Biochimica et Biophysics Acts, 1114 (1992) 163-177
163
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-419X/92/$05.00
BBACAN 87256
The Interleukin-2 receptors: insights into a complex signalling mechanism Yasuhiro Minami, Takeshi Kono, Kyoko Yamada and Tadatsugu Taniguchi Institute for Molecular and Cellular Biology, Osaka University, Suita-shi, Osaka (Japan) (Received 25 May 1992)
Contents I.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
103
!!. Interleukin-2 (IL-2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
164
III. Interleukin-2 receptor (IL-2R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. IL-2 receptor a-chain (IL-2Ra-chain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. IL-2 receptor #-chain (IL-2R/3-chain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
164 164 165
C. Reconstitution of three receptor forms on lymphoid cells by the cloned human a- and ~-chain cDNAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. IL-2 receptor y-chain (IL-2Ry-chain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. C'ytokine receptor superfamily . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
169 169 170 170 171
V. Other biochemical events in the !L-2 signalling process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Raf.l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Pl3.kinase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. ras protein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
171 172 172 172
VI. Conclusion and perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
173
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
173
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
174
Interleukin-2 (IL-2), one of the first lymphokines to be identified, plays a central role in the clonal expansion of activated T-iymphocytes (T.cells) by interacting
Correspondence to: T. Taniguchi, Institute for Molecular and Cellular Biology, Osaka University, 1-3 Yamada-oka, Suita-shi, Osaka 565,
Japan.
166 168 168
IV. Structure-function relationship of the IL-2R #.chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Molecular dissection of the IL-2Rp.chain and its function in signal transduction . . . . . . . . . . . B. IL-2R-coupled tyrosine kinases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Interaction of the IL-2R/3-chain with the src-family kinase p56 ick . . . . . . . . . . . . . . . . . . . . . . D. IL-2R/3 chain and c.fos gene induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I. Introduction
,.~.,..4t
with specific cell surface receptors (IL-2 receptors) [1-4]. Antigen-specific, clonal proliferation of T-cells is initiated via a process of signal transduction, wherein the specific interaction of the antigen-MHC molecules and T-cell antigen receptor complex (TCR) triggers the expression of IL-2 and its homologou,~;receptor (IL-2R). The interaction of IL-2 with IL-2g. is subsequently translated into a complex, yet mostly ,unknovcn,signaltransduction process which leads to i:ell proliferation
[5-8]. i
164
In: addition to its potent T-cell growth-stimulatory activity, IL-2 has ~ n shown to mediate multiple bio. logical ~nctions, including growth and differentiation of B cells [9,I0], generation of iymphokine-activated killer cells [11,12], augmentation of natural killer cells [13] and proliferation and maturation of oligodendrogli~ cells [14]. Furthermore, recent studies have shown that IL-2 can act negatively in regulating cell growth, programming mature T-cells for apoptosis [15]` This evidence also suggests that 11.-,2 is involved in ~diating e~ra-thymic tolerance. These observations suggest that !1-2 delivers various signals to a wide range of cell Wpes via interaction wi~l its receptor, I ~ speci~ cell-surface receptor which binds IL.2 (IL-2R) is composed of at least three distinct polypeptides, the IL.2Rao~ IL-2R/3~ and IL-2Ry-chain, The ~nes e n ~ i n g IL.2 a~d these three receptor Sub~tts have ~en cloned, and their complete primary structures have been deduced [16-21]. In addition, evidence has accumulated which suggests a critical role of the IL-2R0-chain in 11.-2signal transduction [22-25], although the role of the IL-2RT-chain in !1.-2 signalling remains unclear. In this article, we will first describe the molecular nature of IL-2 and its receptor (IL-2R) and then provide an overview of our know° ledge regarding receptor-mediated signal transduction, with a particular emphasis on the structure-function relationship of the IL-2R~-cha~n.
