LATERAL MOBILITY OF FC-GAMMA-RIIA IS REDUCED BY PROTEIN-KINASE-C ACTIVATION

The lateral mobility of membrane proteins can reflect the extent of va rious protein-protein interactions, Using the fluorescence recovery af ter photobleaching technique, me have studied the lateral mobility of human Fc gamma RIIa and some Fc gamma RIIa mutants expressed in either P388D1 cells, a mouse macrophagelike cell line, or in Chinese hamster ovary (CHO) cells [1]. After treatment with phorbol myristate acetate (PMA), only the Fc gamma RIIa molecules capable of mediating rapid en docytosis of immune complexes exhibited a reduced lateral diffusion co efficient with respect to untreated controls, Wild type Fc gamma RIIa expressed in CHO cells, and nonfunctional Fc gamma RIIa mutants expres sed in P388D1 cells did not show any differences upon PMA treatment, T his finding suggests that protein kinase C activation evokes additiona l protein-protein interactions with the cytoplasmic domain of function al Fc gamma RIIa, which reduced receptor lateral mobility, The identit y of these putative interacting proteins and the nature of the interac tions remain to be elucidated.