The role of the insulin-like growth factor system in human cancer

Energy balance and cancer: the role of insulin and insulin-like growth factor-I

Recent theories propose that a Western lifestyle may increase cancer risk through alterations in the metabolism of insulin and insulin-like growth factors (IGF: McKeown-Eyssen, 1994; Giovannucci, 1995; Kaaks, 19%; Werner & LeRoith, 1996). Insulin regulates energy metabolism, and increases the bioactivity of IGF-I, by enhancing its synthesis. and by decreasing several of its binding proteins (IGFBP; IGFBP-1 and -2). Insulin and IGF-I both stimulate anabolic processes as a function of available energy and elementary substrates (e.g. amino acids). The anabolic signals by insulin or IGF-I can promote tumour development by inhibiting apoptosis, and by stimulating cell proliferation. Furthermore, both insulin and IGF-I stimulate the synthesis of sex steroids, and inhibit the synthesis of sex hormone-binding globulin (SFIBG), a binding protein that regulates the bioavailability of circulating sex steroids to tissues. The present paper reviews epidemiological findings relating the risk of cancers of the colo-rectum, pancreas, breast, endometrium and prostate to body size (obesity, height) and physical activity, and discusses the relationships between obesity and physical activity and plasma levels of insulin, IGF-I and IGFBP. Subsequent sections review epidemiological findings relating cancer risk to indices of chronic hyperinsulinaemia, and to plasma levels of IGF-I and IGFBP. Conclusions are that chronic hyperinsulinaemia may be a cause of cancers of the colon, pancreas and endometrium, and also possibly of the breast. On the other hand, elevated plasma IGF-I, as total concentrations or relative to levels of IGFBP-3, appears to be related to an increased risk of prostate cancer, breast cancer in young women, and possibly cob-rectal cancer. For cancers of the endometrium, breast and prostate, these findings are discussed in the context of relationships between insulin and IGF-I and levels of bioavailable sex steroids.

The effects of growth hormone and IGF-1 deficiency on cerebrovascular and brain ageing

Research studies clearly indicate that age-related changes in cellular and tissue function are linked to decreases in the anabolic hormones, growth hormone and insulin-like growth factor (IGF)-1. Although there has been extensive research on the effects of these hormones on bone and muscle mass, their effect on cerebrovascular and brain ageing has received little attention. We have also observed that in response to moderate calorie restriction (a treatment that increases mean and maximal lifespan by 30-40%), age-related decreases in growth hormone secretion are ameliorated (despite a decline in plasma levels of IGF-1) suggesting that some of the effects of calorie restriction are mediated by modifying the regulation of the growth hormone/IGF-1 axis. Recently, we have observed that microvascular density on the surface of the brain decreases with age and that these vascular changes are ameliorated by moderate calorie restriction. Analysis of cerebral blood flow paralleled the changes in vasculature in both groups. Administration of growth hormone for 28 d was also found to increase microvascular density in aged animals and further analysis indicated that the cerebral vasculature is an important paracrine source of IGF-1 for the brain. In subsequent studies, administration of GHRH (to increase endogenous release of growth hormone) or direct administration of IGF-I was shown to reverse the age-related decline in spatial working and reference memory. Similarly, antagonism of IGF-1 action in the brains of young animals impaired both learning and reference memory. Investigation of the mechanisms of action of IGF-1 suggested that this hormone regulates age-related alterations in NMDA receptor subtypes (e.g. NMDAR2A and R2B). The beneficial role of growth hormone and IGF-1 in ameliorating vascular and brain ageing are counterbalanced by their well-recognised roles in age-related pathogenesis. Although research in this area is still evolving, our results suggest that decreases in growth hormone and IGF-1 with age have both beneficial and deleterious effects. Furthermore, part of the actions of moderate calorie restriction on tissue function and lifespan may be mediated through alterations in the growth hormone/IGF-1 axis.

Inhibition of mammary epithelial apoptosis and sustained phosphorylation of Akt/PKB in MMTV-IGF-II transgenic mice

IGF-II is a growth factor implicated in human cancers and animal tumor models. While the mitogenic properties of IGF-II are well documented, its ability to suppress apoptosis in vivo has never been proven. We generated independent MMTV-IGF-II transgenic mice to examine the control of epithelial apoptosis at the morphological, cellular and molecular levels during the physiological event of postlactation mammary involution. Transgenic IGF-II expression was achieved in mammary epithelium and increased IGF-II bioactivity was confirmed by phosphorylation of the insulin receptor substrate-1, a signaling molecule downstream of the type I IGF receptor. IGF-II overexpression induced a delay in mammary involution, as evident by increased mammary gland to body weight ratios and persistence of both functionally intact lobulo-alveoli and mammary epithelial cellularity. The delayed mammary involution resulted from a significant reduction in mammary epithelial apoptosis, and not from increased epithelial proliferation. Recombinant IGF-II pellets implanted into involuting mammary glands of wild-type mice provided further evidence that IGF-II protein inhibited local epithelial apoptosis. At the molecular level, phosphorylated Akt/PKB, but not Erk1 or Erk2, persisted in IGF-II overexpressors and temporally correlated with reduced epithelial apoptosis. Levels of the phosphatase PTEN were unaltered in the transgenic tissue suggesting that the maintenance of Akt/PKB phosphorylation resulted from sustained phosphorylation rather than altered dephosphorylation of PIP-3. Together, this data reveal that IGF-II inhibits apoptosis in vivo and this effect correlates with prolonged phosphorylation of Akt/PKB

A prospective study of insulin-like growth factor-I, IGF-binding proteins-1, -2 and -3 and lung cancer risk in women

Insulin-like growth factor-I (IGF-I) has mitogenic and anti-apoptotic properties and has been implicated in the development of breast, colorectum, prostate and lung cancer. IGF binding proteins (IGFBPs) are not only carrier proteins for IGFs but also hold a central position in IGF ligand-receptor interactions through influences on the bioavailability and distribution of IGFs in the extracellular environment. A case-control study nested within the New York University Women's Health Study Cohort included 93 women diagnosed with lung cancer at least 6 months after recruitment into the study. Two controls (n = 186) were matched to each case on age, date of blood sampling, menopausal status, day of menstrual cycle and questionnaire data of smoking status at the time of blood donation. Serum IGF-I, IGFBP-1, -2 and -3, insulin and cotinine were measured. Mean serum levels of IGF-I, IGFBP-1, -2 and -3 were not significantly different between the case and control groups. Univariate logistic regression analyses showed no association of lung cancer risk with serum levels of IGF-I or any of the IGFBPs. These results remained virtually the same in multivariate analyses, including adjustment for cotinine, time since last meal, BMI, IGF-I or IGFBP-3, respectively. Exclusion of cases diagnosed within 3 years of recruitment in the cohort, or restriction of the analyses to adenocarcinomas only, did not alter these results. Our study does not offer evidence in support of an association between prediagnostic serum levels of IGF-I or IGFBP-1, -2 and -3 and lung cancer risk in women.

