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M F White

Publications and source records attributed to M F White.

At least 145 records · Page 8Linked to original sources
PubMed1994

Insulin receptor substrate-1 (IRS-1) expression in rat brain.

IRS-1 is phosphorylated on tyrosine residues after insulin stimulation and participates in the early events of signal transduction in peripheral insulin-sensitive tissues. This study determined whether neuronal populations in the rat olfactory bulb and hippocampus (brain regions which have very high concentrations of insulin receptors) also express IRS-1 and contain phosphotyrosine, using in situ hybridization, receptor binding, and immunocytochemistry. IRS-1 mRNA was colocalized with insulin receptor mRNA in neuron cell bodies of hippocampus and olfactory bulb. Similarly, IRS-1 immunoreactivity in hippocampus and olfactory bulb was concentrated in layers that contain synapses of these neurons and have both high insulin binding and phosphotyrosine levels. Thus, IRS-1 and insulin receptors are coexpressed in discrete populations of neurons, suggesting a signal transduction mechanism by which insulin may influence metabolism and gene expression in the brain.

Animals↗
PubMed1993

Nck associates with the SH2 domain-docking protein IRS-1 in insulin-stimulated cells.

Nck, an oncogenic protein composed of one SH2 and three SH3 domains, is a common target for various cell surface receptors. Nck is thought to function as an adaptor protein to couple cell surface receptors to downstream effector molecules that regulate cellular responses induced by receptor activation. In this report, we show that Nck forms a stable complex in vivo with IRS-1 in insulin-stimulated cells. The interaction between IRS-1 and Nck is mediated by the binding of the SH2 domain of Nck to tyrosine-phosphorylated IRS-1. Although Nck associates with IRS-1, Nck phosphorylation is not affected by insulin stimulation. Furthermore, in vitro and in vivo studies show that the SH2 domains of Nck, GRB2, and p85 bind distinct phosphotyrosine residues in IRS-1. After insulin stimulation all three signaling molecules can be found complexed to a single IRS-1 molecule. These findings provide further evidence that, in response to insulin stimulation, IRS-1 acts as an SH2 docking protein that coordinates the regulation of various different signaling pathways activated by the insulin receptor.

Adaptor Proteins, Signal Transducing↗
PubMed1993

Dissociation of the tetrameric phosphoglycerate mutase from yeast by a mutation in the subunit contact region.

Phosphoglycerate mutases from different sources exhibit a variety of quaternary structures (tetramer, dimer and monomer). To perturb the tetrameric structure of yeast phosphoglycerate mutase we have prepared a mutant enzyme in which Lys-168 in the subunit-contact region has been replaced by proline. The K168P mutant enzyme undergoes dissociation to dimers at low concentrations; thus on lowering the concentration from 200 micrograms/ml to 5 micrograms/ml the proportion of tetramer falls from 85% to 53%. The tetrameric structure of the wild-type enzyme remains intact over this range of concentrations. The mutant enzyme has similar kinetic properties to the wild-type enzyme, with kcat. being reduced by 26%. Far-u.v. c.d. studies show that there has been a small loss of helical structure in the mutant. Compared with wild-type enzyme, the K168P mutant enzyme is slightly less stable towards proteolysis by trypsin, but significantly less stable towards denaturation by guanidinium chloride, with the midpoint concentration of guanidinium chloride some 50% lower. After denaturation, the mutant enzyme could regain activity and quaternary structure when the guanidinium chloride concentration was lowered to 0.05 M. The properties of the mutant enzyme are discussed in terms of other dimeric phosphoglycerate and bisphosphoglycerate mutases which contain proline at position 168.

Circular Dichroism↗
PubMed1993

Immunocytochemical detection of insulin receptor substrate-1 (IRS-1) in rat brain: colocalization with phosphotyrosine.

