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D LeRoith

Publications and source records attributed to D LeRoith.

At least 145 records · Page 8Linked to original sources
PubMed1993

Role of tyrosine kinase activity in signal transduction by the insulin-like growth factor-I (IGF-I) receptor. Characterization of kinase-deficient IGF-I receptors and the action of an IGF-I-mimetic antibody (alpha IR-3).

The insulin-like growth factor-I (IGF-I) receptor is a member of a large family of transmembrane signal transducing molecules. The defining characteristic of this class of receptors is the intrinsic tyrosine kinase activity of the cytoplasmic domain. While it has been demonstrated that this tyrosine kinase activity is necessary for the action of a number of transmembrane tyrosine kinase receptors, no evidence of this type has been adduced to date with respect to the signaling requirement of the IGF-I receptor. We have now shown that stably transfected NIH-3T3 cell lines overexpressing human IGF-I receptors display increased responses to IGF-I and an IGF-I-mimetic antibody, alpha IR-3, in terms of short, intermediate, and long term actions initiated by activation of the IGF-I receptor. These include receptor autophosphorylation, activation of phosphatidylinositol-3-kinase and 2-deoxyglucose uptake, induction of ornithine decarboxylase gene expression, and stimulation of thymidine incorporation. In short term responses, the kinetics seen with alpha IR-3 were slower than those seen with IGF-I. These effects were severely decreased in clones expressing human IGF-I receptors in which the lysine residue in the ATP-binding site of the tyrosine kinase domain had been mutated to alanine or arginine. This was true for both IGF-I and alpha IR-3. These results indicate that, for all parameters tested, the tyrosine kinase activity of the IGF-I receptor is necessary for activation of the IGF-I-stimulated signal transduction cascade. Additionally, the effects of alpha IR-3 also require tyrosine kinase activity.

3T3 Cells↗
PubMed1993

Regulation of insulin-like growth factor-binding-protein-1, 2, 3, 4, 5, and 6: synthesis, secretion, and gene expression in estrogen receptor-negative human breast carcinoma cells.

Insulin-like growth-factors I and II (IGF-I, II) are potent mitogens for breast carcinoma proliferation. In extracellular fluids, most of the IGF-I and II is associated with specific IGF-binding proteins (IGFBPs). The role of these IGFBPs in IGF action is still not clear, but it has been demonstrated that these proteins may either enhance or inhibit IGF-mediated cellular effects. Synthesis and secretion of IGFBPs have been demonstrated in breast carcinoma cells. In this study, we examined retinoic acid (RA) and IGF-I modulation of IGFBP mRNA and IGFBP levels in two ER-negative human breast carcinoma cell lines. Treatment of MDA-MB-231 and MDA-MB-468 cells with RA increased the levels in conditioned media of a M(r) 42-46-kDa IGFBP, which was immunoprecipitated by an IGFBP-3 antibody. IGF-I also increased the accumulated levels of IGFBP-3 in the conditioned media of both cell lines. Both cell lines expressed high basal levels of IGFBP-3 mRNA; the addition of RA increased IGFBP-3 mRNA levels by 1.5-fold, whereas the addition of IGF-I had no effect on IGFBP-3 mRNA levels in either cell line. The difference in the magnitude of the RA enhancement of IGFBP-3 mRNA levels (1.5-fold) and RA stimulation of IGFBP-3 levels in conditioned media (3.5-4-fold) suggests that some of the effect of RA is at a posttranscriptional level. IGF-I increased the levels of IGFBP-2 and IGFBP-5 in conditioned media by greater than tenfold but had no effect on IGFBP-2 and IGFBP-5 mRNA levels, again suggesting the involvement of posttranscriptional controls. Pretreatment of MDA-MB-468 and MDA-MB-231 cells with IGF-I receptor antibody (alpha IR3) blocked the IGF-I effect on IGFBP-3 levels in the media in both cell lines and IGFBP-2 and IGFBP-5 secreted levels in MDA-MB-468 cell conditioned media. The addition of RA also blocked IGF-I stimulation of IGFBP-2 and IGFBP-5 levels. Cycloheximide treatment completely blocked the RA and/or IGF-I-mediated modulation of these binding proteins, suggesting that these agents enhance IGFBP-3, IGFBP-2, and IGFBP-5 synthesis and consequent secretion. MDA-MB-468 cells expressed IGFBP-5 mRNA, whereas both MDA-MB-231 and MDA-MB-468 expressed IGFBP-6 mRNA. RA enhanced IGFBP-6 gene expression by threefold in MDA-MB-231 cells, whereas IGF-1 had no effect on IGFBP-6 gene expression in either cell line.(ABSTRACT TRUNCATED AT 400 WORDS)

