0013-7227/90/1271-0001$02.00/0 Endocrinology Copyright© 1990 by The Endocrine Society
Vol. 127, No. 1 Printed in U.S.A.
Editorial: The Possible Autocrine/Paracrine and Endocrine Roles of Insulin-Like Growth Factors of Human Tumors Somatomedins were originally detected in serum as GH-dependent effects mediating some of GH's actions and were considered endocrine factors capable of exerting stimulating factors distant from their site of synthesis (1). The first clear evidence that somatomedins could act locally in an autocrine or paracrine mode was provided by Dulak and Teman in 1973 (2). They noted that certain cell types grow in the absence of serum-derived growth factors which led them to postulate that such cells were capable of secreting their own growth factors. They proceeded to isolate from medium conditioned by a rat hepatocyte cell line (BRL-3A), a growth factor with the properties of a somatomedin. Subsequently, it was shown by Marquardt et al., (3) that this growth factor was rat insulin-like growth factor II (IGF-II). Many tumor cell lines are also capable of growth and multiplication in serum-free medium. Todero and DeLarco (4) showed that sarcoma virus transformed mouse 3T3 cells secreted a peptide which reacted in a rat liver radioreceptor assay which is now known to detect primarily IGF-II. The same authors subsequently found that a human fibrosarcoma cell line released a similar peptide into conditioned medium (5). IGF gene expression in tumors Strong evidence exists that some tumors have the molecular machinery for the production of IGFs. Reeve et al. (6) and Scott et al. (7) independently found much higher concentrations of IGF-II messenger RNA (mRNA) in Wilms' tumors by dot-blot and Northern analysis than in normal kidney. Both groups of authors noted that the gene for IGF-II is located on chromosome 11 in close proximity to the Wilms' tumor susceptibility gene. Reeve et al., (6) speculated that the IGF-II gene expression in these tumors occurred as a result of loss of a regulatory gene similar to that postulated for the deReceived March 30,1990. Address correspondence to: Dr. William Daughaday, Washington University School of Medicine, Box 8127, St. Louis, Missouri 63110. Dr. Daughaday is a prior President of The Endocrine Society and well known for his research on growth factors.
velopment of Wilms' tumors although they conceded that IGF-II is an embryonal gene which is active at the developmental stage during which tumor initiation may have occurred. Subsequent work by many investigators have established that a wide range of tumors are associated with increased IGF-II gene expression (Table 1). In the studies of Tricoli et al. (8), colon tumors, particularly of the rectum and rectosigmoid frequently had increased IGFII mRNA. They reported that over 90% of liposarcomas similarly expressed IGF-II gene activity. In another paper, Hoppener et al. (9) reported increased IGF-II mRNAs in both benign leiomyomas and in leiomyosarcoma. Several investigators have found increased IGF-II mRNA in some, but not all hepatomas (10,11). Increased IGF-II mRNA has been reported with neuroectodermal tumors [pheochromocytomas (12) and neuroblastomas (13)]. Many of the tumors which have increased levels of IGF-II mRNAs also contain IGF-I mRNAs, but the amounts present are little increased as compared to the corresponding normal tissue. In some cases, there seem to be an inverse relationship between IGF-I and IGF-II mRNAs. Controversy exists concerning the IGF-I mRNA in breast cancer cells. Huff et al. (14) did Northern blots with IGF-I cDNAs and found transcripts present in liver. Freed and Herington (15) made similar observations. In contrast, Yee et al. (16) carried out RNAse protection assays with a IGF-IA cDNA probe containing the entire coding region of the proIGF-IA molecule. They found no protected transcripts in any of 11 breast cancer cell lines, but did find IGF-I mRNA in breast stromal tissue. They did find IGF-I mRNA in a Ewing's sarcoma and in 3 neuroepitheliomas. IGF peptides in tumors There may be considerable variability in the translation of IGF mRNAs into IGF peptides. Haselbacher et al. (12) found that three pheochromocytomas contained greatly increased concentrations of IGF-II (between 5.3 and 7.1 /ig/g), most of which was present in a 10 kilodal-
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2
EDITORIAL
Endo • 1990 Vol 127 • No 1
TABLE 1. Reports of IGF mRNA, peptides, IGF-I receptors, and IGF metogenic response of human tumors Peptide
mRNA IGF-I Sarcomas FibroHemangiopericyteLeiomyoLipoMesothelialRhabdomyoEwing's Neural Pheochromocytoma Neuroblastoma Neuroepitheloma Meningioma Carcinomas Breast Colon Hepatoma Lung Adeno Epidermoid Small cell Wilm's
IGF-II
IGF-I
17, 18, 27
IGF-II
IGF-I receptor
Mitogenic IGF response
17,18 27,28 28
27 9 8 18 25a
18 25a
25a
16
12,13
13 13
13
25
25
14, 15, 23
15
14, 15, 23
8
24
24
23 22
23
12 13
13 16
14, 15 (16-no) 8(16-no) 10, 11
30 30 23
6, 7, 12
12
22
Numbers refer to publications cited.
