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

Abstract

Heterotrimeric Gα12/13 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 Gα signals to Rho. For example, p115 RhoGEF transduces Gα13 signals to Rho and inhibits Gα12/13 signals via the RhoGEF LH domain which links to Gα subunits. Here, we have evaluated the signaling capacity of Lbc RhoGEF in the context of Gα12/13 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 Gα12- and thrombin-induced activation of an SRE transcriptional reporter, and the levels of inhibition observed is similar to that obtained with an analogous p115 RhoGEF mutant. proto-Lbc mutant expression also led to decreased levels of Gα12-induced RhoA activation in vivo. Complex formation between Gα12 and Lbc forms was detected. Analysis of the Lbc peptide sequence reveals a previously undetected region which may link to Gα subunit signals. These findings support a role for Lbc in Gα12-induced signaling pathways to Rho.