scholarly journals Mitogenic and Metabolic Effects of Type I IGF Receptor Overexpression in Insulin Receptor-Deficient Hepatocytes

Endocrinology ◽  
2001 ◽  
Vol 142 (8) ◽  
pp. 3354-3360 ◽  
Author(s):  
Jane J. Kim ◽  
Byung-Chul Park ◽  
Yoshiaki Kido ◽  
Domenico Accili
Keyword(s):  
Cell Proliferation ◽  
Insulin Receptor ◽  
Glycogen Synthesis ◽  
Insulin Receptors ◽  
Metabolic Effects ◽  
Insulin Receptor Substrate ◽  
Type I ◽  
Wild Type ◽  
Igf I ◽  
Stimulation Of

Abstract We have previously shown that hepatocytes lacking insulin receptors (Ir−/−) fail to mediate metabolic responses, such as stimulation of glycogen synthesis, while retaining the ability to proliferate in response to IGFs. In this study we have asked whether overexpression of type I IGF receptors would rescue the metabolic response of Ir−/− hepatocytes. After IGF-I stimulation, insulin receptor substrate-1 and -2 phosphorylation and PI3K activity were restored to levels similar to or greater than those seen in wild-type cells. Rates of cell proliferation in response to IGF-I increased approximately 2-fold, whereas glycogen synthesis was restored to wild-type levels, but was comparatively smaller than that elicited by overexpression of insulin receptors. In summary, overexpression of IGF-I receptors in Ir−/− hepatocytes normalized insulin receptor substrate-2 phosphorylation and glycogen synthesis to wild-type levels, whereas it increased cell proliferation above wild-type levels. Moreover, stimulation of glycogen synthesis was submaximal compared with the effect of insulin receptor overexpression. We conclude that IGF-I receptors are more efficiently coupled to cell proliferation than insulin receptors, but are less potent than insulin receptors in stimulating glycogen synthesis. The data are consistent with the possibility that there exist intrinsic signaling differences between insulin and IGF-I receptors.

scholarly journals Insulin receptor substrate 1 rescues insulin action in CHO cells expressing mutant insulin receptors that lack a juxtamembrane NPXY motif.

1995 ◽  
Vol 15 (9) ◽  
pp. 4711-4717 ◽  
Author(s):  
D Chen ◽  
D J Van Horn ◽  
M F White ◽  
J M Backer
Keyword(s):  
Insulin Receptor ◽  
Tyrosine Phosphorylation ◽  
Cho Cells ◽  
Glycogen Synthesis ◽  
Insulin Receptors ◽  
Insulin Receptor Substrate ◽  
Insulin Stimulation ◽  
Insulin Receptor Substrate 1 ◽  
Npxy Motif ◽  
Stimulation Of

Insulin signals are mediated through tyrosine phosphorylation of specific proteins such as insulin receptor substrate 1 (IRS-1) and Shc by the activated insulin receptor (IR). Phosphorylation of both proteins is nearly abolished by an alanine substitution at Tyr-960 (A960) in the beta-subunit of the receptor. However, overexpression of IRS-1 in CHO cells expressing the mutant receptor (A960 cells) restored sufficient tyrosine phosphorylation of IRS-1 to rescue IRS-1/Grb-2 binding and phosphatidylinositol 3' kinase activation during insulin stimulation. Shc tyrosine phosphorylation and its binding to Grb-2 were impaired in the A960 cells and were unaffected by overexpression of IRS-1. Although overexpression of IRS-1 increased IRS-1 binding to Grb-2, ERK-1/ERK-2 activation was not rescued. These data suggest that signaling molecules other than IRS-1, perhaps including Shc, are critical for insulin stimulation of p21ras. Interestingly, overexpression of IRS-1 in the A960 cells restored insulin-stimulated mitogenesis and partially restored insulin stimulation of glycogen synthesis. Thus, IRS-1 tyrosine phosphorylation is sufficient to increase the mitogenic response to insulin, whereas insulin stimulation of glycogen synthesis appears to involve other factors. Moreover, IRS-1 phosphorylation is either not sufficient or not involved in insulin stimulation of ERK.

