Telomere maintenance is crucial for the unlimited proliferation of cancer cells and essential for the “stemness” of multiple cancer cells. TAZ is more extensively expressed in triple negative breast cancers (TNBC) than in other types of breast cancers, and promotes proliferation, transformation and EMT of cancer cells. It was reported that TAZ renders breast cancer cells with cancer stem cell features. However, whether TAZ regulates telomeres is still unclear. In this study, we explored the roles of TAZ in the regulation of telomere maintenance in TNBC cells. siRNA and shRNA was used to generate TAZ-depleted TNBC cell lines. qPCR and Southern analysis of terminal restriction fragments techniques were used to test telomere length. Co-immunoprecipitation, Western blotting, immunofluorescence, Luciferase reporter assay and Chromatin-IP were conducted to investigate the underlying mechanism. By knocking down the expression of TAZ in TNBC cells, we found, for the first time, that TAZ is essential for the maintenance of telomeres in TNBC cells. Moreover, loss of TAZ causes senescence phenotype of TNBC cells. The observed extremely shortened telomeres in late passages of TAZ knocked down cells correlate with an elevated hTERT expression, reductions of shelterin proteins, and an activated DNA damage response pathway. Our data also showed that depletion of TAZ results in overexpression of TERRAs, which are a group of telomeric repeat‐containing RNAs and regulate telomere length and integrity. Furthermore, we discovered that TAZ maintains telomere length of TNBC cells likely by facilitating the expression of Rad51C, a crucial element of homologous recombination pathway that promotes telomere replication. This study supports the notion that TAZ is an oncogenic factor in TNBC, and further reveals a novel telomere-related pathway that is employed by TAZ to regulate TNBC.

中文翻译：

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TAZ 通过介导 Rad51C 表达维持 TNBC 细胞中的端粒长度

端粒维持对癌细胞的无限增殖至关重要，对多种癌细胞的“干性”至关重要。TAZ 在三阴性乳腺癌 (TNBC) 中的表达比在其他类型的乳腺癌中更广泛，并促进癌细胞的增殖、转化和 EMT。据报道，TAZ 使乳腺癌细胞具有癌症干细胞特征。然而，TAZ 是否调节端粒仍不清楚。在这项研究中，我们探讨了 TAZ 在调节 TNBC 细胞端粒维持中的作用。siRNA 和 shRNA 用于生成 TAZ 耗尽的 TNBC 细胞系。qPCR 和Southern 分析末端限制性片段技术用于测试端粒长度。免疫共沉淀、蛋白质印迹、免疫荧光、进行荧光素酶报告基因测定和染色质-IP 以研究潜在机制。通过敲低 TNBC 细胞中 TAZ 的表达，我们首次发现 TAZ 对于维持 TNBC 细胞中的端粒至关重要。此外，TAZ 的缺失会导致 TNBC 细胞的衰老表型。在 TAZ 敲低细胞的晚期传代中观察到的极短的端粒与 hTERT 表达升高、shelterin 蛋白减少和激活的 DNA 损伤反应途径相关。我们的数据还表明，TAZ 的消耗导致 TERRA 的过度表达，TERRA 是一组含有端粒重复序列的 RNA，可调节端粒长度和完整性。此外，我们发现 TAZ 可能通过促进 Rad51C 的表达来维持 TNBC 细胞的端粒长度，促进端粒复制的同源重组途径的关键因素。该研究支持 TAZ 是 TNBC 中的致癌因子的观点，并进一步揭示了 TAZ 用于调节 TNBC 的新型端粒相关通路。