PHOSPHORYLATION OF HS1, GAP-ASSOCIATED P190 AND A NOVEL GAP-ASSOCIATED P60 PROTEIN BY CROSS-LINKING OF FC-GAMMA-RIIIA

Human Fc gamma receptor IIIA (hFc gamma RIIIA) cDNA was introduced int o mouse macrophage/monocyte cell line P388D1, and several stable cell clones expressing hFc gamma RIIIA were isolated, This facilitated the study of the biological function of Fc gamma RIIIA in monocytes/macrop hages. The cloned cells showed the high phagocytic activity mediated b y hFc gamma RIIIA, while the original P388D1 cells did not, In order t o examine the phosphorylation of proteins involved in hFc gamma RIIIA signal transduction, these receptors were stimulated by cross-linking, The cross-linking of hFc gamma RIIIA induced a rapid increase in tyro sine phosphorylation of several proteins, including PLC-gamma 1, Syk, HS1, and p21(ras) GAP-associated p190 and p60 proteins, Immunoblotting with a polyclonal antibody specific for the GAP-associated p62 protei n, which was originally found in fibroblasts and is homologous with an RNA-binding protein, revealed that the p60 phosphorylated after cross -linking of hFc gamma RIIIA seemed to represent a novel GAP-associated protein unrelated to the known GAP-associated p62 protein, which was also present in the P388D1 cells.