Search PubMed⌕ Search

Biomedical subjects

D LeRoith

Publications and source records attributed to D LeRoith.

At least 73 records · Page 4Linked to original sources
PubMed1997

Insulin-like growth factor 1 inhibits apoptosis using the phosphatidylinositol 3'-kinase and mitogen-activated protein kinase pathways.

The role of insulin-like growth factor 1 (IGF-1) in preventing apoptosis was examined in differentiated PC12 cells. Induction of differentiation was achieved using nerve growth factor, and apoptosis was provoked by serum withdrawal. After 4-6 h of serum deprivation, apoptosis was initiated, concomitant with a 30% decrease in cell number and a 75% decrease in MTT activity. IGF-1 was capable of preventing apoptosis at concentrations as low as 10(-9) M and as early as 4 h. The phosphatidylinositol 3' (PI3')-kinase inhibitors wortmannin (at concentrations of 10(-8) M) and LY294002 (10(-6) M) blocked the effect of IGF-1. The pp70 S6 kinase (pp70S6K) inhibitor rapamycin (10(-8) M) was, however, less effective in blocking IGF-1 action. Moreover, stable transfection of a dominant-negative p85 (subunit of PI3'-kinase) construct in PC12 cells enhanced apoptosis provoked by serum deprivation. Interestingly, in the cells overexpressing the dominant-negative p85 protein, IGF-1 was still capable of inhibiting apoptosis, suggesting the existence of a second pathway involved in the IGF-1 effect. Blocking the mitogen-activated protein kinase pathway with the specific mitogen-activated protein kinase/extracellular-response kinase kinase inhibitor PD098059 (10(-5) M) inhibited the IGF-1 effect. When wortmannin and PD098059 were given together, the effect was synergistic. The results presented here suggest that IGF-1 is capable of preventing apoptosis by activation of multiple signal transduction pathways.

Androstadienes↗
PubMed1997

Growth hormone treatment induces mammary gland hyperplasia in aging primates.

The decline of growth hormone (GH) and insulin-like growth factor I (IGF-I) production during aging has been likened to the decrease in gonadal steroids in menopause. The repletion of GH/IGF-I levels in aging individuals is suggested to restore the lean tissue anabolism characteristic of youth. In addition to anabolic effects on musculo-skeletal tissues, GH also stimulates mammary glandular growth in some species, although its effects on primate mammary growth remain unclear. Some clinical observations implicate GH in human mammary growth, for example, gynecomastia occurs in some children treated with GH (ref. 6), and tall stature and acromegaly are associated with an increased incidence of breast cancer. To investigate the effects of GH/IGF-I augmentation on mammary tissue in a model relevant to aging humans, we treated aged female rhesus monkeys with GH, IGF-I, GH + IGF-I or saline diluent for 7 weeks. IGF-I treatment was associated with a twofold increase, GH with a three- to fourfold increase, and GH + IGF-I with a four'-to fivefold increase in mammary glandular size and epithelial proliferation index. These mitogenic effects were directly correlated with circulating GH and IGF-I levels, suggesting that either GH or its downstream effector IGF-I stimulates primate mammary epithelial proliferation.

Aging↗
PubMed1997

Developmental and tissue-specific sulfonylurea receptor gene expression.

We have studied the developmental regulation of mouse sulfonylurea receptor (SUR) gene expression throughout several embryonic stages as well as in the adult mouse. To this end we used a 229-bp mouse complementary DNA corresponding to the 3'-end of the SUR gene for in situ hybridization and solution hybridization/ribonuclease protection assays. We found that the SUR gene was expressed as early as embryonic day 12 in the developing pancreas, heart, and central nervous system. These tissues maintained significant levels of SUR messenger RNA (mRNA) throughout development. In addition, SUR mRNA was detected in the submandibular gland, anterior duodenum, dorsal root ganglia, lens, retina, and vibrissae by late developmental stages. SUR mRNA is widely distributed in adult mouse tissues, with the exception of the liver. In the adult pancreas, the SUR gene was expressed exclusively in endocrine tissue. Although significant levels of SUR mRNA were broadly seen throughout the brain, neurons of the cerebellum, hippocampus, and thalamus had especially high levels of SUR mRNA. These findings support the idea that the SUR has important functions in many other tissues in addition to the islets of the pancreas.

