A Conserved Binding Motif Defines Numerous Candidate Target Proteins for Both Cdc42 and Rac GTPases

Peter D Burbelo,David Drechsel,Alan Hall

doi:10.1074/jbc.270.49.29071

Abstract

Rho, Rac, and Cdc42 are small GTPases that regulate the formation of a variety of actin structures and the assembly of associated integrin complexes, but little is known about the target proteins that mediate their effects. Here we have used a motif-based search method to identify putative effector proteins for Rac and Cdc42. A search of the GenBankTM data base for similarity with the minimum Cdc42/Rac interactive binding (CRIB) region of a potential effector protein p65PAK has identified over 25 proteins containing a similar motif from a range of different species. These candidate Cdc42/Rac-binding proteins include family members of the mixed lineage kinases (MLK), a novel tyrosine kinase from Drosophila melanogaster (DPR2), a human protein MSE55, and several novel yeast and Caenorhabditis elegans proteins. Two murine p65PAK isoforms and a candidate protein from C. elegans, F09F7.5, interact strongly with the GTP form of both Cdc42 and Rac, but not Rho in a filter binding assay. Three additional candidate proteins, DPR2, MSE55, and MLK3 showed binding to the GTP form of Cdc42 and weaker binding with Rac, and again no interaction with Rho. These results indicate that proteins containing the CRIB motif bind to Cdc42 and/or Rac in a GTP-dependent manner, and they may, therefore, participate in downstream signaling.

Highlights

Members of the Ras superfamily of small GTPases play a wide variety of cellular signaling roles that mediate proliferation and differentiation, cytoskeletal organization, protein transport, and secretion
Rac and Cdc42, but not Rho, have been shown to activate the c-Jun amino-terminal kinase (JNK) signaling pathway leading to c-Jun transcriptional activation [11, 12]
Over 10 mammalian GTPase-activating proteins (GAPs)1 for Rho family members have been described including BCR, p50rhoGAP, chimaerin, ABR, p190-A, p122, and myr-5 [13]. The ability of these GAP proteins to interact with GTPases in a GTP-dependent manner suggests that in addition to being negative regulators, they may act as effector proteins

Summary

Introduction

Members of the Ras superfamily of small GTPases play a wide variety of cellular signaling roles that mediate proliferation and differentiation, cytoskeletal organization, protein transport, and secretion. A tyrosine kinase containing a SH3 domain, p120ACK, has been shown to bind to Cdc42 in a GTP-dependent manner, its biological role is unclear [18]. The serine/threonine kinase p65PAK, binds to both Cdc42 and Rac (but not Rho) in a GTP-dependent manner, but again it is not known whether p65PAK mediates any of the described biological effects of these GTPases [19, 20].

Results

Conclusion