Plasma insulin-like growth factor I levels in rats are reduced by dietary supplementation of flaxseed or its lignan secoisolariciresinol diglycoside

Flaxseed and its lignan secoisolariciresinol diglycoside (SDG) inhibit mammary tumor development in rats. Increased plasma insulin-like growth factor I (IGF-I) concentrations are associated with increased breast cancer risk. Therefore, the effect of flaxseed (5%) or SDG (1.5 mg/day) supplementation on plasma IGF-I levels was examined in rats treated with or without N-methyl-N-nitrosourea (MNU). In MNU-free rats, flaxseed and SDG reduced plasma IGF-I levels, which were inversely related to urinary lignan excretion. Only flaxseed significantly reduced plasma IGF-I concentrations in MNU-treated rats. The anticancer effect of flaxseed and SDG may be related, in part, to reductions in plasma IGF-I.

Differential requirements of the MAP kinase and PI3 kinase signaling pathways in Src- versus insulin and IGF-1 receptors-induced growth and transformation of rat intestinal epithelial cells

There have been few studies on the specific signaling pathways involved in the transformation of epithelial cells by oncogenic protein tyrosine kinases. Here we investigate the requirement of MAP (MAPK) and phosphatidylinositol 3- (PI3K) kinases in the transformation of rat intestinal epithelial (RIE) cells by oncogenic forms of insulin receptor (gag-IR), insulin-like growth factor-1 receptor (gag-IGFR), and v-Src. MAPK is not significantly activated in cells transformed by gag-IR and gag-IGFR but is activated in v-Src transformed cells. Treatment with PD98059, a MEK inhibitor, at concentrations where MAPK activity was reduced below the basal level showed that MAPK is partially required for the monolayer growth of parental and transformed RIE cells. However, MAPK is not essential for the focus forming ability of the three oncogene-transformed cells. It is also not necessary for the colony forming ability of gag-IR- and gag-IGFR-, but is partially required for v-Src-transformed cells. PI3K is significantly activated in all three oncogene transformed RIE cells. LY294002, a PI3K inhibitor, potently inhibited monolayer growth of all three oncogene-transformed cells. However, at concentrations of LY294002 where activated forms of Akt, a downstream component of the PI3K pathway, were undetectable, colony and focus forming abilities of the v-Src-RIE cells were only slightly affected whereas those of gag-IR/IGFR-RIE cells were greatly inhibited. These results were confirmed using a different pharmacological inhibitor, wortmannin, and a dominant negative form of PI3K, Ap85. Similarly, rapamycin, known to inhibit p70S6 kinase, a downstream component of the PI3K-Akt pathway, also inhibited gag-IR/IGFR-induced, but not v-Src-induced, focus and colony formation. We conclude that the MAPK and PI3K signaling pathways are differentially required for transformation of RIE cells by oncogenic IR and IGFR versus Src and the pattern of requirements is different from that of fibroblast transformation.

The effects of growth hormone and IGF-1 deficiency on cerebrovascular and brain ageing

Research studies clearly indicate that age-related changes in cellular and tissue function are linked to decreases in the anabolic hormones, growth hormone and insulin-like growth factor (IGF)-1. Although there has been extensive research on the effects of these hormones on bone and muscle mass, their effect on cerebrovascular and brain ageing has received little attention. We have also observed that in response to moderate calorie restriction (a treatment that increases mean and maximal lifespan by 30-40%), age-related decreases in growth hormone secretion are ameliorated (despite a decline in plasma levels of IGF-1) suggesting that some of the effects of calorie restriction are mediated by modifying the regulation of the growth hormone/IGF-1 axis. Recently, we have observed that microvascular density on the surface of the brain decreases with age and that these vascular changes are ameliorated by moderate calorie restriction. Analysis of cerebral blood flow paralleled the changes in vasculature in both groups. Administration of growth hormone for 28 d was also found to increase microvascular density in aged animals and further analysis indicated that the cerebral vasculature is an important paracrine source of IGF-1 for the brain. In subsequent studies, administration of GHRH (to increase endogenous release of growth hormone) or direct administration of IGF-I was shown to reverse the age-related decline in spatial working and reference memory. Similarly, antagonism of IGF-1 action in the brains of young animals impaired both learning and reference memory. Investigation of the mechanisms of action of IGF-1 suggested that this hormone regulates age-related alterations in NMDA receptor subtypes (e.g. NMDAR2A and R2B). The beneficial role of growth hormone and IGF-1 in ameliorating vascular and brain ageing are counterbalanced by their well-recognised roles in age-related pathogenesis. Although research in this area is still evolving, our results suggest that decreases in growth hormone and IGF-1 with age have both beneficial and deleterious effects. Furthermore, part of the actions of moderate calorie restriction on tissue function and lifespan may be mediated through alterations in the growth hormone/IGF-1 axis.

Insulin-like growth factor I is a dual effector of multiple myeloma cell growth

Multiple myeloma (MM) is an invariably fatal disease that accounts for approximately 1% to 2% of all human cancers. Surprisingly little is known about the cellular pathways contributing to growth of these tumors. Although the cytokine interleukin-6 has been suggested to be the major stimulus for myeloma cell growth, the role of a second potential growth factor, insulin-like growth factor I (IGF-I), has been less clearly defined. The IGF-I signaling cascade in 8 MM cell lines was examined. In 7 of these, the IGF-I receptor (IGF-IR) was expressed and autophosphorylated in response to ligand. Downstream of IGF-IR, insulin receptor substrate 1 was phosphorylated, leading to the activation of phosphatidylinositol-3′-kinase (PI-3K). PI-3K, in turn, regulated 2 distinct pathways. The first included Akt and Bad, leading to an inhibition of apoptosis; the second included the mitogen-activated protein kinase (MAPK), resulting in proliferation. Biologic relevance of this pathway was demonstrated because in vitro IGF-I induced both an antiapoptotic and a proliferative effect. Importantly, in vivo administration of IGF-I in SCID mice inoculated with the OPM-2 line led to approximately twice the growth rate of tumor cells as in controls. These results suggest that IGF-I activates at least 2 pathways effecting myeloma cell growth and contributes significantly to expansion of these cells in vivo.

