Skin is the largest body organ forming a metabolically active barrier between external and internal environments. The
metabolic barrier is composed of cytochromes P450 (CYPs) that regulate its homeostasis through activation or inactivation of
biologically relevant molecules. In this review we focus our attention on local steroidogenic and secosteroidogenic systems in relation to
skin cancer, e.g., prevention, attenuation of tumor progression and therapy. The local steroidogenic system is composed of locally
expressed CYPs involved in local production of androgens, estrogens, gluco- and mineralo-corticosteroids from cholesterol (initiated by
CYP11A1) or from steroid precursors delivered to the skin, and of their metabolism and/or inactivation. Cutaneous 7-hydroxylases
(CYP7A1, CYP7B1 and CYP39) potentially can produce 7-hydroxy/oxy-steroids/sterols with modifying effects on local tumorigenesis.
CYP11A1 also transforms 7-dehydrocholesterol (7DHC)→22(OH)7DHC→20,22(OH)2-7DHC→7-dehydropregnenolone, which can be
further metabolized to other 5,7- steroidal dienes. These 5,7-dienal intermediates are converted by ultraviolet radiation B (UVB) into
secosteroids which show pro-differentiation and anti-cancer properties. Finally, the skin is the site of activation of vitamin D3 through
two alternative pathways. The classical one involves sequential hydroxylation at positions 25 and 1 to produce active 1,25(OH)2D3,
which is further inactivated through hydroxylation at C24. The novel pathway is initiated by CYP11A1 with predominant production of
20(OH)D3 which is further metabolized to biologically active but non-calcemic D3-hydroxyderivatives. Classical and non-classical
(novel) vitamin D analogs show pro-differentiation, anti-proliferative and anticancer properties. In addition, melatonin is metabolized by
local CYPs. In conclusion cutaneously expressed CYPs have significant effects on skin physiology and pathology trough regulation of its
CYP, melatonin, secosteroids, skin cancer, steroids, vitamin D.
Department of Pathology and Laboratory Medicine, University of Tennessee Health Science Center, 930 Madison Avenue, RM525, Memphis, TN 38163.