Blotting, Western↗
PubMed1993

Paradoxical biological effects of overexpressed insulin-like growth factor-1 receptors in Chinese hamster ovary cells.

One major approach to the study of growth factor receptor action has been to overexpress wild-type or mutant receptors in cultured cells and to evaluate biological responses to exogenous ligand. Studies of this type with insulin and insulin-like growth factor-I (IGF-I) receptors often use Chinese hamster ovary (CHO) cells. We have compared the effect of receptor overexpression in CHO cells and in NIH-3T3 fibroblasts in order to assess the suitability of CHO cells for studies of this nature and the contribution of cell type-specific factors to those responses generally assayed. Overexpression of IGF-I receptors in NIH-3T3 cells resulted in increased sensitivity and maximal responsiveness of thymidine incorporation, 2-deoxyglucose uptake, and phosphatidylinositol-3 (PI3) kinase activation to IGF-I stimulation. In CHO cells, on the other hand, overexpression of either IGF-I or insulin receptors increased the sensitivity of thymidine incorporation to ligand, but maximal responsiveness was unchanged or decreased. Overexpression of the insulin receptor increased sensitivity of glucose uptake and the maximal response of PI3 kinase activation to insulin. Overexpression of the IGF-I receptor did not affect sensitivity or maximal responsiveness of glucose uptake or PI3 kinase activation to IGF-I. These data suggest that IGF-I and insulin signal pathways may differ in CHO cells, and that there may even be divergent IGF-I signaling pathways for short vs. long-term effects. Whether this is a result of differences in the number of endogenous receptors, hybrid receptor formation, or defects in post-receptor signaling, the use of CHO cells to assess receptor function must be approached with caution.

3T3 Cells↗
PubMed1993

Phylogeny of the insulin-like growth factors (IGFs) and receptors: a molecular approach.

The IGFs (IGF-I and IGF-II) are essential for normal mammalian growth and development. Their actions are mediated primarily by their interactions with the type I IGF receptor (IGF-I receptor), a transmembrane tyrosine kinase. The ligands and the IGF-I receptor are structurally related to insulin and to the insulin receptor, respectively. Analysis of evolutionary conservation has often provided insights into essential regions of molecules such as hormones and their receptors. The genes for insulin and IGFs have been partially characterized in a number of vertebrate species extending evolutionarily from humans as far back as fish. The sequences of the exons encoding the mature insulin and IGF peptides are highly conserved among vertebrate species, and IGF-I-like molecules are found in species whose origins extend back as much as 550 million years. The insulin receptor is also highly conserved in vertebrate species, and an insulin-receptor-like molecule has been characterized in Drosophila. In contrast, IGF-I receptors have only been characterized in mammalian species and partially studied in Xenopus, in which the tyrosine kinase domain is highly conserved. Studies are presently being undertaken to analyze in more detail the regulation of the genes encoding this important family of growth factors and the structure/function relationships in the gene products themselves.

Amino Acid Sequence↗
PubMed1993

The regulation of IGF-I receptor gene expression by positive and negative zinc-finger transcription factors.

