Fei You-Jun, Inoue Katsuhisa, Ganapathy Vadivel
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, Georgia 30912, USA.
J Biol Chem. 2003 Feb 21;278(8):6136-44. doi: 10.1074/jbc.M208763200. Epub 2002 Dec 11.
We have cloned and functionally characterized two Na(+)-coupled dicarboxylate transporters, namely ceNaDC1 and ceNaDC2, from Caenorhabditis elegans. These two transporters show significant sequence homology with the product of the Indy gene identified in Drosophila melanogaster and with the Na(+)-coupled dicarboxylate transporters NaDC1 and NaDC3 identified in mammals. In a mammalian cell heterologous expression system, the cloned ceNaDC1 and ceNaDC2 mediate Na(+)-coupled transport of various dicarboxylates. With succinate as the substrate, ceNaDC1 exhibits much lower affinity compared with ceNaDC2. Thus, ceNaDC1 and ceNaDC2 correspond at the functional level to the mammalian NaDC1 and NaDC3, respectively. The nadc1 and nadc2 genes are not expressed at the embryonic stage, but the expression is detectable all through the early larva stage to the adult stage. Tissue-specific expression pattern studies using a reporter gene fusion approach in transgenic C. elegans show that both genes are coexpressed in the intestinal tract, an organ responsible for not only the digestion and absorption of nutrients but also for the storage of energy in this organism. Independent knockdown of the function of these two transporters in C. elegans using the strategy of RNA interference suggests that NaDC1 is not associated with the regulation of average life span in this organism, whereas the knockdown of NaDC2 function leads to a significant increase in the average life span. Disruption of the function of the high affinity Na(+)-coupled dicarboxylate transporter NaDC2 in C. elegans may lead to decreased availability of dicarboxylates for cellular production of metabolic energy, thus creating a biological state similar to that of caloric restriction, and consequently leading to life span extension.
我们从秀丽隐杆线虫中克隆并对两种钠离子偶联二羧酸转运蛋白ceNaDC1和ceNaDC2进行了功能表征。这两种转运蛋白与在黑腹果蝇中鉴定出的Indy基因产物以及在哺乳动物中鉴定出的钠离子偶联二羧酸转运蛋白NaDC1和NaDC3具有显著的序列同源性。在哺乳动物细胞异源表达系统中，克隆的ceNaDC1和ceNaDC2介导各种二羧酸的钠离子偶联转运。以琥珀酸为底物时，ceNaDC1与ceNaDC2相比表现出低得多的亲和力。因此，ceNaDC1和ceNaDC2在功能水平上分别对应于哺乳动物的NaDC1和NaDC3。nadc1和nadc2基因在胚胎阶段不表达，但在幼虫早期到成虫阶段都可检测到表达。在转基因秀丽隐杆线虫中使用报告基因融合方法进行的组织特异性表达模式研究表明，这两个基因在肠道中共表达，肠道是该生物体中不仅负责营养物质消化和吸收，还负责能量储存的器官。使用RNA干扰策略在秀丽隐杆线虫中独立敲低这两种转运蛋白的功能表明，NaDC1与该生物体平均寿命的调节无关，而敲低NaDC2功能会导致平均寿命显著增加。秀丽隐杆线虫中高亲和力钠离子偶联二羧酸转运蛋白NaDC2功能的破坏可能导致细胞代谢能量产生中二羧酸的可用性降低，从而产生类似于热量限制的生物学状态，进而导致寿命延长。