ton (kDa) species indicative of a partially processed proIGF-II. On the other hand, two Wilms' tumors which contained more than 7 times as much IGF-II mRNA than in the pheoopchromocytomas only contained about 5% as much IGF-IL. Increased concentrations of IGF II were found by Daughaday et al. (17) in a fibrosarcoma (originally identified as a leiomyosarcoma). As was the case with the pheochromocytomas, most of this IGF-II was present as the large mol wt big IGF-IL Ron et al. (18) found greatly increased concentrations of IGF-II in a fibrosarcoma and lesser concentration in a fibrous mesothelioma. Explants of these tumors released IGF-II detected by RIA. It was calculated that the tumors were capable of secreting 2.1 and 7.2 /ug/g/24 h. Secretion of IGF binding proteins Virtually all cells that are known to secrete IGFs also secrete IGF binding proteins. Several breast cancer cell lines secrete immunologically detected IGF-I (14,15) and also, IGF binding proteins (14). In the studies of DeLeon et al. (19), IGF binding proteins in the conditioned media of several breast cancer cell lines were cross-linked to IGFs and subjected to polyacrylamide gel electrophoresis (PAGE). At least four different forms of binding protein were identified. Little or no immunoreactivity was detected with a RIA specific for IGF-I amniotic fluid (IGFBP-I). Northern blot also detected only small con-
centrations of IGFBP-I mRNA in two of the four cell lines studied. It may be presumed that the major IGF binding protein secreted by these cell lines was IGFBP2, a form of binding protein associated with fetal stages of development. In another study, Lamson et al. (20) characterized the binding proteins released by a human endometrial cancer cell line (HEC-1). They found two isoforms of the glycosylated IGFBP-3, the major GH-dependent binding protein of human serum. An unglycosylated binding protein had an apparent size of 31 kDa. Extracted mRNA of the HEC-1 cells did not react with a probe of IGFBP1. Therefore, HEC-1 cells differed from normal endometrium which does secrete IGFBP-1. The 31 kDa probably is IGFBP-2. Jaques et al. (21) found that small cell lung carcinomas also secreted 24-32 kDa binding proteins. These cell lines did not contain mRNA reactive with probes for IGFBP-1. Again, this suggests the presence of IGFBP-2. It is as yet unknown how the secretion of IGFBP-2 modify autocrine-paracrine actions on tumor IGFs. IGF receptors in tumors IGF-I type receptors are found in several different tumor types including Wilms' tumor (22), small cell lung carcinoma (23), colon carcinoma (24), meningioma (25), neuroblastoma (11), rhabdomyosarcoma (25a), and leu-
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EDITORIAL kemic lymphoblasts (26). While many of these cell types also contain receptors for the combined IGF-II/mannose-6-phosphate receptor, it is unlikely that this receptor mediates the mitogenic effects of IGF-II. The specific monoclonal antibody IR-3, which blocks IGF-I receptor function, blocks the mitogenic effects of IGF-I and IGFII on small cell lung carcinoma cells (23), neuroblastoma cells (13), and rhabdomyosarcoma cells (25a). Of interest is the observation that monoclonal antibody IR-3 did not block the ability of IGF-II to stimulate cellular motility of rhabdomyosarcoma cells suggesting that this effect may be mediated by the IGF-II/mannose-6-phosphate receptor. Autocrine paracrine role of tumor IGFs The mitogenic activity of some tumor cell lines in the absence of added growth factors can be inhibited by monoclonal antibody IR-3 [small cell lung carcinoma (23), neuroblastoma cells (13), and rhabdomyosarcoma cells (25a)]. This provides evidence that the production of IGFs by these cells was the critical factor in permitting mitogenesis in serum-free medium. Endocrine