Modification of cell constituents with endogenous aldehydes and its biological significance

存在于生命系统中的醛类物质能够对细胞成分（如蛋白质）进行化学修饰。本项目主要研究醛类化合物对DNA甲基化、氧化应激等损伤诱导的基因表达的影响。首先，检测对umuDC和ada基因表达的影响。通过测定umuDC'-'lacZ和ada'-'lacZ融合基因在大肠杆菌中的β -半乳糖苷酶活性来监测基因的表达。在检测的醛类中，甲醛对DNA修复酶（O^6-甲基鸟嘌呤-DNA甲基转移酶）的编码基因ada的表达有轻微的抑制作用。在没有甲基化剂的情况下，甲醛不影响ada基因表达的组成水平。众所周知，不能诱导ada基因表达的细胞对甲基化剂过敏。因此，可以预期甲醛会增强甲基化剂的致突变性。其次，研究了醛类化合物对已知产生活性氧的金属离子诱导的基因表达的影响。金属离子Cd^<2+>和Hg^<2+>对甲基化剂诱导的ada基因表达有抑制作用。体外重组系统的实验结果表明，这些金属可能与Ada蛋白结合，抑制了Ada蛋白的转录促进活性。

Aldehydes which exist in the living system are capable of chemically modifying cell constituents such as protein. The object of this project is focused on the effect of aldehydes on the gene expressions which are induced by DNA lesions such as methylation and oxidative stresses. First, effect on umuDC and ada gene expressions were examined. The gene expressions were monitored by measuring beta-galactosidase activity from umuDC'-'lacZ and ada'-'lacZ fused genes, respectively, in E. coli. Among aldehydes examined, formaldehyde slightly suppressed the expression of ada gene, which encodes DNA repair enzyme, O^6-methyguanine-DNA methyltransferase, induced by methylating agents. Formaldehyde did not affect constitutive level of the ada gene expression in the absence of methylating agents. It is known that cells which are unable to induce ada gene expression are hypersensitive to methylating agents. It may, therefore, be expected that formaldehyde potentiates mutagenicity of methylating agents. Second, the effect of aldehydes on the gene expressions induced by metal ions which are known to produce active oxygen species was examined. Metal ions such as Cd^<2+> and Hg^<2+> showed suppressive effect on the ada gene expression induced by methylating agents. The results obtained from the experiment using in vitro reconstituted system indicated that these metals probably bound to Ada protein leading to inhibition of transcriptional promoting activity of Ada protein.