IRBIT coordinates epithelial fluid and HCO3-secretion by stimulating the transporters pNBC1 and CFTR in the murine pancreatic duct
IRBIT coordinates epithelial fluid and HCO3-secretion by stimulating the transporters pNBC1 and CFTR in the murine pancreatic duct
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DOI：
10.1172/jci36983
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发表时间：
2009-01-01
影响因子：
15.9
通讯作者：
Muallem, Shmuel
中科院分区：
文献类型：
--
作者：
Yang, Dongki;Shcheynikov, Nikolay;Muallem, Shmuel
分泌液和HCO3的分泌是分泌上皮的重要功能。在大多数上皮中，这需要HCO(3)（-）通过基底外侧膜进入，由Na+- hco3 -共转运蛋白pNBC1介导，并由CFTR-SLC26转运蛋白复合物介导，从管腔膜退出。在这里，我们报道了蛋白质IRBIT（肌醇-1,4,5-三磷酸[IP3]受体结合蛋白与IP3一起释放），一种先前确定的pNBC1激活剂，激活pNBC1的基底外侧和管腔CFTR，以协调胰管分泌液体和HCO3-。我们使用视频显微镜和离子选择微电极测量培养小鼠小叶内胰管的液体分泌和Cl-和HCO3-浓度。短干扰rna介导的IRBIT下调可显著抑制导管pNBC1和CFTR活性、腔内Cl-吸收和HCO3-分泌以及相关液体分泌。单通道测量表明，IRBIT通过减少通道平均关闭时间来调节CFTR。此外，在HEK细胞中表达IRBIT构建物表明，pNBC1的激活只需要IRBIT的PEST结构域，而CFTR的激活需要多个IRBIT结构域，这表明IRBIT通过不同的机制激活这些转运体。这些发现将IRBIT定义为上皮液和HCO3分泌的关键协调者，并可能与所有表达cftr的上皮和囊性纤维化有关。
Fluid and HCO3- secretion are vital functions of secretory epithelia. In most epithelia, this entails HCO(3)(-)entry at the basolateral membrane, mediated by the Na+-HCO3- cotransporter, pNBC1, and exit at the luminal membrane, mediated by a CFTR-SLC26 transporters complex. Here we report that the protein IRBIT (inositol-1,4,5-trisphosphate [IP3] receptors binding protein released with IP3), a previously identified activator of pNBC1, activates both the basolateral pNBC1 and the luminal CFTR to coordinate fluid and HCO3- secretion by the pancreatic duct. We used video microscopy and ion selective microelectrodes to measure fluid secretion and Cl- and HCO3- concentrations in cultured murine sealed intralobular pancreatic ducts. Short interference RNA-mediated knockdown of IRBIT markedly inhibited ductal pNBC1 and CFTR activities, luminal Cl- absorption and HCO3- secretion, and the associated fluid secretion. Single-channel measurements suggested that IRBIT regulated CFTR by reducing channel mean close time. Furthermore, expression of IRBIT constructs in HEK cells revealed that activation of pNBC1 required only the IRBIT PEST domain, while activation of CFTR required multiple IRBIT domains, suggesting that IRBIT activates these transporters by different mechanisms. These findings define IRBIT as a key coordinator of epithelial fluid and HCO3- secretion and may have implications to all CFTR-expressing epithelia and to cystic fibrosis.