effects of tumor IGFs There is increasing evidence that the secretion of IGFII by certain tumors may have systemic endocrine insulin-like actions. Nonislet cell tumors, associated with hypoglycemia have been reported to contain increased concentrations of IGF-II mRNA (17, 13, 27), increased concentrations of IGF-II peptides (17,18), and increased secretion of IGF-II peptides in vitro (18). As noted earlier, many tumors may lack the enzymatic machinery for processing proIGF-II to the final 7.5 kDa peptide. Daughaday et al. (17) found that serum from a patient with a fibrosarcoma (originally identified as a leiomyosarcoma) had the same predominance of big IGFII as was present in the tumor. This may become a useful method of distinguishing tumor derived IGF-II from normal IGF-II. In most cases of nonislet tumor hypoglycemia, the secretion of IGF-I and GH are markedly suppressed. This strongly suggests that increased IGF-II secretion by the tumor is exerting an inhibitory effect on GH secretion. A puzzling aspect of the pathphysiology of nonislet cell tumor hypoglycemia is that the total IGF-II measured by RIA is usually normal or reduced. This may be explained by marked abnormalities of the IGF binding in the sera of these patients (28). In a report of three patients with this syndrome there was a virtual complete absence of the 150 kDa ternary complex which normally carries 75% of the serum IGFs. Most of the endogenous IGFs were found as complexes of 60 kDa which suggest that IGFBP-3 was not absent. A deficiency of the acid-
labile complexing protein or an abnormality of its function was postulated. As the 150 kDa IGF complexes pass through the capillary membrane poorly (29), it is likely that the smaller complexes would have increased access to target tissues and therefore, have greatly increased biological action. This would provide an explanation of the induction of hypoglycemia without an elevation of total serum IGF-II. It is as yet unexplained why increased IGF-II action sufficient to induce hypoglycemia does not result in an increase in mesenchymal tissue growth as occurs in acromegaly. Many questions remain unanswered about the endocrine action of tumor-secreted IGFs. In conclusion, the intense research in this field has established that IGFs, particularly IGF-II, are synthesized by many tumors, but processing of proIGF-II is frequently incomplete. Many of the same tumors contain IGF-I receptors and mitogenesis of several tumor cell lines are stimulated by added IGFs. The ability of several tumor cell lines to proliferate in serum-free medium is dependent on the autocrine/paracrine action of IGFs. Certain tumors produce sufficient IGF-II to suppress GH and IGF-I secretion and induce hypoglycemia. William H. Daughaday
References 1. Salmon WD 1957 A hormonally controlled serum factor which stimulates sulfate incorporation by cartilage in vitro. J Lab Clin Med 40:825 2. Dulak NC, Temin HM 1973 A partially purified polypeptide fraction from rat liver cell conditioned medium with multiplicationstimulating activity for embryo fibroblasts. J Cell Physiol 81:153 3. Marquardt H, Todaro GJ, Henderson LE, Oroszlan S 1981 Purification and primary structure of a polypeptide with multiplicationstimulating activity from rat liver cell cultures. Homology with human insulin-like growth factor II. J Biol Chem 256:6859 4. Todaro GJ, DeLarco JE 1978 Growth factors produced by sarcoma virus-transformed cells. Cancer Res 38:4147 5. DeLarco JE, Todaro GJ 1978 A human fibrosarcoma cell line producing multiplication stimulating activity (MSA)-related peptides. Nature 272:356 6. Reeve AE, Eccles MR, Wilkins RJ, Bell GI, Millow LJ 1985 Expressions of insulin-like growth factor-II transcripts in Wilms' tumour. Nature 317:258 7. Scott J, Cowell J, Robertson ME, Priestly LM, Wadley R, Hopkins