title: Relevance of NAC-2, an Na+-coupled citrate transporter, to life span, body size and fat content in Caenorhabditis elegans.
abstract: We have cloned and functionally characterized an Na+-coupled citrate transporter from Caenorhabditis elegans (ceNAC-2). This transporter shows significant sequence homology to Drosophila Indy and the mammalian Na+-coupled citrate transporter NaCT (now known as NaC2). When heterologously expressed in a mammalian cell line or in Xenopus oocytes, the cloned ceNAC-2 mediates the Na+-coupled transport of various intermediates of the citric acid cycle. However, it transports the tricarboxylate citrate more efficiently than dicarboxylates such as succinate, a feature different from that of ceNAC-1 (formerly known as ceNaDC1) and ceNAC-3 (formerly known as ceNaDC2). The transport process is electrogenic, as evidenced from the substrate-induced inward currents in oocytes expressing the transporter under voltage-clamp conditions. Expression studies using a reporter-gene fusion method in transgenic C. elegans show that the gene is expressed in the intestinal tract, the organ responsible for not only the digestion and absorption of nutrients but also for the storage of energy in this organism. Functional knockdown of the transporter by RNAi (RNA interference) not only leads to a significant increase in life span, but also causes a significant decrease in body size and fat content. The substrates of ceNAC-2 play a critical role in metabolic energy production and in the biosynthesis of cholesterol and fatty acids. The present studies suggest that the knockdown of these metabolic functions by RNAi is linked to an extension of life span and a decrease in fat content and body size.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912, USA. yjfei@mail.mcg.edu
authors.forename: You-Jun
authors.initials: YJ
authors.lastname: Fei
authors.forename: Jin-Cai
authors.initials: JC
authors.lastname: Liu
authors.forename: Katsuhisa
authors.initials: K
authors.lastname: Inoue
authors.forename: Lina
authors.initials: L
authors.lastname: Zhuang
authors.forename: Katsuya
authors.initials: K
authors.lastname: Miyake
authors.forename: Seiji
authors.initials: S
authors.lastname: Miyauchi
authors.forename: Vadivel
authors.initials: V
authors.lastname: Ganapathy
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology; D000818:Animals; D030801:Animals, Genetically Modified; D001692:Biological Transport; D001823:Body Composition / Q000235:genetics; D001824:Body Constitution / Q000235:genetics; D017173:Caenorhabditis elegans / Q000033:anatomy & histology / Q000235:genetics / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D002460:Cell Line; D019343:Citric Acid / Q000378:metabolism*; D002952:Citric Acid Cycle; D003001:Cloning, Molecular; D017238:Genes, Helminth; D017930:Genes, Reporter; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D008136:Longevity / Q000235:genetics; D008969:Molecular Sequence Data; D009865:Oocytes; D009928:Organ Specificity; D027361:Organic Anion Transporters / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010857:Pigment Epithelium of Eye / Q000166:cytology; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D029742:Caenorhabditis elegans Proteins; C487723:NAC-2 protein, C elegans; D027361:Organic Anion Transporters; D011993:Recombinant Fusion Proteins; D019343:Citric Acid; D012964:Sodium