scholarly journals Osmotic Shock Inhibits Insulin Signaling by Maintaining Akt/Protein Kinase B in an Inactive Dephosphorylated State

1999 ◽  
Vol 19 (7) ◽  
pp. 4684-4694 ◽  
Author(s):  
Dong Chen ◽  
Raymond V. Fucini ◽  
Ann Louise Olson ◽  
Brian A. Hemmings ◽  
Jeffrey E. Pessin
Keyword(s):  
Protein Kinase ◽  
Insulin Receptor ◽  
Glucose Transport ◽  
Protein Kinase B ◽  
Osmotic Shock ◽  
Glycogen Synthesis ◽  
Type I ◽  
Transport Activity ◽  
Insulin Stimulation ◽  
Stimulation Of

ABSTRACT We have previously reported that insulin and osmotic shock stimulate an increase in glucose transport activity and translocation of the insulin-responsive glucose transporter isoform GLUT4 to the plasma membrane through distinct pathways in 3T3L1 adipocytes (D. Chen, J. S. Elmendorf, A. L. Olson, X. Li, H. S. Earp, and J. E. Pessin, J. Biol. Chem. 272:27401–27410, 1997). In investigations of the relationships between these two signaling pathways, we have now observed that these two stimuli are not additive, and, in fact, osmotic shock pretreatment was found to completely prevent any further insulin stimulation of glucose transport activity and GLUT4 protein translocation. In addition, osmotic shock inhibited the insulin stimulation of lipogenesis and glycogen synthesis. This inhibition of insulin-stimulated downstream signaling occurred without any significant effect on insulin receptor autophosphorylation or tyrosine phosphorylation of insulin receptor substrate 1 (IRS1). Furthermore, there was no effect on either the insulin-stimulated association of the p85 type I phosphatidylinositol (PI) 3-kinase regulatory subunit with IRS1 or phosphotyrosine antibody-immunoprecipitated PI 3-kinase activity. In contrast, osmotic shock pretreatment markedly inhibited the insulin stimulation of protein kinase B (PKB) and p70S6 kinase activities. In addition, the dephosphorylation of PKB was prevented by pretreatment with the phosphatase inhibitors okadaic acid and calyculin A. These data support a model in which osmotic shock-induced insulin resistance of downstream biological responses results from an inhibition of insulin-stimulated PKB activation.

scholarly journals Insulin-like growth factor induces phosphorylation of immunoreactive insulin receptor substrate and its association with phosphatidylinositol-3 kinase in human thymocytes.

1995 ◽  
Vol 182 (2) ◽  
pp. 593-597 ◽  
Author(s):  
R Kooijman ◽  
J J Lauf ◽  
A C Kappers ◽  
G T Rijkers
Keyword(s):  
T Cells ◽  
Growth Factor ◽  
Insulin Receptor ◽  
Signaling Pathway ◽  
Insulin Receptor Substrate ◽  
Type I ◽  
Insulin Like Growth Factor ◽  
Phosphatidylinositol 3 Kinase ◽  
Igf I ◽  
Phosphatidylinositol 3

Insulin receptor substrate 1 (IRS-1) is the principle cellular substrate for insulin and insulin-like growth factor I (IGF-I) receptor signaling. After phosphorylation of tyrosine residues within the YMXM or YXXM motifs, IRS-1 associates with phosphatidylinositol-3 kinase (PI3K). This signaling pathway and the presence of an IRS-1-like molecule have been demonstrated in IRS-1-transfected and in nontransfected hematopoietic cell lines, respectively. IGF-I has been implicated in lymphocyte development and function, and recently, we showed that functional type-I IGF receptors are present on human thymocytes and peripheral T cells. In this study, we addressed IGF-I signal transduction in nontransformed, freshly isolated, human thymocytes, as well as in blood T cells. Using Western blot analysis, we found that IGF-I induced phosphorylation of a 160-180-kD protein (pp170) in human thymocytes and that phosphorylated pp170 becomes associated with PI3K and is recognized by anti-IRS-1. In blood T cells, this immunoreactive IRS-1 (irIRS-1) is less abundantly expressed than in thymocytes, as assessed with immunoblotting. As a consequence, phosphorylated pp170 was not or hardly detectable after stimulation with IGF-I, and irIRS-1 was not detected in PI3K immunoprecipitates from lysates of IGF-I-stimulated T cells. However, IGF-I induced the tyrosine phosphorylation of other cellular proteins, indicating that differential expression of irIRS-1 contributes to a distinct signaling pathway in T cells.