ATP-Binding Cassette Transporters↗
PubMed1997

Changes in facilitative glucose transporter messenger ribonucleic acid levels in the diabetic rat kidney.

Facilitative glucose transporter (GLUTs 1, 2, 4, and 5) messenger RNAs (mRNAs) are differentially distributed in the rat nephron: GLUT1 is widely expressed, GLUT4 is selectively concentrated in thick ascending limbs, and GLUT2 and 5 are exclusively localized in proximal tubules, consistent with differential roles for these transporters in renal glucose handling. In the present study, quantitative in situ hybridization was used to evaluate changes in these mRNA levels during acute (2 and 7 days) and chronic (30, 90, and 180 days) streptozotocin-induced diabetes mellitus (STZ-DM). Medullary GLUT1 and GLUT4 mRNA levels were significantly increased during the acute phase but returned to normal after 1 week. Cortical GLUT1 mRNA levels, however, were decreased significantly from 7 days through 6 months of STZ-DM. Cortical GLUT2 mRNA was slightly increased acutely and increased 5-fold in chronic STZ-DM, with the largest increase focally concentrated in the convoluted portion of the proximal tubule. Proximal tubule GLUT5 mRNA levels also were increased significantly during chronic STZ-DM. In summary, medullary GLUT1 and GLUT4 mRNA levels are acutely increased in STZ-DM, paralleling the increased renal epithelial metabolic activity accompanying early diabetes. Proximal tubular GLUT2 and 5 mRNA levels were increased in chronic STZ-DM, possibly adapting to the increased need for glucose transport out of these epithelial cells, whereas the concomitant decrease in cortical GLUT1 expression may reflect the decreased requirement for basolateral import of glucose into these same cells. Thus, renal GLUTs demonstrate complex, nephron segment-specific and duration-dependent responses to the effects of STZ-DM.

Acute Disease↗
PubMed1997

Insulin-like growth factor-1 inhibition of apoptosis is associated with increased expression of the bcl-xL gene product.

Differentiated PC12 cells, which become dependent on the presence of growth factors in the media and die by apoptosis after several hours of serum deprivation, were used to test the ability of IGF-1 to regulate the endogenous levels of the death-suppressing protein Bcl-xL, IGF-1 was capable of preventing apoptosis of serum-deprived differentiated PC12 cells at physiological concentrations, with optimal results seen at 10(-8) M. Incubation with the hormone resulted in a significant increase of Bcl-x mRNA after 3-6 h incubation and a doubling of Bcl-xL protein levels by 24 h incubation. Our results show that the protective effect of IGF-1 in PC12 cells is associated with an up-regulation of Bcl-xL mRNA and protein levels.

Alternative Splicing↗
PubMed1997

Specific inhibition of insulin-like growth factor-1 and insulin receptor tyrosine kinase activity and biological function by tyrphostins.

A series of the synthetic protein tyrosine kinase inhibitors known as tyrphostins were studied for their effect on insulin-like growth factor-1 and insulin-stimulated cellular proliferation on NIH-3T3 fibroblasts overexpressing either receptor, as well as for their ability to inhibit ligand-stimulated receptor autophosphorylation and tyrosine kinase activity toward exogenous substrates. Several of the tyrphostins tested demonstrated a dramatic effect by inhibiting hormone-stimulated cell proliferation, with IC50s in the submicromolar range, while being unable to block serum-stimulated cell proliferation. The tyrphostins also inhibited receptor autophosphorylation and tyrosine kinase activity, with a higher IC50, in the micromolar range. Most of the tyrphostins tested presented no clear preference for either receptor, although two of them (AG1024 and AG1034) showed significantly lower IC50s for IGF-1 than for insulin receptors. These results suggest that, in spite of the high homology of the kinase regions of both receptors, it could be possible to design and synthesize small molecules capable of discriminating between them. The synthesis of such specific inhibitors could be an excellent tool to establish the precise signalling mechanisms that distinguish between the different effects of these two hormones.

