Kubota Akira, Iwata Hisato, Goldstone Heather M H, Kim Eun-Young, Stegeman John J, Tanabe Shinsuke
Center for Marine Environmental Studies, Ehime University, Matsuyama 790-8577, Japan.
Toxicol Sci. 2006 Aug;92(2):394-408. doi: 10.1093/toxsci/kfl001. Epub 2006 May 5.
The present study characterized cytochrome P4501A (CYP1A) isoforms from common cormorant (Phalacrocorax carbo) with regard to their evolutionary relationships and their roles in disposition of dioxin and related compounds (DRCs). Two clones isolated from a cormorant liver cDNA library were named CYP1A4 and CYP1A5 on the basis of greatest overall amino acid identity shared with chicken (Gallus gallus) CYP1A4 (78%) and CYP1A5 (78%), respectively. Spatial heterogeneity in phylogenetic signal along the sequences strongly indicated that cormorant CYP1A4 and CYP1A5 have undergone partial interparalog gene conversion, similar to chicken and mammalian CYP1As. Phylogenetic analysis of a putatively unconverted region produced a tree topology consistent with the orthology of avian CYP1A5s with mammalian CYP1A2s and avian CYP1A4s with mammalian CYP1A1s. Hepatic CYP1A4 and CYP1A5 mRNA levels in wild cormorants from Lake Biwa, Japan, were quantified to examine the effects of DRCs on isoform-specific expression and to evaluate the toxicokinetics of DRCs in which CYP1A expression is involved. Both CYP1A4 and CYP1A5 mRNA levels were positively correlated with total tetrachlorodibenzo-p-dioxin toxic equivalents and concentrations of each congener in most cases in the liver, suggesting the induction of both enzymes through a shared transcriptional mechanism. The lack of correlation of 2,3,7,8-tetrachlorodibenzofuran and 3,3',4,4'-tetrachlorobiphenyl (PCB77) to CYP1A gene expression is likely due to the rapid metabolism of these two congeners. Liver-to-muscle concentration ratios for most DRC congeners except PCB77 and mono-ortho coplanar polychlorinated biphenyls significantly increased with an elevation of CYP1A4 and CYP1A5 mRNA levels. The present data suggest that hepatic sequestration of some DRCs occurs in cormorant via binding to either CYP1A5 or both CYP1A4 and CYP1A5.
本研究对普通鸬鹚（Phalacrocorax carbo）的细胞色素P4501A（CYP1A）亚型进行了表征，涉及其进化关系以及在二噁英和相关化合物（DRCs）处置中的作用。从鸬鹚肝脏cDNA文库中分离出的两个克隆，分别基于与鸡（Gallus gallus）CYP1A4（78%）和CYP1A5（78%）共享的最大总体氨基酸同一性，命名为CYP1A4和CYP1A5。沿序列的系统发育信号中的空间异质性强烈表明，鸬鹚CYP1A4和CYP1A5经历了部分旁系同源基因转换，类似于鸡和哺乳动物的CYP1A。对一个假定未转换区域的系统发育分析产生了一种树形拓扑结构，与鸟类CYP1A5与哺乳动物CYP1A2的直系同源性以及鸟类CYP1A4与哺乳动物CYP1A1的直系同源性一致。对来自日本琵琶湖的野生鸬鹚肝脏中的CYP1A4和CYP1A5 mRNA水平进行了定量，以研究DRCs对亚型特异性表达的影响，并评估涉及CYP1A表达的DRCs的毒代动力学。在大多数情况下肝脏中，CYP1A4和CYP1A5 mRNA水平均与总四氯二苯并对二噁英毒性当量以及每种同系物的浓度呈正相关，表明这两种酶是通过共同的转录机制被诱导的。2,3,7,8 - 四氯二苯并呋喃和3,3',4,4' - 四氯联苯（PCB77）与CYP1A基因表达缺乏相关性，可能是由于这两种同系物的快速代谢。除PCB77和单邻位共平面多氯联苯外大多数DRC同系物的肝 - 肌肉浓度比随着CYP1A4和CYP1A5 mRNA水平的升高而显著增加。目前的数据表明，鸬鹚体内一些DRCs的肝脏潴留是通过与CYP1A5或CYP1A4和CYP1A5两者结合而发生的。
