Both adhesion to immobilized vitronectin and FcepsilonRI cross-linking cause enhanced focal adhesion kinase phosphorylation in murine mast cells.

Murine mast cells adhere spontaneously to plate-bound vitronectin (VNPB) via alphav-containing integrins, and this adhesive interaction results in an augmented interleukin-3 (IL-3)-dependent mast-cell proliferation. In this report we demonstrate that the activation of murine mast cells through alphav-integrin, as well as through the high affinity immunoglobulin E (IgE) receptor (FcepsilonRI), results in enhanced tyrosine phosphorylation of focal adhesion kinase (FAK), a cytoplasmic protein tyrosine kinase involved in mitogenic and oncogenic signal transduction. While mast cell adhesion to VNPB resulted in enhanced FAK phosphorylation, treatment with soluble vitronectin (VNSOL) failed to do so. Spontaneous mast cell adhesion to entactin (EN) did not induce tyrosine phosphorylation of FAK, demonstrating that not all adhesive interactions lead to the same sequence of biochemical events. Because FAK has intrinsic tyrosine kinase activity, we examined whether activating mast cells via alphav-integrins, or via FcepsilonRI-cross-linking stimulated the in vitro kinase activity of FAK. Both pathways were found independently to activate FAK in mast cells and together appeared additive. Protein kinase C depletion in mast cells and calcium depletion in the medium caused decreased tyrosine phosphorylation of FAK, indicating that optimal tyrosine phosphorylation of FAK is regulated by both pathways. These data are consistent with the conclusion that the tyrosine phosphorylation of FAK represents at least one example of a point of convergence in the intracellular tyrosine phosphorylation cascades induced by alphav integrin-and FcepsilonRI-mediated signal transduction pathways in mast cells.