Brefeldin A-inhibited guanine nucleotide-exchange protein (BIG)2 activates ADP-ribosylation factors, similar to 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 beta 1 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 beta 1-extracellular matrix interactions on actin function and cell translocation, were increased. Treatment of HeLa cells with BIG2 siRNA resulted in perinuclear accumulation of integrin beta 1 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 beta 1 action and actin functions.
