Rose K, Allan A, Gauldie S, Stapleton G, Dobbie L, Dott K, Martin C, Wang L, Hedlund E, Seckl J R, Gustafsson J A, Lathe R
Centre for Genome Research and Centre for Neuroscience, University of Edinburgh, King's Buildings, Edinburgh EH9 3JQ, United Kingdom.
J Biol Chem. 2001 Jun 29;276(26):23937-44. doi: 10.1074/jbc.M011564200. Epub 2001 Apr 4.
The major adrenal steroid dehydroepiandrosterone (DHEA) enhances memory and immune function but has no known dedicated receptor; local metabolism may govern its activity. We described a cytochrome P450 expressed in brain and other tissues, CYP7B, that catalyzes the 7alpha-hydroxylation of oxysterols and 3beta-hydroxysteroids including DHEA. We report here that CYP7B mRNA and 7alpha-hydroxylation activity are widespread in rat tissues. However, steroids related to DHEA are reported to be modified at positions other than 7alpha, exemplified by prominent 6alpha-hydroxylation of 5alpha-androstane-3beta,17beta-diol (A/anediol) in some rodent tissues including brain. To determine whether CYP7B is responsible for these and other activities we disrupted the mouse Cyp7b gene by targeted insertion of an IRES-lacZ reporter cassette, placing reporter enzyme activity (beta-galactosidase) under Cyp7b promoter control. In heterozygous mouse brain, chromogenic detection of reporter activity was strikingly restricted to the dentate gyrus. Staining did not exactly reproduce the in situ hybridization expression pattern; post-transcriptional control is inferred. Lower level staining was detected in cerebellum, liver, and kidney, and which largely paralleled mRNA distribution. Liver and kidney expression was sexually dimorphic. Mice homozygous for the insertion are viable and superficially normal, but ex vivo metabolism of DHEA to 7alpha-hydroxy-DHEA was abolished in brain, spleen, thymus, heart, lung, prostate, uterus, and mammary gland; lower abundance metabolites were also eliminated. 7alpha-Hydroxylation of 25-hydroxycholesterol and related substrates was also abolished, as was presumed 6alpha-hydroxylation of A/anediol. These different enzyme activities therefore derive from the Cyp7b gene. CYP7B is thus a major extrahepatic steroid and oxysterol hydroxylase and provides the predominant route for local metabolism of DHEA and related molecules in brain and other tissues.
主要的肾上腺类固醇脱氢表雄酮（DHEA）可增强记忆和免疫功能，但目前尚未发现其特定的受体；局部代谢可能调控其活性。我们曾描述过一种在脑和其他组织中表达的细胞色素P450，即CYP7B，它可催化氧甾醇和3β-羟基类固醇（包括DHEA）的7α-羟基化反应。我们在此报告，CYP7B mRNA和7α-羟基化活性在大鼠组织中广泛存在。然而，据报道，与DHEA相关的类固醇在7α以外的位置也会发生修饰，例如在包括脑在内的一些啮齿动物组织中，5α-雄烷-3β,17β-二醇（A/二醇）会发生显著的6α-羟基化。为了确定CYP7B是否负责这些及其他活性，我们通过靶向插入IRES-lacZ报告基因盒破坏了小鼠的Cyp7b基因，使报告酶活性（β-半乳糖苷酶）受Cyp7b启动子控制。在杂合子小鼠脑中，报告活性的显色检测显著局限于齿状回。染色结果与原位杂交表达模式并不完全一致；推测存在转录后调控。在小脑、肝脏和肾脏中检测到较低水平的染色，且在很大程度上与mRNA分布平行。肝脏和肾脏的表达存在性别差异。插入纯合子的小鼠是存活的且表面上正常，但在脑、脾、胸腺、心脏、肺、前列腺、子宫和乳腺中，DHEA向7α-羟基-DHEA的体外代谢被消除；丰度较低的代谢产物也被消除。25-羟基胆固醇及相关底物的7α-羟基化也被消除，A/二醇的推测6α-羟基化同样如此。因此，这些不同的酶活性均源自Cyp7b基因。CYP7B thus a major extrahepatic steroid and oxysterol hydroxylase and provides the predominant route for local metabolism of DHEA and related molecules in brain and other tissues.因此，CYP7B是一种主要的肝外类固醇和氧甾醇羟化酶，为脑和其他组织中DHEA及相关分子的局部代谢提供了主要途径。
