CONSTITUTIVE STEROIDOGENESIS DOES NOT REQUIRE THE ACTIONS OF CAMP ON CHOLESTERYL ESTER HYDROLYSIS OR INTERNALIZATION OF PLASMA-MEMBRANE CHOLESTEROL

The R2C Leydig tumor cells demonstrate constitutive steroidogenesis as well as the constitutive production of the steroidogenic acute regula tory peptide (StAR). Since the introduction of StAR into cells does no t by itself reproduce the steroidogenic response of cAMP, the present studies were designed to determine whether processes normally stimulat ed by cAMP in responsive cells were maximally, constitutively expresse d in the R2C cells. Measurements of cholesteryl ester hydrolytic rate and plasma membrane cholesterol internalization revealed that both pro cesses are stimulated by dibutyryl-cAMP in R2C cells. The effect of cA MP on these processes was of the same magnitude as that detected in ho rmonally responsive cells. Thus, in R2C cells the unstimulated basal r ate of either process was sufficient to maintain maximal stimulation o f steroidogenesis.