D. Lopez et al., Steroidogenic factor-1 mediates cyclic 3 ',5 '-adenosine monophosphate regulation of the high density lipoprotein receptor, ENDOCRINOL, 140(7), 1999, pp. 3034-3044
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.