Steroidogenesis in the human skin: 21-hydroxylation in cultured keratinocytes

We have evaluated the metabolism of radiolabeled progesterone (P) by the mi crosomal fraction isolated from HaCaT keratinocytes. P was widely metaboliz ed to different compounds that included DOC (5-7% conversion) thus demonstr ated 21-hydroxylase (21-OHase) activity, a key step in adrenal synthesis of gluco- and mineralocorticoids. However, RT-PCR amplification for the CYPc2 1 transcript of the corresponding gene showed no evidence for gene expressi on in HaCaT cells suggesting that the 21-OHase enzyme present in keratinocy tes is different from that described in adrenal gland. Further characteriza tion showed that whereas estradiol stimulated markedly P metabolism by HaCa T microsomes, with generation of new unidentified compounds, Lineweaver-Bur k analysis of keratinocyte 21-OHase activity showed that the K-m and V-max were unaffected by estrogen. The apparent K-m was 0.6 muM without estradiol and 0.7 muM with estradiol, while the respective V-max values were 60 and 76 nmol/l/min. To conclude, we found extensive metabolism of P in human ker atinocytes, we also provide the first demonstration of 21-OHase activity in this cell system and further showed that it is coded by a gene different f rom the adrenal CYPc21. (C) 2001 Elsevier Science Ltd. All rights reserved.