Insulin-like growth factor I is a dual effector of multiple myeloma cell growth

Multiple myeloma (MM) is an invariably fatal disease that accounts for approximately 1% to 2% of all human cancers. Surprisingly little is known about the cellular pathways contributing to growth of these tumors. Although the cytokine interleukin-6 has been suggested to be the major stimulus for myeloma cell growth, the role of a second potential growth factor, insulin-like growth factor I (IGF-I), has been less clearly defined. The IGF-I signaling cascade in 8 MM cell lines was examined. In 7 of these, the IGF-I receptor (IGF-IR) was expressed and autophosphorylated in response to ligand. Downstream of IGF-IR, insulin receptor substrate 1 was phosphorylated, leading to the activation of phosphatidylinositol-3′-kinase (PI-3K). PI-3K, in turn, regulated 2 distinct pathways. The first included Akt and Bad, leading to an inhibition of apoptosis; the second included the mitogen-activated protein kinase (MAPK), resulting in proliferation. Biologic relevance of this pathway was demonstrated because in vitro IGF-I induced both an antiapoptotic and a proliferative effect. Importantly, in vivo administration of IGF-I in SCID mice inoculated with the OPM-2 line led to approximately twice the growth rate of tumor cells as in controls. These results suggest that IGF-I activates at least 2 pathways effecting myeloma cell growth and contributes significantly to expansion of these cells in vivo.

Tissue distribution of components of the insulin-like growth factor system in sudden infant death and controls

Growth factors may be involved in sudden infant death (SID). Among these factors, the insulin-like growth factor (IGF) family is important in human fetal and perinatal organ growth and development. In order to detect probable differences in the occurrence and distribution of components of the IGF system, tissue samples from liver, lung, skin, parotid and thyroid gland, gut and cerebellum from SID children (n=9) and controls (n=6) aged between 14 and 258 days of life (mean 105 days) were stained immunohistochemically using antibodies against IGF-I, IGF-II and their specific IGF-I-receptor (IGF-IR). In contrast to controls in hepatocytes of SID children a reduction or an absence of immunoreactivity for IGF-I and IGF-IR and a weaker staining for IGF-II was detected. IGF-II in smooth muscle layers in the gut and IGF-I in epithelial cells in intestinal specimens also showed a reduced immunoreactivity in SID children and those who died traumatic deaths. In the other organs examined no significant differences in the distribution of the insulin-like growth factor system between the groups could be detected, indicating that in SID children no fundamental differences or alterations in the physiology of the IGF system occur. Because of the decreased immunostaining of IGFs in the liver and intestine of SID cases, a local dysregulation may be discussed.

Regulation of the insulin-like growth factor-I receptor gene by oncogenes and antioncogenes: implications in human cancer

The insulin-like growth factor-I receptor (IGF-I-R) has a central role in normal cellular proliferation as well as in transformation processes. Transcription of the IGF-I receptor gene is controlled by a number of tumor suppressors, including WT1, p53, and BRCA1. It has been demonstrated that, in their wild-type form, these transcription factors can suppress the activity of the IGF-I-R promoter, with ensuing reduction in the levels of cell-surface IGF binding. On the other hand, a number of oncogenes, including mutant p53 and c-myb, and the fusion protein EWS-WT1 significantly stimulate promoter activity. Interactions between stimulatory and inhibitory transcription factors may determine the level of expression of the IGF-I-R gene and, consequently, the proliferative status of the cell.

Alterations of the 11p15 imprinted region and the IGFs system in a case of recurrent non-islet-cell tumour hypoglycaemia (NICTH)

BACKGROUND AND OBJECTIVE

Non-islet-cell tumour hypoglycaemia (NICTH) is a rare disorder and has been explained by oversecretion of non mature IGF-II and dysregulation of the IGFs sytem. The mechanisms responsible for tumoural IGF-II overexpression in NICTH have been rarely studied. We report an extensive study of IGF-II and IGFBPs as well as chromosome 11p15 gene expression regulation in a case of a pleural fibrosarcoma in a 63-year-old patient presenting with NICTH.

METHODS AND RESULTS

Abnormal high molecular weight precusor forms of IGF-II were present in the patient's serum and were associated with dramatic alterations in the circulating levels of IGF-I, IGF-II and their binding proteins, as well as an inhibition of the somatotroph axis. These alterations returned to normal following complete surgical removal of the tumour. No structural change in chromosome 11p15 region was apparent in the tumour. However, dysregulation of this imprinted region was demonstrated, leading to the loss of imprinting of the IGF-II gene associated with high IGF-II expression, and by contrast decreased level of expression of H19 and p57KIP2 genes. Recurrence of the tumour four years latter was not associated with hypoglycaemia or changes in the levels of circulating IGFs or IGFBPs, despite IGF-II overexpression by the tumour. This suggests that a large tumour volume is required to reach high enough levels to cause changes in the levels of circulating IGFs and IGFBPs, and to cause hypoglycaemia.

CONCLUSION

These results suggest that a dysregulation of gene expression and imprinting of chromosome 11p15 region is associated with tumour growth and IGF-II overexpression in non-islet-cell tumour hypoglycaemia.

Lycopene interferes with cell cycle progression and insulin-like growth factor I signaling in mammary cancer cells

Recent studies have shown that high insulin-like growth factor I (IGF-I) blood level is a risk factor in breast and prostate cancer. The aim of this study was to determine whether the mitogenic activity of IGF-I in mammary cancer cells can be reduced by the dietary carotenoid lycopene. The anticancer activity of lycopene, the major tomato carotenoid, has been suggested by in vitro, in vivo, and epidemiological studies. Growth stimulation of MCF7 mammary cancer cells by IGF-I was markedly reduced by physiological concentrations of lycopene. The inhibitory effects of lycopene on MCF7 cell growth were not accompanied by apoptotic or necrotic cell death, as determined by annexin V binding to plasma membrane and propidium iodide staining of nuclei in unfixed cells. Lycopene treatment markedly reduced the IGF-I stimulation of tyrosine phosphorylation of insulin receptor substrate 1 and binding capacity of the AP-1 transcription complex. These effects were not associated with changes in the number or affinity of IGF-I receptors, but with an increase in membrane-associated IGF-binding proteins, which were previously shown in different cancer cells to negatively regulate IGF-I receptor activation. The inhibitory effect of lycopene on IGF signaling was associated with suppression of IGF-stimulated cell cycle progression of serum-starved, synchronized cells. Moreover, in cells synchronized by mimosine treatment, lycopene delayed cell cycle progression after release from the mimosine block. Collectively, the above data suggest that the inhibitory effects of lycopene on MCF7 cell growth are not due to the toxicity of the carotenoid but, rather, to interference in IGF-I receptor signaling and cell cycle progression.