In peripheral insulin-sensitive tissues, insulin receptor substrate (IRS-1) undergoes tyrosine phosphorylation immediately after cells are stimulated by insulin or insulin-like growth factor-1 (IGF-1), and may function as a molecular link between insulin/IGF-1 receptor tyrosine kinases and enzymes regulating cell growth and metabolism. A fundamental question pertaining to insulin/IGF-1 action in the brain is whether IRS-1 is expressed by neurons. In this study, the distribution of cells containing immunoreactivity to IRS-1 in the brain was determined by immunocytochemistry with polyclonal IRS-1 antiserum, and compared to the localization of immunostaining for phosphotyrosine using polyclonal phosphotyrosine antiserum. The immunostaining results with ABC-peroxidase method and cryostat sections showed the presence of IRS-1 immunoreactivity in many neuron cell bodies throughout the rat forebrain, particularly in the habenula, cerebral cortex and piriform cortex. In the hypothalamus, IRS-1 immunostaining was present in neurons of the paraventricular nucleus, supraoptic nucleus, and arcuate nucleus. The choroid plexus stained intensely for IRS-1. The populations of cells that stained for IRS-1 also showed strong immunostaining for phosphotyrosine. Studies at the cellular level are needed to verify coexpression of IRS-1 and receptors for insulin or IGF-1 by the same neurons, as well as in cells of the choroid plexus. The present results are the first demonstration of IRS-1 expression by neurons in adult mammalian brain. These findings are consistent with the hypothesis that insulin and IGF-1 actions in the brain involve signal transduction mechanisms common to those found in peripheral tissues.

Animals↗
PubMed1993

Phosphorylation of the insulin receptor substrate IRS-1 by casein kinase II.

IRS-1, a principal substrate of the insulin receptor, is phosphorylated on serine, threonine, and tyrosine residues in a variety of tissues during insulin stimulation. Casein kinase II, an insulin-sensitive serine/threonine kinase, catalyzed the in vitro incorporation of 1 to 2 mol of phosphate/mol of recombinant rat IRS-1. Two-dimensional phosphopeptide mapping of IRS-1 phosphorylated by casein kinase II in vitro and IRS-1 immunoprecipitated from intact Chinese hamster ovary cells demonstrated multiple common phosphopeptides, suggesting that overexpressed IRS-1 is a substrate for casein kinase II in these cells. Moreover, the common phosphopeptides that appeared to be insulin-sensitive in intact cells comprised 22% of casein kinase II-catalyzed 32P incorporation into IRS-1 in vitro. These data suggest that casein kinase II mediates a portion of the insulin-stimulated serine/threonine phosphorylation of overexpressed IRS-1 in vivo. By using phosphoamino acid analysis, strong cation exchange analysis, manual Edman degradation, and automated amino acid sequencing, Thr-502 was identified as the major casein kinase II-catalyzed phosphorylation site in rat IRS-1. Furthermore, Ser-99, an additional site labeled at low yield, appeared to be contained in an insulin-sensitive phosphopeptide. Thus, casein kinase II-catalyzed phosphorylation of IRS-1 may be a component of the intracellular insulin signalling cascade.

Amino Acid Sequence↗
PubMed1993

Insulin receptor substrate 1 mediates insulin and insulin-like growth factor I-stimulated maturation of Xenopus oocytes.

Insulin and insulin-like growth factor I (IGF-I) initiate cellular functions by activating their homologous tyrosine kinase receptors. In most mammalian cell types, this results in rapid tyrosine phosphorylation of a high-molecular-weight substrate termed insulin receptor substrate 1 (IRS-1). Previous studies suggest that IRS-1 may act as a "docking" protein that noncovalently associates with certain signal-transducing molecules containing src homology 2 domains; however, direct evidence for the role of IRS-1 in the final biological actions of these hormones is still lacking. We have developed a reconstitution system to study the role of IRS-1 in insulin and IGF-I signaling, taking advantage of the fact that Xenopus oocytes possess endogenous IGF-I receptors but have little or no IRS-1, as determined by immunoblotting with anti-IRS-1 and antiphosphotyrosine antibodies. After microinjection of IRS-1 protein produced in a baculovirus expression system, tyrosyl phosphorylation of injected IRS-1 is stimulated by both insulin and IGF-I in a concentration-dependent manner, with IGF-I more potent than insulin. Furthermore, after IRS-1 injection, both hormones induce a maturation response that correlates well with the amount of injected IRS-1. By contrast, overexpression of human insulin receptors in the Xenopus oocytes does not enhance either IRS-1 phosphorylation or oocyte maturation response upon insulin stimulation. These results demonstrate that IRS-1 serves a critical role in linking IGF-I and insulin to their final cellular responses.

Animals↗
PubMed1993

Insulin stimulates serine and tyrosine phosphorylation in the juxtamembrane region of the insulin receptor.

