Angiotensin II promotes selective uptake of high density lipoprotein cholesterol esters in bovine adrenal glomerulosa and human adrenocortical carcinoma cells through induction of scavenger receptor class B type I

Angiotensin II is one of the main physiological regulators of aldosterone b iosynthesis in the zona glomerulosa of the adrenal cortex. The hormone stim ulates intracellular cholesterol mobilization to the mitochondrion for ster oid biosynthesis. Here we have examined whether angiotensin II also modulat es exogenous lipoprotein cholesterol ester supply to the steroidogenic mach inery and whether this control is exerted on the selective transport of hig h density lipoprotein-derived cholesterol ester to intracellular lipid drop lets through the scavenger receptor class B type I. In bovine adrenal glome rulosa and human NCI H295R adrenocortical carcinoma cells, high density lip oprotein stimulated steroid production. Angiotensin II pretreatment for 24 h potentiated this response. Fluorescence microscopy of cellular uptake of reconstituted high density lipoprotein containing a fluorescent cholesterol ester revealed an initial, time-dependent narrow labeling of the cell memb rane followed by an intense accumulation of the fluorescent cholesterol est er within lipid droplets. At all time points, labeling was more pronounced in cells that had been treated for 24 h with angiotensin III. Fluorescence incorporation into cells was prevented by a monoclonal antibody directed ag ainst apolipoprotein A-I. Upon quantitative fluorometric determination, cho lesterol ester uptake in angiotensin H-treated bovine cells was increased t o 175 +/- 15% of controls after 2 h and to 260 +/- 10% after 4 h of exposur e to fluorescent high density lipoprotein. The amount of scavenger receptor class B type I protein detected in cells treated with angiotensin II for 2 4 h reached 203 +/- 12% of that measured in control cells (n = 3, P < 0.01) . In contrast, low density lipoprotein receptors were only minimally affect ed by angiotensin II treatment. This increase in scavenger receptor class B type I protein was associated with a 3-fold induction of scavenger recepto r class B type I mRNA, which could be prevented by actinomycin D but not by cycloheximide. Similar results were obtained in the human adenocarcinoma c ell line H295R. These observations show that angiotensin II regulates the s cavenger receptor class B type I-mediated selective transport of lipoprotei n cholesterol ester across the cell membrane as a major source of precursor for mineralocorticoid biosynthesis in both human and bovine adrenal cells.