Cellular and subcellular localization of the Nramp2 iron transporter in the intestinal brush border and regulation by dietary iron.
Cellular and subcellular localization of the Nramp2 iron transporter in the intestinal brush border and regulation by dietary iron.
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DOI：
10.1182/blood.v93.12.4406
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发表时间：
1999-06
期刊：
影响因子：
20.3
通讯作者：
F. Canonne-Hergaux;F. Canonne-Hergaux;S. Gruenheid;S. Gruenheid;P. Ponka;P. Ponka;P. Gros;P. Gros
中科院分区：
文献类型：
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作者：
F. Canonne-Hergaux;F. Canonne-Hergaux;S. Gruenheid;S. Gruenheid;P. Ponka;P. Ponka;P. Gros;P. Gros
在小细胞贫血动物模型中的遗传学研究和转运的生化研究表明Nramp2基因参与铁转运。Nramp2产生两种选择性剪接的mrna，它们在3'非翻译区因铁反应元件（IRE）的存在或缺失而不同，并编码两种具有不同羧基末端的蛋白质。针对含有Nramp2羧基或氨基末端的Nramp2融合蛋白产生的抗血清可以帮助区分两种Nramp2蛋白异构体（IRE：异构体I；非IRE：异构体II）。这些抗体用于鉴定Nramp2在正常组织中的细胞和亚细胞定位，并研究饮食缺铁可能的调控作用。免疫印迹实验显示，Nramp2在整个小肠中表达水平较低，在肾脏中表达水平较高。饮食铁缺乏导致Nramp2亚型I仅在十二指肠近端显著上调，而小肠和肾脏的其余部分的表达在饮食铁缺乏的情况下基本保持不变。在近端十二指肠，组织切片的免疫染色研究显示，Nramp2蛋白在缺铁条件下表达丰富，仅限于绒毛，而在隐窝中不存在。在绒毛中，染色仅限于粘膜（肠细胞）的柱状吸收上皮，在分泌粘液的杯状细胞或固有层中无表达。Nramp2在绒毛顶端的三分之二表达最强，在肠细胞顶端极的刷状边缘表达非常强烈，而这些细胞的基底外膜则是Nramp2阴性。这些结果有力地表明Nramp2确实负责十二指肠中不依赖转铁蛋白的铁摄取。这些发现在机体铁获取的整体机制的背景下进行了讨论。
Genetic studies in animal models of microcytic anemia and biochemical studies of transport have implicated the Nramp2 gene in iron transport. Nramp2 generates two alternatively spliced mRNAs that differ at their 3' untranslated region by the presence or absence of an iron-response element (IRE) and that encode two proteins with distinct carboxy termini. Antisera raised against Nramp2 fusion proteins containing either the carboxy or amino termini of Nramp2 and that can help distinguish between the two Nramp2 protein isoforms (IRE: isoform I; non-IRE: isoform II) were generated. These antibodies were used to identify the cellular and subcellular localization of Nramp2 in normal tissues and to study possible regulation by dietary iron deprivation. Immunoblotting experiments with membrane fractions from intact organs show that Nramp2 is expressed at low levels throughout the small intestine and to a higher extent in kidney. Dietary iron starvation results in a dramatic upregulation of the Nramp2 isoform I in the proximal portion of the duodenum only, whereas expression in the rest of the small intestine and in kidney remains largely unchanged in response to the lack of dietary iron. In proximal duodenum, immunostaining studies of tissue sections show that Nramp2 protein expression is abundant under iron deplete condition and limited to the villi and is absent in the crypts. In the villi, staining is limited to the columnar absorptive epithelium of the mucosa (enterocytes), with no expression in mucus-secreting goblet cells or in the lamina propria. Nramp2 expression is strongest in the apical two thirds of the villi and is very intense at the brush border of the apical pole of the enterocytes, whereas the basolateral membrane of these cells is negative for Nramp2. These results strongly suggest that Nramp2 is indeed responsible for transferrin-independent iron uptake in the duodenum. These findings are discussed in the context of overall mechanisms of iron acquisition by the body.