Genomic imprinting of IGF2 and H19 in human meningiomas

A number of genes, including IGF2 and H19, are normally imprinted with preferential expression of the paternal or maternal allele, respectively. Loss of imprinting (LOI) of IGF2 and H19 is found in a number of tumours, suggesting that LOI of IGF2 and/or H19 may play an important role in tumorigenesis. The IGF2 gene codes for a fetal growth factor and the H19 gene is likely to act as an RNA with an antitumour effect. We investigated the imprinting status of IGF2 and H19 in human meningiomas. The normally imprinted IGF2 gene lacks imprint in the leptomeninges and choroid plexus of the brain. To examine the imprinting status of IGF2 and H19 in human meningiomas we used the ApaI polymorphism in exon 9 for the IGF2 gene and the AluI polymorphism in exon 5 for the H19 gene. In total, 24 meningiomas of WHO grade I, II and III were analysed. 15 meningiomas (63%) were informative for the ApaI polymorphism in the IGF2 gene. Monoallelic expression (MAE) for IGF2 was found in 11 out of 15 tumours (73%) which is in contrast to the lack of imprinting status of IGF2 in leptomeninges. Ten cases (42%) were heterozygous for the H19 gene and biallelic expression was found in 3 out of 10 meningiomas (30%). These results indicate that modulation of the imprinting status of IGF2 and H19 may play an important role for the development of meningiomas.

BRCA1 suppresses insulin-like growth factor-I receptor promoter activity: potential interaction between BRCA1 and Sp1

The insulin-like growth factor I receptor (IGF-I-R) has an important role in breast cancer etiology. The receptor is overexpressed by most breast cancers, where it functions as a potent antiapoptotic agent. BRCA1 is a tumor suppressor gene that is mutated in a large fraction of familial breast and ovarian cancers. Cotransfection of Saos-2, MCF7, and CHO cells with IGF-I-R promoter constructs driving luciferase reporter genes, and with a BRCA1 expression vector, suppressed promoter activity in a dose-dependent manner. Functional interactions between BRCA1 and Sp1 in the regulation of the IGF-I-R gene were studied in Schneider cells, a Drosophila cell line which lacks endogenous Sp1. In these cells BRCA1 suppressed 45% of the Sp1-induced trans-activation of the IGF-I-R promoter. These results suggest that BRCA1 is capable of suppressing the IGF-I-R promoter in a number of cell lines, thus resulting in low levels of receptor mRNA and protein. Mutant versions of BRCA1 lacking trans-activational activity can potentially derepress the IGF-I-R promoter. Activation of the overexpressed receptor by locally produced or circulating IGFs may be a crucial step in breast and ovarian cancer progression.

Insulin-like growth factor (IGF) system in the bovine mammary gland and milk

Primary bovine mammary cells express the two IGF receptors (IGF-IR, IGF-IIR), insulin receptor, and four IGFBPs (IGFBP-2, -3, -4, and -5). Examination of the IGF-IR during the mammary gland lactation cycle shows that IGF-IR number declines at parturition, a change that coincides with decreases in the blood level of its ligand, IGF-I. IGF-II and IGF-IIR are largely unchanged. IGFBP-3 is the predominant mammary IGFBP and its concentration also declines in blood and milk during lactation compared to prepartum and involution periods. Time of lactation and pregnancy were the main determinants of milk but not blood IGFBP-3 levels. IGFBP-3 binds to membrane proteins of bovine mammary tissue; an IGFBP-3 binding protein has been identified as bovine lactoferrin. Lactoferrin has the capacity to compete with IGF binding to IGFBP-3. Appearance of both IGFBP-3 and lactoferrin in conditioned media of primary cultures of bovine mammary cells was stimulated by all trans retinoic acid (atRA). Furthermore, atRA was necessary for the entry of exogenously added lactoferrin into the mammary cell nucleus, while IGFBP-3 entry into the nuclei of atRA treated cells required the presence of lactoferrin. These findings reveal a novel role for lactoferrin, suggesting that lactoferrin is critically involved in the regulation of the IGF system during the involution period.

Vegan proteins may reduce risk of cancer, obesity, and cardiovascular disease by promoting increased glucagon activity

Amino acids modulate the secretion of both insulin and glucagon; the composition of dietary protein therefore has the potential to influence the balance of glucagon and insulin activity. Soy protein, as well as many other vegan proteins, are higher in non-essential amino acids than most animal-derived food proteins, and as a result should preferentially favor glucagon production. Acting on hepatocytes, glucagon promotes (and insulin inhibits) cAMP-dependent mechanisms that down-regulate lipogenic enzymes and cholesterol synthesis, while up-regulating hepatic LDL receptors and production of the IGF-I antagonist IGFBP-1. The insulin-sensitizing properties of many vegan diets--high in fiber, low in saturated fat--should amplify these effects by down-regulating insulin secretion. Additionally, the relatively low essential amino acid content of some vegan diets may decrease hepatic IGF-I synthesis. Thus, diets featuring vegan proteins can be expected to lower elevated serum lipid levels, promote weight loss, and decrease circulating IGF-I activity. The latter effect should impede cancer induction (as is seen in animal studies with soy protein), lessen neutrophil-mediated inflammatory damage, and slow growth and maturation in children. In fact, vegans tend to have low serum lipids, lean physiques, shorter stature, later puberty, and decreased risk for certain prominent 'Western' cancers; a vegan diet has documented clinical efficacy in rheumatoid arthritis. Low-fat vegan diets may be especially protective in regard to cancers linked to insulin resistance--namely, breast and colon cancer--as well as prostate cancer; conversely, the high IGF-I activity associated with heavy ingestion of animal products may be largely responsible for the epidemic of 'Western' cancers in wealthy societies. Increased phytochemical intake is also likely to contribute to the reduction of cancer risk in vegans. Regression of coronary stenoses has been documented during low-fat vegan diets coupled with exercise training; such regimens also tend to markedly improve diabetic control and lower elevated blood pressure. Risk of many other degenerative disorders may be decreased in vegans, although reduced growth factor activity may be responsible for an increased risk of hemorrhagic stroke. By altering the glucagon/insulin balance, it is conceivable that supplemental intakes of key non-essential amino acids could enable omnivores to enjoy some of the health advantages of a vegan diet. An unnecessarily high intake of essential amino acids--either in the absolute sense or relative to total dietary protein--may prove to be as grave a risk factor for 'Western' degenerative diseases as is excessive fat intake.

