The regulator of G protein signaling domain of axin selectively interacts with G?12 but not G?13

Abstract

Axin, a negative regulator of the Wnt signaling pathway, contains a canonical regulator of G protein signaling (RGS) core domain. Herein, we demonstrate both in vitro and in cells that this domain interacts with the ? subunit of the heterotrimeric G protein G12 but not with the closely related G?13 or with several other heterotrimeric G proteins. Axin preferentially binds the activated form of G?12, a behavior consistent with other RGS proteins. However, unlike other RGS proteins, that of axin (axinRGS) does not affect intrinsic GTP hydrolysis by G?12. Despite its inability to act as a GTPase-activating protein, we demonstrate that in cells, axinRGS can compete for G?12 binding with the RGS domain of p115RhoGEF, a known G 12-interacting protein that links G12 signaling to activation of the small G protein Rho. Moreover, ectopic expression of axinRGS specifically inhibits G?12 -directed activation of the Rho pathway in MDA-MB 231 breast cancer cells. These findings establish that the RGS domain of axin is able to directly interact with the ? subunit of heterotrimeric G protein G12 and provide a unique tool to interdict G?12-mediated signaling processes. Copyright © 2006 The American Society for Pharmacology and Experimental Therapeutics.