The effect of recombinant interleukin 4 upon protein kinase activities associated with murine and human B lymphocyte plasma membranes

Exposure of plasma membranes isolated from high density resting murine B cells to recombinant IL-4 in the presence of gamma-[32P]-ATP promoted phosphorylation of a protein of Mr = 42,000. The 42 Kd protein kinase substrate could be detected in membranes prepared from low density B cells following a 24 h culture with lipopolysaccharide, but not in membranes prepared from B cells exposed to LPS for 48 h. Treatment of the cells with LPS resulted in the appearance of a number of new membrane-associated phosphoproteins. Treatment with the cytokine also resulted in the disappearance of a protein kinase substrate of Mr = 30,000 from phosphoprotein profiles of membranes prepared from cells exposed to LPS for 24 h. The 42 Kd structure appears to be a protein kinase substrate rather than possessing intrinsic phosphotransferase activity as judged from experiments employing 8-azido-gamma-[32P]-ATP as a photoaffinity label. No 42 Kd species was detectable using this reagent. Experiments employing identical protocols failed to reveal any enhanced or diminished phosphorylation of membrane-associated proteins in human peripheral blood B cells or in human B lymphoma cell lines.