Characterization of Na+/HCO3- cotransporter isoform NBC-3
Characterization of Na+/HCO3- cotransporter isoform NBC-3
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DOI：
10.1152/ajprenal.1999.276.6.f903
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发表时间：
1999-06-01
影响因子：
4.2
通讯作者：
Soleimani, M
中科院分区：
文献类型：
--
作者：
Amlal, H;Burnham, CE;Soleimani, M
Na（+）-HCO（3）（-）共转运蛋白介导HCO转运进入或离开细胞。先前已经鉴定了两种Nai-HCO共转运蛋白（NBC），其被称为NBC-1和NBC-2。用NBC-2cDNA探针筛选来自未诱导的人NT-2细胞的cDNA文库。鉴定并分离了几个克隆。这些克隆的序列分析鉴定了一个新的NBC（这里称为NBC-S）的部分编码区（2kb），其与NBC-1和NBC-8的同源性分别为53%和72%。北方印迹分析表明，NBC-S编码一个4.4 kb的mRNA，其组织分布模式与NBC-1和NBC-S不同。NBC-3在脑和脊柱中高度表达，在气管、甲状腺和肾脏中具有中等水平。与NBC-1相反，NBC-3在胰腺和肾皮质中显示低水平的表达。在肾脏中，NBC-3表达主要限于髓质。培养的小鼠内髓集合管（mIMCD-3）细胞显示高水平的NBC-1和低水平的NBC-3 mRNA表达。使突变的mIMCD-3细胞经受亚致死酸应激，NBC-1的mRNA表达降低了近90%，但Na（+）依赖性HCO（3）（-）共转运活性增加了近7倍（通过DIDS敏感性、Na（+）依赖性、HCO（3）（-）介导的细胞内pH值恢复进行测定）。这种增加与NBC-8 mRNA水平的5.5倍增强有关。NBC在突变体而不是亲本mIMCD-3细胞中显示出对Li（+）的显著亲和力。基于NBC-3的广泛分布，我们认为这种亚型可能通过将HCO（3）（-）从血液转运到细胞而参与细胞pH调节。我们进一步提出，在严重的酸胁迫下，NBC-3的表达增强可能通过介导HCO（3）（-）流入细胞而在细胞存活中发挥重要作用。
Na(+)-HCO(3)(-), cotransporters mediate the transport of HCO, into or out of the cell. Two Nai-HCO, cotransporters (NBC) have been identified previously, which are referred to as NBC-1 and NBC-2. A cDNA library from uninduced human NT-2 cells was screened with an NBC-2 cDNA probe. Several clones were identified and isolated. Sequence analysis of these clones identified a partial coding region (2 kb) of a novel NBC (called here NBC-S), which showed 53% and 72% identity with NBC-1 and NBC-8, respectively. Northern blot analysis revealed that NBC-S encodes a 4.4-kb mRNA with a tissue distribution pattern distinct from NBC-1 and NBC-S. NBC-3 is highly expressed in brain and spinal column, with moderate levels in trachea, thyroid, and kidney. In contrast with NBC-1, NBC-3 shows low levels of expression in pancreas and kidney cortex. In the kidney, NBC-3 expression is predominantly limited to the medulla. Cultured mouse inner medullary collecting duct (mIMCD-3) cells showed high levels of NBC-1 and low levels of NBC-3 mRNA expression. Subjecting the mutagenized mIMCD-3 cells to sublethal acid stress decreased the mRNA expression of NBC-1 by similar to 90% but increased the Na(+)-dependent HCO(3)(-) cotransport activity by similar to 7-fold (as assayed by DIDS-sensitive, Na(+)-dependent, HCO(3)(-)-mediated intracellular pH recovery). This increase was associated with similar to 5.5fold enhancement of NBC-8 mRNA levels. NBC showed significant affinity for Li(+) in the mutant but not the parent mIMCD-3 cells. On the basis of the widespread distribution of NBC-3, we propose that this isoform is likely involved in cell pH regulation by transporting HCO(3)(-) from blood to the cell. We further propose that enhanced expression of NBC-3 in severe acid stress could play an important role in cell survival by mediating the influx of HCO(3)(-) into the cells.