The RhoGAP RRC-1 is required for the assembly or stability of integrin adhesion complexes and is a member of the PIX pathway in muscle

Abstract

GTPases cycle between active GTP bound and inactive GDP bound forms. Exchange of GDP for GTP is catalyzed by guanine nucleotide exchange factors (GEFs). GTPase activating proteins (GAPs) accelerate GTP hydrolysis, to promote the GDP bound form. We reported that the RacGEF, PIX-1, is required for assembly of integrin adhesion complexes (IAC) in striated muscle of Caenorhabditis elegans. In C. elegans, IACs are found at the muscle cell boundaries (MCBs), and bases of sarcomeric M-lines and dense bodies (Z-disks). Screening C. elegans mutants in proteins containing RhoGAP domains revealed that loss of function of rrc-1 results in loss of IAC components at MCBs, disorganization of M-lines and dense bodies, and reduced whole animal locomotion. RRC-1 localizes to MCBs, like PIX-1. The localization of RRC-1 at MCBs requires PIX-1, and the localization of PIX-1 requires RRC-1. Loss of function of CED-10 (Rac) shows lack of PIX-1 and RRC-1 at MCBs. RRC-1 exists in a complex with PIX-1. Transgenic rescue of rrc-1 was achieved with wild type RRC-1 but not RRC-1 with a missense mutation in a highly conserved residue of the RhoGAP domain. Our results are consistent with RRC-1 being a RhoGAP for the PIX pathway in muscle.