Extracellular Signal-Regulated Kinase/Mitogen-Activated Protein Kinase Regulates Actin Organization and Cell Motility by Phosphorylating the Actin Cross-Linking Protein EPLIN

Extracellular signal-regulated kinase (ERK) is important for various cellular processes, including cell migration. However, the detailed molecular mechanism by which ERK promotes cell motility remains elusive. Here we characterize epithelial protein lost in neoplasm (EPLIN), an F-actin cross-linking protein, as a novel substrate for ERK. ERK phosphorylates Ser360, Ser602, and Ser692 on EPLIN in vitro and in intact cells. Phosphorylation of the C-terminal region of EPLIN reduces its affinity for actin filaments. EPLIN colocalizes with actin stress fibers in quiescent cells, and stimulation with platelet-derived growth factor (PDGF) induces stress fiber disassembly and relocalization of EPLIN to peripheral and dorsal ruffles, wherein phosphorylation of Ser360 and Ser602 is observed. Phosphorylation of these two residues is also evident during wound healing at the leading edge of migrating cells. Moreover, expression of a non-ERK-phosphorylatable mutant, but not wild-type EPLIN, prevents PDGF-induced stress fiber disassembly and membrane ruffling and also inhibits wound healing and PDGF-induced cell migration. We propose that ERK-mediated phosphorylation of EPLIN contributes to actin filament reorganization and enhanced cell motility.