Focal adhesion formation is associated with secretion of allergic mediators

Adherence of cells to the extracellular matrix via focal adhesions is known to modulate many cellular functions. However, the role of focal adhesions in the regulation of secretion is unclear. To examine this we have used the RBL-2H3 rat mast cell line, in which we and others have observed cytoskeletal rearrangements and increased cell spreading during secretion. All activators of secretion examined, whether acting specifically through or bypassing the IgE-receptor, induced the assembly of focal adhesions, as defined by the localization of vinculin and talin. The extent of focal adhesion formation correlated with the extent of secretion and the time course of secretion also correlated with that of the assembly of focal adhesions. To examine the mechanism by which focal adhesion formation occurred, the protein kinase C inhibitor bisindolylmaleimide was used. Bisindolylmaleimide caused complete inhibition of both secretion and focal adhesion formation induced by antigen or the calcium ionophore A23187. Although PMA did not induce secretion, it induced focal adhesion assembly which was inhibited by bisindolylmaleimide. The inhibitor had no effect on secretion or focal adhesion formation induced by the ATP analogue, ATP gamma S in permeabilized cells, indicating ATP gamma S acts after the activation of protein kinase C in the secretory pathway. These data provide novel evidence that the formation of focal adhesions may have a role in the process of secretion from mast cells.