Published online 7 September 2004. doi:10.1083/jcb.200404024
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 166, Number 6, 901-912
Phosphorylation of actopaxin regulates cell spreading and migration
Dominic M. Clarke,
Michael C. Brown,
David P. LaLonde, and
Christopher E. Turner
Department of Cell Biology and Developmental Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
Address correspondence to Christopher E. Turner, Dept. of Cell and Developmental Biology, State University of New York Upstate Medical University, 750 East Adams St., Syracuse, NY 13210. Tel.: (315) 464-8598. Fax: (315) 464-8535. email: turnerce{at}upstate.edu
Actopaxin is an actin and paxillin binding protein that localizes to focal adhesions. It regulates cell spreading and is phosphorylated during mitosis. Herein, we identify a role for actopaxin phosphorylation in cell spreading and migration. Stable clones of U2OS cells expressing actopaxin wild-type (WT), nonphosphorylatable, and phosphomimetic mutants were developed to evaluate actopaxin function. All proteins targeted to focal adhesions, however the nonphosphorylatable mutant inhibited spreading whereas the phosphomimetic mutant cells spread more efficiently than WT cells. Endogenous and WT actopaxin, but not the nonphosphorylatable mutant, were phosphorylated in vivo during cell adhesion/spreading. Expression of the nonphosphorylatable actopaxin mutant significantly reduced cell migration, whereas expression of the phosphomimetic increased cell migration in scrape wound and Boyden chamber migration assays. In vitro kinase assays demonstrate that extracellular signal-regulated protein kinase phosphorylates actopaxin, and treatment of U2OS cells with the MEK1 inhibitor UO126 inhibited adhesion-induced phosphorylation of actopaxin and also inhibited cell migration.
Key Words: phosphorylation; migration; adhesion; focal adhesions; Erk
Abbreviations used in this paper: CH, calponin homology; DN MEK1; dominant-negative MEK1; Erk, extracellular signal-regulated protein kinase; IGF, insulin-like growth factor; ILK, integrin-linked kinase; MLCK, myosin light chain kinase; PAK, p21-activated kinase; PBS, paxillin binding subdomain; Quint, quintuple; WT, wild-type.

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