CYTOSOLIC AND MITOCHONDRIAL PROTEINS AS POSSIBLE TARGETS OF CYCLOHEXIMIDE EFFECT ON ADRENAL STEROIDOGENESIS

It is well accepted that protein(s) with a short half-life are require d in the pathway leading to steroid synthesis following stimulation by trophic hormones. A correlation between the disappearance of several proteins in different subcellular compartments and the inhibition of s teroid synthesis produced by cycloheximide (CHx) has also been shown. In the present report we describe the effect of CHx in the stimulation of steroid synthesis using a cell-lee assay. Mitochondrial progestero ne (P4) production was studied by recombination of the different subce llular fractions of adrenal zona fasciculata and determined by radioim munoassay. Soluble factors from ACTH-treated adrenals produced a four- fold stimulation of mitochondrial steroidogenesis (3.0 +/- 0.6 vs. 13. 3 +/- 0.5 ng P4/tube for control and ACTH-treated adrenals respectivel y). Mitochondria obtained from CHx-ACTH-treated adrenals fail to respo nd to soluble ACTH-dependent factors. A permeable analogue of choleste rol (22(R)-OH cholesterol) could overcome the inhibition imposed by CI -LU, confirming the role of mitochondrial proteins in intramitochondri al cholesterol transport. The treatment of the adrenals with CHx 10 mi nutes before ACTH administration abolished also the stimulation induce d by the cytosol on control mitochondria (2.6 +/- 0.5 vs. 13.0 +/- 1.0 ng P4/tube for CIFx-ACTH-treated cytosol vs. ACTH-treated cytosol). A rachidonic acid (AA) added to CHx-ACTH-treated cytosol subdued this in hibition (10.3 +/- 1.2 ng P4/tube). CHx treatment had no effect on the stimulation by ACTH of the cAMP-dependent protein kinase. These resul ts indicate the involvement of a cycloheximide-sensitive protein in th e release of AA in adrenal steroidogenesis.