Integrin alpha v beta 3 differentially regulates adhesive and phagocytic functions of the fibronectin receptor alpha 5 beta 1

The plasma protein fibronectin is an important opsonin in wound repair and host defense. To better understand the process of fibronectin-mediated phagocytosis, we have transfected K562 cells, which endogenously express alpha 5 beta 1, with alpha v beta 3. In these transfectants, antibodies to alpha v beta 3 block phagocytosis of fibronectin-opsonized beads completely, even though half the ingestion occurs through endogenous alpha 5 beta 1 receptors. alpha 5 beta 1-mediated adhesion to fibronectin-coated surfaces is unaffected by alpha v beta 3 ligation. Neither alpha v beta 5 nor alpha M beta 2 ligation affects alpha 5 beta 1 phagocytic function in transfectants expressing these receptors. Pharmacologic data suggest that alpha v beta 3 ligation suppresses the phagocytic competence of high affinity alpha 5 beta 1 receptors through a signal transduction pathway, perhaps involving protein kinase C. In addition to its significance for phagocytosis, alpha v beta 3 regulation of alpha 5 beta 1 function may be significant for its roles in cell migration, metastasis, and angiogenesis.