Brefeldin A-inhibited ADP-ribosylation factor activator BIG2 regulates cell migration via integrin β1 cycling and actin remodeling

Brefeldin A-inhibited guanine nucleotide-exchange protein (BIG)2 activates ADP-ribosylation factors, ∼20-kDa GTPase proteins critical for continuity of intracellular vesicular trafficking by accelerating the replacement of ADP-ribosylation factor-bound GDP with GTP. Mechanisms of additional BIG2 function(s) are less clear. Here, the participation of BIG2 in integrin β1 cycling through actin dynamics during cell migration was identified using small interfering RNA (siRNA) and difference gel electrophoresis analyses. After a 72-h incubation with BIG2 siRNA, levels of cytosolic Arp2, Arp3, cofilin-1, phosphocofilin, vinculin, and Grb2, known to be involved in the effects of integrin β1-extracellular matrix interactions on actin function and cell translocation, were increased. Treatment of HeLa cells with BIG2 siRNA resulted in perinuclear accumulation of integrin β1 and its delayed return to the cell surface. Motility of BIG2-depleted cells was simultaneously decreased, as were actin-based membrane protrusions and accumulations of Arp2, Arp3, cofilin, and phosphocofilin at the leading edges of migrating cells, in wound-healing assays. Taken together, these data reveal a mechanism(s) through which BIG2 may coordinate actin cytoskeleton mechanics and membrane traffic in cell migration via integrin β1 action and actin functions.