B, Pritchard J, Bell GI, Graham CF, Knott TJ 1985 Insulin-like growth factor-II gene expression in Wilms' tumour embryonic tissues. Nature 317:260 8. Tricoli JV, Rail LB, Karakousis CP, Herrera L, Petrelli NJ, Bell GI, Shows TB 1986 Enhanced levels of insulin-like growth factor messenger RNA in human colon carcinomas and liposarcomas. Cancer Res 46:6169 9. Hoppener JWM, Moseelman S, Roholl PJM, Lambrechts C, Slebos RJC, de Pagter-Holthuizen P, Lips CJM, Jansz HS, Sussenbach JS 1988 Expression of insulin-like growth factor-I and -II genes in human smooth muscle tumours. EMBO J 7:1379 10. Cariani E, Lasserre C, Seurin D, Hamelin B, Kemeny F, Franco D, Czech MP, Ullrich A, Brechot C 1988 Differential expression of insulin-like growth factor II mRNA in human primary liver cancers, benign liver tumors, and liver cirrhosis. Cancer Res 48:6844 11. Su T-S, Liu W-Y, Han S-H, Jansen M, Yang-Fen TL, P'eng F-K, Chou C-K 1988 Transcripts of the insulin-like growth factors I and
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EDITORIAL II in human hepatoma. Cancer Res 49:1773 12. Haselbacher GK, Irminger JC, Zapf J, Ziegler WH, Humbel RE 1987 Insulin-like growth factor II in human adrenal pheochromocytoma and Wilms' tumors: expression at mRNA and protein level. Proc Natl Acad Sci USA 84:1104 13. El-Badry OM, Romanus JAJ, Helman LJ, Cooper MJ, Rechler MM, Israel MA 1989 Autonomous growth of a human neuroblastoma cell line is mediated by insulin-like growth factor II. J Clin Invest 84:829 14. Huff KK, Kaufman D, Gabbay KH, Spencer EM, Lippman ME, Dickson RB 1986 Secretion of an insulin-like growth factor-Irelated protein by human breast cancer cells. Cancer Res 46:4613 15. Freed KA, Herington AC 1989 Insulin-like growth factor-I and its autocrine role in growth of MCF-u human breast cancer cells in culture. J Mol Endocrinol 3:183 16. Yee D, Paik S, Lebovic GS, Marcus RR, Favoni RE, Cullen KJ, Lippman ME, Rosen N 1989 Analysis of insulin-like growth factor I gene expression in malignancy: evidence for a paracrine role in human breast cancer. Mol Endocrinol 3:509 17. Daughaday WH, Emanuele MA, Brooks MH, Barbato AL, Kapadia M, Rotwein P 1988 Insulin-like growth factor II synthesis and secretion by a leiomyosarcoma with associated hypoglycemia. N Engl J Med 319:1434 18. Ron D, Powers AC, Pandian MR, Godine JE, Axelrod L 1989 Increased insulin-like growth factor II (IGF-II) production and consequent suppression of growth hormone secretion: a dual mechanism for tumor induced hypoglycemia. J Clin Endocrinol Metab 68:701 19. De Leon DD, Wilson DM, Bakker B, Lamson G, Hintz RL, Rosenfeld RG 1989 Characterization of insulin-like growth factor binding proteins from human breast cancer cells. Mol Endocrinol 3:567 20. Lamson G, Oh Y, Pham H, Giudice LC, Rosenfeld RG 1989 Expression of two insulin-like growth factor-binding proteins in a human endometrial cancer cell line: structural, immunological, and genetic characterization. J Clin Endocrinol Metab 69:852 21. Jaques G, Kiefer P, Rotsch M, Hennig C, Rudiger G, Richter G, Havemann K1989 Production of insulin-like growth factor binding
E n d o • 1990 Vol 127 • No 1
proteins by small-cell lung cancer cell lines. Exp Cell Res 184:396 22. Gansler T, Allen KD, Burant CF, Inabnett T, Scott A, Buse MG, Sens DA, Garvin AJ 1988 Detection of type 1 insulinlike growth factor (IGF) receptors in Wilms' tumors. Am J Pathol 130:431 23. Nakanishi Y, Mulshine JL, Kasprzyk PH, Natale RB, Maneckjee R, Avis I, Treston AM, Gazdar AF, Minna JD, Cuttitta F 1988 Insulin-like growth factor-I can mediate autocrine proliferation of human small cell lung cancer cell lines in vitro. J Clin Invest 82:354 24. Koenuma M, Yamori T, Tsuruo T 1989 Insulin and insulin-like growth factor I stimulate proliferation of metastatic variants of colon carcinoma 26. Jpn J Cancer Res 