Ii. lnt~l~kin.2 (11-2) 11.-2 is a glycoprotein of 15 kDa, produced and secreted by antigen, or mitogen-stimulated T-cells. Although IL-2 was originally descril~d as a T-cell mite. genie factor, subsequent studies have revealed that ~ l l s , NK (natural killer) cells, and LAK (bmpho. kino-activated killer)cells are also responsive to !1.-2. Complete nucl~tide scquen~ analysis of the eDNA encoding the biological~ active human 11.-2 predicted that the precursor consisted of 153 amir,o acids (a,a) with the si~al sequence, 20 amino acids (~.a) in length |26], The carboxy-terminal residues 131-133 and the ~teine ~ues at positions 58 and 105 which form an intra-molccular disulfide bridge are required for biolo~ca! ~tivity and binding [27,28]` The aminoacid sequence of mouse il.-2 shows 63% homolo~. ~th human i1.2 [29,30], it contains '~ unique stretch of 12 consecutive 81utamine repeats (a,a, 15-26) which are absent in the human and bovine IL-2, Bovine 11.-2 has ~ amino.acid homology of 65% with human !i.-2 50~ with routine IU2 [31,32]. The thre~ dimen~1 ~re of human !1.-2 at 3,0-,~ resolution revealed a backbone of six anti-parallel a-helices without any segmem of # secondary structure [33]` The genmnk human 11.-2 8one, encoded by four axons separated by one short and two long introns, is local-
ized to chromosome 4(I [34-36]. Structural analysis of the human and mouse 11.-2 genes revealed the presence of highly conserved sequences within the 5' flanking region [37]. Interestingly, the overall genomic organization of 11..-2 is remarkably similar to those of other cytokines, such as 11.-4 and granulocyte-macrophage colony-stimulating factor (GM-CSF), suggesting that these molecules could have evolved from a common genetic progenitor [38,39]. In the human IL-2 gene, the upstream region spanning from nucleotide -129 and -319 from the CAP site contains DNA sequences functioning as an inducible enhancer required for the mitog©n-specific IL-2 gone activation in T-cells [40-46].
!!!. 11.2 receptor (!1.2R)
Ill-A, IL.2 receptor a.chain (IL-2Ra.chain) The biochemical characterization of the IL-2 binding component on cells was greatly facilitated by the development of a monoclonal antibody (designated as the anti-Tac antibody) which reacts with activated human T-cells [47]` The human IL-2Ra-chain, originally described as the Tac antigen, was identified as a 55 kDa membrane glycoprotein (p55) capable of binding 11.-2 [48,49]` Three groups have employed similar strategies for protein purification and subsequent eDNA cloning for the human IL-2Ra-chain [17-19]. The deduced amino acid sequence of the human IL2Ra-chain indicates a mature protein of 251 amino acids with ~ signal pcptide of 21 amino acids in length. The primary structure of the IL-2Ra-chain shows no significant sequence homology with other known receptor molecules. Furthermore, the ILo2Ra-chain lacks the characteristic structural features of a member of the immunoglobulin superfamily and does not belong to the cytokine receptor superfamily,Within thischain, regions of the amino.terminal 219 a.a. residues, the internal 19 a,a. residues and the carboxy-terminal 13 a,a, residues constitute the extracellular,membrane. spanning and cytoplasmic regions, re.spectively. The extracellular region contains two potential N-linked 81ycosylation sites and multiple possible O-linked carbohydrate addition sites. In addition to these glyco. sylations, the IL-2Ra.chain is post-translationally mod• ified by sulfation and phosphorylation [50,51]. The short cytoplasmic region contains several positively charged amino acids and the primary sites for phosphorylation (Ser-247 and Thr-250). It was reported that the phosphorylation of the IL-2Ra chain did i~ot appear to affect the receptor function [52]. The region from amino acids 1-64 is 22% homologous to amino acids 102-174, suggesting an internal gene duplication event during evohttion, eDNA encoding the routine IL-2Ra chain has also been isolated by low-stringency hybridization studies using human IL-2Ra-chain eDNA
165 as a probe [53,54]. The sequence of the mouse IL2Re-chain shares 72% DNA and 61% amino-acid homology with that of the human IL-2Ra chain. When the cloned human IL-2Ra-cDNA was transfected into lymphoid and non-lymphoid cells, it became evident that the IL-2Ra-chain constitutes only the low-affinity IL-2-binding form, which is non-functional with respect to IL-2 internalization and IL-2 signalling [55,56]. Furthermore, when the human IL-2Ra eDNA was introduced and expressed in murine T-cell lines (EL-4 and CTLL-2), the high-affinity IL-2R, as well as the low-affinity one were reconstituted on cell surface, suggesting a contribution of the a-chain for the high. affinity receptor formation [55,57,58]. By mutational analysis, it was shown that the N-terminal 83 amino-acid residues of the IL-2Ra-chain, especially residues 1-6 and 35-43, were important for IL-2-binding property
