Abnormal behavior of protein kinase C in the human myeloma cell line, RPMI 8226.

Protein kinase C activity of the human myeloma cell line, RPMI 8226, was studied after prepurification on DEAE-cellulose. The total protein kinase activity, eluted at 0.12 M NaCl, was 493 nmol/min/10(10) cells, but 38% was associated with membranes. The lipid dependence of cytosolic and membrane activities was only 52% and 21%, respectively. This activity increased with time, to as much as 200% for the membrane fraction after 7 days, whereas lipid dependence and the PDBu binding properties were lost. This modified activity was not due to the extinction of a copurifying endogenous inhibitor nor to classical PKC proteolysis. TPA-treatment of these cels is accompanied by a rapid, selective and complete loss of lipid-dependent activity of the cytosol, thus benefiting co-migrating lipid independent activity, with no membrane fraction recovery or PKM formation.