Receptor tyrosine kinase stimulates cell-matrix adhesion by phosphatidylinositol 3 kinase and phospholipase C-gamma 1 pathways

Receptor tyrosine kinases are known to be important in growth and differentiation. We have recently found that c-kit, the tyrosine kinase receptor for steel factor, also regulates cell-matrix adhesion. Because Steel factor helps regulate cell migration and localization, this may be an important biologic function. Integrin adhesiveness is regulated within minutes by c-kit. The signaling pathways for tyrosine kinase stimulation of integrin adhesiveness and their relation to pathways that regulate growth and differentiation over much longer time periods remain uncharacterized. We have studied the effector pathways by which receptor tyrosine kinases regulate cell-matrix adhesion using wild-type and mutant forms of the platelet-derived growth factor (PDGF) receptor, which is closely related to c-kit. The PDGF receptor expressed in mast cells is as potent as c-kit in stimulating adhesion to fibronectin. We show that induction of adhesion is regulated through two independent pathways of phosphatidylinositol 3 kinase (PI3K) and phospholipase C- gamma 1 (PLC gamma)-protein kinase C by elimination of autophosphorylation sites required for activation of PI3K and PLC gamma or in combination with downregulation of protein kinase C or wortmannin. By contrast, a receptor mutated in both the PI3K and PLC gamma association sites can still stimulate mast cell growth, indicating a crucial role of these effector molecules in regulating adhesion rather than cell growth.