Steroidogenic factor-1 mediates cyclic 3 ',5 '-adenosine monophosphate regulation of the high density lipoprotein receptor

The high density lipoprotein (HDL) receptor mediates the uptake of choleste rol and cholesteryl esters, substrates for steroidogenesis, from an HDL par ticle in the adrenal gland and gonads. We report here that treatment of rat luteal cells with 1 mM (Bu),cAMP for 24 h dramatically induced (118-fold) HDL receptor messenger RNA levels. The rat HDL receptor promoter contains a steroidogenic factor-1 (SF-l)-binding site (SFBd; 5'-TCAAGGCC-3') through which SF-1 protein binds and activates transcription of this gene in both h uman HTB9 bladder carcinoma and mouse Y1 tumor cells, an effect that is enh anced by cAMP. These observations demonstrate that this motif is required f or both basal and cAMP-induced regulation of the HDL receptor gene. Cotrans fection studies in Kin 8 cells, a Y1 cell line resistant to cAMP activation as a result of a mutation in the protein kinase A (PKA) regulatory subunit , showed that a functional PKA is required for cAMP induction of HDL recept or gene transcription. Deleting the activation function-2 domain (amino aci ds 448-461) or mutating Ser(430), a potential consensus phosphorylation sit e for PKA in the SF-1 protein, decreased both basal and cAMP-induced activa tion of the HDL receptor promoter. These data suggest that these regions wi thin the SF-1 protein are required for both basal and cAMP-induced regulati on of the HDL receptor gene. The mediation of cAMP responsiveness of the HD L receptor gene by SF-1 suggests how important this trans-acting factor is in steroid hormone synthesis by assuring that all required elements (substr ate and enzymes) are present when they are needed for maximal steroid produ ction.