Yanatori Izumi, Yasui Yumiko, Tabuchi Mitsuaki, Kishi Fumio
*Department of Molecular Genetics, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama 701-0192, Japan.
Biochem J. 2014 Aug 15;462(1):25-37. doi: 10.1042/BJ20140225.
DMT1 (divalent metal transporter 1) is the main iron importer found in animals, and ferrous iron is taken up by cells via DMT1. Once ferrous iron reaches the cytosol, it is subjected to subcellular distribution and delivered to various sites where iron is required for a variety of biochemical reactions in the cell. Until now, the mechanism connecting the transporter and cytosolic distribution had not been clarified. In the present study, we have identified PCBP2 [poly(rC)-binding protein 2] as a DMT1-binding protein. The N-terminal cytoplasmic region of DMT1 is the binding domain for PCBP2. An interaction between DMT1 and PCBP1, which is known to be a paralogue of PCBP2, could not be demonstrated in vivo or in vitro. Iron uptake and subsequent ferritin expression were suppressed by either DMT1 or PCBP2 knockdown. Iron-associated DMT1 could interact with PCBP2 in vitro, whereas iron-chelated DMT1 could not. These results indicate that ferrous iron imported by DMT1 is transferred directly to PCBP2. Moreover, we demonstrated that PCBP2 could bind to ferroportin, which exports ferrous iron out of the cell. These findings suggest that PCBP2 can transfer ferrous iron from DMT1 to the appropriate intracellular sites or ferroportin and could function as an iron chaperone.
二价金属转运蛋白1（DMT1）是在动物体内发现的主要铁离子导入蛋白，亚铁离子通过DMT1被细胞摄取。一旦亚铁离子进入胞质溶胶，它就会进行亚细胞分布，并被输送到细胞内各种需要铁离子参与多种生化反应的部位。到目前为止，连接转运蛋白和胞质溶胶分布的机制尚未阐明。在本研究中，我们已鉴定出聚（rC）结合蛋白2（PCBP2）为DMT1结合蛋白。DMT1的N端胞质区域是PCBP2的结合结构域。在体内或体外均未证实DMT1与已知为PCBP2旁系同源物的PCBP1之间存在相互作用。DMT1或PCBP2基因敲低可抑制铁摄取及随后的铁蛋白表达。铁结合的DMT1在体外可与PCBP2相互作用，而铁螯合的DMT1则不能。这些结果表明，由DMT1导入的亚铁离子直接转移至PCBP2。此外，我们还证明PCBP2可与铁转运蛋白结合，后者将亚铁离子转运出细胞。这些发现表明，PCBP2可将亚铁离子从DMT1转移至合适的细胞内位点或铁转运蛋白，并可能作为一种铁伴侣发挥作用。
