The Key Laboratory of Pathobiology, Ministry of Education, College of Basic Medical Sciences, Jilin University, 126 Xinmin Avenue, Changchun, 310021, Jilin, China.
Mol Cell Biochem. 2018 Jun;443(1-2):169-180. doi: 10.1007/s11010-017-3221-8. Epub 2017 Nov 20.
Claudin-6 (CLDN6), a critical tight junction protein acting as a tumor suppressor in breast cancer, is also considered to be a stem cell marker. Triple-negative breast cancer (TNBC) is a subtype of claudin-low and stem cell-like breast cancer which is chemoresistant to multiple anti-cancer drugs. The aim of our study was to determine whether CLDN6 plays a role in chemoresistance of TNBC. We found that overexpression of CLDN6 in TNBC cell line MDAMB231 significantly inhibited cell growth, migration, and invasion. The expression of CLDN6 increased the IC of adriamycin (ADM) and promoted the clonogenic survival. CLDN6 inhibited ADM-induced apoptosis and senescence in MDAMB231 cells. However, P-gp, a resistance-related protein highly associated with chemoresistance, was downregulated by CLDN6 overexpression in MDAMB231 cells. Epithelial mesenchymal transition (EMT) marker E-cadherin was increased, and vimentin was decreased by CLDN6. In addition, stem cell markers OCT4, SOX2, and Nanog were dramatically increased. CLDN6 colocalized and interacted with AF-6. Overexpression of CLDN6 increased the expression of afadin (AF-6) and hampered the activation of ERK signaling. PMA, a specific ERK activator, reversed the expression of EMT and stem cell markers, and decreased chemoresistance of MDAMB231 cells to ADM with a decreased IC and an increased apoptosis resulting from CLDN6. Together, we conclude that CLDN6 enhances the chemoresistance to ADM via activating the AF-6/ERK signaling pathway and up-regulating cancer stem cell characters in MDAMB231 cells.
紧密连接蛋白 6（Claudin-6，CLDN6）作为乳腺癌的抑癌因子，也被认为是一种干细胞标志物。三阴性乳腺癌（Triple-negative breast cancer，TNBC）是一种 Claudin-低表达和干细胞样的乳腺癌亚型，对多种抗癌药物具有耐药性。本研究旨在探讨 CLDN6 是否在 TNBC 的耐药中发挥作用。我们发现，在 TNBC 细胞系 MDAMB231 中过表达 CLDN6 显著抑制细胞生长、迁移和侵袭。CLDN6 的表达增加了阿霉素（Adriamycin，ADM）的 IC，并促进了集落形成存活。CLDN6 抑制 ADM 诱导的 MDAMB231 细胞凋亡和衰老。然而，P-糖蛋白（P-glycoprotein，P-gp）是一种与耐药高度相关的耐药相关蛋白，其在 MDAMB231 细胞中过表达 CLDN6 后被下调。上皮间质转化（Epithelial-mesenchymal transition，EMT）标志物 E-钙黏蛋白增加，波形蛋白减少。此外，干细胞标志物 OCT4、SOX2 和 Nanog 显著增加。CLDN6 与 AF-6 共定位并相互作用。CLDN6 过表达增加了 afadin（AF-6）的表达，并阻碍了 ERK 信号的激活。PMA（一种特异性 ERK 激活剂）逆转了 EMT 和干细胞标志物的表达，降低了 ADM 对 MDAMB231 细胞的耐药性，IC 降低，凋亡增加，这归因于 CLDN6。综上所述，CLDN6 通过激活 AF-6/ERK 信号通路和上调 MDAMB231 细胞中的癌症干细胞特征，增强了对 ADM 的耐药性。
