Characterization of retinoic acid synthases

维甲酸（RA）是一种具有生物活性的小分子脂质，与细胞的分化和增殖有关。RA的功能激活应通过从其代谢到细胞表型反应的几个步骤来调节。RA的合成是RA激活的关键步骤之一，我们已经得到证据表明CYP 1A 1催化了从retinal合成RA。在这两年中，我们研究了体内CYP 1A 1催化RA合成的可能性，发现在着色性干皮病（XP）患者中，由于核切除修复缺陷，给予RA可抑制新肿瘤的形成。这些结果促使我们进一步研究XP成纤维细胞中RA代谢是否异常及其机制。与野生型成纤维细胞相比，HPLC测定了缺乏XP A组（XPA）基因的小鼠成纤维细胞和UV诱导的XPA缺陷癌细胞中RA合成的低活性。RT-PCR和Western blotting分别检测到XPA缺陷的成纤维细胞中细胞色素P450 1A 1和维甲酸受体γ的表达降低。最后，RA亚型的预处理显着保护XPA缺陷的成纤维细胞免受UV诱导的死亡。以上结果提示，XP患者细胞色素P450 1A 1 mRNA表达受损，导致RA合成结构活性降低，可能与紫外线照射共同参与XP皮肤癌变过程。我们最近开始分析芳基烃受体（AhR）敲除小鼠，其在肝脏中具有比正常小鼠更多的视黄酸含量。

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.