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Biomedical subjects

D LeRoith

Publications and source records attributed to D LeRoith.

At least 109 records · Page 6Linked to original sources
PubMed1995

Inhibition of cellular proliferation by the Wilms' tumor suppressor WT1 is associated with suppression of insulin-like growth factor I receptor gene expression.

We have investigated the regulation of the insulin-like growth factor I receptor (IGF-I-R) gene promoter by the Wilms' tumor suppressor WT1 in intact cells. The levels of endogenous IGF-I-R mRNA and the activity of IGF-I-R gene promoter fragments in luciferase reporter constructs were found to be significantly higher in G401 cells (a Wilms' tumor-derived cell line lacking detectable WT1 mRNA) than in 293 cells (a human embryonic kidney cell line which expresses significant levels of WT1 mRNA). To study whether WT1 could suppress the expression of the endogenous IGF-I-R gene, WT1-negative G401 cells were stably transfected with a WT1 expression vector. Expression of WT1 mRNA in G401 cells resulted in a significant decrease in the rate of cellular proliferation, which was associated with a reduction in the levels of IGF-I-R mRNA, promoter activity, and ligand binding and with a reduction in IGF-I-stimulated cellular proliferation, thymidine incorporation, and anchorage-independent growth. These data suggest that a major aspect of the action of the WT1 tumor suppressor is the repression of IGF-I-R gene expression.

Cell Division↗
PubMed1995

Regulation of insulin-like growth factor I transcription by prostaglandin E2 in osteoblast cells.

Insulin-like growth factor I (IGF-I) is a widely expressed abundant autocrine and paracrine factor that regulates the proliferation and differentiation of a variety of cell types. Prostaglandin E2 (PGE2) is a potent stimulator of IGF-I synthesis in bone. We examined the regulation of IGF-I synthesis by PGE2 in osteoblast-enriched (Ob) cells from fetal rat calvaria. PGE2 treatment of Ob cells at 1 microM for 2 h resulted in a 5-fold increase in heterogeneous nuclear RNA levels, as measured by a reverse transcriptase-polymerase chain reaction assay, suggesting an increase in IGF-I gene transcription. RNase protection analysis was used to map the transcriptional start sites in the IGF-I gene that are used in Ob cells. Consistent with other extrahepatic tissues, initiation of transcription occurs primarily at three sites within the 5'-regions of exon 1 of the IGF-I gene. PGE2 treatment did not alter start site usage. The regions upstream of these transcriptional start sites were analyzed by transiently transfecting Ob cells with putative rat IGF-I promoter sequences ligated to a luciferase reporter gene. Constructs containing 1.4 kilobases of the 5'-regions regions of exons 1 and 2 had significant promoter activity. PGE2 treatment of transfected Ob cells increased luciferase activity 5-fold when a 1.4-kilobase exon 1 promoter fragment was tested. This increase in luciferase activity was time and dose dependent. Smaller regions of the exon 1 promoter sequence gave higher basal activity and were less responsive to PGE2. We conclude that regions involved in IGF-I regulation by PGE2 are contained within the IGF-I promoter.

Animals↗
PubMed1995

Growth inhibition of MCF-7 breast cancer cells by stable expression of an insulin-like growth factor I receptor antisense ribonucleic acid.

Insulin-like growth factors (IGFs) play an important role in cellular proliferation, and IGF action appears to be involved in tumorigenesis. To determine the role of the IGF-I receptor in breast cancer cell growth, we stably transfected MCF-7 breast cancer cells with a construct encoding an antisense RNA complementary to the region surrounding the translation initiation site of the IGF-I receptor messenger RNA (mRNA). Control cells were transfected with vector alone. Clones expressing the antisense RNA exhibited a 30% reduction in endogenous IGF-I receptor mRNA levels and a significant reduction in receptor protein levels, as measured by both ligand binding assays and Western blot analysis. Antisense-expressing clones expressed approximately 30,000 receptors/cell compared with approximately 48,000-58,000 receptors/cell in control (neo) cells (P < 0.05). Although endogenous RNA:RNA hybrids were demonstrable in antisense-expressing cells, our results suggest that the major effect of the antisense may be the reduction in mRNA levels and not via an inhibition of translation. The reduction in receptor expression reduced both IGF-I- and serum-stimulated cellular proliferation. The maximum cell number reached at 96 h in the presence of IGF-I (100 ng/ml) was significantly reduced in antisense-expressing clones (22,000-30,000) compared with that in control (neo) cells (39,000-42,000). Furthermore, IGF-I-induced c-fos gene expression was reduced by 30% in the clones expressing the antisense RNA. These results strongly support a role for the IGF-I receptor in the proliferation of human breast cancer cells and suggest that strategies using this type of technology may prove useful in cancer therapy.