scholarly journals Normal Bone Density Obtained in the Absence of Insulin Receptor Expression in Bone

Endocrinology ◽  
2006 ◽  
Vol 147 (12) ◽  
pp. 5760-5767 ◽  
Author(s):  
Regina Irwin ◽  
Hua V. Lin ◽  
Katherine J. Motyl ◽  
Laura R. McCabe
Keyword(s):  
Bone Loss ◽  
Insulin Receptor ◽  
Type I Diabetes ◽  
Receptor Expression ◽  
Type I ◽  
Mrna Levels ◽  
Wild Type ◽  
Marrow Adiposity ◽  
Igf I ◽  
Insulin Receptor Expression

Type I diabetes is characterized by little or no insulin production and hyperglycemic conditions. It is also associated with significant bone loss and increased bone marrow adiposity. To examine the role of reduced insulin signaling in type I diabetic bone loss without inducing hyperglycemia, we used genetically reconstituted insulin receptor knockout mice (IRKO-L1) that are euglycemic as a result of human insulin receptor transgene expression in the pancreas, liver, and brain. RT-PCR analyses demonstrated undetectable levels of insulin receptor expression in IRKO-L1 bone, yet IRKO-L1 bones exhibit similar (and trend toward greater) bone density compared with wild-type animals as determined by microcomputed tomography. More detailed bone analyses indicated that cortical bone area was increased in tibias of IRKO-L1 mice. Osteoblast markers (osteocalcin and runx2 mRNA levels) and resorption markers (serum pyridinoline levels) were similar in wild-type and IRKO-L1 bones. When marrow adiposity was examined, we noticed a decrease in adipocyte number and fatty-acid-binding protein 2 expression in IRKO-L1 mice compared with wild-type mice. Bone marrow stromal cell cultures obtained from wild-type and IRKO-L1 mice demonstrated similar adipogenic and osteogenic potentials, indicating that systemic factors likely contribute to differences in marrow adiposity in vivo. Interestingly, IGF-I receptor mRNA levels were elevated in IRKO-L1 bones, suggesting (in combination with hyperinsulinemic conditions) that increased IGF-I receptor signaling may represent a compensatory response and contribute to the changes in cortical bone. Taken together, these results suggest that reduced insulin receptor signaling in bone is not a major factor contributing to bone loss in type I diabetes.

scholarly journals Insulin-Like Growth Factor I Synergizes with Interleukin 4 for Hematopoietic Cell Proliferation Independent of Insulin Receptor Substrate Expression

1999 ◽  
Vol 19 (5) ◽  
pp. 3816-3828 ◽  
Author(s):  
Lilian Soon ◽  
Lawrence Flechner ◽  
J. Silvio Gutkind ◽  
Lu-Hai Wang ◽  
Renato Baserga ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Growth Factor ◽  
Protein Kinase ◽  
Tyrosine Phosphorylation ◽  
Hematopoietic Cell ◽  
Interleukin 4 ◽  
Insulin Receptor Substrate ◽  
Factor I ◽  
Igf I ◽  
Stimulation Of

