Sponder Gerhard, Mastrototaro Lucia, Kurth Katharina, Merolle Lucia, Zhang Zheng, Abdulhanan Nasrin, Smorodchenko Alina, Wolf Katharina, Fleig Andrea, Penner Reinhold, Iotti Stefano, Aschenbach Jörg R, Vormann Jürgen, Kolisek Martin
Institute of Veterinary-Physiology, Free University of Berlin, Oertzenweg 19b, 14163, Berlin, Germany.
Landesuntersuchungsanstalt Sachsen, Jägerstraße 8/10, Dresden, Germany.
Pflugers Arch. 2016 Jul;468(7):1223-1240. doi: 10.1007/s00424-016-1816-7. Epub 2016 Apr 11.
CNNM2 is associated with the regulation of serum Mg concentration, and when mutated, with severe familial hypomagnesemia. The function and cellular localization of CNNM2 and its isomorphs (Iso) remain controversial. The objective of this work was to examine the following: (1) the transcription-responsiveness of CNNM2 to Mg starvation, (2) the cellular localization of Iso1 and Iso2, (3) the ability of Iso1 and Iso2 to transport Mg(2+), and (4) the complex-forming ability and spectra of potential interactors of Iso1 and Iso2. The five main findings are as follows. (1) Mg-starvation induces CNNM2 overexpression that is markedly higher in JVM-13 cells (lymphoblasts) compared with Jurkat cells (T-lymphocytes). (2) Iso1 and Iso2 localize throughout various subcellular compartments in transgenic HEK293 cells overexpressing Iso1 or Iso2. (3) Iso1 and Iso2 do not transport Mg(2+) in an electrogenic or electroneutral mode in transgenic HEK293 cells overexpressing Iso1 or Iso2. (4) Both Iso1 and Iso2 form complexes of a higher molecular order. (5) The spectrum of potential interactors of Iso1 is ten times smaller than that of Iso2. We conclude that sensitivity of CNNM2 expression to extracellular Mg(2+) depletion depends on cell type. Iso1 and Iso2 exhibit a dispersed pattern of cellular distribution; thus, they are not exclusively integral to the cytoplasmic membrane. Iso1 and Iso2 are not Mg(2+) transporters per se. Both isomorphs form protein complexes, and divergent spectra of potential interactors of Iso1 and Iso2 indicate that each isomorph has a distinctive function. CNNM2 is therefore the first ever identified Mg(2+) homeostatic factor without being a Mg(2+) transporter per se.
CNNM2与血清镁浓度的调节有关，发生突变时则与严重的家族性低镁血症相关。CNNM2及其同形体（Iso）的功能和细胞定位仍存在争议。本研究的目的是检测以下内容：（1）CNNM2对镁缺乏的转录反应性；（2）Iso1和Iso2的细胞定位；（3）Iso1和Iso2转运Mg²⁺的能力；（4）Iso1和Iso2的复合物形成能力以及潜在相互作用分子的谱图。主要有以下五项发现：（1）镁缺乏诱导CNNM2过表达，与Jurkat细胞（T淋巴细胞）相比，JVM-13细胞（淋巴母细胞）中的过表达明显更高。（2）在过表达Iso1或Iso2的转基因HEK293细胞中，Iso1和Iso2定位于各种亚细胞区室。（3）在过表达Iso1或Iso2的转基因HEK细胞中，Iso1和Iso2不以电生或电中性模式转运Mg²⁺。（4）Iso1和Iso2均形成更高分子阶次的复合物。（5）Iso1的潜在相互作用分子谱图比Iso2小十倍。我们得出结论，CNNM2表达对细胞外Mg²⁺耗竭的敏感性取决于细胞类型。Iso1和Iso2表现出分散的细胞分布模式；因此，它们并非仅存在于细胞质膜中。Iso1和Iso2本身不是Mg²⁺转运体。两种同形体均形成蛋白质复合物，Iso1和Iso2潜在相互作用分子的不同谱图表明每种同形体都有独特的功能。因此，CNNM2是首个被鉴定出的镁稳态因子，但其本身并非Mg²⁺转运体。
