Regulatory mechanisms of CIC chloride channels by protein-protein interaction

(1) ClC-2通道的c端被M期特异性周期蛋白依赖性激酶p34^<cdc2>/cyclin B直接磷酸化，并被蛋白磷酸酶1去磷酸化，其中蛋白-蛋白相互作用起着至关重要的作用。ClC-2通道在爪蟾卵母细胞中的表达受磷酸化抑制和去磷酸化激活。(2) Western blot和免疫细胞化学分析显示，ClC-2通道蛋白在细胞周期M期的分裂细胞中表达，在细胞分裂后迅速消失。通过泛素化，PEST序列是短寿命蛋白的标志，在ClC-2的c端存在多个PEST序列。p34^<cdc2>/cyclin B磷酸化ClC-2的^<632>Ser触发ClC-2通道泛素化，这强调了M期特异性泛素化和ClC-2通道蛋白的降解。(3) ClC-3B是一种主要表达于上皮细胞的氯离子通道，定位于上皮细胞的微绒毛。ClC-3B与上皮特异性含pdz蛋白EBP50相互作用，从而与囊性纤维化基因产物囊性纤维化跨膜传导调节因子（CFTR）相互作用。在CFTR存在的情况下，ClC-3B氯离子通道被蛋白激酶A激活，在跨上皮的离子运输中起重要作用。

(1) The C-terminus of ClC-2 channel is directly phosphorylated by M phase-specific cyclin-dependent kinase, p34^<cdc2>/cyclin B, and de-phosphorylated by protein phosphatase 1, for which protein-protein interaction plays a crucial role. ClC-2 channel expressed in Xenopus oocytes is inhibited by phosphorylation and activated by dephosphorylation.(2) Western blot analysis and immunocytochemistry revealed that ClC-2 channel protein is expressed in dividing cells of the M phase of cell cycle, and promptly disappears after cell division. The PEST sequence is a signature of short-lived proteins via ubiquitination, and multiple PEST sequences are present in the C-terminus of ClC-2. Phosphorylation of ^<632>Ser of ClC-2 by p34^<cdc2>/cyclin B triggers ClC-2 channel ubiquitination, which underlines M phase-specific ubiquitination and degradation of ClC-2 channel protein.(3) ClC-3B is a chloride channel expressed predominantly in epithelial cells and is localized in its microvilli. ClC-3B interacts With EBP50, an epithelia-specific PDZ-containing protein, and thereby interacts with cystic fibrosis transmembrane conductance regulator (CFTR), a product of cystic fibrosis gene. ClC-3B chloride channel is activated by protein kinase A in the presence of CFTR, and is important in ionic transport across the epithelia.