Free cholesterol induces activation but not translocation of protein kinase C in cultured ascites tumour cells

Abstract

Ascites tumour cells, cultivated in a serum replacement medium with low mitogenic activity supplemented with free cholesterol or cholesterol complexed to digitonine, were used to study protein kinase C (PKC) activation and its translocation from the cytosol to the membrane compartment. Activity of partially purified PKC was assessed by the Ca 2+/phospholipid-dependent phosphorylation of histone as substrate. Straurosporine-sensitive PKC activity was increased by a factor of about three in the membrane compartment as the result of cholesterol supplementation with about 90% of total activity in the membrane, and the remaining 10% in the cytosolic function. A translocation of enzyme mass from the cytosol to the membrane compartment was not induced under these conditions, as documented by the enzyme-linked immuno adsorbent assay using a monoclonal anti-PKC antibody, In cells cultivated in the presence of the cholesterol-digitonide complex PKC activation was not observed, suggesting an inadequate utilization of cholesterol as membrane constituent.