[59]. Resting T-cells do not express IL-2Ra-chains, but they are rapidly and transiently induced following activatio~ with antigen or mitogen [5,6.60]. The IL-2R~chain has also been identified on a wide variety of cells, including thymocytes, activated B-cells, macrophages, IL-3-dependent bone-marrow-derived cell lines, epidermal Langerhans cells, Kupffer cells of the liver and oligodendroglial cells, suggesting a potential role of IL-2 in those cells [9,14,61-63]. The genomic human IL-2Ra-chain gene has been assigned to chromosome 10, bands p14-15 [64]. The gene is composed of eight exons separated by seven introns, and it spans at least 25 kb. The gene contains multiple CAP sites and regulatory cis elements are present within the 5' flanking region that direct mitogen-induced activation of the !L-2Ra gene in T-cells [65-67]. Although both IL-2 and IL-2Ra are transiently expressed in T-cells through similar stimuli, expression of the receptor gene is not as stringently regulated as the 11,-2 gene. In normal T-cells, for example, the IL-2 receptor gene can be activated in response to 12.O.tetradecanoylphorbol-13-acetate (TPA), but the IL-2 gene activation requires stimulation with both calcium ionophore and TPA, suggesting the existence of similar but distinct mechanisms of gene activation for both genes [68]. In fact, the 5' regulatory regions that appear to bc responsible for the expression of these genes do not show apparent homolo ~ with each other, pointing out further that the nuclear transcription factor(s) required for the full activation of 11,-2 and the receptor gene are not the same [69].
III-B. IL-2 receptor I3-chain (IL-2Rl3.chain) Another component of IL-2R (now referred as the IL-2R~ chain) was bioehemicaily identified by affinity cross-linking experiments [70-73]. Molecular and bio-
chemical characterization of the IL-2R/3-chain was facilitated by the development of monoclonal antibodies [74]. Expression cloning of the eDNA for the human IL-2R/3-chain was performed using the monoclonal antibodies (see below) on the basis of the method initially described by Seed et ai. [75]. Briefly, eDNA libraries were prepared using poI~
163
© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-419X/92/$05.00
BBACAN 87256
The Interleukin-2 receptors: insights into a complex signalling mechanism Yasuhiro Minami, Takeshi Kono, Kyoko Yamada and Tadatsugu Taniguchi Institute for Molecular and Cellular Biology, Osaka University, Suita-shi, Osaka (Japan) (Received 25 May 1992)
Contents I.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
103
!!. Interleukin-2 (IL-2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
164
III. Interleukin-2 receptor (IL-2R) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. IL-2 receptor a-chain (IL-2Ra-chain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. IL-2 receptor #-chain (IL-2R/3-chain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
164 164 165
C. Reconstitution of three receptor forms on lymphoid cells by the cloned human a- and ~-chain cDNAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. IL-2 receptor y-chain (IL-2Ry-chain) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. C'ytokine receptor superfamily . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
169 169 170 170 171
V. Other biochemical events in the !L-2 signalling process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Raf.l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Pl3.kinase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. ras protein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
171 172 172 172
VI. Conclusion and perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
173
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
173
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
174
Interleukin-2 (IL-2), one of the first lymphokines to be identified, plays a central role in the clonal expansion of activated T-iymphocytes (T.cells) by interacting
Correspondence to: T. Taniguchi, Institute for Molecular and Cellular Biology, Osaka University, 1-3 Yamada-oka, Suita-shi, Osaka 565,
Japan.
