β-arrestin 2-dependent activation of ERK1/2 is required for ADP-induced paxillin phosphorylation at Ser83 and microglia chemotaxis

Microglia play crucial roles in increased inflammation in the central nervous system upon brain injuries and diseases. Extracellular ADP has been reported to induce microglia chemotaxis and membrane ruffle formation through P2Y12 receptor. In this study, we examined the role of ERK1/2 activation in ADP-induced microglia chemotaxis. ADP stimulation increases the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and paxillin phosphorylation at Tyr31 and Ser83. Inhibition of ERK1/2 significantly inhibited paxillin phosphorylation at Ser83 and the retraction of membrane ruffles, causing inefficient chemotaxis. Close examination of dynamics of focal adhesion (FA) formation with green fluorescent protein-paxillin revealed that the disassembly of FAs in U0126-treated cells was significantly impaired. Depletion of beta-Arrestin 2 (beta-Arr2) with short hairpin RNA markedly reduced the phosphorylation of ERK1/2 and Pax/Ser83, indicating that beta-Arr2 is required for ERK1/2 activation upon ADP stimulation. A large fraction of phosphorylated ERK1/2 and beta-Arr2 were translocated and co-localized at focal contacts in the newly forming lamellipodia. Examination of kinetics and rate constant of paxillin formation and disassembly revealed that the phosphorylation of paxillin at Tyr31 by c-Src appears to be involved in adhesion formation upon ADP stimulation while Ser83 required for adhesion disassembly. (c) 2012 Wiley Periodicals, Inc.