Specific association of phosphatidylinositol 3-kinase with the protooncogene product Cbl in Fc gamma receptor signaling

A tyrosine-phosphorylated protein with a molecular mass of 115 kDa was reported to be tightly associated with the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase, when the enzyme was essentially activated upon ligand engagement of Fc gamma receptors (Fc gamma R) leading to engulfment of IgG-coated erythrocytes by phagocytes [Ninomiya et al, (1994) J. Biol. Chem, 269, 22732-22737]. Here, the 115-kDa protein is identified as the product of human c-cbl protooncogene. Crosslinking of Fc gamma RII on the surface of THP-1 cells triggered (a) prominent tyrosine phosphorylation of Chl, (b) activation of PI 3-kinase that was immunoprecipitated with the anti-Cbl or the anti-phosphotyrosine antibody, and (c) specific association of Cbl with p85. Thus, Cbl functions in phagocytes as a result of its association with PI 3-kinase in response to Fc gamma R ligation.