Compartmentalization of corticotropin-dependent steroidogenic factors in adrenal cortex: evidence for a post-translational cascade in stimulation of the cholesterol side-chain split.

A sensitive cell-free assay was developed for the analysis of corticotropin-dependent factors that stimulate the rate-limiting step of adrenal steroidogenesis. In this assay adrenal post-mitochondrial supernates from corticotropin-stimulated rats caused a 10- to 100-fold increase in the de novo synthesis of pregnenolone and progesterone. A similar stimulation was observed by corresponding fractions from Leydig cells and mouse Y-1 adrenal tumor cells, but not from rat liver. Subcellular fractionation of rat adrenal tissue showed several steroidogenic factors to be present in various compartments. Recombination of them produced highly synergistic effects. The activation of some components could also be demonstrated in vitro, suggesting a cascade of events possibly linking the cAMP-dependent phosphorylation pathway with the rate-limiting step. Cycloheximide prevented the production of these steroidogenic factors in vivo upon stimulation but had no effect in vitro, suggesting a post-translational cascade involved in the activation of the cholesterol side-chain split.