Disease relevance of IRS1

• Down-regulation of IRS1 and IRS2 was also seen in HCV core-transgenic mice livers and HCV core-transfected human hepatoma cells [1].
• On the basis of these experiments, TRS1 and IRS1 are proposed to be important intermediaries in the cascade of cytomegalovirus gene expression [2].
• A genotype combination analysis of the non-synonymous polymorphisms in the IRS1, IRS2 and SHC1 genes did not show any effect on breast cancer risk [3].
• We observed a significant interaction between IRS1 genotype and aspirin/NSAIDs use and risk of colorectal cancer [4].
• RESULTS: Having at least one R allele (GR or RR) for IRS1 G972R was associated with an increased risk of colon cancer [odds ratio 1.4, 95% confidence interval (95% CI) 1.1-1.9] [5].

High impact information on IRS1

• Overall, ligand binding by IRS-1 and Shc PTB domains is similar, but residues critical for phosphotyrosine recognition are not conserved [6].
• The PTB domains of IRS-1 and Shc share a common fold with pleckstrin homology domains [6].
• SUMMARY: Crystal structures of the insulin receptor substrate-1 (IRS-1) phosphotyrosine-binding (PTB) domain, alone and complexed with the juxtamembrane region of the insulin receptor, show how this domain recognizes phosphorylated "NPXY" sequence motifs [6].
• Mutation of Y497 to F yielded receptors that caused little or no IRS-1 phosphorylation in response to huIL-4 when expressed in 32D-IRS-1 cells [7].
• Furthermore, a glutathione-S-transferase fusion protein containing the I4R motif-bound IRS-1, tyrosine kinase(s), and other unidentified phosphoproteins with molecular sizes of 140, 80, and 55 kd [7].

Chemical compound and disease context of IRS1

• Carbobenzoxy-l-leucyl-l-leucyl-l-leucinal, a potent proteosomal proteolysis inhibitor, blocked down-regulation of IRS1 and IRS2 in HCV core-transfected hepatoma cells [1].
• Agents such as free fatty acids, cytokines, angiotensin II, endothelin-1, amino acids, cellular stress and hyperinsulinemia, which induce insulin resistance, lead to both activation of several serine/threonine kinases and phosphorylation of IRS1 [8].
• We tested whether anti-IRS1 siRNA could inhibit growth and survival of estrogen-sensitive MCF-7 breast cancer cells, when used alone or in combination with TAM [9].
• In breast cancer cells, 17-beta-estradiol (E2) upregulates the expression of insulin receptor substrate 1 (IRS-1), a molecule transmitting insulin-like growth factor-I (IGF-I) signals through the PI-3K/Akt survival pathways [10].
• RNAi-mediated silencing of insulin receptor substrate 1 (IRS-1) enhances tamoxifen-induced cell death in MCF-7 breast cancer cells [9].
• Protein tyrosine phosphatases (PTPs) appear to be important for the IRS-1 cleavage because tyrosine phosphorylation of the insulin receptor was decreased in hypoxia and IRS-1 cleavage could be blocked either with H(2)O(2) or with vanadate, each of which inhibits PTPs [11].

Biological context of IRS1

• Using loss- and gain-of-function S6K1 constructs, we demonstrate a requirement for the catalytic activity of S6K1 in both direct and indirect regulation of IRS1 serine phosphorylation [12].
• Transient transfection of parental CHO cells with an insulin receptor substrate 1 (IRS1) expression plasmid enhanced insulin downstream signaling in a biphasic manner, whereas IRS1 transfection of CHO/IR cells inhibited insulin signaling in a dose-dependent fashion [13].
• To assess the relative effects of various insulin receptor, IRS1, and Grb2 levels on insulin signaling, parental CHO cells were transiently transfected with various combinations of expression plasmids encoding these proteins [13].
• Consistent with the Shc-Grb2 pathway as the major route for insulin-stimulated c-Fos and AP-1 transcriptional activation, the IRS1-mediated inhibition was reversed by transfection with an expression plasmid for Grb2 [13].
• This study investigated the effect of salicylic acid on phorbol 12-myristate 13-acetate (PMA)- and TNFalpha-induced insulin resistance in a human embryonic kidney 293 (HEK293) cell line stably expressing recombinant human IRS1 [14].

Anatomical context of IRS1

• Although expression of IRS1 resulted in a biphasic increase of insulin signaling in parental CHO cells, coexpression of IRS1 with the insulin receptor resulted in inhibition of signaling [13].
• IRS1 is preferentially depleted from the high-speed pellet fraction in TSC1/2-deficient mouse embryo fibroblasts or in HEK293/293T cells overexpressing Rheb [12].
• Moreover, SH2-B directly enhanced autophosphorylation of insulin receptor and tyrosine phosphorylation of IRS1 and IRS2 in an SH2 domain-dependent manner in cultured cells [15].
• The association of variants in IRS1 with type 2 diabetes and type 2 diabetes-related phenotypes and the differential expression of IRS1 in adipocytes and skeletal muscle suggest a role of this gene in the pathogenesis of type 2 diabetes in Pima Indians [16].
• Finally, small interfering RNA (siRNA)-specific gene silencing targeted specifically against p47(phox) (p47siRNA), in both L6 and primary myotubes, reduced the cognate protein expression, decreased NADPH oxidase activity, restored Ang II-impaired IRS1 and Akt activation as well as GLUT4 translocation by insulin [17].