Insulin-stimulated autophosphorylation of the cytoplasmic juxtamembrane region of the human insulin receptor was examined by Tricine/SDS-PAGE. Various mutant receptor molecules were used to identify two tryptic phosphopeptides associated with the juxtamembrane region which accounts for 15% of the autophosphorylation of partially purified insulin receptor. These phosphopeptides were immunoprecipitated with an antipeptide antibody against the juxtamembrane sequence and were phosphorylated exclusively on tyrosine. Substitution of both Tyr960 and Tyr953 with alanine eliminated insulin-stimulated phosphorylation of the juxtamembrane region without affecting tyrosine autophosphorylation in the C terminus or regulatory regions. Monosubstitution of Tyr960 with phenylalanine or alanine reduced phosphorylation in the juxtamembrane region by more than 50%, and manual Edman degradation indicated that Tyr960 was phosphorylated in wild-type receptor. In vivo, phosphorylation of the juxtamembrane region accounts for one-third of the insulin receptor phosphorylation and contains both phosphoserine and phosphotyrosine. Deletion of Tyr960 and 11 adjacent amino acids eliminated insulin-stimulated phosphorylation of the juxtamembrane region. Substitution of Tyr960 reduced this phosphorylation by more than 50%. The insulin receptor also undergoes serine phosphorylation outside of the juxtamembrane region which depends on the presence of Tyr1151. Together with our previous studies, this report suggests that phosphorylation of Tyr960 may play an important role in signal transduction by the insulin receptor.

Amino Acid Sequence↗
PubMed1993

Common elements in interleukin 4 and insulin signaling pathways in factor-dependent hematopoietic cells.

Interleukin 4 (IL-4), insulin, and insulin-like growth factor I (IGF-I) efficiently induced DNA synthesis in the IL-3-dependent murine myeloid cell lines FDC-P1 and FDC-P2. Although these factors could not individually sustain long-term growth of these lines, a combination of IL-4 with either insulin or IGF-I did support continuous growth. The principal tyrosine-phosphorylated substrate observed in FDC cells stimulated with IL-4, previously designated 4PS, was of the same size (170 kDa) as the major substrate phosphorylated in response to insulin or IGF-I. These substrates had phosphopeptides of the same size when analyzed by digestion with Staphylococcus aureus V8 protease, and each tightly associated with the 85-kDa component of phosphatidylinositol 3-kinase after factor stimulation. IRS-1, the principal substrate phosphorylated in response to insulin or IGF-I stimulation in nonhematopoietic cells, is similar in size to 4PS. However, anti-IRS-1 antibodies failed to efficiently precipitate 4PS, and some phosphopeptides generated by V8 protease digestion of IRS-1 were distinct in size from the phosphopeptides of 4PS. Nevertheless, IL-4, insulin, and IGF-I were capable of stimulating tyrosine phosphorylation of IRS-1 in FDC cells that expressed this substrate as a result of transfection. These findings indicate that (i) IL-4, insulin, and IGF-I use signal transduction pathways in FDC lines that have at least one major feature in common, the rapid tyrosine phosphorylation of 4PS, and (ii) insulin and IGF-I stimulation of hematopoietic cell lines leads to the phosphorylation of a substrate that may be related to but is not identical to IRS-1.

Animals↗
PubMed1993

Substitution of His-181 by alanine in yeast phosphoglycerate mutase leads to cofactor-induced dissociation of the tetrameric structure.

The structure and stability of a mutated yeast phosphoglycerate mutase in which His-181 has been replaced by alanine have been studied. The secondary, tertiary and quaternary structures of the mutant enzyme in the absence of ligands are essentially identical to those of the wild-type enzyme as revealed by c.d., fluorescence and cross-linking studies. The mutant enzyme is slightly less stable than the wild-type enzyme towards denaturation by guanidium chloride (GdnHCl). On addition of cofactor 2,3-bisphosphoglycerate, the wild-type enzyme shows increased stability towards GdnHCl. However, addition of cofactor causes dramatic changes in the structure of the mutant enzyme, leading to dissociation of the tetrameric form to dimeric and monomeric species.

2,3-Diphosphoglycerate↗
PubMed1993

Association of IRS-1 with the insulin receptor and the phosphatidylinositol 3'-kinase. Formation of binary and ternary signaling complexes in intact cells.