Breast Neoplasms↗
PubMed1995

Localization of growth hormone receptor/binding protein messenger ribonucleic acid (mRNA) during rat fetal development: relationship to insulin-like growth factor-I mRNA.

Although GH plays a key role in postnatal growth, prenatal growth is thought to be GH independent. However, recent data has shown GH receptor/binding protein (GHR/BP) to be present in rat fetal tissues as early as fetal stage E12. The aim of the present study was to investigate tissue-specific production of the GHR/BP messenger RNA (mRNA) and its relationship to locally transcribed insulin-like growth factor-I (IGF-I) mRNA in the fetus. We have used in situ hybridization to localize GHR/BP and IGF-I mRNAs in 16.5-, 18.5-, and 20.5-day-old rat fetuses. Furthermore, because the two parameters of the IGF-I gene differentially respond to GH stimulation, we have also investigated the presence and localization of promoter-specific IGF-I mRNAs. We found the distribution of IGF-I and GHR/BP mRNAs to be widespread but distinct during the fetal stages examined. High levels of IGF-I mRNA were found in connective tissues or their precursors, including the dermis, perichondrium, and gut. In contrast, GHR/BP mRNA exhibited three distinct patterns of distribution. First, GHR/BP mRNA was found at epithelial sites adjacent to sites of IGF-I transcription. Second, GHR/BP and IGF-I mRNAs were found to colocalize in some connective tissues, but GHR/BP mRNA levels in these sites were often lower than at other sites (i.e. epithelial) of GHR/BP gene transcription. Third, GHR/BP mRNA was also found in regions remote from IGF-I mRNA, including the nerve ganglia and inner olfactory bulb. Using promoter-specific IGF-I RNA probes, we detected only promoter 1 transcripts in all fetal tissues examined. The only exception occurred in specialized epithelial cells of the cochlea where we detected high levels of both promoter 1- and 2-derived IGF-I transcripts. We have thus demonstrated a distinct distribution of GHR/BP and IGF-I mRNAs in the developing rat fetus with coordinate expression at some sites. These findings suggest a role of GH or a GH-like peptide, acting both directly and indirectly via IGF-I, in fetal growth and development.

Animals↗
PubMed1995

Single tyrosine substitution in the insulin-like growth factor I receptor inhibits ligand-induced receptor autophosphorylation and internalization, but not mitogenesis.

The tyrosine kinase domains of the insulin and insulin-like growth factor I (IGF-I) receptors play an essential role in signal transduction. After ligand binding, these receptors undergo autophosphorylation, with a cluster of three tyrosines (residues 1131, 1135, and 1136 in the IGF-I receptor) being the first to be phosphorylated. Mutation of the ATP-binding site or substitution of this triple tyrosine cluster in the catalytic domain blocks essentially all of the functions of these receptors. Using stably transfected NIH-3T3 cell lines, we studied the effect of a mutation of tyrosine 1131 of the triple tyrosine cluster of the IGF-I receptor to phenylalanine. This mutation significantly reduced IGF-I-induced beta-subunit autophosphorylation, whereas phosphorylation of the endogenous substrate IRS-1 was unaffected. Despite the reduction in autophosphorylation and receptor internalization, IGF-I-induced thymidine incorporation and cellular proliferation were unaffected. Thus, the extent of receptor autophosphorylation and internalization does not appear to be a limiting factor for IGF-I-stimulated mitogenesis.

3T3 Cells↗
PubMed1995

Expression of insulin-like growth factor binding proteins in the rat kidney: effects of long-term diabetes.