New growth factors for imaginal discs

Several families of peptide growth factors are implicated in regulating cell growth and proliferation of vertebrate cells in culture. Genetic studies in Drosophila implicate some of these factors in growth control in vivo. A recent report identifies a new family of growth factors, related to chitinase enzymes, required by Drosophila imaginal disc cells in culture. It will be of interest to determine how such factors relate to size regulation during development.

Insulin-like growth factor II signaling in neoplastic proliferation is blocked by transgenic expression of the metalloproteinase inhibitor TIMP-1

Insulin-like growth factor (IGF) II is overexpressed in many human cancers and is reactivated by, and crucial for viral oncogene (SV40 T antigen, [TAg])-induced tumorigenesis in several tumor models. Using a double transgenic murine hepatic tumor model, we demonstrate that tissue inhibitor of metalloproteinase 1 (TIMP-1) blocks liver hyperplasia during tumor development, despite TAg-mediated reactivation of IGF-II. Because the activity of IGFs is controlled by IGF-binding proteins (IGFBPs), we investigated whether TIMP-1 overexpression altered the IGFBP status in the transgenic liver. Ligand blotting showed that IGFBP-3 protein levels were increased in TIMP-1-overexpressing double transgenic littermates, whereas IGFBP-3 mRNA levels were not different, suggesting that TIMP-1 affects IGFBP-3 at a posttranscriptional level. IGFBP-3 proteolysis assays demonstrated that IGFBP-3 degradation was lower in TIMP-1-overexpressing livers, and zymography showed that matrix metalloproteinases (MMPs) were present in the liver homogenates and were capable of degrading IGFBP-3. As a consequence of reduced IGFBP-3 proteolysis and elevated IGFBP-3 protein levels, dissociable IGF-II levels were significantly lower in TIMP-1-overexpressing animals. This decrease in bioavailable IGF-II ultimately resulted in diminished IGF-I receptor signaling in vivo as evidenced by diminished receptor kinase activity and decreased tyrosine phosphorylation of the IGF-I receptor downstream effectors, insulin receptor substrate 1 (IRS-1), extracellular signal regulatory kinase (Erk)-1, and Erk-2. Together, these results provide evidence that TIMP-1 inhibits liver hyperplasia, an early event in TAg-mediated tumorigenesis, by reducing the activity of the tumor-inducing mitogen, IGF-II. These data implicate the control of MMP-mediated degradation of IGFBPs as a novel therapy for controlling IGF bioavailability in cancer.

Isolation of DICE1: a gene frequently affected by LOH and downregulated in lung carcinomas

In the development and progression of sporadic tumors multiple tumor suppressor genes are inactivated that may be distinct from predisposing cancer genes. Previously, a tumor suppressor locus on human chromosome 13q14 that is distinct from the retinoblastoma predisposing gene 1 (RB1) has been identified in lung, head and neck, breast, ovarian and prostate tumors. By an approach that combines genomic difference cloning and positional cloning we isolated the cDNA of a novel gene (DICE1) located at 13q14.12-14.2. The DICE1 gene is highly conserved in evolution and its mRNA is expressed in a wide variety of fetal and adult tissues. The DICE1 cDNA encodes a predicted protein of 887 amino acids corresponding to an 100 kD protein that shows 92.9% identity to the carboxy-terminal half of the mouse EGF repeat transmembrane protein DBI-1. The DBI-1 protein interferes with the mitogenic response to insulin-like growth factor 1 (IGF-I) and is presumably involved in anchorage-dependent growth. When compared to normal lung tissue expression of the DICE1 mRNA was reduced or undetectable in the majority of non-small cell lung carcinomas analysed. The location of the DICE1 gene in the region of allelic loss, its high evolutionary conservation and the downregulation of expression in carcinoma cells suggests that DICE1 is a candidate tumor suppressor gene in non-small cell lung carcinomas and possibly in other sporadic carcinomas.

Circulating levels of human insulin-like growth factor binding protein-6 (IGFBP-6) in health and disease as determined by radioimmunoassay

OBJECTIVE

Insulin-like growth factor binding protein-6 (IGFBP-6) is a relatively unknown member of a family of six specific structurally related IGF binding proteins which are involved in the modulation of the biological effects of the IGFs. A distinctive property of IGFBP-6 is its preferential affinity for IGF-II relative to IGF-I. In order to obtain more insight into the clinical significance and regulation of circulating levels of IGFBP-6 we developed a specific radioimmunoassay (RIA) for this protein.

DESIGN AND PATIENTS

Selected human biological fluids and plasma from 847 normal subjects were analysed. In addition, plasma samples from patients with different disorders (i.e. GH-deficiency, acromegaly, cancer, corticosteroid-treated children suffering from different kinds of severe illness and chronic renal failure) were investigated.

MEASUREMENTS

The IGFBP-6 assay is competitive, utilizing a rabbit polyclonal antibody raised against a synthetic peptide comprising amino acids 90-118 of the hIGFBP-6 sequence and an additional tyrosine residue. It is calibrated against recombinant human (rh)IGFBP-6. The 125I tracer is prepared by iodination of the synthetic peptide. There is no significant cross-reactivity with other IGFBPs and no interference with the IGFs.

RESULTS

Extensive normative range values for IGFBP-6 were determined using 847 plasma samples from normal males and females, ranging from 0 to 75 years of age. IGFBP-6 levels increased gradually (about two-fold) with age. In childhood the plasma levels of IGFBP-6 in females tended to be slightly higher than those for males. For the adult population the reverse was observed. Overall, the mean +/- SD value for males was higher than that for females (149 +/- 57 vs. 139 +/- 45 micrograms/l, P < 0.004). GH status did not appear to influence IGFBP-6 level since normal levels were found for both untreated acromegalic patients and GH-deficient subjects. GH treatment of the latter group of patients did not alter IGFBP-6 in plasma. Pharmacological doses of glucocorticosteroids affected circulating IGFBP-6 levels only slightly. IGFBP-6 levels in plasma samples derived both from children with acute lymphoblastic leukaemia and from patients with various types of solid neoplasms were generally within the normal range. In contrast, plasma samples from four of six patients with non-islet cell tumour induced hypoglycaemia (NICTH) showed elevated concentrations of IGFBP-6 (SDS > 2.9). An excess of IGFBP-6 was also found in plasma of both dialysed and non-dialysed prepubertal growth retarded children with chronic renal failure (CRF) (mean SDS: 23.0 and 9.3, respectively). IGFBP-6 levels were inversely correlated with glomerular filtration rate. In a group of CRF patients who underwent renal transplantation circulating IGFBP-6 levels were markedly lower (mean SDS: 4.6). The presence of IGFBP-6 could also be demonstrated in several other human biological fluids. Low amounts were detected in saliva (3-12 micrograms/l) and breast milk (6-45 micrograms/l) while the levels in amniotic fluid and follicular fluid were comparable with those determined in normal plasma. The IGFBP-6 content of cerebrospinal fluid (CSF) ranged between 25 and 87 micrograms/l, which is rather high in relation to the relatively low concentration of total protein in this body fluid.

