Analysis of the protein carboxyl methyltransferase gene as a brain specific repair enzyme

异天冬氨酸蛋白羧甲基转移酶(PIMT)催化蛋白质和多肽中D-天冬氨酸和L-异天冬氨酸残基的甲酯化，将改变的残基转化为正常的L-天冬氨酸残基，并被认为通过外消旋和脱酰胺来修复受损的蛋白质。我们已经报道了PIMT基因主要在脑和睾丸中表达，并测定了这些序列。我们还证明了白内障晶状体上皮细胞中的mRNA水平显著低于正常年龄匹配的晶状体组织中的mRNA水平。据推测，低剂量X射线照射促进了细胞的增殖，延长了体内和体外细胞的存活率。低水平电离辐射的生理益处被称为辐射兴奋效应。本研究通过检测辐射刺激下培养的大鼠成纤维细胞中PIMT基因表达水平的变化，以阐明其兴奋作用的机制。比较0、25、50和75cGy射线照射后培养细胞中PIMT基因的表达。照射后3d，PIMT基因表达水平分别增加约1.5倍和2倍。这些结果提示，PIMT可能在兴奋机制中起重要作用。

An isoaspartyl protein carboxyl methyltransferase (PIMT) catalyzes the methyl esterification of D-aspartyl and L-isoaspartyl residues in proteins and peptides, converts the altered residues to normal L-aspartic acid residues, and is presumed to function in the repair of damaged proteins by racemization and deamidation. We have reported that the PIMT gene is expressed mainly in the brain and testis and have determined these cDNA sequences. We have also proved that the mRNA levels in cataractous lens epithelia are significantly lower than those in normal age-matched lens tissue. It is postulated that low dose X-irradiation facilitates the proliferation and prolongs the survival rate of the cells in vivo and in vitro. The physiological benefit from low level ionizing radiation is called as radiation hormesis. In this study, we examined the change of the PIMT mRNA levels in rat cultured fibroblast cells stimulated by irradiation to clarify the mechanism of the hormesis effect. We compared the PIMT gene expression in the cultured cells after 0, 25, 50 and 75 cGy irradiation. Three days after 50 and 75 cGy irradiation, PIMT mRNA levels increased about 1.5 and 2 times, respectively. These results suggest that the PIMT might play an important role in the hormesis mechanism.