3T3 Cells↗
PubMed1997

Mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways are not sufficient for insulin-like growth factor I-induced mitogenesis and tumorigenesis.

Insulin-like growth factor-I (IGF-I) and insulin are known to activate a signaling cascade involving ras --> kappa raf-1 --> mitogen-activated protein (MAP) kinase kinase (MEK) --> p42/p44 MAP kinase (Erk-1 and -2). Recent reports suggest that activation of this ras/MAP kinase pathway is involved in mitogenesis and c-fos transcription but is not required for insulin action on metabolic processes such as glycogen synthesis, lipogenesis, and GLUT-4-mediated glucose transport. Previously we and others have demonstrated that substitution of both tyrosines at positions 1250 and 1251 in the carboxy-terminal region of the human IGF-I receptor has relatively small effects on receptor and endogenous substrate phosphorylation but completely abrogated the ability of these cells to form tumors in nude mice or proliferate in response to IGF-I in culture. Replacement of the tyrosine at position 1316 also did not affect the kinase activity of the receptor with respect to autophosphorylation or phosphorylation of endogenous substrates but did reduce the ability of the receptor to mediate mitogenic or tumorigenic signals. To further characterize the role of these tyrosines in IGF-I receptor function, we have used three distinct approaches to examine the ras/MAP kinase pathway in IGF-I-induced mitogenesis and tumorigenesis in NIH-3T3 cells overexpressing wild-type and mutated IGF-I receptors: 1) tyrosine phosphorylation of the MAP kinases Erk-1 and -2; 2), mobility shifts indicative of MAP kinase phosphorylation; and 3) in vitro MAP kinase activation. We have also examined IGF-I-induced phosphatidylinositol (PI) 3-kinase activation in the same cell lines. By each method we show that the IGF-I-induced MAP kinase phosphorylation/activation and PI 3-kinase activation, are not different between cells overexpressing wild-type IGF-I receptors and cells carrying IGF-I receptors having tyrosine motifs replaced at positions 1250 and 1251. We conclude that mitogenic and tumorigenic signals involving tyrosine residues in the C-terminal domain of the IGF-I-receptor include pathways other than the MAP kinase and PI 3-kinase pathways.

3T3 Cells↗
PubMed1997

Tyrosine residues in the C-terminal domain of the insulin-like growth factor-I receptor mediate mitogenic and tumorigenic signals.

We investigated cellular proliferation, the transforming activity, and activation of known signal transduction pathways in NIH-3T3 cells stably expressing insulin-like growth factor-I receptors (IGF-IRs) with amino acid substitutions in the carboxy(C)-terminal domain. The mutant receptors contained substitutions of both tyrosines 1250 and 1251 with phenylalanine and histidine (amino acids present in the analogous positions in the insulin receptor), as well as phenylalanine 1310 replaced by tyrosine (IsY clones) to resemble the placement of tyrosine residues in the C-terminal domain of the insulin receptor. As a control for the IsY clones, a second mutant receptor was expressed with a substitution of phenylalanine 1310 with tyrosine only (DBY clones). Clones expressing IGF-IRs with the IsY substitutions had a significantly slower rate of growth compared with cells expressing an equivalent number of wild-type IGF-IRs (NWT). In contrast, the DBY clones showed relatively normal growth rates. Cells with wild-type IGF-IR demonstrated a transformed phenotype in soft agar assays. The IsY clones lost the transforming ability of the wild type IGF-IR, whereas DBY clones formed colonies. IGF-I-stimulated autophosphorylation of the IGF-IR and tyrosine phosphorylation of IRS-1 and SHC, known substrates in the IGF-IR signal transduction pathway, were studied. Mutated IGF-IRs (IsY and DBY) did not alter the IGF-I-induced tyrosine phosphorylation of these proteins. Furthermore, the mutated IGF-IRs did not alter Grb2 association with phosphorylated IRS-1 and SHC. IGF-I stimulation of Crk-II phosphorylation, a novel substrate of the IGF-IR, was similar in cells expressing mutated and wild-type IGF-IRs. IGF-I-induced activation of phosphatidylinositol (PI) 3'-kinase was equivalent in cells expressing either mutant or wild-type IGF-IRs. These data suggest that the IGF-IR mediates, at least in part, cellular proliferation and increased transforming ability through its C-terminal domain. The exact postreceptor signaling pathway(s) involved have yet to be fully elucidated.