ABSTRACT In the present study, we investigated the potential role of insulin-like growth factor I (IGF-I) receptor (IGF-IR) in cell proliferation by overexpressing it in 32D myeloid progenitor cells. The overexpression of IGF-IR caused the transfectants to proliferate in response to IGF-I in the absence of insulin receptor substrate (IRS) expression. The activation of overexpressed wild-type IGF-IR, but not that of an ATP-binding mutant of IGF-IR, resulted in the increased tyrosine phosphorylation of several intracellular proteins, including SHC, Src homology 2-containing inositol-5-phosphatase, protein kinase C-δ, and Erk2. Grb2 association with SHC and mitogen-activated protein kinase (MAPK) activity was also enhanced in response to IGF-I stimulation. Interestingly, the stimulation of the IGF-IR transfectants with interleukin 4 (IL-4) also resulted in strong mitogenesis independent of IRS expression. Moreover, IGF-I and/or IL-4 induced long-term cell growth of the IGF-IR transfectants. IL-4 was able to synergize with IGF-I for DNA synthesis, even in the parental 32D cells and a pro-B-cell line, Baf3, indicating the physiological importance of the two growth factors in hematopoietic cell proliferation. IL-4 stimulation of the IGF-IR transfectants resulted in enhanced tyrosine phosphorylation of SHC, Erk2, and signal transducer and activator of transcription 6 (STAT6) proteins. Both IL-4 and IGF-I were able to induce c-myc early response gene expression, and this expression was maximal in the presence of both factors. Finally, we demonstrated that a MAPK kinase inhibitor was able to suppress mitogenesis of the IGF-IR transfectants in response to IGF-I and/or IL-4. Together, our results suggest that IL-4 synergizes with IGF-I for hematopoietic cell proliferation, likely through cross talk between SHC/Grb2/MAPK and STAT6 pathways and through c-myc gene up-regulation.

scholarly journals Insulin Receptor Substrate-1 Is Required for Bone Anabolic Function of Parathyroid Hormone in Mice

Endocrinology ◽  
2005 ◽  
Vol 146 (6) ◽  
pp. 2620-2628 ◽  
Author(s):  
Masayuki Yamaguchi ◽  
Naoshi Ogata ◽  
Yusuke Shinoda ◽  
Toru Akune ◽  
Satoru Kamekura ◽  
...  
Keyword(s):  
Insulin Receptor ◽  
Insulin Receptor Substrate ◽  
Wild Type ◽  
Paracrine Factor ◽  
Protein Levels ◽  
Anabolic Action ◽  
Igf I ◽  
In The Wild ◽  
Biochemical Analyses

Abstract Bone anabolic action of PTH has been suggested to be mediated by induction of IGF-I in osteoblasts; however, little is known about the molecular mechanism by which IGF-I leads to bone formation under the PTH stimulation. This study initially confirmed in mouse osteoblast cultures that PTH treatment increased IGF-I mRNA and protein levels and alkaline phosphatase activity, which were accompanied by phosphorylations of IGF-I receptor, insulin receptor substrate (IRS)-1 and IRS-2, essential adaptor molecules for the IGF-I signaling. To learn the involvement of IRS-1 and IRS-2 in the bone anabolic action of PTH in vivo, IRS-1−/− and IRS-2−/− mice and their respective wild-type littermates were given daily injections of PTH (80 μg/kg) or vehicle for 4 wk. In the wild-type mice, the PTH injection increased bone mineral densities of the femur, tibia, and vertebrae by 10–20% without altering the serum IGF-I level. These stimulations were similarly seen in IRS-2−/− mice; however, they were markedly suppressed in IRS-1−/− mice. Although the PTH anabolic effects were stronger on trabecular bones than on cortical bones, the stimulations on both bones were blocked in IRS-1−/− mice but not in IRS-2−/− mice. Histomorphometric and biochemical analyses showed an increased bone turnover by PTH, which was also blunted by the IRS-1 deficiency, though not by the IRS-2 deficiency. These results indicate that the PTH bone anabolic action is mediated by the activation of IRS-1, but not IRS-2, as a downstream signaling of IGF-I that acts locally as an autocrine/paracrine factor.

scholarly journals AMP-Activated Protein Kinase Inhibits IGF-I Signaling and Protein Synthesis in Vascular Smooth Muscle Cells via Stimulation of Insulin Receptor Substrate 1 S794 and Tuberous Sclerosis 2 S1345 Phosphorylation

2010 ◽  
Vol 24 (6) ◽  
pp. 1218-1229 ◽  
Author(s):  
Junyu Ning ◽  
David R. Clemmons
Keyword(s):  
Protein Synthesis ◽  
Protein Kinase ◽  
Insulin Receptor ◽  
Tyrosine Phosphorylation ◽  
Pi3k Pathway ◽  
Insulin Receptor Substrate ◽  
Pathway Activation ◽  
Igf I ◽  
Amp Activated Protein Kinase ◽  
Stimulation Of

