Goytain Angela, Hines Rochelle M, Quamme Gary A
Department of Medicine, Vancouver Hospital, Koerner Pavilion, 2211 Wesbrook Mall, Vancouver, British Columbia, Canada V6T 1Z37.
Am J Physiol Cell Physiol. 2008 Oct;295(4):C944-53. doi: 10.1152/ajpcell.00091.2008. Epub 2008 Jul 30.
We used microarray analysis to identify renal cell transcripts that were upregulated with low magnesium. One transcript, identified as NIPA2 (nonimprinted in Prader-Willi/Angelman syndrome) subtype 2, was increased over twofold relative to cells cultured in normal magnesium. The deduced sequence comprises 129 amino acids with 8 predicted transmembrane regions. As the secondary structure of NIPA2 conformed to a membrane transport protein, we expressed it in Xenopus oocytes and determined that it mediated Mg(2+) uptake with two-electrode voltage-clamp and fluorescence studies. Mg(2+) transport was electrogenic, voltage dependent, and saturable, demonstrating a Michaelis affinity constant of 0.31 mM. Unlike other reported Mg(2+) transporters, NIPA2 was very selective for the Mg(2+) cation. NIPA2 mRNA is found in many tissues but particularly abundant in renal cells. With the use of immunofluorescence, it was shown that NIPA2 protein was normally localized to the early endosomes and plasma membrane and was recruited to the plasma membrane in response to low extracellular magnesium. We conclude that NIPA2 plays a role in magnesium metabolism and regulation of renal magnesium conservation.
我们使用微阵列分析来鉴定在低镁条件下上调的肾细胞转录本。其中一个转录本被鉴定为普拉德-威利/安吉尔曼综合征非印记基因2（NIPA2）亚型2，相对于在正常镁浓度下培养的细胞，其表达量增加了两倍多。推导的序列包含129个氨基酸，有8个预测的跨膜区域。由于NIPA2的二级结构符合膜转运蛋白的特征，我们在非洲爪蟾卵母细胞中表达了它，并通过双电极电压钳和荧光研究确定它介导了镁离子（Mg(2+)）的摄取。镁离子转运是生电性的、电压依赖性的且具有饱和性，米氏亲和常数为0.31 mM。与其他报道的镁离子转运体不同，NIPA2对镁离子阳离子具有高度选择性。NIPA2 mRNA在许多组织中都有发现，但在肾细胞中尤为丰富。通过免疫荧光技术显示，NIPA2蛋白通常定位于早期内体和质膜，并且在细胞外镁浓度低时会被募集到质膜。我们得出结论，NIPA2在镁代谢和肾脏镁离子保留的调节中发挥作用。
