Doctor

THE JOURNAL

OF

BIOLOGICAL CHEMISTRY

Vol. 272, No. 47, Issue of November 21, pp. 29911–29918, 1997
Printed in U.S.A.

A Molecular Basis for Insulin Resistance
ELEVATED SERINE/THREONINE PHOSPHORYLATION OF IRS-1 AND IRS-2 INHIBITS THEIR BINDING TO
THE JUXTAMEMBRANE REGION OF THE INSULIN RECEPTOR AND IMPAIRS THEIR ABILITY TO UNDERGO
INSULIN-INDUCED TYROSINE PHOSPHORYLATION*
(Receivedfor publication, May 20, 1997, and in revised form, August 20, 1997)

Keren Paz‡, Rina Hemi§, Derek LeRoith¶, Avraham Karasik§, Eytan Elhanany , Hannah Kanety§,
and Yehiel Zick‡**
From the ‡Department of Molecular Cell Biology, the Weizmann Institute of Science, Rehovot 76100, Israel, the §Institute
of Endocrinology, Chaim Sheba Medical Center, Tel-Hashomer 52621, Israel, the ¶DiabetesBranch, National Institutes of
Health, Bethesda, Maryland 20982, and the Department of Biochemistry, Israel Institute for Biological Research,
Ness Ziona, 70400, Israel

* This work was supported by research grants from the Kekst Foundation (to Y. Z.), the Israel Ministry of Health (to Y. Z.), the Tolz
Foundation (to Y. Z.), the Israel Cancer Research Fund (to H. K.), the
Israel Cancer Association(to A. K.) and the Israel Science Foundation
(founded by the Israel Academy of Sciences and Humanities) (to H. K.,
and A. K.) and by Grant 196130 from the Juvenile Diabetes Foundation
International (to Y. Z.). The costs of publication of this article were
defrayed in part by the payment of page charges. This article must
therefore be hereby marked “advertisement” in accordance with 18U.S.C. Section 1734 solely to indicate this fact.
** Incumbent of the Philip Harris and Gerald Ronson Career Development Chair in Diabetes Research. To whom correspondence should be
addressed. Fax: 972-8-9342-380; E-mail: Lizick@weizmann.weizmann.
ac.il.
This paper is available on line at http://www.jbc.org

The insulin receptor (IR)1 is an heterotetrameric transmembrane glycoprotein composed oftwo extracellular subunits
and two transmembrane subunits linked by disulfide bonds.
The subunits contain the insulin-binding domain while the
transmembrane subunits function as a tyrosine-specific protein kinase (IRK) that undergoes autophosphorylation following insulin binding (reviewed in Ref. 1). Autophosphorylation
activates the IRK (2) and enables it to phosphorylate endogenous proteinsubstrates, including Shc (3) and the insulin receptor substrates IRS-1 (4) and IRS-2 (5), to further propagate
the insulin signal. IRS-1 and IRS-2, two related protein substrates of IRK, have a highly conserved amino terminus, which
contains a pleckstrin homology domain and a phosphotyrosinebinding (PTB) domain, and a poorly conserved carboxyl terminus with several tyrosine phosphorylationmotifs. IRS-1 and
IRS-2 also contain over 30 Ser/Thr residues in consensus phosphorylation sites (4, 5). The relative roles of IRS-1 and IRS-2 in
mediating insulin action is presently unknown, although IRS-2
functions as an alternative substrate of IR in IRS-1 null mice
(6), which manifest a mild form of insulin resistance.
Insulin resistance is a state in which target cells fail to
respond toordinary levels of circulating insulin (7). At the
molecular level, impaired insulin signaling results from mutations or post-translation modifications of the insulin receptor
itself or any of its downstream effector molecules. A major
negative regulatory role to insulin action is attributed to agents
that enhance Ser/Thr phosphorylation of either the receptor
itself or of its downstreameffectors, which reduce IRK activity
or its ability to phosphorylate substrate proteins (see Refs. 8
and 9 for reviews). For example, insulin’s counter-regulatory
hormones such as epinephrine or glucagon increase cAMP levels, activate the cAMP-dependent protein kinase, and increase
the Ser(P)/Thr(P) content of the insulin receptor, which results
in an insulin-resistant state. Similarly, okadaic...