Identification of IQGAP as a Putative Target for the Small GTPases, Cdc42 and Rac1

doi:10.1074/jbc.271.38.23363

Identification of IQGAP as a Putative Target for the Small GTPases, Cdc42 and Rac1*

From the ^‡ Division of Signal Transduction, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-01,
^§ Department of Biochemistry, Hiroshima University School of Medicine, 1-2-3 Kasumi, Minami-ku, Hiroshima 734,
^¶ Kazusa DNA Research Institute, 1532-3 Yanauchino, Kisarazu 292, and
^∥ Central Laboratories for Key Technology, Kirin Brewery Co. Ltd., 1-13-5 Fukuura, Kanazawa-ku, Yokohama 236, Japan

^″ To whom correspondence should be addressed. Tel.: 81-7437-2-5440; Fax: 81-7437-2-5449; E-mail: kaibuchi{at}bs.aist-nara.ac.jp

Abstract

Cdc42 and Rac1 have been implicated in the regulation of various cell functions such as cell morphology, polarity, and cell proliferation. We have partially purified a Cdc42- and Rac1-associated protein with molecular mass of about 170 kDa (p170) from bovine brain cytosol. This protein interacted with guanosine 5′-(3-O-thio)triphosphate (GTPγS)·glutathione S-transferase (GST)-Cdc42 and GTPγS·GST-Rac1 but not with the GDP·GST-Cdc42, GDP·GST-Rac1, or GTPγS·GST-RhoA). We identified p170 as an IQGAP, which is originally identified as a putative Ras GTPase-activating protein. Recombinant IQGAP specifically interacted with GTPγS·Cdc42 and GTPγS·Rac1. The C-terminal fragment of IQGAP was responsible for their interactions. IQGAP was specifically immunoprecipitated with dominant-active Cdc42^Val12 or Rac1^Val12 from the COS7 cells expressing Cdc42^Val12 or Rac1^Val12, respectively. Immunofluorescence analysis revealed that IQGAP was accumulated at insulin- or Rac1-induced membrane ruffling areas. This accumulation of IQGAP was blocked by the microinjection of the dominant-negative Rac1^Asn17 or Cdc42^Asn17. Moreover, IQGAP was accumulated at the cell-cell junction in MDCK cells, where α-catenin and ZO-1 were localized. These results suggest that IQGAP is a novel target molecule for Cdc42 and Rac1.

Footnotes

↵* This study was supported by grants-in-aid for Scientific Research and for Cancer Research from the Ministry of Education, Science, Sports and Culture, Japan, and by a grant from the Yamanouchi Foundation for Research on Metabolic Disease. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

WASP

Wiskott-Aldrich syndrome protein

GAP

GTPase-activating protein

GST

glutathione S-transferase

HA

hemagglutinin

PAGE

polyacrylamide gel electrophoresis

GTPγS

guanosine 5′-(3-O-thio)triphosphate

CRIB

Cdc42/Rac1 interactive binding region.
↵² Identifications of p90, p110, p122, and p140 will be described elsewhere.
↵³ A detailed analysis will be described elsewhere.
- Received June 17, 1996.