The IGF-I-R gene promoter is a TATA-less, CAAT-less, GC-rich promoter which contains potential binding sites for the Sp1 and WT1 zinc-finger transcription factors. We have shown that Sp1 positively activates the IGF-I-R promoter. Since both the Sp1 and IGF-I-R genes are widely expressed, it is possible that Sp1 is one of the main regulators of IGF-I-R gene expression. This is supported by the correlation between the distribution and developmental regulation of Sp1 and IGF-I-R gene expression, in that both genes appear to be co-regulated during normal development. In a model of human neoplasm, WT, we have demonstrated increased expression of the IGF-I-R gene, which may result from loss of repression of the IGF-I-R promoter by another Zn(2+)-finger protein, the WT1 tumor suppressor gene product. Future studies will define whether other disease states in which the IGF-I-R gene is highly expressed are also associated with loss of negative regulation of the IGF-I-R promoter by WT1 or other tumor suppressor gene products.

Animals↗
PubMed1993

Hepatic tyrosine-phosphorylated proteins identified and localized following in vivo inhibition of protein tyrosine phosphatases: effects of H2O2 and vanadate administration into rat livers.

Injection of a combination of H2O2 and vanadate (H/V) into the portal vein of rat livers resulted in inhibition of protein tyrosine phosphatase activity and led to a dramatic enhanced in vivo protein tyrosine phosphorylation. Some of the phosphorylated proteins were identified as the beta-subunit of the insulin receptor, the insulin receptor substrate 1 (pp185), PLC-gamma (pp145), and a 100 kDa PLC-gamma-associated protein. Immunofluorescense and immune electron microscopy of frozen liver sections with anti-P-Tyr antibodies revealed that most of the tyrosine-phosphorylated proteins are localized in close proximity to the plasma membrane in intercellular adherence junctions and tight junction regions. This close in vivo association between membranal protein tyrosine kinases, their target proteins, and cytoskeletal elements could enable formation of 'signaling complexes' which may play a role in transmembrane signal transduction. By affinity chromatography over immobilized anti-P-Tyr antibodies, a large number of these tyrosine-phosphorylated proteins were partially purified.

Animals↗
PubMed1993

The role of insulin-like growth factors in diabetic kidney disease.

Early renal manifestations of type I diabetes include kidney enlargement, increased glomerular filtration rate, and renal plasma flow. These hemodynamic changes may be caused by a number of factors, including growth hormone and/or insulin-like growth factor-I (IGF-I). Streptozotocin-induced insulinopenic diabetes in rats represents a model of human type I diabetes and is associated with the early hemodynamic changes in the kidney seen in poorly controlled type I diabetic patients. These changes are preceded by an accumulation of IGF-I peptide in the kidney. Insulin-like growth factor-I is not locally produced, but rather accumulates from circulating IGF-I, trapped by increased levels of IGF-binding proteins, particularly IGF-binding protein-1. The hemodynamic effects, reproduced by infusions of recombinant human IGF-I in normal rats, may be blocked by co-infusion of a kinin-receptor antagonist, suggesting that at least one of the mechanisms involved is the kallikrein-kinin system. These studies strongly support the notion that the IGF system may play a role in early hemodynamic manifestations of the diabetic kidney. Whether these effects lead to long-term diabetic renal disease remains to be studied.

Animals↗
PubMed1993

Structure of the chum salmon insulin-like growth factor I gene.

