Tumor Necrosis Factor -induced Phosphorylation of Insulin Receptor Substrate-1 (IRS-1)

doi:10.1074/jbc.270.40.23780

Tumor Necrosis Factor -induced Phosphorylation of Insulin Receptor Substrate-1 (IRS-1)

POSSIBLE MECHANISM FOR SUPPRESSION OF INSULIN-STIMULATED TYROSINE PHOSPHORYLATION OF IRS-1 (*)

From the (1)Institute of Endocrinology
(2)the Department of Surgery, Sheba Medical Center, Tel Hashomer, Israel 52621 and
the (3)Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel 52900

^¶ To whom correspondence should be addressed:
Inst. of Endocrinology, Sheba Medical Center, Tel Hashomer, 52621, Israel.
Tel: 972-3-5302802; Fax: 972-3-5302803.

Abstract

Tumor necrosis factor-α (TNF) has been suggested to be the mediator of insulin resistance in infection, tumor cachexia, and obesity. We have previously shown that TNF diminishes insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1). The current work examines potential mechanisms that mediate this event. TNF effect on IRS-1 in Fao hepatoma cells was not associated with a significant reduction in insulin receptor tyrosine kinase activity as measured in vitro but impaired the association of IRS-1 with phosphatidylinositol 3-kinase, localizing TNF impact to IRS-1. TNF did not increase protein-tyrosine phosphatase activity and protein-tyrosine phosphatase inhibition by vanadate did not change TNF effect on IRS-1 tyrosine phosphorylation, suggesting that protein-tyrosine phosphatases are not involved in this TNF effect. In contrast, TNF increased IRS-1 phosphorylation on serine residues, leading to a decrease in its electrophoretic mobility. TNF effect on IRS-1 tyrosine phosphorylation was not abolished by inhibiting protein kinase C using staurosporine, while inactivation of Ser/Thr phosphatases by calyculin A and okadaic acid mimicked it. Our data suggest that TNF induces serine phosphorylation of IRS-1 through inhibition of serine phosphatases or activation of serine kinases other than protein kinase C. This increased serine phosphorylation interferes with insulin-induced tyrosine phosphorylation of IRS-1 and impairs insulin action.

Footnotes

↵^§ This work was submitted in partial fulfillment of the requirements for the Masters of Science degree at Bar-Ilan University.
↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. This study was supported by a project grant from the Israel Cancer Research Fund (to H. K. and M. Z. P.) and a grant from the Revson Foundation of the Israeli Academy of Sciences (to A. K.).
↵¹ The abbreviations used are:

TNF

tumor necrosis factor-α

PAGE

polyacrylamide gel electrophoresis

IR

insulin receptor

IRS-1

insulin receptor substrate-1

Ab

antibody

MAP

mitogen-activated protein

PI

phosphatidylinositol.
- Received June 23, 1995.
- Revision received July 31, 1995.