Associations of IRS1 with chemical compounds

• In contrast, m-HT did not modulate IRS1, phosphoinositide 3-kinase, or PKB activity [18].
• Based on these expression differences and the known physiologic role of IRS1, this gene was investigated as a candidate gene for susceptibility to type 2 diabetes in Pima Indians, a population with an extremely high incidence and prevalence of type 2 diabetes [16].
• Salicylic acid pretreatment completely reversed the effects of PMA and TNFalpha on both Akt and IRS1 [14].
• RESULTS: Concomitant with reductions in mitochondrial membrane potential (DeltaPsim) and ATP synthesis, production of IRS1 and solute carrier family 2 (facilitated glucose transporter), member 4 (SLC2A4, formerly known as GLUT4) were reduced [19].
• Prevalence of CYP21 mutations and IRS1 variant among women with polycystic ovary syndrome and adrenal androgen excess [20].
• These results suggest that a feed-forward mechanism may exist whereby insulin activation of Akt leads to phosphorylation of IRS-1 at Ser(629), resulting in decreased phosphorylation of IRS-1 at Ser(636) and enhanced downstream signaling [21].

Physical interactions of IRS1

• Notably, a fraction of the cytosolic ER-alpha colocalized and coprecipitated with IRS-1 and IRS-2, indicating a possible common destination for these proteins [10].
• The activated receptors of IL-4 and IGF-I both docked to IRS-1 and IRS-2 and invoked IRS complex formation with phosphatidylinositol (PI) 3-kinase, as assessed by immunoprecipitation and detection of the precipitated compounds by immunoblot analysis [22].
• There was also a tendency for a decrease in Grb2 binding to IRS-1 and insulin-stimulated mitogen-activated protein kinase activity, however, these were not statistically significant [23].
• Furthermore, these results are consistent with the notion that SH-PTP2 may bind to IRS-1 through its SH2 domains in response to insulin and dephosphorylate the phosphotyrosine residue to which it binds, thereby regulating its association with IRS-1 [24].
• Recently, IRS-1 was found to interact with alphav beta3 integrins upon insulin stimulation [25].

Enzymatic interactions of IRS1

• This interaction was confirmed in a "pull down" experiment using a glutathione S-transferase fusion protein containing the C terminus of the human SERCA isoform and phosphorylated IRS-1 in vitro and could be blocked by a FLVRES-like domain peptide present in the human SERCA sequence [26].
• Recombinant SH-PTP2 specifically dephosphorylated a synthetic phosphopeptide corresponding to the sequence surrounding Tyr-1172 of IRS-1, a putative binding site for SH-PTP2 [24].
• Phosphopeptide mapping showed that insulin-dependent in vivo sites of IRS-1 serine phosphorylation were comparable to those of PAS kinase phosphorylated IRS-1 [27].
• Recombinant IRS-1 was phosphorylated on tyrosines upon incubation with purified EGFR from A431 cells and 32P-labeled ATP [28].
• We present the NMR structure of the PTB domain of insulin receptor substrate-1 (IRS-1) complexed to a tyrosine-phosphorylated peptide derived from the IL-4 receptor [29].

Regulatory relationships of IRS1

• These results provide new insight into novel molecular interactions involving PTP1B and GRB2 that may influence the steady-state capacity of IRS-1 to function as a phosphotyrosine scaffold and possibly affect the balance of postreceptor insulin signaling [30].
• Insulin resistance induced by high glucose and high insulin precedes insulin receptor substrate 1 protein depletion in human adipocytes [31].
• Additionally, phenylarsine oxide, an inhibitor of protein-tyrosine phosphatases, inactivated SH-PTP2 in vitro and increased the insulin-induced association of SH-PTP2 with IRS-1 [24].
• The decrease in IRS-1 amount resulted in a reduction in its tyrosine phosphorylation and the alteration of insulin-induced protein kinase B activation and AS160 phosphorylation [32].
• IL-4 rapidly induced IRS-1 and IRS-2 phosphorylation in ZR-75-1 human breast cancer cell lines [33].
• Targeting of the IRS-1 3'-untranslated region (UTR) by miR145 was confirmed using a reporter gene (luciferase) expressing the miR145 binding sites of the IRS-1 3'-UTR [34].

Other interactions of IRS1

• Insulin receptor substrate (IRS) proteins are tyrosine phosphorylated and mediate multiple signals during activation of the receptors for insulin, insulin-like growth factor 1 (IGF-1), and various cytokines [35].
• During insulin stimulation, IRS-1 and IRS-2 strongly bound p85alpha/beta, which activated phosphatidylinositol (PI) 3-kinase, protein kinase B (PKB)/Akt, and p70(s6k), and promoted the phosphorylation of BAD [35].
• Neither IRS-1 nor IRS-2 was detectably activated by IFN-gamma [36].
• Tyrosine dephosphorylation and deactivation of insulin receptor substrate-1 by protein-tyrosine phosphatase 1B. Possible facilitation by the formation of a ternary complex with the Grb2 adaptor protein [30].
• When evaluated as a ratio of activity versus IRS-1 to that versus p-nitrophenyl phosphate, PTP1B remained significantly more active by 3.1-293-fold, respectively [30].

Analytical, diagnostic and therapeutic context of IRS1

• The effect of IRS1 expression on the formation of multisubunit signaling complexes was determined by a series of indirect co-immunoprecipitations [37].
• The treatment of the Zucker obese rats with rosiglitazone also reversed the high circulating levels of non-esterified fatty acids, which have been shown to be correlated with increased IRS1 serine phosphorylation in other animal models [38].
• Insulin resistance in human adipocytes occurs downstream of IRS1 after surgical cell isolation but at the level of phosphorylation of IRS1 in type 2 diabetes [39].
• Instead, immunoblotting experiments with an Ab to IRS-2 revealed that induction of granulocytic differentiation caused a large increase in IRS-2, and this occurred in the absence of detectable IRS-1 protein [40].
• Despite genotyping 9,000 people and >95% power to reproduce the estimated OR from the recent meta-analysis, we were unable to replicate the association of the IRS-1 G972R polymorphism with type 2 diabetes [41].

References