Department of Molecular Biology, University of Geneva, Geneva, Switzerland.
PLoS One. 2013;8(2):e55873. doi: 10.1371/journal.pone.0055873. Epub 2013 Feb 7.
The cytoplamic junctional proteins cingulin and paracingulin have been implicated in the regulation of gene expression in different cultured cell models. In renal epithelial MDCK cells, depletion of either protein results in a Rho-dependent increase in the expression of claudin-2. Here we examined MDCK cell clones depleted of both cingulin and paracingulin (double-KD cells), and we found that unexpectedly the expression of claudin-2, and also the expression of ZO-3 and claudin-3, were decreased, while RhoA activity was still higher than in control cells. The decreased expression of claudin-2 and other TJ proteins in double-KD cells correlated with reduced levels of the transcription factor GATA-4, and was rescued by overexpression of GATA-4, but not by inhibiting RhoA activity. These results indicate that in MDCK cells GATA-4 is required for the expression of claudin-2 and other TJ proteins, and that maintenance of GATA-4 expression requires either cingulin or paracingulin. These results and previous studies suggest a model whereby cingulin and paracingulin redundantly control the expression of specific TJ proteins through distinct GATA-4- and RhoA-dependent mechanisms, and that in the absence of sufficient levels of GATA-4 the RhoA-mediated upregulation of claudin-2 is inhibited.
细胞质连接蛋白桩蛋白和副桩蛋白被认为参与了不同培养细胞模型中基因表达的调控。在肾上皮细胞 MDCK 中，这两种蛋白的耗竭导致 Rho 依赖性 Claudin-2 表达增加。在这里，我们研究了同时耗尽桩蛋白和副桩蛋白的 MDCK 细胞克隆（双 KD 细胞），结果出人意料的是，Claudin-2 的表达以及 ZO-3 和 Claudin-3 的表达都降低了，而 RhoA 活性仍高于对照细胞。双 KD 细胞中 Claudin-2 和其他 TJ 蛋白表达的降低与转录因子 GATA-4 的水平降低有关，而过表达 GATA-4 可以挽救这一现象，但抑制 RhoA 活性则不能。这些结果表明，在 MDCK 细胞中，GATA-4 是 Claudin-2 和其他 TJ 蛋白表达所必需的，并且 GATA-4 的表达需要桩蛋白或副桩蛋白。这些结果和以前的研究表明了一种模型，即桩蛋白和副桩蛋白通过不同的 GATA-4 和 RhoA 依赖的机制冗余地控制特定 TJ 蛋白的表达，并且在没有足够水平的 GATA-4 时，RhoA 介导的 Claudin-2 上调被抑制。
