Protein kinase C in adrenal cells: possible role in regulation of steroid synthesis

Abstract

Y-1 adrenal tumor cells and rat fasciculata cells were shown to possess an enzyme with the properties of protein kinase C. Activity was stimulated by Ca 2+ and phospholipid (specially phosphatidylserine). Enzyme activity was stimulated by addition of phorbol ester to cell homogenate (ED 50 10 nM) and inhibited by trifluoperazine (ID 50 10 μM). ACTH and cyclic AMP added to Y-1 cells increased the activity of protein kinase C. Dose-response curves with ACTH showed that the hormone was effective in stimulating protein kinase C at lower concentrations than those required to increase steroid synthesis. When phorbol ester was added to Y-1 cells, total kinase C activity was diminished. Neither phorbol ester nor ACTH causes redistribution of protein kinase C between membranes and cytosol. Phorbol ester also stimulates steroid production by Y-1 cells. Protein kinase C phosphorylates 5 protein in Y-1 cells (67, 61, 32, 16 and < 14.4 kDa). Puromycin and cyclohemixide increase the activity of protein kinase C in adrenal cells. It is concluded that protein kinase C may play an ancillary role in regulation of adrenal steroid synthesis but does not mediate the classical steroidogenic response that results from activation of adenylate cyclase by ACTH.