CYP26C1 Is a Hydroxylase of Multiple Active Retinoids and Interacts with Cellular Retinoic Acid Binding Proteins
作者:Guo Zhong、David Ortiz、Alex Zelter、Abhinav Nath、Nina Isoherranen
DOI:10.1124/mol.117.111039
日期:2018.5
The clearance of retinoic acid (RA) and its metabolites is believed to be regulated by the CYP26 enzymes, but the specific roles of CYP26A1, CYP26B1, and CYP26C1 in clearing active vitamin A metabolites have not been defined. The goal of this study was to establish the substrate specificity of CYP26C1, and determine whether CYP26C1 interacts with cellular retinoic acid binding proteins (CRABPs). CYP26C1 was found to effectively metabolize all- trans retinoic acid ( at RA), 9- cis -retinoic acid (9- cis -RA), 13- cis -retinoic acid, and 4-oxo- at RA with the highest intrinsic clearance toward 9- cis -RA. In comparison with CYP26A1 and CYP26B1, CYP26C1 resulted in a different metabolite profile for retinoids, suggesting differences in the active-site structure of CYP26C1 compared with other CYP26s. Homology modeling of CYP26C1 suggested that this is attributable to the distinct binding orientation of retinoids within the CYP26C1 active site. In comparison with other CYP26 family members, CYP26C1 was up to 10-fold more efficient in clearing 4-oxo- at RA (intrinsic clearance 153 μ l/min/pmol) than CYP26A1 and CYP26B1, suggesting that CYP26C1 may be important in clearing this active retinoid. In support of this, CRABPs delivered 4-oxo- at RA and at RA for metabolism by CYP26C1. Despite the tight binding of 4-oxo- at RA and at RA with CRABPs, the apparent Michaelis-Menten constant in biological matrix ( K m) value of these substrates with CYP26C1 was not increased when the substrates were bound with CRABPs, in contrast to what is predicted by free drug hypothesis. Together these findings suggest that CYP26C1 is a 4-oxo- at RA hydroxylase and may be important in regulating the concentrations of this active retinoid in human tissues.
视黄酸(RA)及其代谢物的清除被认为是由CYP26酶调控的,但CYP26A1、CYP26B1和CYP26C1在清除活性维生素A代谢物中的具体作用尚未明确。本研究的目标是建立CYP26C1的底物特异性,并确定CYP26C1是否与细胞视黄酸结合蛋白(CRABPs)相互作用。研究发现,CYP26C1能够有效地代谢全反式视黄酸(at RA)、9-顺式视黄酸(9-cis-RA)、13-顺式视黄酸和4-氧-全反式视黄酸,其中对9-cis-RA的内源性清除率最高。与CYP26A1和CYP26B1相比,CYP26C1对视黄醇类化合物展现出不同的代谢物谱,提示CYP26C1的活性位点结构与其他CYP26酶存在差异。CYP26C1的同源建模表明,这与视黄醇在CYP26C1活性位点内的不同结合取向有关。与其他CYP26家族成员相比,CYP26C1在清除4-氧-全反式视黄酸方面的效率高达CYP26A1和CYP26B1的10倍(内源性清除率为153 μl/min/pmol),这表明CYP26C1在清除这一活性视黄醇方面可能具有重要意义。支持这一点的是,CRABPs将4-氧-全反式视黄酸和全反式视黄酸输送给CYP26C1进行代谢。尽管4-氧-全反式视黄酸和全反式视黄酸与CRABPs结合紧密,但在生物基质中这些底物与CYP26C1的表观米氏常数(K m)在底物与CRABPs结合时并未增加,这与自由药物假说的预测相反。这些发现共同表明,CYP26C1是一种4-氧-全反式视黄酸羟化酶,可能在调节人类组织中这一活性视黄醇的浓度方面具有重要作用。