Role of IRS and PHIP on Insulin-Induced Tyrosine Phosphorylation and Distribution of IRS Proteins

Abstract

ABSTRACT. To analyze the functional differences of the insulin receptor substrate (IRS) family, the N-terminal fragments containing the pleckstrin homology (PH) domains and the phosphotyrosine-binding (PTB) domains of IRS (IRS-N) proteins, as well as intact IRS molecules, were expressed in Cos-1 cells, and insulin-induced tyrosine phosphorylation and subcellular distribution of IRS proteins were analyzed. In contrast to the distinct affinities toward phosphoinositides, these IRS-N fragments non-selectively inhibited insulin-induced tyrosine phosphorylation of IRS-1, IRS-2 and IRS-3, among which IRS3-N was most effective. The mutations of IRS-1 disrupting all the phosphoinositide-binding sites in both the PH and PTB domains significantly but not completely suppressed tyrosine phosphorylation of IRS-1, which was further inhibited by coexpression of all the IRS-N proteins examined. In contrast, the N-terminal PH domain-interacting region (PHIP-N) of PH-interacting protein (PHIP) did not impair tyrosine phosphorylation of either IRS molecule. The analysis using confocal microscopy also demonstrated that all the IRS-N proteins, but not PHIP-N, suppressed targeting of IRS-1 to the plasma membrane in response to insulin. Moreover, the phosphoinositide affinity-disrupting mutations of IRS-1 significantly impaired but did not completely abrogate the insulin-induced translocation of IRS-1 to the plasma membrane, which was further suppressed by IRS1-N overexpression. These findings suggest that both insulin-induced tyrosine phosphorylation and the cell surface targeting of IRS proteins may be regulated in a similar manner through a target molecule common to the members of the IRS family, and distinct from phosphoinositides or PHIP.

The full‐length isoform of the mouse pleckstrin homology domain‐interacting protein (PHIP) is required for postnatal growth

“…PHIP1 is highly expressed in the pancreatic β cells and was shown to be required for pancreatic β‐cell proliferation [13]. In addition, PHIP, an alternatively spliced isoform of PHIP1, was isolated as an IRS‐1 interacting protein and was previously showed to be involved in insulin signal transduction [12,18]. Thus, we next assessed whether PHIP1‐deficient mice were defective in glucose metabolism.…”

Exenatide improves hepatocyte insulin resistance induced by different regional adipose tissue

“…Most of the current research focuses on the phosphorylation of IRS1. Insulin can activate the IRS kinase, which can phosphorylate the serine/threonine of IRS, thereby interrupting the binding of IRS to downstream effectors, resulting in IR ( 46 , 47 ). Rector RS et al.…”

The Biological Activity of Structurally Defined Inositol Glycans

“…(3) Adaptor proteins (IRS-1, IRS-2) bind to the phosphorylated receptor and then (4) their tyrosine residues are phosphorylated by the IR kinase activity. IRS proteins are localized to the plasma membrane during this event, perhaps through the interaction with phosphatidylinositol-4,5-diphosphate [19]. (5) The p85 regulatory domain of phosphatidylinositol 3 kinase (PI3K) docks with the phosphorylated sites of IRS1/2.…”