Recent studies have shown that the renal synthesis of insulin-like growth factor binding proteins (IGFBPs) is altered in insulin-deficient diabetes mellitus, suggesting that these changes may be implicated in the alterations in renal function and morphology that accompany diabetes. To investigate the time course and the precise cellular distribution of changes in IGFBP expression, we used quantitative in situ hybridization to analyze renal IGF-I and IGFBP-1 to -5 messenger RNA (mRNA) localization and levels from 2 days to 6 months after the onset of streptozotocin-induced diabetes. There was an immediate sharp decline in IGF-I mRNA levels in the outer medulla that persisted for up to 3 months and a much smaller reduction in IGF-I mRNA levels in the medullary thick ascending limbs (MTALs). In nondiabetic animals, IGFBP-1 mRNA is most abundant in the MTALs. Immediately after the induction of diabetes, however, there was a greater than 2-fold increase in cortical IGFBP-1 mRNA and a 75% decrease in IGFBP-1 mRNA in MTALs. These changes persisted for up to 6 months in the diabetic animals. In contrast, IGFBP-5 mRNA levels were increased in the outer medulla and decreased in the cortex of diabetic kidneys. No significant changes in renal IG-FBP-2 mRNA levels or distribution were noted, and changes in IG-FBP-3 and -4 mRNA levels were subtle. In summary, streptozotocin-induced diabetes is associated with very prominent and complex alterations in renal IGF system gene expression, including robust increases in cortical IGFBP-1 and profound decreases in cortical IG-FBP-5 mRNA and medullary IGF-I mRNA levels. The divergent changes in IGFBP-1 and -5 mRNA levels in cortex vs. outer medulla indicate that regulation of IGFBP mRNA levels is quite complex.

Albuminuria↗
PubMed1995

Modulation of insulin-like growth factor I (IGF-I) receptors and membrane-associated IGF-binding proteins in endometrial cancer cells by estradiol.

Insulin-like growth factor I (IGF-I) receptors and membrane-associated IGF-binding proteins (IGFBPs) were examined in Ishikawa endometrial cancer cells. Our findings suggest that about 95% of [125I]IGF-I is bound to membrane-associated IGFBPs rather than to IGF-I receptors. Specifically, [125I]IGF-I binding to cell membranes could be completely displaced by cold IGF-I or IGF-II, but not by insulin, suggesting that binding was primarily due to IGFBPs. This was confirmed by using [125I]des-(1-3)IGF-I as the ligand. Des-(1-3) IGF-I binds with high affinity to IGF-I receptors, but with markedly lower affinity to IGFBPs. [125I]Des-(1-3)IGF-I bound to Ishikawa cells was displaced by IGF-I, IGF-II, and insulin. These results suggest that measuring IGF-I receptor levels using labeled IGF-I may be misleading. Accordingly, we evaluated the differential binding of [125I]IGF-I and [125I]des-(1-3)IGF-I to study the involvement of the IGF system in the stimulation of Ishikawa cell growth by estradiol. IGF-I stimulates Ishikawa cell proliferation, but at low concentrations, and this stimulation is largely dependent on the presence of estradiol. Estradiol caused a 2.5-fold increase in IGF-I receptor levels. Moreover, estradiol reduced soluble IGFBP levels, presumably increasing the availability of IGFs for their receptors. This elevation in IGF-I receptor levels and the decrease in IGFBP levels were accompanied by a 3.5-fold increase in IGF-I receptor messenger RNA and a 2.5-fold decrease in IGFBP messenger RNAs. These experiments suggest that estradiol sensitizes endometrial cancer cells to the effects of IGFs by simultaneously elevating receptor levels and decreasing (potentially inhibitory) IGFBP levels.

Binding, Competitive↗
PubMed1995

Alternative leader sequences in insulin-like growth factor I mRNAs modulate translational efficiency and encode multiple signal peptides.

Rat insulin-like growth factor I (IGF-I) mRNAs contain multiple 5'-untranslated regions due to the use of leader exons transcribed from several transcription initiation sites and to alternative splicing within leader exon 1. Synthetic RNAs with 5'-ends corresponding to the use of exon 1 transcription initiation sites were translated in vitro into prepro-IGF-I peptides initiated at a Met-48 codon in exon 1 or a Met-22 codon in exon 3, and RNAs with a 5'-end corresponding to the major exon 2 transcription start site were translated into a prepro-IGF-I peptide initiated at a Met-32 codon in exon 2. All forms of prepro-IGF-I were processed by canine pancreatic microsomes, suggesting that all these prepeptides function as signal peptides. The translational efficiency of IGF-I RNAs was inversely proportional to the length of the 5'-untranslated region. Mutation of the first of three upstream AUG codons in exon 1, which potentially initiates a 14-amino acid open reading frame, did not affect prepro-IGF-I translation. The other two AUG codons are immediately followed by stop codons. The absence of both upstream AUG codons in a completely spliced exon 1-derived RNA enhanced the in vitro and in vivo translatability of this RNA as compared with the full-length RNA. Mutation of the downstream initiation codon in particular increased translational efficiency in vitro and in intact cells, suggesting that an inefficient reinitiation event at the Met-48 codon contributes to the poorer translation of IGF-I mRNAs in which these upstream AUGUGA motifs occur. We conclude that IGF-I mRNAs potentially encode multiple forms of preproIGF and that specific differences in their 5'-untranslated regions provide a molecular basis for translational control of IGF-I biosynthesis.

