Endocrine Abstracts

Human skin is a target tissue for circulating androgens released from the adrenal glands and gonads but local steroid production may also occur in human skin. StAR is a cholesterol transporter protein that controls the rate-limiting step in steroid synthesis and is regulated by steroidogenic factor (SF-1) in the adrenal glands. We have demonstrated the expression of StAR mRNA by RT-PCR in primary dermal papilla cells and in the immortalised human keratinocyte cell line HaCaT. StAR transcription in HaCaT cells was investigated using deletion and mutant constructs of the StAR-promoter linked to a luciferase reporter gene. Basal activity of a -1300bp StAR promoter construct was 11-fold (P<0.001) higher than the promoterless control and this significantly increased to 29-fold (P<0.001) with a truncated -235bp StAR construct. EGF (10nM) significantly stimulated StAR transcription (-1300bp construct, 1.5-fold, P<0.01, -235bp construct, 2-fold, P<0.001) while 8-Br-cAMP (0.5mM) only stimulated the -235bp construct (1.7-fold, P<0.05). Mutation of the SF-1 or Sp1 binding sites in the -235bp StAR promoter reduced native promoter activity to 57% (P<0.001) and 69% (P<0.001), respectively. Mutating both the SF-1 and Sp1 binding sites resulted in even greater inhibition of basal promoter activity (12%, P<0.001). EGF and 8-Br-cAMP stimulation of the 235bp promoter was also obliterated in the presence of the double mutant. Our investigations demonstrate for the first time that StAR protein mRNA is expressed in human epidermal keratinocytes and that both SF-1 and Sp1 binding sites are necessary for basal and full transcriptional responsiveness to EGF and 8-Br-cAMP. The regulation of the StAR protein gene by EGF is a novel finding and the expression of StAR in skin further supports the hypothesis that human skin is a steroidogenic organ. (Supported by a SBRLSMD PhD studentship)