3T3 Cells↗
PubMed1997

Short-term effects of growth hormone and insulin-like growth factor I on cancellous bone in rhesus macaque monkeys.

The purpose of our study was to determine the effects of GH and insulin-like growth factor I (IGF-I) administration singly and in combination on vertebral, tibial, and femoral bone in aged female monkeys as well as the various treatment effects on serum hormone levels and osteocalcin gene expression. Twenty-one ovulating female monkeys (rhesus macaque), aged 16-20 yr (5-6 kg), were divided into four groups to receive the following treatment for 7 weeks via Alzet pumps inserted sc: A, eluant (control group); B, recombinant human IGF-I (rhIGF-I; 120 micrograms/kg.day); C) rhGH (100 micrograms/kg.day); D, combination of rhIGF-I (120 micrograms/kg.day) and rhGH (100 micrograms/kg.day). Serum was assayed serially for glucose, IGF-I, GH, and IGF-binding protein-3 levels. All groups received double labeling with calcein. On the day of death, the primates' second lumbar vertebrae, tibiae, and femora were carefully dissected, fixed in 70% ethanol, and subjected to histomorphometric analysis. Ribonucleic acid was extracted from contralateral tibiae for the purpose of osteocalcin gene expression analysis. Serum glucose was unaffected by treatment. Serum GH was significantly elevated in groups C and D, whereas serum IGF-I and IGFBP-3 were only significantly increased in group D. Histomorphometric analysis showed no significant differences or trends for bone volume in any treatment group. Bone formation rate, surface and/or bone volume referent were significantly higher in both groups treated with GH (C and D) in tibia and femur, with a similar trend in vertebrae. The increase in bone formation rate was due mainly to a significant increase in mineral apposition rate, but there was also an increase in tibial mineralizing surface by GH by factorial analysis (P < 0.05). There were significant treatment effects on osteoid surface and osteoclastic surface in femur in the combination treatment group vs. the controls. Osteocalcin gene expression analysis supported an enhanced expression in both groups treated with GH. These findings are consistent with a short term effect of GH to increase bone remodeling and predominantly osteoblastic activity in the appendicular skeleton. In contrast, other than an isolated increase in osteoclastic surface in femoral bone, IGF-I, when administered alone, was unable to significantly influence bone formation or resorption activity in this short term study.

Animals↗
PubMed1997

Induction of renal kallikrein and renin gene expression by insulin and IGF-I in the diabetic rat.

The renal kallikrein-kinin system and the renin-angiotensin system are implicated in the pathogenesis of diabetic nephropathy. We have shown that renal kallikrein and renin gene expression are altered by diabetes. To investigate the cellular mechanisms responsible for these changes, we examined the effects of acute insulin and insulin-like growth factor I (IGF-I) treatment on renal kallikrein-kinin and renin-angiotensin system components. Three weeks after induction of diabetes, we measured renal kallikrein and renin mRNA levels, renal kallikrein and renal renin activity, and plasma renin activity in control and diabetic rats and diabetic rats treated with insulin or IGF-I for 2 or 5 h. In diabetic rats, kallikrein and renin mRNA levels were reduced >50% compared with control rats. Renal tissue kallikrein levels and plasma renin activity were decreased, whereas renal renin content was unchanged. Insulin increased kallikrein and renin mRNA levels after 2 h. IGF-I, at a dosage that stimulated kallikrein mRNA levels in control rats, had no effect on renal kallikrein and renin content or mRNA levels in diabetic rats. However, infusion of a fivefold higher IGF-I dosage resulted in a two- to threefold increase in kallikrein and renin mRNA levels in 2 h. These data suggest that 1) diabetes suppresses kallikrein and renin gene expression, and these abnormalities are reversed by insulin or IGF-I; and 2) the diabetic state produces resistance to IGF-I induction of kallikrein and renin gene expression. These changes in regulated synthesis of kallikrein and renin in the kidney may underlie renal vascular changes that develop in diabetes.

