized a cDNA coding for IL6 dependent DNA binding protein, which is responsible for IL6 mediated induction in several acute-phase proteins. The IL6 dependent DNA binding protein exhibited a very high level of homology with human NF-1~6, suggesting that it.is the rat homolog of NI-IL6. Furthermore, their observation that both the DNA-binding activity and the transactivating capacity of IL6 dependent DNA binding protein are induced in hepatoma cells by treatment with IL-~, implicates the gene encoding the IL6 dependent DNA binding protein (NI-1~6) as a nuclear target of IL-~ and its product as a mediator of the IL6 dependent transcriptional activation. The characterization of the mechanisms through which NI-IL6 is activated will help to elucidate the nuclear events in the IL-~ signal transduction pathway.
Conclusion Many cytokines and their corresponding receptors have been cloned. Comparison of the primary structures of these cytokine receptors has revealed the existence of the Fig.3. From cytokine receptors to activation of transcription facnew cytokine receptor family, suggesting that members tors. may have evolved from a common ancestral adhesive to DNA, whereas p65 cannot bind by itself. An IxB-like!? , ’molqztie. A two-chain model (ligand-binding and signal transducing subunits), first identified in the IL-~ recepmolecule has also been cloned [ 35.1. The cDNA encodes. tor system, has been found in several other cytokine a protein of 317 amino acids with one domain containreceptor systems and several transcription factors that ing five tandem repeats of the ankyrin motif, similar to may be nuclear targets in cytopne signaling pathways the precursor of the p50 subunit. The presence of these have recently been identified. Despite recent progress repeats in IxB may indicate that IxB keeps NF-xB in the in the cytokine field, signal transduction by cytokine cytoplasm by linking the complex to cytoplasmic strucreceptors is still poorly understood. However, research tures through these ankyrin repeats. concentrated on identification of kipa6es or molecules as Recently the gene encoding the xB binding subunit sociated with cyt&ne receptors or transcription factors, (plOO), and also p49 by altemativee splicing was cloned will soon provide a better understanding of this area. [36*]. ~100 is most closely related to the ~105 subunit of NK)cB. p49 can form a heterodimer with p65 and act in synergy to simulate the xB-binding genes. c- relalso binds Note added in proof to the xB site and forms a heterodimer with the p50 subunit. A functional distinction between rebp50, p4’+p65 Recent work has reinforced the hypothesis that the highand p50-p65 heterodimers awaits further investigation. affinity receptors for GM-CSF, IL-3, and IL-5 share a com-
NF-IL6
A recently cloned transcription factor, termed NI-Iti may also be a pleiotropic mediator of many inducible genes (Fig. 3). NI-IL6 was initially identified as a nuclear factor binding to the IL-1 responsive element of the IL-~ gene. Direct cloning of human NF-IL6 revealed its homology with CCAAT/enhancer binding protein (C/EBP), a liver enriched transcription factor [37*]. C/EBP and W-IL6 recognize the same nucleotide sequence, but exhibit distinct patterns of expression. C/EBP is expressed in liver and adipose tissues, whereas NF-IL6 is produced in many cell types in response to a variety of stimuli including lipopolysaccharide, IL-l, TNF and IL-~. Recently, several studies showed that C/EBP-like factors may be involved in the expression of several acute-phase proteins includ-
mon associate molecule (KH97) in the human, whereas the GM-CSF and IL-5 receptors share a common associate molecule (AIC2B) in the mouse [3!+41]. Gearing et al. [42] cloned the receptor for LIF, which is highly similar to gp130. Also the Iinding that the high-affinity receptor for LIF and oncostatin M share gp130, a signal transducer for IL-~, has been recently presented [43].
References
and recommended
reading
Papers of particular interest, published within the annual period of review, have been highlighted as: . of special interest .. of outstanding interest 1.
EN, F&IN M4 HOUSMANDE: The Dominant-white Spotting (W) Locus of the Mouse Encodes the c-kit Protooncogene. Cell 1988, 553185-192.
GEISSLER
311
312
LvmDhocvte activation and effector functions 2.
CHABOT B, STEPHENSONDA, CAHPMANVM, BESMERP, BERNSTEIN A: The Proto-oncogene c-kit Encoding a Transmembrane
Tyrosine Kinase Receptor Nature 1988, 355:m9.
Maps to the Mouse W Locus.
