Verbavatz J M, Van Hoek A N, Ma T, Sabolic I, Valenti G, Ellisman M H, Ausiello D A, Verkman A S, Brown D
Department of Medicine, Massachusetts General Hospital, Charlestown 02129.
J Cell Sci. 1994 Apr;107 ( Pt 4):1083-94. doi: 10.1242/jcs.107.4.1083.
Two recently cloned water channels, CHIP28 and WCH-CD, are homologous to MIP26, an integral membrane channel-forming protein found in lens fiber plasma membranes. CHIP28 is found in basolateral and apical plasma membranes of kidney proximal tubules and thin descending limbs of Henle, whereas WCH-CD is apically located in collecting duct principal cells. So far, the putative water channel that may be responsible for the high constitutive permeability of principal cell basolateral membranes has not been identified. Interestingly, freeze-fracture electron microscopy has shown that characteristic orthogonal arrays of intramembrane particles (OAPs) are found on the basolateral plasma membranes of collecting duct principal cells, and that morphologically identical OAPs present in lens fiber cell plasma membranes contain the protein MIP26. Similar OAPs have also been detected on plasma membranes of other cell types including gastric parietal cells, astroglial cells and skeletal muscle fibers. By indirect immunofluorescence, western blotting and northern blotting, MIP26 was found only in lens fibers. In addition, functional studies on reconstituted and oocyte-expressed MIP26 excluded the possibility that MIP26 might be a basolateral water channel in the kidney. However, a polyclonal antibody raised against skeletal muscle sarcolemmal vesicles, which are enriched in OAPs, produced an intense staining of principal cell basolateral plasma membranes in kidney collecting duct and immunoprecipitated a 28 kDa protein from kidney papilla. The immunoprecipitated protein from papilla was not recognized by anti-CHIP28 or anti-MIP26 antibodies, indicating that principal cell basolateral membranes contain a novel member of the CHIP/MIP family. Because this antibody also stained brain astrocyte end feet, which are enriched in OAPs, it is possible that the 28 kDa protein is related to these structures. We conclude that OAPs probably contain related but distinct proteins that may have different membrane channel functions in different cell types.
最近克隆出的两个水通道蛋白CHIP28和WCH-CD，与MIP26同源，MIP26是一种存在于晶状体纤维质膜中的整合膜通道形成蛋白。CHIP28存在于肾近端小管的基底外侧质膜和髓袢细降支中，而WCH-CD位于集合管主细胞的顶端。到目前为止，尚未确定可能导致主细胞基底外侧膜具有高组成性通透性的假定水通道。有趣的是，冷冻蚀刻电子显微镜显示，在集合管主细胞的基底外侧质膜上发现了特征性的膜内颗粒正交阵列（OAPs），并且晶状体纤维细胞质膜中存在的形态相同的OAPs含有蛋白MIP26。在包括胃壁细胞、星形胶质细胞和骨骼肌纤维在内的其他细胞类型的质膜上也检测到了类似的OAPs。通过间接免疫荧光、蛋白质印迹和Northern印迹分析发现，MIP26仅存在于晶状体纤维中。此外，对重组和卵母细胞表达的MIP进行的功能研究排除了MIP26可能是肾脏基底外侧水通道的可能性。然而，针对富含OAPs的骨骼肌肌膜囊泡产生的多克隆抗体，在肾集合管主细胞基底外侧质膜上产生了强烈的染色，并从肾乳头中免疫沉淀出一种28 kDa的蛋白质。来自乳头的免疫沉淀蛋白未被抗CHIP28或抗MIP抗体识别，这表明主细胞基底外侧膜含有CHIP/MIP家族的一个新成员。由于该抗体也对富含OAPs的脑星形胶质细胞终足进行了染色，因此有可能28 kDa的蛋白质与这些结构有关。我们得出结论，OAPs可能包含相关但不同的蛋白质，这些蛋白质在不同细胞类型中可能具有不同的膜通道功能。
