Activation of Rac1 by Rho‐guanine nucleotide dissociation inhibitor‐β with defective isoprenyl‐binding pocket

Abstract

Rho-guanine nucleotide dissociation inhibitor-beta (RhoGDIbeta), a regulator for Rho GTPases, is implicated in cancer cell progression. We reported that C-terminal truncated RhoGDIbeta (DeltaC(166-201)-RhoGDIbeta) promoted metastasis through activating Rac1 signaling pathway in ras-transformed fibroblast cells. To better understand the mechanism of Rac1 activation by DeltaC(166-201)-RhoGDIbeta during metastasis, the amount of GTP-bound Rac1 was measured as the activation level of Rac1 in cells expressing various mutant RhoGDIbeta with sequential C-terminal deletions. Three C-terminal hydrophobic amino acid residues (Trp191, Leu193, and Ile195) supposed to interact with isoprenyl groups of Rac1, was indispensable for a proper regulation of Rac1 activation/inhibition. Deletion of this region led RhoGDIbeta to continuously associate with GTP-bound Rac1, provoking constitutive activation of Rac1. Thus, impaired interaction of RhoGDIbeta with Rac1 isoprenyl groups possibly makes RhoGDIbeta function as a positive regulator for Rac1 during metastasis.