WILUAMSDE, EISENMANJ, BAIRD A, RAUCH C, NESS KV, MARCH CJ, PARK IS, MARTIN U, M~CHLZUKIDY, BOSWELLHS, ET AL: Identllication of a Ligand for the c-kit Proto-Oncogene. Cell 1990, 63:167-174. Reports the purification and biological activities of a novel MGF. 3. .
4. .
COPEIAM) NG, GILBERTDJ, CHO BC, DONOVAN PJ, JENKINSNA, COSMAN D, ANDERSON D, LYMANSD, WILLIAMS DE: Mast CeU
Growth Factor Maps Near the Steel Locus on Mouse Chromosome 10 and is Deleted In a Number of Steel Alleles. Cell 1990, 63:175-183. This paper documents that the MGF gene maps near S1 in the distal region of mouse chromosome 10 and is deleted in a number of Slalleles. 5. .
ZSEBO KM, WYWCH J, MCNIECE IK, Lu HS, SMITH DA, KARKARE SB, SACHDEVRK, YUSCHENKOFFVN, BIRKETT NC, WILUAMS LR, ET AL: Identification, Purification and Biological Characterl-
zation of Hematopoietic Stem Cell Factor from Buffalo Rat Liver-conditioned Medium. Cell 1990, 63:195-201. Describes the purification and biological characterization of a novel growth factor, SCF. 6. .
.
PAUL SR, BENNET F, CALVETI’JA, I KELIEHERK, WOOD CR, DA, YANG O’HARARM, LFARY AC, SISLEY B, CWUCSC, WILLIAMS Y-C: Molecular Cloning of a cDNA Encoding Interleukin 11, a Stromal Cell-derived Lymphopoietic and Hematopoietic Cytokine. Proc Natl Acad Sci U S A 1990, 87:7512-7516. Reports molecular cloning of a novel interleukin derived from a stromal cell line.
13. .
14. .
MURRAY R, LEE F, CHIU CP: The Genes for Leukemia Inhibitory Factor and Interleukin-6 are Expressed in Mouse Blastocysts Prior to the Onset of Hemopoiesis. Mol Cell Biol 1990, 10:4953-4956. This paper documents that both IL-~ and LIF genes, but not IL-3 or GM-CSF genes, are expressed in blastocysts in vivo.
SCHM~ RM, BR~NNSE, SNODGRASSHR: Hematopoietic Development of Embryonic Stem Cells in Vitro: Cytokine and Receptor Gene Expression. Genes Dev 1991, 5:72%740. These authors suggest that IL-3 and GM-CSF are not critical to early in vitro hematopoietic development and that the expression of SLF, Epo, IL-4 and IL-~ may be important during the early stages of embryonic stem-cell differentiation. 15. .
16.
ZSEBO KM, WILLL~MSDA, GEISSIER EN, BROUDY VC, MARTIN FH, A%INS HL, HSU R-Y, BIRKETT NC, OKINO KH, MURIXXK
DC, ET AL: Stem Cell Factor is of the Mouse and its Ligand for Receptor. Cell 1990, 63:21%224. Reports the molecular cloning of mouse vide biological and physical evidence that receptor. 7.
Matsui et al. [ ll**] and also suggest involvement of SLF and c-kit in the organization of the neural tube and brain.
Encoded at the Sl Locus the c-kit Tyrosine Kinase SCF. The authors also proSCF is a l&and for the c-kit
HUANGE, NOCKAK, BEIER DR, CHU T-Y, BUCK J, IAHM H-W, WELLNERD, LEDERP, BESMERP: The Hematopoietic Growth
Factor KL is Encoded by the SZ Locus and is the Ligand of the c-kii Receptor, the Gene Product of the W Locus. Cell 1990, 63~225235. A description of the molecular cloning of a mouse hemopoietic growth factor, KL
BAZANJF: Structural Design and Molecular Evolution of a Cytukine Receptor Superfamily. Proc Nat1 Acud Sci USA 1990, 87~6934-6938. This paper describes the predictive tertiary structure of a cytokine receptor superfamily, and presents implications for the evolutionary emergence of the cytokine receptor superfamily from primitive adhesive modules. 17. ..
18. BAZANJF: Haemopoietic Receptors and Helical Cytokines. . Immunol To&y 1990, 11:350-354. ReporS a structural model for cytoine-receptor interaction. 19.
