Ikari Akira, Watanabe Ryo, Sato Tomonari, Taga Saeko, Shimobaba Shun, Yamaguchi Masahiko, Yamazaki Yasuhiro, Endo Satoshi, Matsunaga Toshiyuki, Sugatani Junko
Laboratory of Biochemistry, Department of Biopharmaceutical Sciences, Gifu Pharmaceutical University, Gifu, Japan; School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Biochim Biophys Acta. 2014 Sep;1843(9):2079-88. doi: 10.1016/j.bbamcr.2014.05.017. Epub 2014 Jun 4.
Claudin-2 is expressed in human lung adenocarcinoma tissue and cell lines, although it is absent in normal lung tissue. However, the role of claudin-2 in cell proliferation and the regulatory mechanism of intracellular distribution remain undefined. Proliferation of human adenocarcinoma A549 cells was decreased by claudin-2 knockdown together with a decrease in the percentage of S phase cells. This knockdown decreased the expression levels of ZONAB and cell cycle regulators. Claudin-2 was distributed in the nucleus in human adenocarcinoma tissues and proliferating A549 cells. The nuclear distribution of ZONAB and percentage of S phase cells were higher in cells exogenously expressing claudin-2 with a nuclear localization signal than in cells expressing claudin-2 with a nuclear export signal. Nuclear claudin-2 formed a complex with ZO-1, ZONAB, and cyclin D1. Nuclear distribution of S208A mutant, a dephosphorylated form of claudin-2, was higher than that of wild type. We suggest that nuclear distribution of claudin-2 is up-regulated by dephosphorylation and claudin-2 serves to retain ZONAB and cyclin D1 in the nucleus, resulting in the enhancement of cell proliferation in lung adenocarcinoma cells.
紧密连接蛋白2（Claudin-2）在人肺腺癌组织和细胞系中表达，而在正常肺组织中不存在。然而，Claudin-2在细胞增殖中的作用以及细胞内分布的调控机制仍不明确。Claudin-2基因敲低可降低人肺腺癌A549细胞的增殖，并使S期细胞百分比降低。这种基因敲低还降低了锌指蛋白与富含GCG元件的结合蛋白（ZONAB）和细胞周期调节因子的表达水平。Claudin-2分布于人肺腺癌组织和增殖的A549细胞的细胞核中。与带有核输出信号的Claudin-2表达细胞相比，带有核定位信号的Claudin-2外源表达细胞中ZONAB的核分布和S期细胞百分比更高。核内Claudin-2与紧密连接蛋白1（ZO-1）、ZONAB和细胞周期蛋白D1形成复合物。Claudin-2的去磷酸化形式S208A突变体的核分布高于野生型。我们认为，Claudin-2的核分布通过去磷酸化上调，且Claudin-2可将ZONAB和细胞周期蛋白D1保留在细胞核中，从而增强肺腺癌细胞的增殖。