80:51 25. Kurihara M, Tokunaga Y, Tsutsumi K, Kawaguchi T, Shigematsu K, Niwa M, Mori K 1989 Characterization of insulin-like growth factor I and epidermal growth factor receptors in meningioma. J Neurosurg 71:538 25a.El-Badry OM, Minniti C, Kohn EC, Houghton PJ, Daughaday WH, Helman LJ 1990 Insulin like growth factor II acts on an autocrine growth and motility factor in human rhadomyosarcoma tumors. Cell Growth Differ, in press 26. Lee PDK, Rosenfeld RG, Hintz RL, Smith SD 1986 Characterization of insulin-like growth factors I and II, and growth hormone receptors on human leukemic lymphoblasts. J Clin Endocrinol Metab 62:28 27. Lowe WL Jr, Roberts CT Jr, LeRoith D, Rojeski MT, Merimee TJ, Fui ST, Keen H, Arnold D, Mersey J, Gluzman S, Spratt D, Eastman RC, Roth J 1989 Insulin-like growth factor-II in nonislet cell tumors associated with hypoglycemia: increased levels of messenger ribonucleic acid. J Clin Endocrinol Metab 69:1153 28. Daughaday WH, Kapadia M 1989 Significance of abnormal serum binding of insulin-like growth factor II in the development of hypoglycemia in patients with non-islet-cell tumors. Proc Natl Acad Sci USA 86:6778 29. Binoux M, Hossenlopp P 1988 Insulin-like growth factor (IGF) and IGF-binding proteins: comparison of human serum and lymph. J Clin Endocrinol Metab 67:509 30. Minuto F, Del Monte P, Barreca A, Fortini P, Cariola, Catrambone G, Giordano G 1986 Evidence for an increased somatomedin-C/ insulin-like growth factor I content in primary human lung tumors. Cancer Res 46:985
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Vol. 127, No. 1 Printed in U.S.A.
Editorial: The Possible Autocrine/Paracrine and Endocrine Roles of Insulin-Like Growth Factors of Human Tumors Somatomedins were originally detected in serum as GH-dependent effects mediating some of GH's actions and were considered endocrine factors capable of exerting stimulating factors distant from their site of synthesis (1). The first clear evidence that somatomedins could act locally in an autocrine or paracrine mode was provided by Dulak and Teman in 1973 (2). They noted that certain cell types grow in the absence of serum-derived growth factors which led them to postulate that such cells were capable of secreting their own growth factors. They proceeded to isolate from medium conditioned by a rat hepatocyte cell line (BRL-3A), a growth factor with the properties of a somatomedin. Subsequently, it was shown by Marquardt et al., (3) that this growth factor was rat insulin-like growth factor II (IGF-II). Many tumor cell lines are also capable of growth and multiplication in serum-free medium. Todero and DeLarco (4) showed that sarcoma virus transformed mouse 3T3 cells secreted a peptide which reacted in a rat liver radioreceptor assay which is now known to detect primarily IGF-II. The same authors subsequently found that a human fibrosarcoma cell line released a similar peptide into conditioned medium (5). IGF gene expression in tumors Strong evidence exists that some tumors have the molecular machinery for the production of IGFs. Reeve et al. (6) and Scott et al. (7) independently found much higher concentrations of IGF-II messenger RNA (mRNA) in Wilms' tumors by dot-blot and Northern analysis than in normal kidney. Both groups of authors noted that the gene for IGF-II is located on chromosome 11 in close proximity to the Wilms' tumor susceptibility gene. Reeve et al., (6) speculated that the IGF-II gene expression in these tumors occurred as a result of loss of a regulatory gene similar to that postulated for the deReceived March 30,1990. Address correspondence to: Dr. William Daughaday, Washington University School of Medicine, Box 8127, St. Louis, Missouri 63110. Dr. Daughaday is a prior President of The Endocrine Society and well known for his research on growth factors.
