Kurihara H, Anderson J M, Farquhar M G
Division of Cellular and Molecular Medicine, University of California, San Diego, La Jolla.
Proc Natl Acad Sci U S A. 1992 Aug 1;89(15):7075-9. doi: 10.1073/pnas.89.15.7075.
ZO-1 is a 225-kDa peripheral membrane protein present in all tight junctions. It was recently shown to consist of two isoforms that differ in the presence of an internal 80-amino acid domain termed motif-alpha. To obtain information on their distribution and potential functional significance we have localized the two isoforms in rat kidney by using antibodies that recognize either both ZO-1 isoforms or the larger, motif-alpha-containing isoform. By immunofluorescence, staining with both antibodies was demonstrated at all tight junctions of tubular epithelial cells and the epithelial cells of Bowman's capsule. In contrast, the motif-alpha-containing isoform was absent from the slit diaphragms of the glomerular epithelium and the tight junctions of glomerular and peritubular capillary endothelial cells. This restricted isoform expression was confirmed by immunoblot analysis comparing proteins from purified glomeruli with those from kidney cortex or medulla. Thus, while both isoforms are expressed in typical epithelial tight junctions, only a single isoform, lacking motif-alpha, is expressed in the highly specialized slit diaphragms, where the intercellular spaces are normally open, and in endothelial junctions, which are readily opened by physiologic signals. The differential expression of ZO-1 isoforms in structurally and functionally distinct junctions in the kidney suggests that they may contribute to defining the variable functional properties, in particular the lability of these intercellular junctions.
ZO-1是一种存在于所有紧密连接中的225 kDa外周膜蛋白。最近发现它由两种异构体组成，这两种异构体在一个称为基序α的内部80个氨基酸结构域的存在上有所不同。为了获得有关它们的分布和潜在功能意义的信息，我们使用能识别两种ZO-1异构体或较大的含基序α异构体的抗体，在大鼠肾脏中定位了这两种异构体。通过免疫荧光法，在肾小管上皮细胞和鲍曼囊上皮细胞的所有紧密连接处均显示出两种抗体的染色。相比之下，肾小球上皮的裂孔隔膜以及肾小球和肾小管周围毛细血管内皮细胞的紧密连接处不存在含基序α的异构体。通过免疫印迹分析比较纯化肾小球与肾皮质或髓质中的蛋白质，证实了这种异构体表达的局限性。因此，虽然两种异构体均在典型的上皮紧密连接处表达，但在高度特化的裂孔隔膜（细胞间间隙通常开放）和内皮连接处（易被生理信号打开）中仅表达一种缺乏基序α的异构体。肾脏中结构和功能不同的连接处ZO-1异构体的差异表达表明，它们可能有助于确定这些细胞间连接的可变功能特性，特别是其不稳定性。