CONCLUSIONS

Measurements of IGFBP-6 have been shown so far to be of relatively minor clinical relevance. The exceptions are chronic renal failure patients and subjects with large tumours and non-islet cell tumour induced hypoglycaemia who may exhibit elevated circulating levels of this IGFBP. The physiological significance of this observation remains to be elucidated. The possibility of quantifying IGFBP-6 by specific RIA will facilitate further in vitro and in vivo studies of its regulation and function in man.

Insulin receptor isoform A, a newly recognized, high-affinity insulin-like growth factor II receptor in fetal and cancer cells

Insulin-like growth factor II (IGF-II) is a peptide growth factor that is homologous to both insulin-like growth factor I (IGF-I) and insulin and plays an important role in embryonic development and carcinogenesis. IGF-II is believed to mediate its cellular signaling via the transmembrane tyrosine kinase type 1 insulin-like growth factor receptor (IGF-I-R), which is also the receptor for IGF-I. Earlier studies with both cultured cells and transgenic mice, however, have suggested that in the embryo the insulin receptor (IR) may also be a receptor for IGF-II. In most cells and tissues, IR binds IGF-II with relatively low affinity. The IR is expressed in two isoforms (IR-A and IR-B) differing by 12 amino acids due to the alternative splicing of exon 11. In the present study we found that IR-A but not IR-B bound IGF-II with an affinity close to that of insulin. Moreover, IGF-II bound to IR-A with an affinity equal to that of IGF-II binding to the IGF-I-R. Activation of IR-A by insulin led primarily to metabolic effects, whereas activation of IR-A by IGF-II led primarily to mitogenic effects. These differences in the biological effects of IR-A when activated by either IGF-II or insulin were associated with differential recruitment and activation of intracellular substrates. IR-A was preferentially expressed in fetal cells such as fetal fibroblasts, muscle, liver and kidney and had a relatively increased proportion of isoform A. IR-A expression was also increased in several tumors including those of the breast and colon. These data indicate, therefore, that there are two receptors for IGF-II, both IGF-I-R and IR-A. Further, they suggest that interaction of IGF-II with IR-A may play a role both in fetal growth and cancer biology.

Effect of insulin-like growth factor 1 on PHA-stimulated cord blood mononuclear cell telomerase activity

Telomerase may contribute to the capacity for cell replication by compensating for the loss of telomere length. Exploring the use of biological modifiers in increasing cellular replicative potential through telomerase activity may be useful for in vitro expansion of haemopoietic stem cells for transplantation or lymphoid cells for adoptive immunotherapy. In this study we showed for the first time that insulin-like growth factor 1 (IGF-1) modulated telomerase activity in human cord blood mononuclear cells (MNC) and some of the known functional determinants of telomerase activity. We found that cord blood MNC expressed constitutively a low level of telomerase activity and human telomerase reverse transcriptase (hTRT) mRNA, and a high level of human telomerase RNA component (hTR) and telomerase-associated protein-1 (TP1) mRNA. Interestingly, IGF-I alone did not increase the telomerase activity of cord blood MNC but could enhance the PHA-induced increase in telomerase activity. These alterations in telomerase activity were not completely in phase with those of proliferation response. On the other hand, IGF-I did not alter hTRT mRNA expression but enhanced the PHA-induced increase in hTRT whereas TP1 mRNA expression was stimulated by either IGF-I or PHA but showed no additive increase when stimulated by both IGF-1 and PHA. Neither IGF-1 nor PHA altered hTR expression. Finally, the temporal dynamics of hTRT mRNA expression and telomerase activity in cord blood MNC over 5 d in culture were not totally concordant. suggesting that key factors other than hTRT were involved in regulating telomerase activity in cord blood MNC. The modulatory effect of IGF-1 on telomerase activity supports its potential role in increasing replicative potential of cord blood lymphoid cells or haemopoietic stem cells.

Structure of the IGF-binding domain of the insulin-like growth factor-binding protein-5 (IGFBP-5): implications for IGF and IGF-I receptor interactions

Binding proteins for insulin-like growth factors (IGFs) IGF-I and IGF-II, known as IGFBPs, control the distribution, function and activity of IGFs in various cell tissues and body fluids. Insulin-like growth factor-binding protein-5 (IGFBP-5) is known to modulate the stimulatory effects of IGFs and is the major IGF-binding protein in bone tissue. We have expressed two N-terminal fragments of IGFBP-5 in Escherichia coli; the first encodes the N-terminal domain of the protein (residues 1-104) and the second, mini-IGFBP-5, comprises residues Ala40 to Ile92. We show that the entire IGFBP-5 protein contains only one high-affinity binding site for IGFs, located in mini-IGFBP-5. The solution structure of mini-IGFBP-5, determined by nuclear magnetic resonance spectroscopy, discloses a rigid, globular structure that consists of a centrally located three-stranded anti-parallel beta-sheet. Its scaffold is stabilized further by two inside packed disulfide bridges. The binding to IGFs, which is in the nanomolar range, involves conserved Leu and Val residues localized in a hydrophobic patch on the surface of the IGFBP-5 protein. Remarkably, the IGF-I receptor binding assays of IGFBP-5 showed that IGFBP-5 inhibits the binding of IGFs to the IGF-I receptor, resulting in reduction of receptor stimulation and autophosphorylation. Compared with the full-length IGFBP-5, the smaller N-terminal fragments were less efficient inhibitors of the IGF-I receptor binding of IGFs.

