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Mol Cell Biol, February 1998, p. 762-770, Vol. 18, No. 2
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Characterization of a Rac1- and RhoGDI-Associated Lipid Kinase Signaling Complex

Kimberley F. Tolias,1,2,* Anthony D. Couvillon,1 Lewis C. Cantley,1,2 and Christopher L. Carpenter1,3

Division of Signal Transduction, Beth Israel Deaconess Medical Center,1 and Departments of Cell Biology2 and Medicine,3 Harvard Medical School, Boston, Massachusetts

Received 11 August 1997/Returned for modification 27 September 1997/Accepted 4 November 1997

Rho family GTPases regulate a number of cellular processes, including actin cytoskeletal organization, cellular proliferation, and NADPH oxidase activation. The mechanisms by which these G proteins mediate their effects are unclear, although a number of downstream targets have been identified. The interaction of most of these target proteins with Rho GTPases is GTP dependent and requires the effector domain. The activation of the NADPH oxidase also depends on the C terminus of Rac, but no effector molecules that bind to this region have yet been identified. We previously showed that Rac interacts with a type I phosphatidylinositol-4-phosphate (PtdInsP) 5-kinase, independent of GTP. Here we report the identification of a diacylglycerol kinase (DGK) which also associates with both GTP- and GDP-bound Rac1. In vitro binding analysis using chimeric proteins, peptides, and a truncation mutant demonstrated that the C terminus of Rac is necessary and sufficient for binding to both lipid kinases. The Rac-associated PtdInsP 5-kinase and DGK copurify by liquid chromatography, suggesting that they bind as a complex to Rac. RhoGDI also associates with this lipid kinase complex both in vivo and in vitro, primarily via its interaction with Rac. The interaction between Rac and the lipid kinases was enhanced by specific phospholipids, indicating a possible mechanism of regulation in vivo. Given that the products of the PtdInsP 5-kinase and the DGK have been implicated in several Rac-regulated processes, and they bind to the Rac C terminus, these lipid kinases may play important roles in Rac activation of the NADPH oxidase, actin polymerization, and other signaling pathways.

* Corresponding author. Mailing address: Division of Signal Transduction, Harvard Institute of Medicine, 1007, 330 Brookline Ave., Boston, MA 02215. Phone: (617) 667-0941. Fax: (617) 667-0957. E-mail: ktolias{at}bidmc.harvard.edu.




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