8.
ANDERSON DM, LVMANSD, BAIRD A, WIGNALL JM, EISENMAN J, RAUCHC, MARCHCJ, BO~WEXLS, GIMPELSD, COSMAND, WILLIAMS DE: Molecular Cloning of Mast CeU Growth Factor, a Hematopoietin that is Active in Both Membrane Bound and Soluble Forms. Cell 1990, 63:23>243. Reports the molecular cloning of a mouse mast cell growth factor. .
Wm ON: Steel Locus Defines New Multiple Growth Factor. Cell 1990, 63:4-6. &is is a mini-review summarizing a remarkable series of papers concerning a ligand for the c-kit receptor.
9.
10. .
FLANACANJG, CHAN DC, LEDER P: Transmembrane
Form of the Kit Llgand Growth Factor is Determined by Altemative Splicing and is Missing in the S@ Mutant. Cell 1991, 64:10251035. Tissue-specI!ic alternative splicing gives rise to a transmembrane form and a soluble form of SLF. Sl mutants have no transmembrane form,
12. .
KESHETE, LVMANSD, WILLIAMS DE, ANDERSON DM, JENKINSNA, COPELAND NG, PARADA LF: Embryonic RNA Expression Pat-
terns of the c-kit Receptor and its Cognate Ligand Suggest Multiple Functional Roles in Mouse Development. EMBOJ 1991, 10:24252435. The authors performed in situ hybridization analysis to compare the expression proliles of SLF and c-kit transcripts during mouse embryogenesis. The results are in agreement with the data reported by
TAGA T, HIL%I M, HIRATAY, YAMA.SAKI K, YASUKAWA K, MATSUDA T, HIRANOT, KISHIMOTOT: Interleukin-6 Triggers the Association of its Receptor with a Possible Signal Transducer, gp130. Cell 1989, 58:573581.
M, Spsro M, HIRANOT, TAGAT, KISHIMOTO T: HIBI M, MKJRAKAM~ Molecular Cloning and Expression of an IL-6 Signal Transducer, gp130. Cell 1990, 63:114%1157. Molecular cloning of a non l&and binding but signal transducing subunit of the IL-6 receptor, gp130, revealed that it also belongs to a member of the qtokine receptor family. 20. ..
21. .
DAMS S, ALDRICH TH, VALENZUELADM, WONG V, FURTH ME, SQUINTO SP, YANCOPOULOS GD: The Receptor for Ciliaty
Neurotrophic Factor. Science 1991, 253:5’+63. Molecular cloning of the receptor for ciliary neurotrophic factor. The absence of a cytoplasmic domain in the ciliary neurotropic receptor and its high degree of homology with the IL-~ receptor suggest that it may use a signal transducer resembling the IL-~ signal transducer, gp130. 22.
11. ..
MATSUIY, BEI KM, HOGANBLM: Embryonic Expression of a Hematopoietic Growth Factor Encoded by the SZ Locus and the Ligand for c-kit. Nature 1990, 34766749. In situ hybridization analysis reveals that SCF, the l&and for c-kit, is expressed during embryogenesis in cells associated with both the migratory pathways and homing sites of melanoblasts, germ cells and hematopoietic stem cells, This indicates that the c-kit receptor-SCF ligand system may have an important role in ceU migration.
BURKERTU, VONRUDENT, WAGNEREF: Early Fetal Hematopietic Development from In Vitro Differentiated Embryonic Stem Cells. New Biologist 1991, 3:69%708.
23.
ITOH N, YONEHARA S, SCHREURSJ, GORMANDM, MARWAMA K, ISHII A, YAHARA I, ARAl K-I, MIYAJIMA A: Cloning of an Interleukin-3 Receptor Gene: A Member of a Distinct Receptor Gene Family. Science 1990, 247:324327.
* GORMAN DM,
ITOH N, KITAMURA T, SCHREUR~J, YONEHARA S, YAHARA I, ARAI K-I, MIYAJIMAA: Cloning and Expressing of
a Gene Encoding an Interleukin 3 Receptor like Proteik Indetification of Another Member of the Cytokine Receptor Gene Family. Proc Nat1 Acud Sci U S A 1990, 87~54595463. 24. .
