Peripheral-type benzodiazepine receptors mediate translocation of cholesterol from outer to inner mitochondrial membranes in adrenocortical cells

• Published in: The Journal of biological chemistry Vol. 265; no. 25; pp. 15015 - 15022
• Main Authors: KRUEGER, K. E, PAPADOPOULOS, V
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 05.09.1990
• Subjects: Adrenal Cortex - metabolism; Adrenocorticotropic Hormone - pharmacology; Animals; benzodiazepines; Biological and medical sciences; Cell Line; Cell physiology; cholesterol; Cholesterol - metabolism; Electron Transport Complex IV - metabolism; Fundamental and applied biological sciences. Psychology; Intracellular Membranes - metabolism; Isoquinolines - pharmacology; Kinetics; Membrane and intracellular transports; mitochondria; Mitochondria - metabolism; Molecular and cellular biology; Monoamine Oxidase - metabolism; Pregnenolone - biosynthesis; Receptors, GABA-A - physiology; Rodentia; Adrenal cortex; Biomembrane; Benzodiazepine receptor; Membrane translocation; Cholesterol; Vertebrata; Mitochondria; Membrane receptor; Regulation(control); Mammalia; Cell line; Mouse; Steroidogenesis; Mechanism of action
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)77217-7

In previous studies we demonstrated that peripheral-type benzodiazepine receptors (PBR) were coupled to steroidogenesis in several adrenocortical and Leydig cell systems (Mukhin, A.G., Papadopoulos, V., Costa, E., and Krueger, K.E. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 9813-9816; Papadopoulos, V., Mukhin, A.G., Costa, E., and Krueger, K.E. (1990) J. Biol. Chem. 265, 3772-3779). The current study elucidates the specific step in the steroid biosynthetic pathway by which PBR mediate the stimulation in steroid hormone production. The adrenocorticotropin (ACTH)-responsive Y-1 mouse adrenocortical cell line was used to compare the mechanisms by which ACTH and PK 11195 (a PBR ligand) stimulate steroidogenesis. The effects of these agents were studied at three stages along the steroid biosynthetic pathway: 1) secretion of 20 alpha OH-progesterone by Y-1 cell cultures; 2) pregnenolone production by isolated mitochondrial fractions; 3) quantities of cholesterol resident in outer and inner mitochondrial membrane fractions. Steroid synthesis stimulated by ACTH was blocked by cycloheximide, an effect documented by other laboratories characterized by an accumulation of mitochondrial cholesterol specifically in the outer membrane. In contrast, PK 11195-stimulated steroidogenesis was not inhibited by cycloheximide, and the magnitude of the stimulation was markedly enhanced when the cells were pretreated with cycloheximide and ACTH. When isolated mitochondria were used, stimulation of pregnenolone production by PK 11195 was largely independent of exogenously supplied cholesterol, indicating that PBR act on cholesterol already situated within the mitochondrial membranes. This phenomenon was found to be the result of a translocation of cholesterol from outer to inner mitochondrial membranes induced by the PBR ligand. These studies therefore suggest that mitochondrial intermembrane cholesterol transport in steroidogenic cells is mediated by a mechanism coupled to PBR.