velopment of Wilms' tumors although they conceded that IGF-II is an embryonal gene which is active at the developmental stage during which tumor initiation may have occurred. Subsequent work by many investigators have established that a wide range of tumors are associated with increased IGF-II gene expression (Table 1). In the studies of Tricoli et al. (8), colon tumors, particularly of the rectum and rectosigmoid frequently had increased IGFII mRNA. They reported that over 90% of liposarcomas similarly expressed IGF-II gene activity. In another paper, Hoppener et al. (9) reported increased IGF-II mRNAs in both benign leiomyomas and in leiomyosarcoma. Several investigators have found increased IGF-II mRNA in some, but not all hepatomas (10,11). Increased IGF-II mRNA has been reported with neuroectodermal tumors [pheochromocytomas (12) and neuroblastomas (13)]. Many of the tumors which have increased levels of IGF-II mRNAs also contain IGF-I mRNAs, but the amounts present are little increased as compared to the corresponding normal tissue. In some cases, there seem to be an inverse relationship between IGF-I and IGF-II mRNAs. Controversy exists concerning the IGF-I mRNA in breast cancer cells. Huff et al. (14) did Northern blots with IGF-I cDNAs and found transcripts present in liver. Freed and Herington (15) made similar observations. In contrast, Yee et al. (16) carried out RNAse protection assays with a IGF-IA cDNA probe containing the entire coding region of the proIGF-IA molecule. They found no protected transcripts in any of 11 breast cancer cell lines, but did find IGF-I mRNA in breast stromal tissue. They did find IGF-I mRNA in a Ewing's sarcoma and in 3 neuroepitheliomas. IGF peptides in tumors There may be considerable variability in the translation of IGF mRNAs into IGF peptides. Haselbacher et al. (12) found that three pheochromocytomas contained greatly increased concentrations of IGF-II (between 5.3 and 7.1 /ig/g), most of which was present in a 10 kilodal-
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2
EDITORIAL
Endo • 1990 Vol 127 • No 1
TABLE 1. Reports of IGF mRNA, peptides, IGF-I receptors, and IGF metogenic response of human tumors Peptide
mRNA IGF-I Sarcomas FibroHemangiopericyteLeiomyoLipoMesothelialRhabdomyoEwing's Neural Pheochromocytoma Neuroblastoma Neuroepitheloma Meningioma Carcinomas Breast Colon Hepatoma Lung Adeno Epidermoid Small cell Wilm's
IGF-II
IGF-I
17, 18, 27
IGF-II
IGF-I receptor
Mitogenic IGF response
17,18 27,28 28
27 9 8 18 25a
18 25a
25a
16
12,13
13 13
13
25
25
14, 15, 23
15
14, 15, 23
8
24
24
23 22
23
12 13
13 16
14, 15 (16-no) 8(16-no) 10, 11
30 30 23
6, 7, 12
12
22
Numbers refer to publications cited.
ton (kDa) species indicative of a partially processed proIGF-II. On the other hand, two Wilms' tumors which contained more than 7 times as much IGF-II mRNA than in the pheoopchromocytomas only contained about 5% as much IGF-IL. Increased concentrations of IGF II were found by Daughaday et al. (17) in a fibrosarcoma (originally identified as a leiomyosarcoma). As was the case with the pheochromocytomas, most of this IGF-II was present as the large mol wt big IGF-IL Ron et al. (18) found greatly increased concentrations of IGF-II in a fibrosarcoma and lesser concentration in a fibrous mesothelioma. Explants of these tumors released IGF-II detected by RIA. It was calculated that the tumors were capable of secreting 2.1 and 7.2 /ug/g/24 h. Secretion of IGF binding proteins Virtually all cells that are known to secrete IGFs also secrete IGF binding proteins. Several breast cancer cell lines secrete immunologically detected IGF-I (14,15) and also, IGF binding proteins (14). In the studies of DeLeon et al. (19), IGF binding proteins in the conditioned media of several breast cancer cell lines were cross-linked to IGFs and subjected to polyacrylamide gel electrophoresis (PAGE). At least four different forms of binding protein were identified. Little or no immunoreactivity was detected with a RIA specific for IGF-I amniotic fluid (IGFBP-I). Northern blot also detected only small con-
