Department of Molecular Pathology, Nara Medical University, 840 Shijo-cho, Kashihara 634-8521, Nara, Japan.
Department of Urology, Nara Medical University, 840 Shijo-cho, Kashihara 634-8522, Nara, Japan.
Int J Mol Sci. 2022 Jun 10;23(12):6516. doi: 10.3390/ijms23126516.
The tight junction (TJ) protein claudin-4 (CLDN4) is overexpressed in bladder urothelial carcinoma (BUC) and correlates with cancer progression. However, the mechanism of CLDN4 upregulation and promotion of malignant phenotype is not clear. Here, we analyzed 157 cases of BUC and investigated the hypomethylation of CpG island in the promoter DNA and its correlation with cancer progression. In hypomethylated cases, CLDN4 expression, cell proliferation, stemness, and epithelial-mesenchymal transition were increased. Treatment of three human BUC cell lines with the demethylating agent aza-2'-deoxycytidine (AZA) led to excessive CLDN4 expression, and, specifically, to an increase in CLDN4 monomer that is not integrated into the TJ. The TJ-unintegrated CLDN4 was found to bind integrin β1 and increase stemness, drug resistance, and metastatic ability of the cells as well as show an anti-apoptosis effect likely via FAK phosphorylation, which reduces upon knockdown of CLDN4. Thus, CLDN4 is overexpressed in BUC by an epigenetic mechanism and the high expression enhances the malignant phenotype of BUC via increased levels of TJ-unintegrated CLDN4. promoter DNA methylation is expected to be a novel indicator of BUC malignant phenotype and a new therapeutic target.
紧密连接 (TJ) 蛋白 Claudin-4 (CLDN4) 在膀胱尿路上皮癌 (BUC) 中过度表达，并与癌症进展相关。然而，CLDN4 上调及其促进恶性表型的机制尚不清楚。在这里，我们分析了 157 例 BUC，并研究了启动子 DNA 中 CpG 岛的低甲基化及其与癌症进展的相关性。在低甲基化病例中，CLDN4 的表达、细胞增殖、干性和上皮-间充质转化增加。用去甲基化剂阿扎 -2'-脱氧胞苷 (AZA) 处理三种人 BUC 细胞系导致 CLDN4 过度表达，特别是 TJ 未整合的 CLDN4 单体增加。发现 TJ 未整合的 CLDN4 与整合素 β1 结合，增加细胞的干性、耐药性和转移能力，并具有抗细胞凋亡作用，可能通过 FAK 磷酸化，而 CLDN4 的敲低会降低 FAK 磷酸化。因此，CLDN4 通过表观遗传机制在 BUC 中过度表达，高表达通过增加 TJ 未整合的 CLDN4 水平增强 BUC 的恶性表型。启动子 DNA 甲基化有望成为 BUC 恶性表型的一个新指标和一个新的治疗靶点。