Insulin-like growth factor I (IGF-I) plays a major role in development and metabolism. Currently, the cDNA-derived primary structure of IGF-I is known for some mammals and for chicken, frog, and salmon. Additionally, the organization of the human, rat, and chicken IGF-I genes has been established. The investigation of IGF-I gene structure in fish would extend the evolutionary picture for this hormone and facilitate our understanding of the features of the IGF-I gene that are common to all vertebrate species. The cloned chum salmon IGF-I gene appears to be much more compact than the mammalian and avian genes, being less than 20 kb in length. As in other species, however, the mature IGF-I peptide appears to consist of 70 amino acids and is encoded by exons 2 and 3. Intriguingly, exon 1-encoded 5'-untranslated region sequences are highly conserved, while the coding sequences at the 3' end of the same exon are less conserved. The amino terminus of the signal peptide is four amino acids shorter than in the mammalian and avian peptides. The end of the B domain, the C, A, and D domains, and the first part of the E peptide are encoded by exon 3, but the exon 3-encoded E peptide sequence is 27 amino acids longer than in other species. These extra 27 amino acids, encoded by both coho and chum salmon cDNAs, may be deleted by alternative splicing, as suggested from the sequence of a coho salmon IGF-I cDNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Distinct promoters in the rat insulin-like growth factor-I (IGF-I) gene are active in CHO cells.

In mammals, IGF-I mRNAs contain one of two different leader exon sequences that encode different 5'-untranslated regions (UTRs) and signal peptides. The pattern and regulation of expression of these exon 1 and exon 2-derived mRNAs suggests that the expression of each is controlled by a distinct regulatory region. In order to assess this possibility, DNA fragments consisting of sequences flanking and including the exon 1 and exon 2 transcription initiation sites were cloned into a luciferase expression vector and plasmid DNAs were transiently transfected into Chinese hamster ovary (CHO) cells. A fragment containing approximately 1.1 kb of sequence flanking the most upstream exon 1 transcription initiation site and 362 bp of exon 1 sequence did not stimulate luciferase activity. However, fragments containing 133 bp of 5'-flanking sequence and either 362 or 192 bp of exon 1 sequence stimulated luciferase activity significantly above that seen with a promoterless control plasmid. When the -133/+362 fragment was cloned in the opposite orientation with respect to the luciferase cDNA, the same level of promoter activity was observed. Removal of approximately 860 bp from the inactive fragment (i.e., approximately 782 bp of flanking sequence and approximately 74 bp of exon 1 sequence) resulted in promoter activity which was significantly greater than that seen with the promoterless luciferase expression vector, but which was less than that observed with fragments containing the proximal 133 bp of 5'-flanking sequence. Plasmids containing approximately 1.5 kb or 0.5 kb of flanking sequence and 44 bp of exon 2 sequence also significantly stimulated luciferase activity. These results constitute the first demonstration that both exon 1 and exon 2 transcription start sites are associated with distinct and potentially independently regulatable promoters and provide a molecular basis for the differential expression of these leader exons by developmental, tissue-specific and hormonal factors.

Animals↗
PubMed1993

Insulin-like growth factor I gene expression by primary cultures of ovarian cells: insulin and dexamethasone dependence.

A growing body of information now supports the existence of a complete intraovarian insulin-like growth Factor I (IGF-I) system replete with ligands, receptors, and binding protein(s). However, studies concerned with the regulation of ovarian IGF-I gene expression remain scarce. It was thus the objective of this communication to evaluate the expression of the IGF-I gene in the immature rat ovary under in vitro conditions. Whole ovarian dispersates or isolated granulosa cells were cultured for up to 96 h under serum-free conditions in the absence or presence of the indicated experimental agents. Extracted total RNA was subjected to a sensitive solution hybridization/RNase protection assay using 32P-labeled rat IGF-I and/or type I IGF receptor antisense RNA probes. Cultured in the absence or presence of FSH (100 ng/ml), whole ovarian dispersates (or isolated granulosa cells) displayed time-dependent (FSH-independent) decrements in the relative abundance of IGF-I transcripts apparent as early as 3 h after the onset of culture. No evidence of recovery was apparent by 96 h of culture. The apparent lack of an FSH effect did not reflect diminished biopotency as attested to by the ability of the hormone to promote time-dependent increments in the accumulation of progesterone. Importantly, the apparent decrease in ovarian IGF-I gene expression proved to be IGF-I specific in that type I IGF receptor transcripts displayed a substantial and sustained (for up to 96 h) FSH-independent increase beginning at the 24-h time point. At no point were IGF-II transcripts detected. The apparent decrease in the expression of IGF-I did not reflect the lack of extracellular matrix support in that neither laminin, collagen, nor whole serum supported sustained ovarian IGF-I gene expression. Treatment of whole ovarian dispersates with pharmacological concentrations of either insulin (1 micrograms/ml) or dexamethasone (10(-7) M) did not reverse the decline in IGF-I gene expression. Importantly, however, the combined application of both insulin and dexamethasone resulted in virtually complete preservation of IGF-I gene expression, the relative abundance of the corresponding transcripts proving uniform throughout. Taken together, these in vitro observations reveal irreversible (FSH-independent) decrements in ovarian IGF-I (but not type I IGF receptor) gene expression, the preservation of which required the concurrent provision of both insulin and dexamethasone.

