The CYP monooxygenase, CYP2B12, is the first identified skin-specific cytochrome P450 enzyme. It is characterized by high, constitutive expression in an extrahepatic tissue, the sebaceous glands of cutaneous tissues. It is expressed exclusively in a subset of differentiated keratinocytes called sebocytes, as demonstrated by Northern blot analysis, in situ hybridization, and polymerase chain reaction. The onset of its expression coincides with the morphological appearance of sebaceous glands in the neonatal rat. Recombinant CYP2B12 produced in Escherichia coli epoxidizes arachidonic acid to 11,12-and 8,9-epoxyeicosatrienoic acids (80 and 20% of total metabolites, respectively). The identification of arachidonic acid as a substrate for this skin-specific CYP monooxygenase suggests an endogenous function in keratinocytes in the generation of bioactive lipids and intracellular signaling.Mammalian CYP monooxygenases (CYP gene superfamily) oxidatively metabolize small, hydrophobic compounds, including steroids, sterols, fatty acids, fat-soluble vitamins, drugs, and toxins (1). These enzymes are expressed in most mammalian tissues, where they function in the biosynthesis or catabolism of endogenous and exogenous substrates. Members of the CYP2B gene subfamily are often called phenobarbital-inducible cytochrome P450 enzymes because phenobarbital treatment results in transcriptional activation of certain hepatic CYP2B genes (2). A typical CYP2B monooxygenase has 16-hydroxylase activity with androgenic steroids, such as testosterone, and is expressed in the liver and organs such as kidney, lung, and testis (2).CYP2B12 has long been known to be an unusual member of the CYP2B gene subfamily. The gene encoding this enzyme (CYP2B12) was discovered by Atchison and Adesnik (3). Originally called gene 4, it was one of several partial genomic clones that proved the multiplicity of the CYP2B gene subfamily. Gene 4 expression was not detected in the liver or other organs but rather in preputial glands (4), the large, paired sebaceous glands beneath the genital skin in rodents. This finding led Friedberg et al. (4) to isolate and characterize a full-length cDNA corresponding to gene 4 from a preputial gland cDNA library. More than 10 years after its discovery, the novel cytochrome P450 named CYP2B12 is now recognized as the first identified skin-specific cytochrome P450 enzyme.CYP2B12 has remained enigmatic not only for its restricted tissue-specific expression but also because its substrate was not identified. No activity could be demonstrated with preputial gland microsomes using typical CYP2B substrates, such as testosterone, androstenedione, benzphetamine, and ethoxy-, pentoxy-, and benzoyresorufin (2, 4). Our preliminary investigations of a novel CYP2B in mouse skin 1 having sequence homology to rat CYP2B12 renewed interest in this cutaneous P450 enzyme. We report here that CYP2B12 is a gene product unique to sebocytes, a subset of differentiated keratinocytes, and that arachidonate is a substrate for CYP2B12. It is hypothesiz...

Epidermal growth factor (EGF) is a potent epithelial cell mitogen and induces eicosanoid production in many cell types. The present study examined signaling mechanisms for EGF in the renal proximal tubule, where high concentrations of cytochrome P-450 epoxygenase have been reported. In primary cultures of rabbit proximal tubule cells, EGF (30 nM) increased endogenous epoxyeicosatrienoic acid (EET) levels 5.3 +/- 1.4-fold within 10 min (n = 6). In these cells EGF-stimulated [3H]thymidine incorporation was significantly inhibited by the cytochrome P-450 inhibitors ketoconazole or clotrimazole but not by the cyclooxygenase inhibitor indomethacin. In fura 2-loaded proximal tubule cells, EGF caused a concentration-dependent increase in cytosolic Ca2+ concentration ([Ca2+]i), due to Ca2+ influx, which was inhibited by either ketoconazole or SKF-525A but not by indomethacin. Addition of 5,6-EET (0.5 microM) also induced Ca2+ influx in proximal tubule cells, whereas 8,9-11,12-, or 14,15-EET did not. In cells treated with bis(2-amino-5-methylphenoxy)ethane N,N,N',N'-tetraacetic acid tetraacetoxy-methyl ester to chelate [Ca2+]i, EGF-stimulated [3H]thymidine incorporation. These results indicate that EGF increases EET levels in proximal tubule and suggest that 5,6-EET or its metabolites may be a modulator of EGF-induced [Ca2+]i increases and involved in mitogenesis.