Insulin stimulates the formation of binary and ternary signaling complexes between the phosphatidylinositol (PtdIns) 3'-kinase, IRS-1, and the insulin receptor in vivo. Binary complex formation between IRS-1 and the PtdIns 3'-kinase occurs in intact cells and requires the tyrosyl phosphorylation IRS-1, as mutant insulin receptors which weakly phosphorylate IRS-1 in vivo do not mediate formation of IRS-1/PtdIns 3'-kinase complexes in transfected CHO cells. Association with IRS-1 involves as much as 70% of total cellular PtdIns 3'-kinase activity. Insulin also stimulates the formation of ternary signaling complexes, as both IRS-1 and the PtdIns 3'-kinase are present in anti-insulin receptor immunoprecipitates from insulin-stimulated cells. Overexpression of IRS-1 in CHO cells increases the amount of PtdIns 3'-kinase activity in alpha IR immunoprecipitates, and IRS-1 markedly increases the in vitro binding of p85 alpha and PtdIns 3-kinase activity to anti-receptor immunoprecipitates. The mechanism for this association is unknown, but appears to involve the binding of IRS-1/PtdIns 3'-kinase complexes to the insulin receptor. The formation of binary and ternary complexes between the insulin receptor, IRS-1 and the PtdIns 3'-kinase may play a critical role in transmission of the insulin signal.

Amino Acid Sequence↗
PubMed1993

The SH2/SH3 domain-containing protein GRB2 interacts with tyrosine-phosphorylated IRS1 and Shc: implications for insulin control of ras signalling.

GRB2, a small protein comprising one SH2 domain and two SH3 domains, represents the human homologue of the Caenorhabditis elegans protein, sem-5. Both GRB2 and sem-5 have been implicated in a highly conserved mechanism that regulates p21ras signalling by receptor tyrosine kinases. In this report we show that in response to insulin, GRB2 forms a stable complex with two tyrosine-phosphorylated proteins. One protein is the major insulin receptor substrate IRS-1 and the second is the SH2 domain-containing oncogenic protein, Shc. The interactions between GRB2 and these two proteins require ligand activation of the insulin receptor and are mediated by the binding of the SH2 domain of GRB2 to phosphotyrosines on both IRS-1 and Shc. Although GRB2 associates with IRS-1 and Shc, it is not tyrosine-phosphorylated after insulin stimulation, implying that GRB2 is not a substrate for the insulin receptor. Furthermore, we have identified a short sequence motif (YV/IN) present in IRS-1, EGFR and Shc, which specifically binds the SH2 domain of GRB2 with high affinity. Interestingly, both GRB2 and phosphatidylinositol-3 (PI-3) kinase can simultaneously bind distinct tyrosine phosphorylated regions on the same IRS-1 molecule, suggesting a mechanism whereby IRS-1 could provide the core for a large signalling complex. We propose a model whereby insulin stimulation leads to formation of multiple protein--protein interactions between GRB2 and the two targets IRS-1 and Shc. These interactions may play a crucial role in activation of p21ras and the control of downstream effector molecules.

Adaptor Proteins, Signal Transducing↗
PubMed1993

Insulin-stimulated oocyte maturation requires insulin receptor substrate 1 and interaction with the SH2 domains of phosphatidylinositol 3-kinase.

Xenopus oocytes from unprimed frogs possess insulin-like growth factor I (IGF-I) receptors but lack insulin and IGF-I receptor substrate 1 (IRS-1), the endogenous substrate of this kinase, and fail to show downstream responses to hormonal stimulation. Microinjection of recombinant IRS-1 protein enhances insulin-stimulated phosphatidylinositol (PtdIns) 3-kinase activity and restores the germinal vesicle breakdown response. Activation of PtdIns 3-kinase results from formation of a complex between phosphorylated IRS-1 and the p85 subunit of PtdIns 3-kinase. Microinjection of a phosphonopeptide containing a pYMXM motif with high affinity for the src homology 2 (SH2) domain of PtdIns 3-kinase p85 inhibits IRS-1 association with and activation of the PtdIns 3-kinase. Formation of the IRS-1-PtdIns 3-kinase complex and insulin-stimulated PtdIns 3-kinase activation are also inhibited by microinjection of a glutathione S-transferase fusion protein containing the SH2 domain of p85. This effect occurs in a concentration-dependent fashion and results in a parallel loss of hormone-stimulated oocyte maturation. These inhibitory effects are specific and are not mimicked by glutathione S-transferase fusion proteins expressing the SH2 domains of ras-GAP or phospholipase C gamma. Moreover, injection of the SH2 domains of p85, ras-GAP, and phospholipase C gamma do not interfere with progesterone-induced oocyte maturation. These data demonstrate that phosphorylation of IRS-1 plays an essential role in IGF-I and insulin signaling in oocyte maturation and that this effect occurs through interactions of the phosphorylated YMXM/YXXM motifs of IRS-1 with SH2 domains of PtdIns 3-kinase or some related molecules.