centrations of IGFBP-I mRNA in two of the four cell lines studied. It may be presumed that the major IGF binding protein secreted by these cell lines was IGFBP2, a form of binding protein associated with fetal stages of development. In another study, Lamson et al. (20) characterized the binding proteins released by a human endometrial cancer cell line (HEC-1). They found two isoforms of the glycosylated IGFBP-3, the major GH-dependent binding protein of human serum. An unglycosylated binding protein had an apparent size of 31 kDa. Extracted mRNA of the HEC-1 cells did not react with a probe of IGFBP1. Therefore, HEC-1 cells differed from normal endometrium which does secrete IGFBP-1. The 31 kDa probably is IGFBP-2. Jaques et al. (21) found that small cell lung carcinomas also secreted 24-32 kDa binding proteins. These cell lines did not contain mRNA reactive with probes for IGFBP-1. Again, this suggests the presence of IGFBP-2. It is as yet unknown how the secretion of IGFBP-2 modify autocrine-paracrine actions on tumor IGFs. IGF receptors in tumors IGF-I type receptors are found in several different tumor types including Wilms' tumor (22), small cell lung carcinoma (23), colon carcinoma (24), meningioma (25), neuroblastoma (11), rhabdomyosarcoma (25a), and leu-
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EDITORIAL kemic lymphoblasts (26). While many of these cell types also contain receptors for the combined IGF-II/mannose-6-phosphate receptor, it is unlikely that this receptor mediates the mitogenic effects of IGF-II. The specific monoclonal antibody IR-3, which blocks IGF-I receptor function, blocks the mitogenic effects of IGF-I and IGFII on small cell lung carcinoma cells (23), neuroblastoma cells (13), and rhabdomyosarcoma cells (25a). Of interest is the observation that monoclonal antibody IR-3 did not block the ability of IGF-II to stimulate cellular motility of rhabdomyosarcoma cells suggesting that this effect may be mediated by the IGF-II/mannose-6-phosphate receptor. Autocrine paracrine role of tumor IGFs The mitogenic activity of some tumor cell lines in the absence of added growth factors can be inhibited by monoclonal antibody IR-3 [small cell lung carcinoma (23), neuroblastoma cells (13), and rhabdomyosarcoma cells (25a)]. This provides evidence that the production of IGFs by these cells was the critical factor in permitting mitogenesis in serum-free medium. Endocrine effects of tumor IGFs There is increasing evidence that the secretion of IGFII by certain tumors may have systemic endocrine insulin-like actions. Nonislet cell tumors, associated with hypoglycemia have been reported to contain increased concentrations of IGF-II mRNA (17, 13, 27), increased concentrations of IGF-II peptides (17,18), and increased secretion of IGF-II peptides in vitro (18). As noted earlier, many tumors may lack the enzymatic machinery for processing proIGF-II to the final 7.5 kDa peptide. Daughaday et al. (17) found that serum from a patient with a fibrosarcoma (originally identified as a leiomyosarcoma) had the same predominance of big IGFII as was present in the tumor. This may become a useful method of distinguishing tumor derived IGF-II from normal IGF-II. In most cases of nonislet tumor hypoglycemia, the secretion of IGF-I and GH are markedly suppressed. This strongly suggests that increased IGF-II secretion by the tumor is exerting an inhibitory effect on GH secretion. A puzzling aspect of the pathphysiology of nonislet cell tumor hypoglycemia is that the total IGF-II measured by RIA is usually normal or reduced. This may be explained by marked abnormalities of the IGF binding in the sera of these patients (28). In a report of three patients with this syndrome there was a virtual complete absence of the 150 kDa ternary complex which normally carries 75% of the serum IGFs. Most of the endogenous IGFs were found as complexes of 60 kDa which suggest that IGFBP-3 was not absent. A deficiency of the acid-
labile complexing protein or an abnormality of its function was postulated. As the 150 kDa IGF complexes pass through the capillary membrane poorly (29), it is likely that the smaller complexes would have increased access to target tissues and therefore, have greatly increased biological action. This would provide an explanation of the induction of hypoglycemia without an elevation of total serum IGF-II. It is as yet unexplained why increased IGF-II action sufficient to induce hypoglycemia does not result in an increase in mesenchymal tissue growth as occurs in acromegaly. Many questions remain unanswered about the endocrine action of tumor-secreted IGFs. In conclusion, the intense research in this field has established that IGFs, particularly IGF-II, are synthesized by many tumors, but processing of proIGF-II is frequently incomplete. Many of the same tumors contain IGF-I receptors and mitogenesis of several tumor cell lines are stimulated by added IGFs. The ability of several tumor cell lines to proliferate in serum-free medium is dependent on the autocrine/paracrine action of IGFs. Certain tumors produce sufficient IGF-II to suppress GH and IGF-I secretion and induce hypoglycemia. William H. Daughaday