Animals↗
PubMed1995

Regulation of insulin-like growth factor I receptor gene expression by Sp1: physical and functional interactions of Sp1 at GC boxes and at a CT element.

The insulin-like growth factor I (IGF-I) receptor mediates signal transduction by the IGFs and plays a critical role in growth and development. The proximal promoter region of the rat IGF-I receptor gene contains multiple Sp1 consensus-binding sites (GC boxes). Various promoter fragments fused to a luciferase reporter gene were transiently cotransfected together with an Sp1 expression vector into Drosophila Schneider cells, which lack endogenous Sp1. A proximal promoter fragment containing 476 nucleotides of 5'-flanking region and 640 nucleotides of 5'-untranslated region was strongly activated by Sp1 (an average of 116-fold), and progressive 5'-deletions of the promoter that sequentially removed GC boxes reduced Sp1 activation to 15-fold over basal promoter activity. DNase I footprinting studies with purified Sp1 protein revealed four GC boxes in the 5'-flanking region of the promoter and one homopurine/homopyrimidine motif (CT element) in the 5'-untranslated region that bound Sp1. Mutation of the CT element reduced Sp1 activation by 70%. Taken together, these results demonstrate that Sp1 can regulate expression of the IGF-I receptor promoter by acting both on GC boxes in the 5'-flanking region of the promoter and on a CT element in the 5'-untranslated region.

Animals↗
PubMed1995

Growth hormone (GH) modulates insulin-like growth factor I (IGF-I) and type I IGF receptor mRNA levels in the ovary of prepubertal GH-deficient rats.

In order to explore the potential role of growth hormone (GH) in modulating insulin-like growth factor I (IGF-I) gene expression in the prepubertal rat ovary, female rats were rendered GH deficient by neonatal administration of monosodium glutamate (MSG). One group of rats received vehicle and served as the control. At 21 days of age, MSG-treated rats received either GH or vehicle for 2 weeks. On days 21, 24, 28 and 31 animals were weighed and subsets were sacrificed for liver RNA extraction. The remaining animals were sacrificed at day 35 when livers and ovaries were collected, and serum was obtained for GH determinations. The IGF-I mRNA levels were estimated by Northern blots and corroborated further by slot-blot analysis. The MSG-treated rats had lower body weights (p < 0.01) and GH levels (p < 0.05) than controls. Growth hormone replacement significantly accelerated the weight gain of MSG-treated rats. At day 24 and thereafter, three RNA IGF-I species (7.5, 1.8 and 0.8-1.2 kB) were seen in the liver. In the ovary, at age 35 days, two major IGF-I mRNA species (7.5 and 0.8-1.2 kb) were seen. The MSG treatment consistently reduced the levels of both IGF-I mRNA species in the ovary. Growth hormone administration partially restored their expression, both in the liver and in the ovary. In addition, ovarian type IIGF receptor mRNA levels were increased in the MSG-treated rats when compared to controls. This trend was reversed by GH replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Role of GH and IGF-I in the regulation of IGF-I, IGF-I receptor and IGF binding protein gene expression in the rat spleen.