Amino Acid Sequence↗
PubMed1993

Pleiotropic insulin signals are engaged by multisite phosphorylation of IRS-1.

IRS-1 (insulin receptor substrate 1) is a principal insulin receptor substrate that undergoes tyrosine phosphorylation during insulin stimulation. It contains over 20 potential tyrosine phosphorylation sites, and we suspect that multiple insulin signals are enabled when the activated insulin receptor kinase phosphorylates several of them. Tyrosine-phosphorylated IRS-1 binds specifically to various cellular proteins containing Src homology 2 (SH2) domains (SH2 proteins). We identified some of the tyrosine residues of IRS-1 that undergo insulin-stimulated phosphorylation by the purified insulin receptor and in intact cells during insulin stimulation. Automated sequencing and manual radiosequencing revealed the phosphorylation of tyrosine residues 460, 608, 628, 895, 939, 987, 1172, and 1222; additional sites remain to be identified. Immobilized SH2 domains from the 85-kDa regulatory subunit (p85 alpha) of the phosphatidylinositol 3'-kinase bind preferentially to tryptic phosphopeptides containing Tyr(P)-608 and Tyr(P)-939. By contrast, the SH2 domain in GRB2 and the amino-terminal SH2 domain in SHPTP2 (Syp) specifically bind to Tyr(P)-895 and Tyr(P)-1172, respectively. These results confirm the p85 alpha recognizes YMXM motifs and suggest that GRB2 prefers a phosphorylated YVNI motif, whereas SHPTP2 (Syp) binds to a phosphorylated YIDL motif. These results extend the notion that IRS-1 is a multisite docking protein that engages various downstream regulatory elements during insulin signal transmission.

Amino Acid Sequence↗
PubMed1993

IRS-1 is a common element in insulin and insulin-like growth factor-I signaling to the phosphatidylinositol 3'-kinase.

IRS-1 is a unique cytosolic protein that becomes tyrosine phosphorylated during insulin stimulation of intact cells and immediately associates with the phosphatidylinositol 3'-kinase (PtdIns 3'-kinase). The insulin-like growth factor-I (IGF-I) receptor also mediated the tyrosine phosphorylation of IRS-1 and increased the amount of PtdIns 3'-kinase activity bound to IRS-1 in Chinese hamster ovary cells. Purified insulin receptor and IGF-I receptor phosphorylated recombinant baculovirus-produced IRS-1 on similar sites in vitro, and phosphorylated baculovirus-produced IRS-1 bound PtdIns 3'-kinase activity from lysates of quiescent cells. Treatment of cells with IGF-I activated the PtdIns 3'-kinase, suggesting that IGF-I activates the PtdIns 3'-kinase through IRS-1 binding to p85 in a manner similar to insulin. Chinese hamster ovary cells overexpressing IRS-1 demonstrated increased tyrosine phosphorylation of IRS-1, and more PtdIns 3'-kinase activity associated with IRS-1 in these cells. These data demonstrate that IRS-1 is a common element for signal transmission by the IGF-I and insulin receptors.

Animals↗
PubMed1993

The new elements of insulin signaling. Insulin receptor substrate-1 and proteins with SH2 domains.