References 1. Salmon WD 1957 A hormonally controlled serum factor which stimulates sulfate incorporation by cartilage in vitro. J Lab Clin Med 40:825 2. Dulak NC, Temin HM 1973 A partially purified polypeptide fraction from rat liver cell conditioned medium with multiplicationstimulating activity for embryo fibroblasts. J Cell Physiol 81:153 3. Marquardt H, Todaro GJ, Henderson LE, Oroszlan S 1981 Purification and primary structure of a polypeptide with multiplicationstimulating activity from rat liver cell cultures. Homology with human insulin-like growth factor II. J Biol Chem 256:6859 4. Todaro GJ, DeLarco JE 1978 Growth factors produced by sarcoma virus-transformed cells. Cancer Res 38:4147 5. DeLarco JE, Todaro GJ 1978 A human fibrosarcoma cell line producing multiplication stimulating activity (MSA)-related peptides. Nature 272:356 6. Reeve AE, Eccles MR, Wilkins RJ, Bell GI, Millow LJ 1985 Expressions of insulin-like growth factor-II transcripts in Wilms' tumour. Nature 317:258 7. Scott J, Cowell J, Robertson ME, Priestly LM, Wadley R, Hopkins B, Pritchard J, Bell GI, Graham CF, Knott TJ 1985 Insulin-like growth factor-II gene expression in Wilms' tumour embryonic tissues. Nature 317:260 8. Tricoli JV, Rail LB, Karakousis CP, Herrera L, Petrelli NJ, Bell GI, Shows TB 1986 Enhanced levels of insulin-like growth factor messenger RNA in human colon carcinomas and liposarcomas. Cancer Res 46:6169 9. Hoppener JWM, Moseelman S, Roholl PJM, Lambrechts C, Slebos RJC, de Pagter-Holthuizen P, Lips CJM, Jansz HS, Sussenbach JS 1988 Expression of insulin-like growth factor-I and -II genes in human smooth muscle tumours. EMBO J 7:1379 10. Cariani E, Lasserre C, Seurin D, Hamelin B, Kemeny F, Franco D, Czech MP, Ullrich A, Brechot C 1988 Differential expression of insulin-like growth factor II mRNA in human primary liver cancers, benign liver tumors, and liver cirrhosis. Cancer Res 48:6844 11. Su T-S, Liu W-Y, Han S-H, Jansen M, Yang-Fen TL, P'eng F-K, Chou C-K 1988 Transcripts of the insulin-like growth factors I and
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EDITORIAL II in human hepatoma. Cancer Res 49:1773 12. Haselbacher GK, Irminger JC, Zapf J, Ziegler WH, Humbel RE 1987 Insulin-like growth factor II in human adrenal pheochromocytoma and Wilms' tumors: expression at mRNA and protein level. Proc Natl Acad Sci USA 84:1104 13. El-Badry OM, Romanus JAJ, Helman LJ, Cooper MJ, Rechler MM, Israel MA 1989 Autonomous growth of a human neuroblastoma cell line is mediated by insulin-like growth factor II. J Clin Invest 84:829 14. Huff KK, Kaufman D, Gabbay KH, Spencer EM, Lippman ME, Dickson RB 1986 Secretion of an insulin-like growth factor-Irelated protein by human breast cancer cells. Cancer Res 46:4613 15. Freed KA, Herington AC 1989 Insulin-like growth factor-I and its autocrine role in growth of MCF-u human breast cancer cells in culture. J Mol Endocrinol 3:183 16. Yee D, Paik S, Lebovic GS, Marcus RR, Favoni RE, Cullen KJ, Lippman ME, Rosen N 1989 Analysis of insulin-like growth factor I gene expression in malignancy: evidence for a paracrine role in human breast cancer. Mol Endocrinol 3:509 17. Daughaday WH, Emanuele MA, Brooks MH, Barbato AL, Kapadia M, Rotwein P 1988 Insulin-like growth factor II synthesis and secretion by a leiomyosarcoma with associated hypoglycemia. N Engl J Med 319:1434 18. Ron D, Powers AC, Pandian MR, Godine JE, Axelrod L 1989 Increased insulin-like growth factor II (IGF-II) production and consequent suppression of growth hormone secretion: a dual mechanism for tumor induced hypoglycemia. J Clin Endocrinol Metab 68:701 19. De Leon DD, Wilson DM, Bakker B, Lamson G, Hintz RL, Rosenfeld RG 1989 Characterization of insulin-like growth factor binding proteins from human breast cancer cells. Mol Endocrinol 3:567 20. Lamson G, Oh Y, Pham H, Giudice LC, Rosenfeld RG 1989 Expression of two insulin-like growth factor-binding proteins in a human endometrial cancer cell line: structural, immunological, and genetic characterization. J Clin Endocrinol Metab 69:852 21. Jaques G, Kiefer P, Rotsch M, Hennig C, Rudiger G, Richter G, Havemann K1989 Production of insulin-like growth factor binding
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