Abstract AMP-activated protein kinase (AMPK) inhibits IGF-I actions, but the mechanism by which AMPK functions is undefined. This study identified signaling events that were induced by AMPK that mediated inhibition of IGF-I-stimulated phosphoinosotide-3-kinase (PI3K) pathway activation. The AMPK activator metformin stimulated AMPK Thr172 phosphorylation and inhibited IGF-I-stimulated phosphorylation of Akt/tuberous sclerosis 2 (TSC2)/mammalian target of rapamycin (mTOR)/p70S6 kinase (p70S6K). Expression of constitutively active forms of AMPK suppressed IGF-I-stimulated activation of Akt/TSC2/mTOR/p70S6K and protein synthesis, whereas AMPK knockdown resulted in enhanced responses to IGF-I. To determine the mechanism by which AMPK inhibited IGF-I signaling, the role of insulin receptor substrate-1 (IRS-1) was examined. Both metformin and constitutively activated AMPK enhanced phosphorylation of IRS-1 Ser794, which led to decreased IRS-1 tyrosine phosphorylation and recruitment of the p85 subunit of PI3K. Overexpression of IRS-1 S794A was associated with increased IGF-I-stimulated IRS-1 tyrosine phosphorylation, p85 association, and protein synthesis. To determine whether other signaling molecules mediated the effect of AMPK, TSC2 function was examined. Cells overexpressing TSC2/S1345A (the site of AMPK phosphorylation) were less responsive to metformin-induced inhibition of p70S6 kinase. These findings are relevant to whole animal physiology because administration of metformin to mice resulted in inhibition of IGF-I-stimulated phosphorylation of Akt/mTOR/p70S6K. In conclusion, AMPK functions to inhibit IGF-I-stimulated PI3K pathway activation through stimulation of IRS-1 serine 794 phosphorylation. Because IGF-I is an important stimulant of the anabolic response, this effect of AMPK could account for part of its inhibitory effect on protein synthesis, thus allowing more efficient energy use by other cellular processes.

scholarly journals The Insulin-Like Growth Factor I Receptor-Induced Interaction of Insulin Receptor Substrate-4 and Crk-II

Endocrinology ◽  
2001 ◽  
Vol 142 (5) ◽  
pp. 1835-1840 ◽  
Author(s):  
M. Karas ◽  
A. P. Koval ◽  
Y. Zick ◽  
D. LeRoith
Keyword(s):  
Growth Factor ◽  
Insulin Receptor ◽  
Receptor Activation ◽  
Sh2 Domain ◽  
Insulin Receptor Substrate ◽  
Insulin Like Growth Factor ◽  
Igf I ◽  
Docking Proteins ◽  
C And N ◽  
Stimulation Of

Abstract Stimulation of the insulin or insulin-like growth factor (IGF)-I receptor results in activation of several signaling pathways. Proteins of the insulin receptor substrate (IRS) family play important roles in mediating these signaling cascades. To date, four members of the IRS family of docking proteins have been characterized. Recently, we have reported that stimulation of the IGF-I receptor in 293 HEK cells regulates interaction of the newly discovered IRS-4 molecule with the Crk family of proteins. In the present study, we characterize the molecular basis of these interactions. C- and N termini truncation analysis of IRS-4 demonstrated that the region between amino acids 678 and 800 of the IRS-4 molecule is involved in this interaction. This region contains a cluster of four tyrosines (Y700, Y717, Y743, and Y779). We hypothesize that one or more of these tyrosines are involved in the interaction between the SH2 domain of the Crk-II molecule when IRS-4 is phosphorylated upon IGF-I receptor activation. Additional mutational analyses confirmed this hypothesis. Interestingly, none of these four tyrosines was individually critical for the interaction between Crk-II and IRS-4, but when all four tyrosines were simultaneously mutated to phenylalanine, the IGF-I induced interaction between these molecules was abolished. Taken together, these results suggest a novel mechanism of Crk-II binding to tyrosine phosphorylated proteins.

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