Animals↗
PubMed1993

Growth hormone (GH) stimulates insulin-like growth factor-I (IGF-I) and IGF-I-binding protein-3, but not GH receptor gene expression in livers of juvenile rats.

In the adult rat, expression of the liver GH receptor, insulin-like growth factor-I (IGF-I), and IGF-I-binding protein-3 (IGFBP-3) genes has been shown to be under GH control. Additionally, hypophysectomy and GH treatment have a differential effect on the relative abundance of liver IGF-I mRNA variants in adult rats. To further elucidate the time of appearance and the extent of GH control of liver GH receptor, IGF-I, and IGFBP-3 gene expression, we studied the effect of hypophysectomy and GH and IGF-I treatment in juvenile rats. Male Wistar rats were hypophysectomized (Hx) on postnatal day 26 and received twice daily sc injections of saline, recombinant human GH (2.5 U/kg.day), or recombinant human IGF-I (500 micrograms/kg.day) for 7 days. Sham-operated rats received the same treatment. Hx animals also received T4 (20 micrograms/kg.day). In Hx animals, there was a significant reduction in body weight (69.8 +/- 6.6 vs. 100.4 +/- 5.4 g; P < 0.001). GH, but not IGF-I, treatment increased body weight (79.6 +/- 9.6 g after GH vs. 69.8 +/- 6.6 g before GH; P < 0.05). GH treatment partially maintained liver, kidney, and lung weights in Hx animals and increased them in intact animals, whereas IGF-I treatment did so only in the lungs of intact and Hx animals. Serum GH and IGF-I levels were markedly reduced in Hx animals compared with those in intact controls, and GH treatment maintained, albeit partially, circulating IGF-I levels compared with those in saline-treated Hx animals. IGF-I mRNA levels were markedly reduced in Hx liver (25.0 +/- 5.4%; P < 0.001 compared with intact controls). GH treatment for 7 days increased IGF-I mRNA levels by 4.8-fold over the levels in 9-day Hx animals and increased IGF-I mRNA levels by 2.2-fold in control rats. Hypophysectomy decreased exon 2-containing transcripts by 7.0-fold and exon 1-containing transcripts by 4.1-fold. GH treatment, however, affected both exon 1- and exon 2-containing transcripts similarly. Hepatic IGFBP-3 mRNA levels were reduced in Hx (53.2 +/- 1.8%; P < 0.01 compared with intact controls) and IGF-treated Hx animals, but were not decreased in Hx GH-treated animals (100.6 +/- 9.5). No changes in GH receptor or GH-binding protein mRNA levels were caused by Hx, GH, or IGF-I treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Luteinizing hormone-releasing hormone antagonists interfere with autocrine and paracrine growth stimulation of MCF-7 mammary cancer cells by insulin-like growth factors.

