Lateral mobility of FcγRIIa is reduced by protein kinase C activation

The lateral mobility of membrane proteins can reflect the extent of various protein-protein interactions. Using the fluorescence recovery after photobleaching technique, we have studied the lateral mobility of human FcγRIIa and some FcγRIIa 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 FcγRIIa molecules capable of mediating rapid endocytosis of immune complexes exhibited a reduced lateral diffusion coefficient with respect to untreated controls. Wild type FcγRIIa expressed in CHO cells, and nonfunctional FcγRIIa mutants expressed in P388D1 cells did not show any differences upon PMA treatment. This finding suggests that protein kinase C activation evokes additional protein-protein interactions with the cytoplasmic domain of functional FcγRIIa, which reduced receptor lateral mobility. The identity of these putative interacting proteins and the nature of the interactions remain to be elucidated.