Characterization of retinoic acid synthases

视黄酸（Retinoic acid， RA）是一种具有生物活性的小脂类物质，与细胞分化和增殖有关。RA的功能激活应经过细胞内从代谢到表型反应的几个步骤的调节。RA的合成是RA激活的关键步骤之一，我们已经得到了CYP1A1从视网膜催化RA合成的证据。在这两年中，我们研究了CYP1A1在体内催化RA合成的可能性。在有核切除修复缺陷的色素性干皮病（XP）患者中，RA可抑制新肿瘤的形成。然而，这种抑制不是由于增强了紫外线损伤DNA的去除。这些结果促使我们研究RA代谢在XP成纤维细胞中是否异常以及潜在的机制是什么。与野生型成纤维细胞相比，HPLC检测到缺乏XPA组（XPA）基因的小鼠成纤维细胞和紫外线诱导的缺乏XPA的癌细胞的RA合成活性较低。此外，我们通过RT-PCR观察到XPA缺陷成纤维细胞中细胞色素P450 1A1的表达受损，western blotting观察到XPA缺陷癌细胞中视黄酸受体γ的表达降低。最后，RA同种异构体的预处理可显著保护XPA缺陷成纤维细胞免受紫外线诱导的死亡。这些结果表明，细胞色素P450 1A1 mRNA表达受损导致RA合成结构活性降低，至少与紫外线照射一起可能参与XP患者的皮肤癌发生。为了研究RA与CYP1A1之间的关系，我们最近开始分析芳烃受体（AhR）敲除小鼠，其肝脏中维甲酸含量高于正常小鼠。

Retinoic acid (RA) is a bio-active small lipid related with cell differentiation and proliferation. The functional activation of RA should be regulated by several steps from its metabolism to phenotypic response in the cell. The RA synthesis is one of the critical step for the RA activation and we have gotten a evidence that CYP1A1 catalyzed RA synthesis from retinal. During this two years, we have investigated the possibility of RA synthesis catalyzed by CYP1A1 in vivo.New tumor formation was suppressed by RA administration in xeroderma pigmentosum (XP) patients who have a defect in nuclear excision repair. However, the inhibition is not due to enhanced removal of UV-damaged DNA.These results promoted us to investigate whether or not RA metabolism is abnormal in XP fibroblasts and what the underlying mechanism is. Compared with wild type fibroblasts, low activities of RA synthesis were determined on HPLC in mouse fibroblasts lacking XP group A (XPA) gene and UV-induced XPA deficient cancer cells. Moreover, we observed an impaired expression of cytochrome P450 1A1 in XPA deficient fibroblasts by RT-PCR and decreased expression of retinoic acie receptor γ in XPA deficient cancer cells by western blotting. Finally, pretreatment of RA isoforms significantly protected the XPA deficient fibroblasts from UV-induced death. These results suggest that decreased structure activity of RA synthesis, resulting from impaired mRNA expression of cytochrome P450 1A1 may, at least together with UV irradiation, involve in skin carcinogenesis in XP patients.To investigate the relationship between RA an CYP1A1 with another approach, we recently started analyzing Arylhydrocarbon Receptor (AhR) knockout mice which has more retinoic acid contents in the liver than that of normal mice.