Control of low density lipoprotein receptor gene expression in steroidogenic cells

Low density lipoprotein (LDL)-carried cholesterol is a primary substrate for steroid hormone synthesis by luteinized human granulosa cells. Chorionic gonadotropin and 8-bromo-cAMP both increase LDL receptor levels in granulosa cells by stimulating accumulation of the receptor mRNA. LDL and 25-hydroxycholesterol reduce LDL receptor expression, but this suppressive effect is partially overcome by 8-bromo-cAMP. Using fusion gene constructs containing the LDL receptor gene promoter transfected into JEG-3 cells, a cyclic AMP responsive enhancer could not be identified in the LDL receptor gene upstream promoter in transfection studies. We suggest that the LDL receptor gene in human steroidogenic cells is under negative control by a sterol effector, but that a cyclic AMP triggered process overcomes, to some extent, the sterol-mediated suppression. The detailed mechanisms by which sterol and cyclic AMP modulate LDL receptor gene expression remain to be elucidated.Key words: low density lipoproteins, low density lipoprotein receptors, cholesterol, steroidogenesis, gonadotropins.