166 168 168
IV. Structure-function relationship of the IL-2R #.chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Molecular dissection of the IL-2Rp.chain and its function in signal transduction . . . . . . . . . . . B. IL-2R-coupled tyrosine kinases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Interaction of the IL-2R/3-chain with the src-family kinase p56 ick . . . . . . . . . . . . . . . . . . . . . . D. IL-2R/3 chain and c.fos gene induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I. Introduction
,.~.,..4t
with specific cell surface receptors (IL-2 receptors) [1-4]. Antigen-specific, clonal proliferation of T-cells is initiated via a process of signal transduction, wherein the specific interaction of the antigen-MHC molecules and T-cell antigen receptor complex (TCR) triggers the expression of IL-2 and its homologou,~;receptor (IL-2R). The interaction of IL-2 with IL-2g. is subsequently translated into a complex, yet mostly ,unknovcn,signaltransduction process which leads to i:ell proliferation
[5-8]. i
164
In: addition to its potent T-cell growth-stimulatory activity, IL-2 has ~ n shown to mediate multiple bio. logical ~nctions, including growth and differentiation of B cells [9,I0], generation of iymphokine-activated killer cells [11,12], augmentation of natural killer cells [13] and proliferation and maturation of oligodendrogli~ cells [14]. Furthermore, recent studies have shown that IL-2 can act negatively in regulating cell growth, programming mature T-cells for apoptosis [15]` This evidence also suggests that 11.-,2 is involved in ~diating e~ra-thymic tolerance. These observations suggest that !1-2 delivers various signals to a wide range of cell Wpes via interaction wi~l its receptor, I ~ speci~ cell-surface receptor which binds IL.2 (IL-2R) is composed of at least three distinct polypeptides, the IL.2Rao~ IL-2R/3~ and IL-2Ry-chain, The ~nes e n ~ i n g IL.2 a~d these three receptor Sub~tts have ~en cloned, and their complete primary structures have been deduced [16-21]. In addition, evidence has accumulated which suggests a critical role of the IL-2R0-chain in 11.-2signal transduction [22-25], although the role of the IL-2RT-chain in !1.-2 signalling remains unclear. In this article, we will first describe the molecular nature of IL-2 and its receptor (IL-2R) and then provide an overview of our know° ledge regarding receptor-mediated signal transduction, with a particular emphasis on the structure-function relationship of the IL-2R~-cha~n.
Ii. lnt~l~kin.2 (11-2) 11.-2 is a glycoprotein of 15 kDa, produced and secreted by antigen, or mitogen-stimulated T-cells. Although IL-2 was originally descril~d as a T-cell mite. genie factor, subsequent studies have revealed that ~ l l s , NK (natural killer) cells, and LAK (bmpho. kino-activated killer)cells are also responsive to !1.-2. Complete nucl~tide scquen~ analysis of the eDNA encoding the biological~ active human 11.-2 predicted that the precursor consisted of 153 amir,o acids (a,a) with the si~al sequence, 20 amino acids (~.a) in length |26], The carboxy-terminal residues 131-133 and the ~teine ~ues at positions 58 and 105 which form an intra-molccular disulfide bridge are required for biolo~ca! ~tivity and binding [27,28]` The aminoacid sequence of mouse il.-2 shows 63% homolo~. ~th human i1.2 [29,30], it contains '~ unique stretch of 12 consecutive 81utamine repeats (a,a, 15-26) which are absent in the human and bovine IL-2, Bovine 11.-2 has ~ amino.acid homology of 65% with human !i.-2 50~ with routine IU2 [31,32]. The thre~ dimen~1 ~re of human !1.-2 at 3,0-,~ resolution revealed a backbone of six anti-parallel a-helices without any segmem of # secondary structure [33]` The genmnk human 11.-2 8one, encoded by four axons separated by one short and two long introns, is local-
ized to chromosome 4(I [34-36]. Structural analysis of the human and mouse 11.-2 genes revealed the presence of highly conserved sequences within the 5' flanking region [37]. Interestingly, the overall genomic organization of 11..-2 is remarkably similar to those of other cytokines, such as 11.-4 and granulocyte-macrophage colony-stimulating factor (GM-CSF), suggesting that these molecules could have evolved from a common genetic progenitor [38,39]. In the human IL-2 gene, the upstream region spanning from nucleotide -129 and -319 from the CAP site contains DNA sequences functioning as an inducible enhancer required for the mitog©n-specific IL-2 gone activation in T-cells [40-46].