Since the discovery of insulin and its receptor, the downstream elements responsible for the pleiotropic insulin signal have been difficult to define. The recently discovered insulin receptor substrate, IRS-1, provides an innovative and simple way to think about this problem: IRS-1 may mediate the control of various cellular processes by insulin. Overexpression of IRS-1 enhances insulin-stimulated DNA synthesis in Chinese hamster ovary cells, and microinjection of IRS-1 protein potentiates the maturation of Xenopus oocytes. We suspect that insulin signals are enabled when the activated insulin receptor kinase phosphorylates specific tyrosine residues in IRS-1. These phosphorylated sites associate with high affinity to cellular proteins that contain SH2 (src homology-2) domains. This association is specific and depends on the amino acid sequence surrounding the phosphotyrosine residue and the isoform of the SH2 domain. A growing number of SH2 domain-containing proteins have been identified, and we suspect that IRS-1 has the potential to simultaneously regulate many of them. We have only begun to identify the specific proteins that associate with phosphorylated IRS-1. One of them, the phosphatidylinositol 3'-kinase, is activated when the SH2 domains in its 85,000-M(r) regulatory subunit bind to phosphorylated IRS-1. IRS-1 also interacts with other proteins such as SHPTP2, a novel SH2 domain-containing Tyr phosphatase, and GRB-2/sem-5, a protein that is implicated in p21ras signaling. The interaction between phosphorylated IRS-1 and multiple SH2 domain-containing proteins may ultimately explain the pleiotropic effects of insulin.

Amino Acid Sequence↗
PubMed1993

Human skeletal muscle insulin receptor substrate-1. Characterization of the cDNA, gene, and chromosomal localization.

Insulin receptor substrate-1 is a major substrate of insulin receptor Tyr kinase. We have now cloned the IRS-1 cDNA from human skeletal muscle, one of the most important target tissues of insulin action, localized and cloned the human IRS-1 gene, and studied the expression of the protein in Chinese hamster ovary cells. Human IRS-1 cDNA encodes a 1242 amino acid sequence that is 88% identical with rat liver IRS-1. The 14 potential Tyr phosphorylation sites include 6 Tyr-Met-X-Met motifs and 3 Tyr-X-X-Met motifs that are completely conserved in human IRS-1. Human IRS-1 has > 50 possible Ser/Thr phosphorylation sites and one potential ATP-binding site close to the NH2-terminal. The human IRS-1 gene contains the entire 5'-untranslated region and protein coding region in a single exon and was localized on chromosome 2 q36-37 by in situ hybridization. By Northern blot analysis, IRS-1 mRNA is rare and consists of two species of 6.9 and 6 kilobase. By using quantitative polymerase chain reaction after reverse transcription of total RNA from human fetal tissues, IRS-1 mRNA could be identified in all tissues. When human IRS-1 cDNA was expressed in Chinese hamster ovary cells, the protein migrated between 170,000-180,000 M(r) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and was rapidly Tyr phosphorylated upon insulin stimulation. Thus, IRS-1 is widely expressed and highly conserved across species and tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Expression and function of IRS-1 in insulin signal transmission.

IRS-1 is a major insulin receptor substrate which may play an important role in insulin signal transmission. The mRNA for IRS-1 in rat cells and tissues is about 9.5 kilobases (kb). Rat liver IRS-1 was stably expressed in Chinese hamster ovary (CHO) cells (CHO/IRS-1). Although its calculated molecular mass is 131 kDa, IRS-1 from quiescent cells migrated between 165 and 170 kDa during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. IRS-1 was phosphorylated strongly on serine residues and weakly on threonine residues before insulin stimulation. Insulin immediately stimulated tyrosine phosphorylation of IRS-1, and after 10-30 min with insulin its apparent molecular mass increased to 175-180 kDa. Expression of the human insulin receptor and rat IRS-1 together in CHO/IR/IRS-1 cells increased the basal serine phosphorylation of IRS-1 and strongly increased tyrosine phosphorylation during insulin stimulation. Purified insulin receptors directly phosphorylated baculovirus-produced IRS-1 exclusively on tyrosine residues. By immunofluorescence, IRS-1 was absent from the nucleus, but otherwise distributed uniformly before and after insulin stimulation. Some IRS-1 associated with the insulin receptor during insulin stimulation. In addition, a phosphatidylinositol 3'-kinase associated with IRS-1 during insulin stimulation, and this association was more sensitive to insulin in CHO cells overexpressing the insulin receptor (CHO/IR cells), more responsive to insulin to CHO/IRS-1 cells, and both sensitive and responsive in CHO/IR/IRS-1 cells. Similarly, insulin-stimulated DNA synthesis was more sensitive to insulin in CHO/IR cells, and more responsive in CHO/IRS-1 cells; however, insulin-stimulated DNA synthesis was sensitive but poorly responsive to insulin in CHO/IR/IRS-1 cells. Together, these results suggest that IRS-1 is a direct physiologic substrate of the insulin receptor and may play an important role in insulin signal transmission.

Amino Acid Sequence↗