To characterize the expression of the IGF-I system in the spleen and its role in spleen growth, we have studied the effect of hypophysectomy and the action of either GH or IGF-I treatment on the expression of several components of the IGF system in the rat. Female Sprague-Dawley rats were hypophysectomized (Hx) on postnatal day 50, and five animals each received twice-daily sc injections of saline, bovine GH (bGH; 84 micrograms/animal/day), or recombinant human IGF-I (rhIGF-I; 125 micrograms/animal/day) for 11 days. Compared to sham-operated controls, Hx animals exhibited a reduction in both body (192.6 +/- 5.6 g (mean +/- S.E.M.) vs. 268.6 +/- 6.0 g; P < 0.001) and spleen weights (0.42 +/- 0.03 g vs. 0.84 +/- 0.06 g; P < 0.001). The reduction in body and spleen weights in Hx animals was partially prevented by both bGH and rhIGF-I. Body weights were 234.2 +/- 5.3 g (P < 0.001) after bGH and 213.8 +/- 6.3 g (P < 0.05) after rhIGF-I. Spleen weights were 0.56 +/- 0.048 after bGH P < 0.01 and 0.53 +/- 0.05 g after rhIGF-I (P < 0.05). Serum GH and IGF-I levels were markedly reduced in Hx animals and bGH partially maintained IGF-I levels. Hypophysectomy reduced spleen IGF-I mRNA levels (30.6 +/- 7.5% of control values; P < 0.05) and this reduction was prevented by bGH (96.6 +/- 24.2%; NS) but not by rhIGF-I (39.9 +/- 5.0% NS vs. Hx). There were no changes in GH receptor or IGF-I receptor mRNA levels in Hx or bGH or rhIGF-I-treated animals. When IGF-I binding protein (IGFBP) mRNA levels were studied under these conditions, we found that IGFBP-1 mRNA was not detected in spleen; IGFBP-2 mRNA levels were reduced in Hx rats (67.9 +/- 7.4% of control values, P < 0.05) and bGH treatment prevented this reduction (95.5 +/- 12.2%, NS). IGFBP-3 mRNA levels were not affected by hypophysectomy or by bGH treatment, but were reduced in rhIGF-treated rats (69.6 +/- 3.0%, P < 0.05). On the other hand, IGFBP-4 mRNA levels were increased in Hx rats (136.4 +/- 15.9% of control values, P < 0.05) and bGH treatment prevented this increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Role of the carboxyl-terminal domains of the insulin and insulin-like growth factor I receptors in receptor function.

The insulin and insulin-like growth factor I receptors (IR and IGF-IR, respectively) are heterotetrameric tyrosine kinases consisting of two extracellular ligand-binding alpha subunits and two transmembrane catalytic beta subunits. A number of lines of evidence have suggested that the IR and IGF-IR differ with respect to their ability to elicit mitogenic versus metabolic events upon activation by cognate ligands. To ascertain the contribution of the poorly conserved carboxyl-terminal domains to the differential functioning of the IR and IGF-IR, we have constructed receptor chimeras in which the carboxyl-terminal domain of one receptor was fused to the remainder of the heterologous receptor. The responses of a number of parameters after ligand stimulation were examined in stably transfected NIH-3T3 cells expressing the chimeric receptors or the analogous wild-type receptor sequence. Replacement of the IR carboxyl terminus with that of the IGF-IR severely affected insulin-stimulated responses, whereas substitution of the carboxyl terminus of the IGF-IR with that of the IR had a minimal effect. These data suggest that the carboxyl-terminal domains of the IR and IGF-IR are not interchangeable and that the mitogenic activity of the IR can be influenced by sequences present in the carboxyl-terminal domain. The analogous functions of the IGF-IR, on the other hand, do not appear to be greatly affected by the presence of the IR carboxyl-terminal domain.

3T3 Cells↗
PubMed1994

Transcriptional repression of the insulin-like growth factor I receptor (IGF-I-R) gene by the tumor suppressor WT1 involves binding to sequences both upstream and downstream of the IGF-I-R gene transcription start site.

The insulin-like growth factor-I receptor (IGF-I-R) has been implicated in the etiology and/or progression of Wilms' tumor, a pediatric malignancy of the kidney that is often associated with deletion or mutation of the WT1 tumor suppressor gene. The expression of the IGF-I-R gene is increased in Wilms' tumor as compared with normal kidney tissue. Furthermore, the levels of IGF-I-R mRNA in individual tumors have been shown to be inversely correlated to the levels of WT1 mRNA, suggesting that the expression of the IGF-I-R gene is under the negative control of WT1. The activity of an IGF-I-R promoter/luciferase construct in Chinese hamster ovary cells was reduced by cotransfection of a WT1 expression vector. An analysis of various reporter constructs containing different portions of the IGF-I-R 5'-flanking and 5'-untranslated regions suggested that the effect of WT1 depends on the number of WT1 binding sites present, with sites located both upstream and downstream of the IGF-I-R transcription start site involved in mediating this effect. Using the purified zinc finger domain of WT1 in gel retardation and DNase I footprinting assays, we mapped five sites in the 5'-flanking and six sites in the 5'-untranslated regions that were involved in WT1 binding. In addition, the initiator element of the IGF-I-R gene contains a sequence that binds WT1. Thus, the repression of IGF-I-R promoter activity by the WT1 tumor suppressor gene product involves multiple interactions of its zinc finger domain with WT1 binding sites located both 5' and 3' of the transcription initiation site.