!!!. 11.2 receptor (!1.2R)
Ill-A, IL.2 receptor a.chain (IL-2Ra.chain) The biochemical characterization of the IL-2 binding component on cells was greatly facilitated by the development of a monoclonal antibody (designated as the anti-Tac antibody) which reacts with activated human T-cells [47]` The human IL-2Ra-chain, originally described as the Tac antigen, was identified as a 55 kDa membrane glycoprotein (p55) capable of binding 11.-2 [48,49]` Three groups have employed similar strategies for protein purification and subsequent eDNA cloning for the human IL-2Ra-chain [17-19]. The deduced amino acid sequence of the human IL2Ra-chain indicates a mature protein of 251 amino acids with ~ signal pcptide of 21 amino acids in length. The primary structure of the IL-2Ra-chain shows no significant sequence homology with other known receptor molecules. Furthermore, the ILo2Ra-chain lacks the characteristic structural features of a member of the immunoglobulin superfamily and does not belong to the cytokine receptor superfamily,Within thischain, regions of the amino.terminal 219 a.a. residues, the internal 19 a,a. residues and the carboxy-terminal 13 a,a, residues constitute the extracellular,membrane. spanning and cytoplasmic regions, re.spectively. The extracellular region contains two potential N-linked 81ycosylation sites and multiple possible O-linked carbohydrate addition sites. In addition to these glyco. sylations, the IL-2Ra.chain is post-translationally mod• ified by sulfation and phosphorylation [50,51]. The short cytoplasmic region contains several positively charged amino acids and the primary sites for phosphorylation (Ser-247 and Thr-250). It was reported that the phosphorylation of the IL-2Ra chain did i~ot appear to affect the receptor function [52]. The region from amino acids 1-64 is 22% homologous to amino acids 102-174, suggesting an internal gene duplication event during evohttion, eDNA encoding the routine IL-2Ra chain has also been isolated by low-stringency hybridization studies using human IL-2Ra-chain eDNA
165 as a probe [53,54]. The sequence of the mouse IL2Re-chain shares 72% DNA and 61% amino-acid homology with that of the human IL-2Ra chain. When the cloned human IL-2Ra-cDNA was transfected into lymphoid and non-lymphoid cells, it became evident that the IL-2Ra-chain constitutes only the low-affinity IL-2-binding form, which is non-functional with respect to IL-2 internalization and IL-2 signalling [55,56]. Furthermore, when the human IL-2Ra eDNA was introduced and expressed in murine T-cell lines (EL-4 and CTLL-2), the high-affinity IL-2R, as well as the low-affinity one were reconstituted on cell surface, suggesting a contribution of the a-chain for the high. affinity receptor formation [55,57,58]. By mutational analysis, it was shown that the N-terminal 83 amino-acid residues of the IL-2Ra-chain, especially residues 1-6 and 35-43, were important for IL-2-binding property
[59]. Resting T-cells do not express IL-2Ra-chains, but they are rapidly and transiently induced following activatio~ with antigen or mitogen [5,6.60]. The IL-2R~chain has also been identified on a wide variety of cells, including thymocytes, activated B-cells, macrophages, IL-3-dependent bone-marrow-derived cell lines, epidermal Langerhans cells, Kupffer cells of the liver and oligodendroglial cells, suggesting a potential role of IL-2 in those cells [9,14,61-63]. The genomic human IL-2Ra-chain gene has been assigned to chromosome 10, bands p14-15 [64]. The gene is composed of eight exons separated by seven introns, and it spans at least 25 kb. The gene contains multiple CAP sites and regulatory cis elements are present within the 5' flanking region that direct mitogen-induced activation of the !L-2Ra gene in T-cells [65-67]. Although both IL-2 and IL-2Ra are transiently expressed in T-cells through similar stimuli, expression of the receptor gene is not as stringently regulated as the 11,-2 gene. In normal T-cells, for example, the IL-2 receptor gene can be activated in response to 12.O.tetradecanoylphorbol-13-acetate (TPA), but the IL-2 gene activation requires stimulation with both calcium ionophore and TPA, suggesting the existence of similar but distinct mechanisms of gene activation for both genes [68]. In fact, the 5' regulatory regions that appear to bc responsible for the expression of these genes do not show apparent homolo ~ with each other, pointing out further that the nuclear transcription factor(s) required for the full activation of 11,-2 and the receptor gene are not the same [69].
III-B. IL-2 receptor I3-chain (IL-2Rl3.chain) Another component of IL-2R (now referred as the IL-2R~ chain) was bioehemicaily identified by affinity cross-linking experiments [70-73]. Molecular and bio-
chemical characterization of the IL-2R/3-chain was facilitated by the development of monoclonal antibodies [74]. Expression cloning of the eDNA for the human IL-2R/3-chain was performed using the monoclonal antibodies (see below) on the basis of the method initially described by Seed et ai. [75]. Briefly, eDNA libraries were prepared using poI~
