Expression of Dominant Negative Mutant SHPTP2 Attenuates Phosphatidylinositol 3′-Kinase Activity via Modulation of Phosphorylation of Insulin Receptor Substrate-1

Satoshi Ugi,Hiroshi Maegawa,Atsunori Kashiwagi,Masaaki Adachi,Jerrold M Olefsky,Ryuichi Kikkawa

doi:10.1074/jbc.271.21.12595

Abstract

To clarify the role of protein-tyrosine phosphatase (PTPase) containing Src homology 2 regions (SHPTP2) in insulin signaling, either wild-type or mutant SHPTP2 (delta PTP; lacking full PTPase domain) was expressed in Rat 1 fibroblasts overexpressing human insulin receptors. In response to insulin, phosphorylation of insulin receptor substrate 1 (IRS-1), IRS-1-associated PTPase activities and phosphatidylinositol (PI) 3'-kinase activities were slightly enhanced in wild-type cells when compared with those in the parent cells transfected with hygromycin-resistant gene alone. In contrast, introduction of delta PTP inhibited insulin-induced association of IRS-1 with endogenous SHPTP2 and impaired both insulin-stimulated phosphorylation of IRS-1 and activation of PI 3'-kinase. Furthermore, decreased content of p85 subunit of PI 3'-kinase was also found in mutant cells. Consistently, the insulin-stimulated mitogen-activated protein kinase activities and DNA synthesis were also enhanced in wild-type cells, but impaired in mutant cells. Thus, the interaction of SHPTP2 with IRS-1 may be associated with modulation of phosphorylation levels of IRS-1, resulting in the changes of PI 3'-kinase and mitogen-activated protein kinase activity. Furthermore, an impaired insulin signaling in mutant cells may be partly reflected in a decreased content of p85 protein of PI 3'-kinase.

Highlights

To clarify the role of protein-tyrosine phosphatase (PTPase) containing Src homology 2 regions (SHPTP2) in insulin signaling, either wild-type or mutant SHPTP2 (⌬PTP; lacking full PTPase domain) was expressed in Rat 1 fibroblasts overexpressing human insulin receptors
The mutant clone (MT15) expressed 2–3-fold more endogenous rat SHPTP2 as shown in Fig. 1B, total PTPase activity immunoprecipitated with ␣GST-Src homology 2 (SH2)-SHPTP2 antiserum was similar to that of pHyg cells
Cells were incubated with or without 100 nM insulin, and PTPase activity of SHPTP2 in the resultant supernatant fraction after removal of PTPase associated with insulin receptor substrate 1 (IRS-1) using ␣GST-IRS-1 antiserum was measured as described under “Experimental Procedures.”

Summary

EXPERIMENTAL PROCEDURES

Materials—Purified porcine insulin was a gift from Novo-Nordisk Pharmar (Copenhagen, Denmark) and Eli Lilly Co. (Indianapolis, IN). Western Blot Analysis of p85 Subunit of PI 3Ј-Kinase in the Cells— The cells were homogenized and the cell lysate (40 ␮g of protein) was resolved by SDS-PAGE, electrotransferred to Immobilon-P, and immunoblotted using two different specific antibodies (polyclonal ␣p85 and monoclonal anti-p85 antibody). Confluent cells in six-well plates were starved for 24 h in serumfree Dulbecco’s modified Eagle’s medium, stimulated with insulin at 37 °C for 10 min. The cell lysates were centrifuged and 10 ␮l of the supernatants were assayed for kinase activity, in a final volume of 40 ␮l containing 1 ␮M protein kinase inhibitor, 50 ␮M ATP, 2 ␮Ci of [␥-32P]ATP, and 20 ␮g of myelin basic protein at 25 °C for 15 min. The p values were determined by Scheffe’s multiple comparison test, and p Ͻ 0.05 was considered statistically significant

RESULTS

Cell line

DISCUSSION