Inducible expression of protein kinase Calpha suppresses steroidogenesis in Y-1 adrenocortical cells.

We have previously shown that protein kinase C (PKC) suppresses steroidogenesis in Y-1 adrenocortical cells. To ask directly if the PKCalpha isoform mediates this suppression, we have developed Y-1 cell lines in which PKCalpha is expressed from a tetracycline-regulated promoter. Induction of PKCalpha expression in these cell lines results in decreased P450 cholesterol side-chain cleavage enzyme (P450-SCC) activity as judged by the conversion of hydroxycholesterol to pregnenolone. Transcription of a P450-SCC promoter-luciferase construct is also reduced when PKCalpha expression is increased. However, expression of PKCalpha has no effect on 8-bromo-cAMP induction of steroidogenesis, indicating that these pathways function independently to regulate steroidogenesis. To determine the relationship between endogenous PKC activity and steroidogenesis, we examined 12 Y-1 subclones that were isolated by limited dilution cloning. In each of these subclones, steroid production correlates inversely with total PKC activity and with the expression of PKCalpha but not PKCepsilon or PKCzeta. These studies define for the first time the role of a specific PKC isoform (PKCalpha) in regulating steroidogenesis and P450-SCC activity in adrenocortical cells.