Several studies have supported the idea that LH-releasing hormone (LHRH) antagonists have a direct effect on mammary tumor cells. In this study, we have evaluated the potential role of the insulin-like growth factors (IGFs) on the growth of MCF-7 mammary tumor cells and the effect of LHRH analogs on IGF action. The mitogenic effects of IGF-I, IGF-II, and insulin were compared. IGF-I was found to be 3 times more potent than IGF-II and 30 times more potent than insulin, suggesting that the effects of these growth factors are mediated by the IGF-I receptor. IGFs released by MCF-7 cells were measured by specific RIA after acid extraction and chromatography, so as to avoid the interference of IGF-binding proteins. MCF-7 cells secreted IGF-II, but not IGF-I. Estradiol (10(-9) mol/L) stimulated IGF-II release; this release preceded the effect of estradiol on cell growth. The LHRH antagonist [Ac-D-Nal(2)1,D-Phe(4Cl)2,D-Pal(3)3,D-Cit6,D-Ala10] LHR H (SB-75, CETRORELIX) inhibited basal, estrogen-induced, and IGF-induced growth. Moreover, this antagonist almost completely inhibited IGF-II release from MCF-7 cells. This effect preceded the inhibition of tumor cell growth. We conclude that a LHRH antagonist can inhibit the growth of breast tumors by interfering with the autocrine action of IGF-II and by directly inhibiting the growth stimulatory effect of IGFs.

Analysis of Variance↗
PubMed1993

Regulation of insulin-like growth factor (IGF) binding protein-5 in the T47D human breast carcinoma cell line by IGF-I and retinoic acid.

The T47D human breast carcinoma cell line has been shown to synthesize insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs) and IGF-I receptors, and to exhibit a mitogenic response to exogenous IGF-I. We have used T47D cells to investigate the regulation of IGFBPs by IGF-I and retinoic acid (RA), agents that affect cell proliferation and have been shown to regulate IGFBP levels in other cell types. Exposure of T47D cells to IGF-I resulted in the appearance of IGFBP-2, -4, and -5 in conditioned medium but had no effect on the levels of IGFBPs in Triton X-100-extracted cells. This effect was most pronounced for IGFBP-5 and was also elicited by an IGF-I analog that retains affinity for IGFBPs but not by insulin or IGF analogs that have decreased affinity for IGFBPs. Additionally, this effect was not associated with a change in IGFBP-5 messenger RNA (mRNA) levels; however, the appearance of IGFBP-5 in the conditioned medium was inhibited by an anti-IGF-I receptor antibody (alpha IR-3). RA decreased IGFBP-5 mRNA levels and cell-associated IGFBP-5 in both the presence and absence of IGF-I and inhibited the IGF-I-stimulated secretion of IGFBP-5 into T47D cell conditioned medium. These results suggest that IGF-I increases IGFBP-5 levels in the T47D cell line both through direct interaction with IGFBP-5 as well as through a receptor-mediated process that does not require direct interaction with IGFBPs. The latter results are consistent with an effect of IGF-I on a factor that may modulate an IGFBP protease activity. The inhibitory effect of RA, on the other hand, appears to be due primarily to regulation of IGFBP-5 mRNA levels. Thus, IGFBP-5 accumulation appears to be positively regulated by IGF-I, potentially at the level of susceptibility to proteolysis, and negatively regulated at the level of gene expression by RA.

Breast Neoplasms↗
PubMed1993

Expression of insulin-like growth factor-I (IGF-I) and IGF-II and the IGF-I, IGF-II, and insulin receptor genes and localization of the gene products in the human ovary.