Animals↗
PubMed1996

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.

Base Sequence↗
PubMed1996

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.

Base Sequence↗
PubMed1996

Involution of the lactating mammary gland is inhibited by the IGF system in a transgenic mouse model.

Development of the mammary gland during puberty, pregnancy, and lactation is controlled by steroid and peptide hormones and growth factors. To determine the role of the insulin-like growth factors (IGFs) in this process we developed a transgenic model using the whey acidic protein (WAP) gene to direct expression of rat IGF-I and human IGF binding protein-3 (IGFBP-3) to mammary tissue during late pregnancy and throughout lactation. High levels of expression of transgenic IGF-I and IGFBP-3 were seen in lobular-alveolar cells by in situ hybridization. There was no obvious effect on mammary development during pregnancy and lactation; indeed, mothers were capable of nursing their pups normally and the only structural difference seen in the mammary glands at peak lactation was an overall smaller size of the alveoli. We also evaluated the role of IGF-I and IGFBP-3 in the remodeling of mammary tissue during involution. Compared with control animals, the process of involution was modified in both transgenic lines. The degree of apoptotic cells was lower in the WAP-IGF-I and WAP-BP-3 expressing mice. In addition, there was a more quiescent pattern of involution with residual lobular secretary ability and a muted host inflammatory reaction with fewer lumenal microcalcifications. These results demonstrate that IGF-I and IGFBP-3 may modulate the involutionary process of the lactating mammary gland.

Animals↗
PubMed1996

The proto-oncogene product c-Crk associates with insulin receptor substrate-1 and 4PS. Modulation by insulin growth factor-I (IGF) and enhanced IGF-I signaling.

The Crk proto-oncogene product is an SH2 and SH3 domain-containing adaptor protein which we have previously shown to become rapidly tyrosine phosphorylated in response to stimulation with insulin-like growth factor I (IGF-I) in NIH-3T3 cells. In order to further characterize the role of Crk in the IGF-I signaling pathway, NIH-3T3 and 293 cells were stably transfected with an expression vector containing the Crk cDNA. The various resultant 3T3-Crk clones expressed Crk at approximately 2-15-fold higher levels than parental 3T3 cells. In 3T3-Crk cells, Crk immunoreactivity was detected in insulin receptor substrate-1 (IRS-1) immunoprecipitates. Stimulation with IGF-I resulted in a dissociation of Crk protein from IRS-1. In contrast, the association of the related adaptor protein Grb2 with IRS-1 was enhanced by IGF-I stimulation. Similar results were obtained in stably transfected 293-Crk cells, which express both IRS-1 and the IRS-1-related signaling protein 4PS. In these cells, IRS-1 and 4PS both associated with Crk, and this association was also decreased by IGF-I treatment, whereas the association of Grb2 with IRS-1 and 4PS was enhanced by IGF-I. Overexpression of Crk also enhanced IGF-I-induced mitogenesis of NIH-3T3 cells, as measured by [3H]thymidine incorporation. The levels of IGF-I-induced mitogenesis were proportional to the level of Crk expression. These results suggest that Crk is a positive effector of IGF-I signaling, and may mediate its effects via interaction with IRS-1 and/or 4PS.

3T3 Cells↗
PubMed1996

Interaction between the insulin receptor and its downstream effectors. Use of individually expressed receptor domains for structure/function analysis.

A structural analysis has been carried out to determine which part of the intracellular domain of the insulin receptor (IR) beta subunit is involved in direct interaction with the receptor substrates IRS-1 and Shc. Toward this end, the juxtamembrane (JM) domain (amino acids 943-984) and the carboxyl-terminal (CT) region (amino acids 1245-1 331) of IR were expressed in bacteria as (His)6-fusion peptides, and their interaction with IRS-1 and Shc was studied. We could demonstrate that the CT region of IR was sufficient to bind Shc, although significant, but much lower binding of Shc to the JM region could be detected as well. Furthermore, in vitro Tyr phosphorylation of the CT region potentiated its interactions with Shc 2-fold. In contrast, the JM region, but not the CT domain of the IR, was sufficient to mediate interactions between the IR and IRS-1. These interactions did not involve the pleckstrin homology (PH) region of IRS-1, since an IRS-1 mutant, in which four "blocks" of the PH domain (Pro5-Pro65) were deleted, interacted with the JM region of IR with the same efficiency as native IRS-1. These results suggest that the IR interacts with its downstream effectors through distinct receptor regions, and that autophosphorylation of Tyr residues located at the CT domain of the IR can modulate these interactions.