Survival factors and apoptosis

This chapter will explore the role of survival factors in suppression of apoptosis, and illustrate how survival signals play a critical role in the survival of both normal and tumor cells. Survival factors necessary for the development and maintenance of the nervous system and hemopoietic system will be surveyed. This will be followed by a detailed discussion of the role of insulin-like growth factor I (IGF-I) and its receptor in suppression of apoptosis. The importance of survival signals from the IGF-IR for development and tumorigenesis will be discussed, and results of a mutational analysis of the receptor to assign domains necessary for suppression of apoptosis will be summarized. Finally, a discussion of the signal transduction pathways involved in survival factor-signaling will review the roles played by PI-3 kinase and AKT and speculate on how activation of these kinases by survival factors might regulate the apoptotic pathway.

IGFBP-2 expression in a human cell line is associated with increased IGFBP-3 proteolysis, decreased IGFBP-1 expression and increased tumorigenicity

Insulin-like growth factors (IGF-I and -II) play an active role in cell proliferation. In biological fluids, they are non-covalently bound to high-affinity binding proteins (IGFBPs), at least 6 species of which have been identified to date, but with poorly defined functions. One of these IGFBPs, IGFBP-2, is secreted by most cell lines and appears to be involved in cell proliferation. A human epidermoid carcinoma cell line, KB 3.1, which produces IGFBP-1 and -3 and small amounts of IGFBP-4, but no IGFBP-2, was stably transfected with an expression vector comprising IGFBP-2 complementary DNA (cDNA), whose expression was placed under the control of the constitutive and ubiquitous cytomegalovirus promoter. After an s.c. injection of these IGFBP-2-expressing KB 3.1 cells into nude mice, tumours developed more quickly than in controls, they were 3 to 4 times larger and grew about 3 times as fast. Concomitant with IGFBP-2 expression in these tumours, were a decrease in IGFBP-1 expression and an increase in IGFBP-3 proteolysis, both of which increase the bioavailability of the IGF-II produced by the cells. The increased IGFBP-3 proteolysis most probably resulted from amplified expression of tissue-type plasminogen activator (t-PA) and depression of its inhibitor (PAI-I) observed in IGFBP-2-expressing xenografts. Our findings suggest that IGFBP-2 plays a role in this model of experimental tumorigenesis via a mechanism that remains unclear, but appears to involve increased protease activity and IGF-II bioavailability.

Genomic imprinting and cancer

Genomic imprinting is the phenomenon by which individual alleles of certain genes are expressed differentially according to their parent of origin. The alleles appear to be differentially marked during gametogenesis or during the early part of development. This mark is heritable but reversible from generation to generation, implying a stable epigenetic modification. Approximately 25 imprinted genes have been identified to date, and dysregulation of a number of these has been implicated in tumour development. The normal physiological role of many imprinted genes is in the control of cell proliferation and fetal growth, indicating potential mechanisms of action in tumour formation. Both dominant and recessive modes of action have been postulated for the role of imprinted genes in neoplasia, as a result of effective gene dosage alterations by epigenetic modification of the normal pattern of allele specific transcription. The aim of this review is to assess the importance of imprinted genes in generating tumours and to discuss the implications for novel mechanisms of transforming mutation.

Post-translational processing of the insulin-like growth factor-2 precursor. Analysis of O-glycosylation and endoproteolysis

Insulin-like growth factor-2 (IGF-2) is expressed in most embryonic tissues and is required for normal development during gestation. After birth IGF-2 expression is extinguished in most tissues, but the gene is often reactivated during tumorigenesis. Tumors secrete high molecular weight forms of IGF-2 that result from aberrant post-translational processing of pro-IGF-2. As a first step toward understanding how high molecular weight IGF-2 peptides might contribute to tumor progression, we have characterized the biosynthesis of IGF-2 in a human embryonic cell line. We have found that pro-IGF-2 can initially form two disulfide isomers that undergo rearrangement to a single conformation in vivo. The addition of N-acetylgalactosamine to Ser71, Thr72, Thr75, and Thr139 likely occurs in the cis- Golgi apparatus. Sialic acid addition begins in the trans- Golgi apparatus, but IGF-2 peptides must reach the trans-Golgi network for oligosaccharide maturation to be completed. Endoproteolysis occurs concomitant to or slightly after oligosaccharide maturation. Cleavage was observed only at Arg104, resulting in the secretion of IGF-2-(1-104) and free E-peptide. Proteolysis required basic residues in the P1 (Arg104) and P4 (Arg101) positions, was completely blocked by a furin inhibitor, and was enhanced by coexpression with furin, PACE4, PC6A, PC6B, and LPC. These data suggest that members of the subtilisin-related proprotein convertase family mediate processing of pro-IGF-2 at Arg104. We did not detect the IGF-2 peptides that are most abundant in normal serum, mature IGF-2, and IGF-2-(1-87), in this expression system, which indicates that novel endoproteases are responsible for generating these products.

Selenium, calcium channel blockers, and cancer risk--the Yin and Yang of apoptosis?

It is increasingly clear that apoptosis plays a crucial role in the promotional phase of cancer development. Initiated pre-neoplastic clones in rat liver experience a high rate of apoptosis, and this rate has an important impact on the survival and growth of these clones. Suppression of apoptosis appears to be a universal property of cancer promoters, suggesting conversely that agents which inhibit cancer induction during the promotional phase increase the rate of apoptosis in initiated cells. Modulation of apoptosis is a likely explanation for recent striking evidence that use of calcium channel blockers substantially increases, whereas supplemental selenium substantially decreases, human cancer incidence. Non-genotoxic measures which are likely to upregulate apoptosis in pre-neoplastic/neoplastic cells--and thus may be useful in prevention and/or therapy--include selenium, retinoids/carotenoids, green tea polyphenols, caloric restriction, downregulation of IGF-I activity, high-dose tamoxifen and other protein kinase C antagonists, withdrawal or blockade of trophic hormones, isoflavones, limonene, vitamin D and cholecalciferol analogs, dietary fiber/sodium butyrate, hyperthermia, benzaldehyde derivatives, and creatine.

DBI-1, a novel gene related to the notch family, modulates mitogenic response to insulin-like growth factor 1

The insulin-like growth factor 1 (IGF-1) receptor has been found to transform fibroblast cells when overexpressed. The removal of 108 aa from the C-terminus of the IGF-1 receptor abolishes the transforming ability of the receptor without affecting its ability to induce cell growth. The availability of this mutant receptor provides a means to examine the changes in gene expression which take place during transformation, solely in response to an increased number of IGF-1 receptors. Using differential display, we have examined differences in gene expression between cells expressing a wild-type, transforming IGF-1 receptor and cells expressing a C-terminally truncated, nontransforming IGF-1 receptor. We have cloned a novel 6. 3-kb cDNA transcript (DBI-1) which is expressed at much lower levels in cells containing the wild-type IGF-1 receptor. The predicted protein sequence of DBI-1 contains seven EGF-like repeats, which bear >90% sequence identity to the rat Notch 2 protein. The cDNA also contains a potential DEAD box in the C-terminal region. The DBI-1 message is detected at relatively high levels in cardiac tissue and at lower levels in lung, liver, and kidney. Antibodies generated to a unique region of the DBI-1 protein recognize a protein of 88 kDa, which is localized in the nucleus. Overexpression of DBI-1 in cells which contain the wild-type IGF-1 receptor diminishes the mitogenic response to IGF-1.

