Role of Lbc RhoGEF in Gα12/13-induced signals to Rho GTPase

Heterotrimeric Galpha12/13 signals induce cellular responses such as serum response element (SRE)-mediated gene transcription via Rho GTPase. Guanine nucleotide exchange factors (GEFs) are strong candidates for linking Got signals to Rho. For example, p 115 RhoGEF transduces Galpha13 signals to Rho and inhibits Galpha12/13 signals via the RhoGEF LH domain which links to Galpha subunits. Here, we have evaluated the signaling capacity of Lbc RhoGEF in the context of Galpha12/13 signals. In vitro GEF assays indicate that baculoviral-expressed proto-Lbc has minimal exchange activity, implying that a stimulus is required for Lbc activity in vivo. Expression of a catalytically inactive proto-Lbc mutant in HEK293T cells attenuates Galpha12- and thrombin-induced activation of an SRE transcriptional reporter, and the levels of inhibition observed is similar to that obtained with an analogous p 115 RhoGEF mutant. proto-Lbc mutant expression also led to decreased levels of Galpha12-induced RhoA activation in vivo. Complex formation between Galpha12 and Lbc forms was detected. Analysis of the Lbc peptide sequence reveals a previously undetected region which may link to Got subunit signals. These findings support a role for Lbc in Galpha12-induced signaling pathways to Rho. (C) 2003 Elsevier Inc. All rights reserved.