HAYAsHmA K, KITAMLJRA T, GORMANDM, ARABK-I, YOKOTA T, MNAJIMA AZ Molecular Cloning of a Second Subunit of the
Receptor for Human Granulocyte-Macrophage Colony-stimulating Factor (GM-CSF): Reconstitution of a High-atlinity GM-CSF Receptor. Prcc Nat1 Acud Sci .!I S A 1990, 87~96559659. This paper indicates that the IL-3 receptor-like cDNA (KH97) encodes a second subunit of the high-affinity human GM-CSF receptor.
Mechanisms 25.
26.
LOPEZ AF, EG~ON JM, GILUS D, PARK Is, CLARK S, VAD.U MA: Reciprocal Inhibition of Sinding Between Interleukin 3 and Granulocyte-macrophage Colony-stimulating Factor to Human Eosinophils. Proc Nat1 Acad Sci U S A 1989, 867022. IQPEZ AF, EG~ON
JM, LYONSB, TAPLF( PM, To LB, PARKLS,
CLARKSC, VADASMA: Human Interleukin-3 Inhibits the Binding of Granulocyte-macrophage Colony-stimulating Factor and Interleukin-5 to BasophiIs and Strongly Enhances their Functional Activation. J Cell P&i01 1990, 1456977.
of soluble
mediators
Akira and Kishimoto
Molecular cloning of the p65 subunit of NFxB is described. It is also reported that the p65 subunit is related to rel, like ~50. 35.
HAXILL S, BEG AA, TOMPKINSSM, MOIUUSJS, YUR~CHKO AD,
.
SAMPSON-J•
A, MONDAL K, RALPH P, BALDWIN AS: Char-
acterization of an Immediate-early Gene Induced in Adherent Monocytes that Encodes IxB-like Activity. Cell 1991, 65:1281-1289. Keports molecular cloning of a putative IxB molecule. .SCHMD RM, PERKINS ND, DUCKFZTI CS, ANDREWS PC, NABEL GJ: Cloning of an NK-xB Subunit Which Stimulates
27. .
KIT~URA T, HAYA~HIDA K, SAKAMAKI K, YOKOTA T, ARAI K~ I, MNAJIMAA: Reconstitution of Functional Receptors for Human Granulocyte/Macrophage Colony-stimulating Factor (GM-CSF): Evidence that the Protein Encoded by the AIC2B cDNA is a Subunit of the Murine GM-CSF Receptor. Proc Nat1 Acud Sci CTS A 1991, 88:5082-5086. This paper indicates that the IL-3 receptor-like cDNA (AlC2B) encodes a second subunit of the high-affinity mouse GM~CSF receptor.
36.
28. .
DEVOS R, PLAETINCK J, VAN DER HEYDEN J, CORNEUS S, VANDEKERCKHOVE J, FIERS W, TAVERNERJ: Molecular Basis of a High Allinity Murine Interleukir-5 Receptor. EMBO J 1991, 8:2133-2137. This paper documents that a high-affinity mouse IL-5 receptor is composed of the low-affinity mouse IL-5 receptor and the mouse IL-3 receptor-like protein.
37.
GEXRINGDP, COSMAND: Homology of the p40 Subunit of Natural Killer Cell Stlmulatory Factor (NKSF) with the Extracellular Domain of the Interleukin-6 Receptor. Cell 1991, 66+10. The authors show that NKSF ~40 shares extensive amino acid sequence homology with the entire extracellular domain of the human IL-~ receptor, and present the possibility that NKSF ~75, a complex of soluble receptor-like ~40 and ~35, transduces its signal through the NKSF receptor in a similar fashion to the IL-&soluble 1~~6receptor. -
Pou V, MANCINIFP, CORTESE R: IL-6DBP, a Nuclear Protein Involved in Interleukin-6 Signal Transduction, Defines a New Family of Leucine Zipper Proteins Related to C/EBP. Cell, 1990, 63643453. Molecular cloning of IL6 dependent DNA binding protein, a nuclear factor binding to the IL6 responsive elements of several acute phase proteins,It was demonstrated that IL6 stimulation increased the binding activltieti as well as the transcriptional activities in hepatocytes.
29. .
30. .
HATAKEYAMAM, KONO T, KOBAYA~HI N, KAWAHARA A, LEVIN SD, PERUUTER RM, TANICUCHI T: Interaction of the IL-
2 Receptor with the SYC-Family Kinase p5Wck: Identilication of Novel Intermolecular Association. Science 1991, 252315251528. This paper documents a physical association between a cytokine receptor family member and a tyrosine kinase. 31.
