Kuwahara Shoji, Aranami Fumito, Segawa Hiroko, Onitsuka Akemi, Honda Naoko, Tominaga Rieko, Hanabusa Etsuyo, Kaneko Ichiro, Yamanaka Setsuko, Sasaki Shohei, Ohi Akiko, Nomura Kengo, Tatsumi Sawako, Kido Shinsuke, Ito Mikiko, Miyamoto Ken-ichi
Department of Molecular Nutrition, Institution of Health Biosciences, the University of Tokushima Graduate School, Tokushima, Japan.
J Med Invest. 2012;59(1-2):116-26. doi: 10.2152/jmi.59.116.
Mutations in the SLC34A3 gene, a sodium-dependent inorganic phosphate (Pi) cotransporter, also referred to as NaPi IIc, causes hereditary hypophosphatemic rickets with hypercalciuria (HHRH), an autosomal recessive disorder. In human and rodent, NaPi IIc is mainly localized in the apical membrane of renal proximal tubular cells. In this study, we identified mouse NaPi IIc variant (Npt2c-v1) that lacks the part of the exon 3 sequence that includes the assumed translation initiation site of Npt2c. Microinjection of mouse Npt2c-v1 cRNA into Xenopus oocytes demonstrated that Npt2c-v1 showed sodium-dependent Pi cotransport activity. The characterization of pH dependency showed activation at extracellular alkaline-pH. Furthermore, Npt2c-v1 mediated Pi transport activity was significantly higher at any pH value than those of Npt2c. In an in vitro study, the localization of the Npt2c-v1 protein was detected in the apical membrane in opossum kidney cells. The expression of Npt2c-v1 mRNA was detected in the heart, spleen, testis, uterus, placenta, femur, cerebellum, hippocampus, diencephalon and brain stem of mouse. Using mouse bone primary cultured cells, we showed the expression of Npt2c-v1 mRNA. In addition, the Npt2c protein was detected in the spermatozoa head. Thus, Npt2c-v1 was expressed in extra-renal tissues such as epididymal spermatozoa and may function as a sodium-dependent phosphate transporter.
SLC34A3基因发生突变，该基因是一种钠依赖性无机磷酸盐（Pi）共转运体，也被称为NaPi IIc，会导致伴高钙尿症的遗传性低磷血症佝偻病（HHRH），这是一种常染色体隐性疾病。在人类和啮齿动物中，NaPi IIc主要定位于肾近端小管细胞的顶端膜。在本研究中，我们鉴定出小鼠NaPi IIc变体（Npt2c-v1），其缺少外显子3序列的一部分，该部分包含假定的Npt2c翻译起始位点。将小鼠Npt2c-v1的cRNA显微注射到非洲爪蟾卵母细胞中，结果表明Npt2c-v1具有钠依赖性Pi共转运活性。对pH依赖性的表征显示在细胞外碱性pH条件下被激活。此外，在任何pH值下，Npt2c-v1介导的Pi转运活性均显著高于Npt2c。在一项体外研究中，在负鼠肾细胞的顶端膜中检测到了Npt2c-v1蛋白的定位。在小鼠的心脏、脾脏、睾丸、子宫、胎盘、股骨、小脑、海马体、间脑和脑干中检测到了Npt2c-v1 mRNA的表达。使用小鼠骨原代培养细胞，我们展示了Npt2c-v1 mRNA的表达。此外，在精子头部检测到了Npt2c蛋白。因此，Npt2c-v1在附睾精子等肾外组织中表达，并可能作为一种钠依赖性磷酸盐转运体发挥作用。
