Identification of a novel Cdc42 GEF that is localized to the PAT-3-mediated adhesive structure

In the model organism Caenorhabditis elegans, UNC-112 is colocalized with PAT-3/beta-integrin and is a critical protein in the formation of PAT-3-mediated adhesive structure in body-wall muscle cells. However, the signaling pathway downstream of PAT-3/UNC-112 is largely unknown. To clarify the signaling pathway from PAT-3/UNC-112 to the actin cytoskeleton, we searched for and identified a novel Dbl homology/pleckstrin homology (DH/PH) domain containing protein, UIG-1 (UNC-112-interacting guanine nucleotide exchange factor-1). UIG-1 was colocalized with UNC-112 at dense bodies in body-wall muscle cells. UIG-1 showed CDC-42-specific GEF activity in vitro and induced filopodia formation in NIH 3T3 cells. Depletion of CDC-42 or PAT-3 in the developmental stage, by RNAi, prevented the formation of continuous actin filament in body-wall muscle cells. Taken together, these results suggest that UIG-1 links a PAT-3/UNC-112 complex to the CDC-42 signaling pathway during muscle formation.