MJ, BALTIMORE D: NF-xb: A Pleiotropic of Inducible and Tissue-specitic Gene Control. 581227-229.
32.
KIERANM, BU\NKV, LLXEAT F, VANDEKERCKHO~E J, ~~SPEICH
..
F, Ix BAIL 0, URBAN MB, KOURIISKV P, BAEUERLEPA, ISRAAELA: Subunit of NF-xB is Identical to Factor The DNA Siding
LENARE
..
GHOSH S, GWORD AM, RMERE I& TEMPST P, NOLAN GP, BAL~MORE D: Cloning of the ~50 DNA Binding Subunit of
NF-xB: Homology to rel and dorsal. Cell 1990, 62:101%1029. Reports molecular cloning of the ~50 subunit of the transcription factor NF-xB. ~50 shows remarkable homology, at the amino-terminal end, with the onogene v-rel 34. .
HIV Transcription in Synergy with p65. Nature 1991, 352~733-736. Molecular cloning of a novel subunit of the NFxB complex is described. Thls subunit is most related to the ~105 (~50 precursor). The complex of this subunit and ~65 is found to be more potent transcriptionally than the ~5~~65 heterodimer.
.
NOL%NGP, GHOSH S, LIOU H-C, TEMPST P, BAL~MORE D: DNA binding and IlcB Inhibition of the Cloned p65 Subunit of NF-xB, a rel-Related Polypeptide. Cell 1991, 64961-969.
AKIRAS, ISSHW H, SUGITA T, TANABE0, KINOSHXA S, NISHIO Y, NAKAJIMAT, HIRANO T, KISHIMOTO T: A Nuclear Factor for
IL-6 Expression (NF-IL6) is a Member of a C/EBP Family. EMBO J 1990, 9:1897-1906. Molecular cloning of a transcription factor involved in IL-~ expression is documented. This revealed the existence of a new family with leuclne zipper structure related to C/EBP. 38. .
39.
KITAMURAT, SATO N, ARAI K-I, MNAJIMAA: Expression Cloning of the Human IL-3 Receptor cDNA Reveals a Shared p Subunit for the Human IL-3 and GM-CSF Receptors. Cell 1991, 66:1165-1174.
40.
TAKAKIS, MITA S, KITAMURA T, YONEHARAS, YAMAGUCHI N, TOMINAGA 4 M~AJIMA A, TAKATSU K: Identification of the Second Subunit of the Murlne Interleuldn-5 Receptor: Interleukin-3 Receptor-like Protein, AICZB is a Component of the High-affinity Interleukin-5 Receptor. EMBO J 1991, 10:2833-2838.
Mediator Cell 1989,
KBF-1 and Homologous to the rel Oncogene Product. Cell 1990, 62:1007-1018. Describes molecular cloning of the transcription factor KBFl invoked in the expression of the class I MHC antigen. KBFl is identical to the 50 kD DNA-binding subunit of NF-xB. KBF also displays extensive amino-acid homology with the v-rel oncogene. 33.
.
41.
TAVENIERJ, DEVOS R, CORNELISS, TLJY~ENST, \(Am DER -EN J, FIERYW, PIAETINCK G: A Human High&in@ Interleukin-5
Receptor (ILSR) is Composed of and IL5-Specific a Chain and a !.3Chain Shared with the Receptor for GM-CSF. Cell 1991, 66:1175-1184 42.
GEARING DP, THUT CJ, VAN DEN BOS T, GIMPEL SD, DEIANEY PB, KING J, PRICE V, COSMAN D ANDBECKMAN MP: Leukemia
Inhibitory Factor Receptor is Structurally Related to the IL-6 Signal Transducer, gp130. EMBO J 1991, 10:283’+2848. 43.
GF,ARINGDP, COMEAU MR, FRIEND DJ, GIMPEL SD, THUT CJ, MCCOURTY J, BRASHERKK, KING-J4 GILLISS, MOSLF~ B, ZIEGLER SF AND COSMAN D: The IL-~ Signal Transducer, gp130: An
Oncostadn M Receptor and tin&y Converter Receptor. Science 1992, 255:1434-1437. S Akira and T Klshimoto, Suita, Osaka 565, Japan.
Division of Immunology
l-3,
for the LIF
Yamadaoka
313
