Rodriguez-Antona Cristina, Axelson Magnus, Otter Charlotta, Rane Anders, Ingelman-Sundberg Magnus
Division of Molecular Toxicology, Institute of Environmental Medicine, Karolinska Institute, 17177 Stockholm.
J Biol Chem. 2005 Aug 5;280(31):28324-31. doi: 10.1074/jbc.M502309200. Epub 2005 Jun 2.
The cytochrome P450 3A7 (CYP3A7) is the most abundant CYP in human liver during fetal development and first months of postnatal age, playing an important role in the metabolism of endogenous hormones, drugs, differentiation factors, and potentially toxic and teratogenic substrates. Here we describe and characterize a novel enzyme, CYP3A7.1L, encompassing the CYP3A7.1 protein with the last four carboxyl-terminal amino acids replaced by a unique sequence of 36 amino acids, generated by splicing of CYP3A7 with CYP3AP1 RNA. The corresponding CYP3A7-3AP1 mRNA had a significant expression in liver, kidney, and gastrointestinal tract, and its presence was found to be tissue-specific and dependent on the developmental stage. Heterologous expression in yeast revealed that CYP3A7.1L was a functional enzyme with a specific activity similar to that of CYP3A7.1 and, in some conditions, a different hydroxylation specificity than CYP3A7.1 using dehydroepiandrosterone as a substrate. CYP3A7.1L was found to be polymorphic due to a mutation at position -6 of the first splicing site of CYP3AP1 (CYP3A7_39256T-->A), which abrogates the pseudogene splicing. This polymorphism had pronounced interethnic differences and was in linkage disequilibrium with other functional polymorphisms described in the CYP3A locus: CYP3A72 and CYP3A51. Therefore, the resulting CYP3A haplotypes express different sets of enzymes within the population. In conclusion, a novel mechanism, consisting of the splicing of the pseudogene CYP3AP1 to CYP3A7, causes the formation of the novel CYP3A7.1L having a different tissue distribution and functional properties than the parent CYP3A7 enzyme, with possible developmental, physiological, and toxicological consequences.
细胞色素P450 3A7（CYP3A7）是胎儿发育期间及出生后最初几个月人肝脏中含量最丰富的细胞色素P450，在内源性激素、药物、分化因子以及潜在有毒和致畸底物的代谢中发挥重要作用。在此，我们描述并鉴定了一种新型酶CYP3A7.1L，它包含CYP3A7.1蛋白，其羧基末端最后四个氨基酸被由CYP3A7与CYP3AP1 RNA剪接产生的独特36个氨基酸序列所取代。相应的CYP3A7 - 3AP1 mRNA在肝脏、肾脏和胃肠道中有显著表达，并且发现其存在具有组织特异性且依赖于发育阶段。在酵母中的异源表达表明，CYP3A7.1L是一种功能酶，其比活性与CYP3A7.1相似，并且在某些条件下，以脱氢表雄酮为底物时，其羟基化特异性与CYP3A7.1不同。由于CYP3AP1第一个剪接位点 - 6位置的突变（CYP3A7_39256T→A），导致假基因剪接缺失，CYP3A7.1L被发现具有多态性。这种多态性存在明显的种族间差异，并且与CYP3A基因座中描述的其他功能多态性：CYP3A72和CYP3A51处于连锁不平衡状态。因此，所产生的CYP3A单倍型在人群中表达不同的酶组。总之，一种由假基因CYP3AP1与CYP3A7剪接组成的新机制，导致形成了一种新型CYP3A7.1L，其组织分布和功能特性与亲本CYP3A7酶不同，可能具有发育、生理和毒理学后果。
