ZRP-1 controls Rho GTPase-mediated actin reorganization by localizing at cell-matrix and cell-cell adhesions.

Focal adhesion protein ZRP-1/TRIP6 has been implicated in actin reorganization and cell motility. The role of ZRP-1, however, remained obscure because previously reported data are often conflicting one another. In the present study, we examined roles of ZRP-1 in HeLa cells. ZRP-1 is localized to the cell-cell contact sites as well as to cell-matrix contact sites in HeLa cells. RNA-interference-mediated depletion of ZRP-1 from HeLa cells revealed that ZRP-1 is essential not only for the formation of stress fibers and assembly of mature focal adhesions, but also for the actin reorganization at cell-cell contact sites and for correct cell-cell adhesion and, thus, for collective cell migration. Impairment of focal adhesions and stress fibers caused by ZRP-1 depletion has been associated with reduced tyrosine phosphorylation of FAK. However, maturation of focal adhesions could not be recovered by expression of active FAK. Interestingly, stress fibers in ZRP-1-depleted cells were ameliorated by exogenous expression of RhoA. We also found that total Rac1 activity is elevated in ZRP-1-depleted cells, resulting in abnormal burst of actin polymerization and dynamic membrane protrusions. Taken together, we conclude that that ZRP-1 plays a crucial role in coupling the cell-matrix/cell-cell-contact signals with Rho GTPase-mediated actin remodeling by localizing at cell-matrix and cell-cell contact sites.