Identification of MYO18A as a novel interacting partner of the PAK2/βPIX/GIT1 complex and its potential function in modulating epithelial cell migration

The p21-activated kinase (PAK) 2 is known to be involved in numerous biological functions, including the regulation of actin reorganization and cell motility. To better understand the mechanisms underlying this regulation, we herein used a proteomic approach to identify PAK2-interacting proteins in human epidermoid carcinoma A431 cells. We found that MYO18A, an emerging member of the myosin superfamily, is a novel PAK2 binding partner. Using a siRNA knockdown strategy and in vitro binding assay, we discovered that MYO18A binds to PAK2 through the βPIX/GIT1 complex. Under normal conditions, MYO18A and PAK2 colocalized in lamellipodia and membrane ruffles. Interestingly, knockdown of MYO18A in cells did not prevent formation of the PAK2/βPIX/GIT1 complex, but rather apparently changed its localization to focal adhesions. Moreover, MYO18A-depleted cells showed dramatic changes in morphology and actin stress fiber and membrane ruffle formation and displayed increases in the number and size of focal adhesions. Migration assays revealed that MYO18A-depleted cells had decreased cell motility, and reexpression of MYO18A restored their migration ability. Collectively, our findings indicate that MYO18A is a novel binding partner of the PAK2/βPIX/GIT1 complex and suggest that MYO18A may play an important role in regulating epithelial cell migration via affecting multiple cell machineries.