Exon Loss Accounts for Differential Sorting of Na-K-Cl Cotransporters in Polarized Epithelial Cells
Exon Loss Accounts for Differential Sorting of Na-K-Cl Cotransporters in Polarized Epithelial Cells
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DOI：
10.1091/mbc.e08-05-0478
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发表时间：
2008-10-01
影响因子：
3.3
通讯作者：
Forbush, Biff
中科院分区：
文献类型：
--
作者：
Carmosino, Monica;Gimenez, Ignacio;Forbush, Biff
肾Na-K-Cl协同转运蛋白（NKCC 2）选择性表达于哺乳动物肾细胞的顶膜，是临床上重要的袢利尿剂的靶点。相反，“分泌型”NKCC 1协同转运蛋白定位于许多上皮细胞的基底外侧膜。为了鉴定指导NKCC运输的分选信号，我们在两种亚型之间产生嵌合体，并在极化的肾上皮细胞系中表达这些构建体。该分析揭示了NKCC 2中含有顶端分选信息的氨基酸延伸。NKCC 1 C末端含有双亮氨酸基序，其构成其基底外侧分选信号的最小必需组分。缺乏该基序的NKCC 1表现为顶端蛋白。对NKCC基因结构的检查揭示，该双亮氨酸基序由NKCC 1中不存在于NKCC 2中的额外外显子编码。该外显子的系统发育分析表明，该外显子从编码基底外侧NKCC 1的基因的进化丢失构成了一种新的机制，该机制解释了NKCC 2基因编码的蛋白质的顶端分选。
The renal Na-K-Cl cotransporter (NKCC2) is selectively expressed in the apical membranes of cells of the mammalian kidney, where it is the target of the clinically important loop diuretics. In contrast, the "secretory" NKCC1 cotransporter is localized in the basolateral membranes of many epithelia. To identify the sorting signal(s) that direct trafficking of NKCCs, we generated chimeras between the two isoforms and expressed these constructs in polarized renal epithelial cell lines. This analysis revealed an amino acid stretch in NKCC2 containing apical sorting information. The NKCC1 C terminus contains a dileucine motif that constitutes the smallest essential component of its basolateral sorting signal. NKCC1 lacking this motif behaves as an apical protein. Examination of the NKCC gene structure reveals that this dileucine motif is encoded by an additional exon in NKCC1 absent in NKCC2. Phylogenetic analysis of this exon suggests that the evolutionary loss of this exon from the gene encoding the basolateral NKCC1 constitutes a novel mechanism that accounts for the apical sorting of the protein encoded by the NKCC2 gene.