DIETHYLUMBELLIFERYL PHOSPHATE INHIBITS STEROIDOGENESIS BY INTERFERINGWITH A LONG-LIVED FACTOR ACTING BETWEEN PROTEIN-KINASE-A ACTIVATION AND INDUCTION OF THE STEROIDOGENIC ACUTE REGULATORY PROTEIN (STAR)

Diethylumbelliferyl phosphate (DEUP) is an organophosphate cholesteryl ester hydrolase inhibitor that blocks steroidogenesis mainly by preve nting cholesterol transport into the mitochondria of steroidogenic cel ls. In the present study, we show that DEUP blocks the cAMP-stimulated mitochondrial accumulation of the 30-kDa mitochondrial proteins (rece ntly named steroidogenic acute regulatory StAR proteins) that are beli eved to be the cycloheximide-sensitive factors induced by trophic horm ones and cAMP. Inhibition of mitochondrial StAR accumulation by DEUP i s dose dependent and closely parallels inhibition of progesterone synt hesis. Stimulated lactate production, another cAMP-dependent process i n MA-10 cells, is also inhibited by DEUP, Inhibition of protein kinase A (PKA) action would explain the inhibition of these two unrelated pr ocesses. However, the cytosolic PKA activity of DEUP-treated MA-10 cel ls was normal. Moreover, the activity of purified PKA was unaffected b y DEUP. The inhibition of StAR synthesis was not caused by a direct ef fect of DEUP on the labile proteins since DEUP-treated cells required more than 24 h to recover steroidogenic capacity after DEUP treatment. Further evidence that the synthesis of StAR was not directly affected was obtained using the constitutively active R2C cells. Progesterone synthesis by these cells also involves StAR, but neither StAR synthesi s or steroid synthesis is sensitive to DEUP. Lactate formation in dibu tyryl-cAMP-stimulated R2C cells is, however, sensitive to inhibition b y DEUP. These data can be best explained by DEUP acting on a long-live d factor involved in the cAMP/PKA response pathway, but not involved i n constitutive steroidogenesis.