A Novel Cytochrome P450 Expressed Primarily in Brain
Journal of Biological Chemistry
hct-1 (hippocampal transcript) was detected in a differential screen of a rat hippocampal cDNA library. Expression of hct-1 was enriched in the formation but was also detected in rat liver and kidney, though at much lower levels; expression was barely detectable in testis, ovary, and adrenal. In liver, unlike brain, expression was sexually dimorphic; hepatic expression was greatly reduced in female rats. In mouse, brain expression was widespread, with the highest levels being detected in corpus
... detected in corpus callosum; only low levels were detected in liver. Sequence analysis of rat and mouse hct-1 cDNAs revealed extensive homologies with cytochrome P450s (CYPs), a diverse family of heme-binding monooxygenases that metabolize a range of substrates including steroids, fatty acids, and xenobiotics. Among the CYPs, hct-1 is most similar (39% at the amino acid sequence) to cholesterol 7␣-hydroxylase (CYP7) and contains a postulated steroidogenic domain present in other steroidmetabolizing CYPs but clearly represents a type of CYP not previously reported. Genomic Southern analysis suggests that a single gene corresponding to hct-1 is present in mouse, rat, and human. hct-1 is unusual in that, unlike all other CYPs described, the primary site of expression is in the brain. Similarity to CYP7 and other steroid-metabolizing CYPs may argue that hct-1 (CYP7B) plays a role in steroid metabolism in brain, notable because of the documented ability of brain-derived steroids (neurosteroids) to modulate cognitive function in vivo. Cytochromes P450, a diverse group of heme-containing monooxygenases (termed CYPs) 1 (for nomenclature see Nelson et al. (1)), catalyze a variety of oxidative conversions, notably of steroids but also of fatty acids and xenobiotics. Though most abundantly expressed in the testis, ovary, placenta, adrenal, and liver, the brain is a further site of CYP expression (2-6).