The serine phosphorylations in the IRS-1 PIR domain abrogate IRS-1 and IR interaction

초록

Serine phosphorylations on insulin receptor substrate 1 (IRS - 1) by diverse kinases aoccur widely during obesity - , stress - , and inflammation - induced conditions in models of insulin resistance and type 2 diabetes. In this study, we define a region within the human IRS - 1, which is directly C - terminal to the PTB domain encompassing numerous serine phosphorylation sites including Ser307 (mouse Ser302) and Ser312 (mouse 307) creating a phosphorylation insulin resistance (PIR) domain. We demonstrate that the IRS - 1 PTB - PIR with its unphosphorylated serine residues interacts with the insulin receptor (IR) but loses the IR - binding when they are phosphorylated. Surface plasmon resonance studies further confirm that the PTB - PIR binds stronger to IR than just the PTB domain, and that phosphorylations at Ser307, Ser312, Ser315, and Ser323 within the PIR domain result in abrogating the binding. Insulin - responsive cells containing the mutant IRS - 1 with all these four serines changed into glutamates to mimic phosphorylations show decreased levels of phosphorylations in IR, IRS - 1, and AKT compared to the wild - type IRS - 1. Hydrogen-deuterium exchange mass spectrometry experiments indicating the PIR domain interacting with the N - terminal lobe and the hinge regions of the IR kinase domain further suggest the possibility that the IRS - 1 PIR domain protects the IR from the PTP1B - mediated dephosphorylation.

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