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Oxysterol 7-alpha-hydroxylase 1 OKDB#: 2750
 Symbols: CYP7B1 Species: human
 Synonyms: CP7B,  Locus: 8q21.3 in Homo sapiens


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General Comment Early onset of puberty and early ovarian failure in CYP7B1 knockout mice Omoto Y, et al . CYP7B1 is the enzyme responsible for hydroxylation and termination of the estrogenic actions of the androgen metabolite, 5alpha-androstane-3beta, 17beta-diol (3betaAdiol). 3betaAdiol is estrogenic in ERalpha or ERbeta positive cells only if they do not express CYP7B1. In this study we show that female CYP7B1(-/-) mice experience early onset of growth of the uterus and mammary glands and commence estrus cycles 2 days earlier than their wild-type littermates. Adult mammary glands and uteri appear to be under continuous estrogenic stimulation. We conclude that, by cell-specific regulation of the estrogenicity of 3betaAdiol, CYP7B1 performs two major tasks: (i) it allows 3betaAdiol to have growth inhibitory effects through ERbeta and (ii) it permits estradiol-specific activation of estrogen receptors by protection of certain cells from the estrogenic effects of 3betaAdiol. When CYP7B1 is inactivated, 3betaAdiol activates estrogen receptors indiscriminately, and the overall effect is prolonged and inappropriate exposure to estrogen.

NCBI Summary: This gene encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids and other lipids. This endoplasmic reticulum membrane protein catalyzes the first reaction in the cholesterol catabolic pathway of extrahepatic tissues, which converts cholesterol to bile acids. This enzyme likely plays a minor role in total bile acid synthesis, but may also be involved in the development of atherosclerosis, neurosteroid metabolism and sex hormone synthesis.
General function Enzyme
Comment
Cellular localization Mitochondrial
Comment
Ovarian function Follicle development, Steroid metabolism
Comment
Expression regulated by
Comment
Ovarian localization Oocyte, Granulosa
Comment Analysis of mRNA from various tissues has revealed that, in addition to the brain, prostate, and pituitary, CYP7B1 was also expressed in urogenital organs, such as testis and ovary (12). The bile acid synthesis pathway is present and functional in the human ovary. Smith LP et al. BACKGROUND: Bile acids, end products of the pathway for cholesterol elimination, are required for dietary lipid and fat-soluble vitamin absorption and maintain the balance between cholesterol synthesis in the liver and cholesterol excretion. They are composed of a steroid structure and are primarily made in the liver by the oxidation of cholesterol. Cholesterol is also highly abundant in the human ovarian follicle, where it is used in the formation of the sex steroids. METHODOLOGY/PRINCIPAL FINDINGS: Here we describe for the first time evidence that all aspects of the bile acid synthesis pathway are present in the human ovarian follicle, including the enzymes in both the classical and alternative pathways, the nuclear receptors known to regulate the pathway, and the end product bile acids. Furthermore, we provide functional evidence that bile acids are produced by the human follicular granulosa cells in response to cholesterol presence in the culture media. CONCLUSIONS/SIGNIFICANCE: These findings establish a novel pathway present in the human ovarian follicle that has the capacity to compete directly with sex steroid synthesis.
Follicle stages
Comment
Phenotypes
Mutations 1 mutations

Species: mouse
Mutation name: None
type: null mutation
fertility: subfertile
Comment: Early onset of puberty and early ovarian failure in CYP7B1 knockout mice. Omoto Y et al. CYP7B1 is the enzyme responsible for hydroxylation and termination of the estrogenic actions of the androgen metabolite, 5alpha-androstane-3beta, 17beta-diol (3betaAdiol). 3betaAdiol is estrogenic in ERalpha or ERbeta positive cells only if they do not express CYP7B1. In this study we show that female CYP7B1(-/-) mice experience early onset of growth of the uterus and mammary glands and commence estrus cycles 2 days earlier than their wild-type littermates. Adult mammary glands and uteri appear to be under continuous estrogenic stimulation. We conclude that, by cell-specific regulation of the estrogenicity of 3betaAdiol, CYP7B1 performs two major tasks: (i) it allows 3betaAdiol to have growth inhibitory effects through ERbeta and (ii) it permits estradiol-specific activation of estrogen receptors by protection of certain cells from the estrogenic effects of 3betaAdiol. When CYP7B1 is inactivated, 3betaAdiol activates estrogen receptors indiscriminately, and the overall effect is prolonged and inappropriate exposure to estrogen.

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Links
OMIM (Online Mendelian Inheritance in Man: an excellent source of general gene description and genetic information.)
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created: March 4, 2005, 8:07 a.m. by: hsueh   email:
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last update: April 7, 2010, 12:05 p.m. by: hsueh    email:



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