Animals↗
PubMed1996

Growth hormone (GH) status regulates GH receptor and GH binding protein mRNA in a tissue- and transcript-specific manner but has no effect on insulin-like growth factor-I receptor mRNA in the rat.

The effect of growth hormone-deficiency (GHD) and treatment with recombinant bovine GH (bGH) or human IGF-I (hIGF-I) for 10 days on the expression of GH receptor (GHR), GH binding protein (GHBP) and of insulin-like growth factor-I receptor (IGF-IR) mRNA was examined using dw/dw and normal Lewis rats. Hepatic GHR and GHBP mRNA expression was significantly lower in dw/dw rats in comparison to Lewis rats (P < 0.01) while specific 125I-bGH binding to hepatic microsomal membranes was significantly higher (P < 0.01), suggesting a reduction in hepatic GHR turnover with GHD. Treatment with bGH reduced hepatic specific 125I-bGH binding in dw/dw rats, but had no effect in Lewis rats. Treatment with hIGF-I increased hepatic specific 125I-bGH binding in Lewis rats. Hepatic GHR and GHBP mRNA expression was not changed by bGH or hIGF-I treatment, suggesting that differences in hepatic specific 125I-bGH binding may be due to posttranscriptional mechanisms. GHBP mRNA expression was higher in kidney, heart, and muscle of dw/dw rats in comparison to Lewis rats (P < 0.01), while GHR mRNA abundance was not changed. Treatment of dw/dw rats with hIGF-I or bGH resulted in a coordinate reduction of GHR and GHBP mRNAs in kidney (P < 0.01). IGF-IR mRNA was not detected in liver and despite reduced plasma IGF-I levels and IGF-I mRNA expression IGF-IR mRNA abundance was not changed in nonhepatic tissues by GHD. Our data suggest that changes in plasma IGF-I levels and local IGF-I mRNA do not influence IGF-IR mRNA expression, while GHR and GHBP mRNA expression in different rat tissues are regulated independently. The increased nonhepatic GHBP mRNA expression with GHD suggests that nonhepatic GHBP may have an important physiological function distinct from that of GHBP in liver or in plasma.

Animals↗
PubMed1996

Regulation of insulin-like growth factor I receptor gene expression by the Wilms' tumor suppressor WT1.

THe insulin-like growth factor I receptor (IGF-I-R) has been implicated in the etiology and/or progression of Wilms' tumor, or nephroblastoma, a pediatric neoplasm of the kidney that is often associated with deletion or mutation of the WT1 tumor suppressor gene. The levels of IGF-I-R mRNA in the tumors were sixfold higher than in normal adjacent kidney tissue and were inversely correlated to the levels of WT1 mRNA, suggesting that the expression of the IGF-I-R gene is under inhibitory control by WT1. Cotransfection of an IGF-I-R promoter-luciferase reporter construct together with a WT1 expression vector resulted in a dose-dependent suppression of promoter activity. Multiple WT1 binding sites were mapped in the 5'-flanking and 5'-untranslated regions of the IGF-I-R gene using gel retardation and DNaseI footprinting assays. Thus, suppression of the IGF-I-R promoter by WT1 involves multiple interactions of its zinc finger domain with sites located both upstream and downstream of the transcription initiation site. Finally, we showed that expression of the endogenous IGF-I-R gene is decreased in G401 cells stably transfected with a WT1 expression vector. Reduction in expression of the IGF-I-R gene is associated with a decrease in a number of IGF-I-mediated biological effects. Thus, deletion or mutation of the WT1 gene in Wilms' tumor and other malignancies can result in overexpression of the receptor, with enhanced autocrine/paracrine activation by locally produced or circulating IGFs.

Animals↗