Essential roles of ERK-mediated phosphorylation of vinexin in cell spreading, migration and anchorage-independent growth

Vinexin is an adaptor protein supposed to play pivotal roles in various cellular events such as cell adhesion, cytoskeletal organization, signa ling and gene expression. Despite the possible importance, physiological functions and regulatory mechanisms of vinexin are largely unknown. In addition, although vinexin was reported to be phosphorylated by extracellular signal-regulated kinase ( ERK), physiological significance of the phosphorylation remains to be elucidated. Here we carried out characterization of endogenous vinexin and found that it was enriched at the leading edge of migrating cells and focal adhesions of spread cells. In the analyses using ERK-phosphorylated vinexin-specific antibody, the phosphorylation signal was also detected at the leading edges of migrating cells and at cell periphery of spreading cells, whereas only faint signal was observed at focal adhesions of well-spread cells. We then established LNCaP cell lines stably expressing GFP-fused vinexin beta or two mutants at Ser189 that mimic the ERK-phosphorylated or -unphosphorylated vinexinb. Based on the analyses using the lines, the phosphorylation was likely to inhibit the cell spreading and migration. On the other hand, anchorage-independent cell growth was inhibited by unphosphorylated vinexin beta. Taken together, ERK-mediated phosphorylation of vinexinb is strongly suggested to occur in a spatio-temporally regulated manner and play important roles in cell spreading, migration and anchorage-independent growth.