We examined the expression of the genes encoding the insulin-like growth factors (IGFs) and their receptors (r) and the localization of their gene products in specific cellular compartments of the human ovary. mRNA was localized by in situ hybridization with specific human 35S-labeled antisense RNA probes, and protein was detected by immunocytochemistry with specific antisera. We studied 34 follicles (10 ovaries), which included both dominant and small antral follicles. In dominant follicles, no IGF-I mRNA was seen in either thecal or granulosa cells (GC), but IGF-Ir mRNA was expressed in GC. In contrast, abundant IGF-II mRNA was found exclusively in GC, whereas the IGF-IIr gene was expressed in both thecal cells and GC. Insulin receptor mRNA was widely distributed and expressed in all cell types, including stromal cells. Small antral follicles contained both IGF-I and IGF-II mRNA, which was restricted to thecal cells. Although IGF-Ir message was detected only in GC, IGF-IIr mRNA was expressed in both granulosa and thecal cells. As in dominant follicles, insulin receptor mRNA was found in thecal, granulosa, and stromal cells. No IGF-I immunoreactivity was seen in either dominant or small antral follicles; however, immunostaining for the other gene products demonstrated that each of these proteins colocalized with its corresponding mRNA. Thus, the relative distribution of ligand and receptor transcripts and protein in cellular compartments of the human ovary observed in this study supports the presence of an intraovarian IGF system and suggests that both autocrine and paracrine mechanisms of IGF action occur between GC and thecal cells. We conclude that 1) IGF-II, rather than IGF-I, is the principal IGF in human ovarian follicles, being synthesized in thecal cells in small antral follicles and in GC in dominant follicles; 2) in small antral follicles, IGF-II acts in an autocrine fashion in thecal cells and in a paracrine fashion in GC; 3) in dominant follicles, granulosa-derived IGF-II acts in an autocrine manner in GC; and 4) the presence of transcripts and proteins corresponding to the IGF and insulin receptors in cellular compartments of human ovaries may also provide target sites for the action of circulating ligands with a potential extraovarian role in the regulation of folliculogenesis.

Adult↗
PubMed1993

Up-regulation of insulin-like growth factor-I (IGF-I) receptor gene expression in patients with reduced serum IGF-I levels.

We have analysed the expression of the IGF-I receptor gene in lymphocytes of patients with low levels of circulating IGF-I (four patients with isolated GH deficiency (IGHD) and one Laron-type dwarf (LTD)) in comparison with a control group exhibiting normal serum IGF-I levels and endocrine profiles. 125I-Labelled IGF-I binding assays were performed on erythrocytes to determine the number of IGF-I binding sites per cell and their dissociation constants. Erythrocytes from patients with IGHD or LTD contained significantly (P = 0.002) more receptors per cell (10.9 +/- 3.1 binding sites/cell), with a reduced affinity (Kd = 0.49 +/- 0.05 nM), than erythrocytes from controls (2.0 +/- 0.4 sites/cell; Kd = 0.14 nM). The levels of IGF-I receptor mRNA in circulating lymphocytes were determined by an RNA template-specific reverse transcription/polymerase chain reaction method. There was a statistically significant increase in IGF-I receptor mRNA levels in lymphocytes from patients with LTD or IGHD when compared with controls (3108.1 +/- 775.9 vs 576.0 +/- 465.7 arbitrary units, P = 0.006). The increased level of IGF-I binding due to increased IGF-I receptor gene expression may represent a compensatory up-regulation process activated in response to the low levels of IGF-I in the circulation of patients with LTD or IGHD.

Base Sequence↗
PubMed1993

Nutritional regulation of insulin-sensitive glucose transporter gene expression in rat cardiac muscle.

The effects of fasting and refeeding on the levels of mRNA encoding the insulin-sensitive glucose transporter (GLUT4) in rat cardiac and skeletal muscle were investigated using solution hybridization/RNase protection assays with a rat GLUT4 antisense RNA probe. In addition, the effects of these nutritional states on GLUT1 mRNA levels in several non-insulin-sensitive tissues were examined using a GLUT1 antisense RNA probe. Fasting for 48 hr significantly decreased GLUT4 mRNA levels in heart, with levels significantly increased over control levels by 24 hr after refeeding. In contrast, GLUT4 mRNA levels in skeletal muscle increased with fasting and returned to control levels with refeeding. No significant changes in GLUT1 mRNA were seen after fasting and refeeding in several non-insulin-sensitive tissues studied. These results suggest that altered GLUT4 gene expression is observed in different nutritional (insulin) states in insulin-sensitive tissues, and suggests a potential role for insulin in mediating these changes in gene expression.

Animal Nutritional Physiological Phenomena↗