Alternative Splicing↗
PubMed1994

Elevated protein tyrosine phosphatase activity and increased membrane viscosity are associated with impaired activation of the insulin receptor kinase in old rats.

Insulin resistance is very common in the elderly, and may be associated with glucose intolerance or frank diabetes. In previous studies we demonstrated that insulin resistance in old Wistar rats is associated with decreased autophosphorylation and activation of the hepatic insulin receptor kinase (IRK) in vivo. We now show that this defect can be reproduced in vitro, where the extent of insulin-induced activation of IRK in liver membranes of old rats was decreased by approximately 50% compared with young controls. The defect could be largely abolished after solubilization of the membranes with Triton X-100. We also show that: (a) the viscosity of membranes from the old rats was significantly (P < 0.001, n = 4) higher (by 15%) compared with young controls; (b) incubation of plasma membranes from old animals with lecithin liposomes, which lowered their cholesterol levels, partially abolished the defect in IRK activation; and (c) Triton extracts of liver membranes prepared from old rats did not interfere with the activation of IRK derived from young controls. Additionally, non-membrane components did contribute to the development of this defect. We observed a significant (approximately 30%) (P < 0.001, n = 18) elevation of cytosolic protein tyrosine phosphatase (PTP) activity directed against the beta subunit of the insulin receptor in livers of old rats. No such elevation of PTP activity could be demonstrated with synthetic substrates. Our findings are consistent with a model in which increased membrane viscosity as well as enhancement of a cytosolic PTP activity both markedly inhibit the activation in vivo of the hepatic IRK in old animals.

Aging↗
PubMed1994

Insulin-like growth factor-binding protein enhancement of insulin-like growth factor-I (IGF-I)-mediated DNA synthesis and IGF-I binding in a human breast carcinoma cell line.

The insulin-like growth factors (IGFs) are potent mitogens for malignant cell proliferation. The majority of secreted IGFs are bound to specific IGF-binding proteins (IGFBPs) that are secreted by a large number of cells. These proteins may either inhibit or enhance IGF actions. Breast carcinoma cells secrete a variety of IGFBPs. We have previously demonstrated that retinoic acid (RA) inhibition of IGF-I-stimulated MCF-7 cell proliferation is associated with increased IGFBP-3 levels in the conditioned media. We therefore investigated the effect of recombinant IGFBP-3 as well as IGFBP-2, -4 and -5 on IGF-I stimulation of DNA synthesis and IGF-I binding in the MCF-7 human breast carcinoma cell line. IGFBP-2 and -3 enhanced IGF-I stimulation of DNA synthesis in MCF-7 cells while IGFBP-4 and -5 had no effect. Transfection of MCF-7 cells with an IGFBP-3 expression vector resulted in the enhanced secretion of IGFBP-3 with an accompanying increase in IGF-I binding as well as increased cell proliferation upon treatment of the cells with IGF-I. IGF-I preincubation of MCF-7 cells transfected with control pSVneo plasmids results in cells refractory to further IGF-I stimulation of thymidine incorporation while IGF-I continues to stimulate [3H]-thymidine incorporation in IGFBP-3-transfected MCF-7 cells, suggesting that IGFBP-3 protects the cells from IGF-I-mediated down regulation of its receptor. Therefore, IGFBP-3 secreted by MCF-7 cells can enhance IGF-I stimulation of DNA synthesis, increase IGF-I binding to these cells, and prevent IGF-I-induced desensitization of its own receptor, suggesting that IGFBP-3 plays a significant role in IGF-I-mediated breast carcinoma proliferation.

Breast Neoplasms↗
PubMed1994

Platelet-derived growth factor increases the activity of the promoter of the insulin-like growth factor-1 (IGF-1) receptor gene.

Stimulation by platelet-derived growth factor (PDGF) is known to increase the number of IGF-I binding sites in cells in culture. We show here that PDGF also increases the levels of IGF-1 receptor mRNA. Using cell lines stably transfected with an expression plasmid in which the reporter luciferase gene is under the control of the rat IGF-1 receptor gene promoter, we find that PDGF increases the activity of this promoter. A short IGF-1 receptor gene promoter, comprising about 100 base pairs of the sequence immediately upstream of the initiation of transcription site, is sufficient for a response to the stimulatory action of PDGF. These results suggest that an increase in RNA levels and in promoter activity may play an important role in the increase in IGF-1 receptor levels that occurs after stimulation by PDGF.

3T3 Cells↗