Structure and function of the insulin-like growth factor I receptor

Insulin-like growth factors I and II (IGF-I, IGF-II) were originally identified as potent mitogens and as the mediators of growth hormone action. Besides being mitogenic, however, these polypeptide growth factors play a crucial role in cell survival, and contribute to transformation and to maintenance of the malignant phenotype. Here we will discuss signaling by the IGFs, focusing specifically on the structure and function of the IGF-I receptor and the domains of this receptor responsible for distinct IGF functions: mitogenesis, transformation, and protection from apoptosis. We will also compare the structural domains of the related but functionally distinct receptor for insulin.

The aromatase inhibitor letrozole in advanced breast cancer: effects on serum insulin-like growth factor (IGF)-I and IGF-binding protein-3 levels

Serum insulin-like growth factor (IGF)-I and IGF-binding protein-3 levels were measured in two groups of postmenopausal women with advanced breast cancer, who received the aromatase inhibitor letrozole 0.5 or 2.5 mg p.o. once daily. Blood samples were obtained from 15 patients in each dose group at baseline, and one and three months after starting therapy. Circulating IGF-I and IGFBP-3 concentrations were determined by means of radioimmunoassay. In both dosage groups a statistically significant increase in the IGF-I levels was observed during three months of letrozole treatment (P=0.003). In addition, the multiple testing procedure yielded in the whole patient population a significant result in the comparison between mean IGF-I values after three months of therapy and those observed at baseline (P=0.004), the estimated average increase being of 24%. No significant result was obtained in the analysis for the dose effect (P=0.077) and for the time x dose interaction (P=0.208). Circulating IGFBP-3 levels did not appear to be affected by letrozole treatment in either of the dose groups. This is the first report concerning the short-term effects of letrozole on components of the IGF system in breast cancer patients; further investigations are warranted in order to confirm these preliminary data.

Perinatal lethality in H19 enhancers-Igf2 transgenic mice

The insulin-like growth factor II (IGFII) is a mitogen for a number of cell types in vitro and is required for normal embryonic growth. It has been hypothesized that overexpression of IGF2 is responsible for the increased growth and tumor predisposition in patients with Beckwith-Wiedemann syndrome. Association of increased levels of IGFII with increased growth is also incorporated in a current model for the evolution of Igf2 imprinting. Different experimental approaches to increasing IGFII levels in the mouse have yielded different results with respect to its effects on growth, viability, and tumor development. To investigate the consequences of IGf2 overexpression in the embryonic period, without alterations in the activity of other genes, we produced transgenic mice that express the Igf2 gene under the control of the H19 enhancers. Transgene expression in the embryonic period had no significant effect on the overall size of the embryos, but was associated with perinatal lethality in homozygous, and some heterozygous, mice. A large fraction of homozygous mice also developed a cleft palate. These findings indicate that overexpression of Igf2 can have an adverse effect on viability in the absence of a pronounced effect on overall body growth. The results are consistent with the view that growth and perinatal viability are affected differently by Igf2 overexpression in endodermal and mesodermal tissues.

The IGF-I receptor gene promoter is a molecular target for the Ewing's sarcoma-Wilms' tumor 1 fusion protein

Desmoplastic small round cell tumor (DSRCT) is an abdominal malignancy in children which is characterized by a recurrent chromosomal translocation, t(11;22)(p13;q12). This rearrangement results in the fusion of the ubiquitously expressed EWS1 gene to the Wilms' tumor suppressor (WT1) gene. The chimeric protein contains the N-terminal domain of EWS1 fused to the DNA-binding domain of WT1, including zinc fingers 2-4. Because WT1 has been shown previously to bind and repress the insulin-like growth factor I (IGF-I-R) promoter, we investigated whether this promoter is, in addition, a target for the aberrant EWS/WT1 transcription factor. EWS/WT1 activated the IGF-I-R promoter approximately 340%, whereas a fusion protein containing a three-amino acid insert (KTS) between zinc fingers 3 and 4 had no effect. On the other hand, expression vectors encoding either WT1 or EWS1 reduced the activity of the promoter to 46 and 58% of control values, respectively. Results of gel shift assays indicate that the binding affinity of EWS/WT1 to a fragment of the 5'-flanking region of the receptor promoter was higher than the affinity of WT1 itself. Consistent with the results of functional assays, the binding of EWS/WT1(+KTS) was significantly reduced. Due to the central role of the IGF-I-R in tumorigenesis, activation of the receptor promoter by EWS/WT1 may constitute a potential mechanism for the etiology and/or progression of DSRCT.

Wild-type and mutant p53 differentially regulate transcription of the insulin-like growth factor I receptor gene

The insulin-like growth factor I receptor (IGF-I-R) plays a critical role in transformation events. It is highly overexpressed in most malignant tissues where it functions as an anti-apoptotic agent by enhancing cell survival. Tumor suppressor p53 is a nuclear transcription factor that blocks cell cycle progression and induces apoptosis. p53 is the most frequently mutated gene in human cancer. Cotransfection of Saos-2 (os-teosarcoma-derived cells) and RD (rhabdomyosarcoma-derived cells) cells with IGF-I-R promoter constructs driving luciferase reporter genes and with wild-type p53 expression vectors suppressed promoter activity in a dose-dependent manner. This effect of p53 is mediated at the level of transcription and it involves interaction with TBP, the TATA box-binding component of TFIID. On the other hand, three tumor-derived mutant forms of p53 (mut 143, mut 248, and mut 273) stimulated the activity of the IGF-I-R promoter and increased the levels of IGF-I-R/luciferase fusion mRNA. These results suggest that wild-type p53 has the potential to suppress the IGF-I-R promoter in the postmitotic, fully differentiated cell, thus resulting in low levels of receptor gene expression in adult tissues. Mutant versions of p53 protein, usually associated with malignant states, can derepress the IGF-I-R promoter, with ensuing mitogenic activation by locally produced or circulating IGFs.