BACKGROUND Tamoxifen (TAM) resistance is a critical clinical challenge in the treatment of ERa+ breast cancer. However, the underlying mechanisms involved in TAM-resistance are not fully understood. Here we study the efficacy of UBR5 in predicting TAM-resistance in ERa+ breast cancer. METHODS Western blot RT-PCR and IHC staining were used to evaluate UBR5 protein and mRNA levels in ERa+ breast cancer cell and tissues. MTT assays and colony formation assays were used to measure cell proliferation. The xeno-graft tumor model was used for in vivo study. We performed protein stability assay and ubiquitin assay to detect β-catenin protein degradation. Immuno-precipitation assay was used to detect the interaction between UBR5 and β-catenin. The ubiquitin-based immuno-precipitation based assay was used to detect the ubiquitination of β-catenin. RESULTS High UBR5 expression was correlated with poor prognosis in ER+ breast cancer. Importantly, UBR5 expression was remarkably upregulated in TAM-refractory breast cancer tissues compared with their primary paired TAM-untreated tissues. Additionally, UBR5 overexpression caused tamoxifen-resistance in vitro, whereas UBR5 knockdown increased TAM sensitivity. Mechanistic investigations revealed that UBR5 overexpression, through its ubiquitin ligase catalyzing activity, led to up-regulation of β-catenin expression and activity. Finally, our results confirmed that TAM-resistance promoting effects by UBR5 in ERa+ breast cancer cells was at least partly due to β-catenin stabilization, and inhibition of the UBR5/β-catenin signaling re-sensitizing the resistant breast cancer cells to tamoxifen in vivo. CONCLUSIONS These findings suggested that UBR5/β-catenin signaling might be a potential therapeutic target for TAM-resistant ERa+ breast cancer.

中文翻译：

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UBR5 过表达通过稳定 β-连环蛋白导致 ERa+ 乳腺癌的不良预后和他莫昔芬耐药性。

背景 他莫昔芬 (TAM) 耐药性是治疗 ERa+ 乳腺癌的关键临床挑战。然而，涉及 TAM 抗性的潜在机制尚不完全清楚。在这里，我们研究了 UBR5 在预测 ERa+ 乳腺癌中 TAM 抗性方面的功效。方法采用蛋白质印迹RT-PCR和IHC染色法评估ERa+乳腺癌细胞和组织中UBR5蛋白和mRNA水平。MTT测定和集落形成测定用于测量细胞增殖。异种移植肿瘤模型用于体内研究。我们进行了蛋白质稳定性测定和泛素测定以检测 β-catenin 蛋白质降解。采用免疫沉淀法检测 UBR5 与 β-catenin 的相互作用。基于泛素的免疫沉淀法用于检测β-连环蛋白的泛素化。结果 高 UBR5 表达与 ER+ 乳腺癌的不良预后相关。重要的是，与未治疗的原代配对 TAM 组织相比，TAM 难治性乳腺癌组织中 UBR5 的表达显着上调。此外，UBR5 过表达在体外引起他莫昔芬抗性，而 UBR5 组合式增加了 TAM 敏感性。机理研究表明，UBR5 过表达，通过其泛素连接酶催化活性，导致 β-连环蛋白表达和活性的上调。最后，我们的结果证实 UBR5 在 ERa+ 乳腺癌细胞中的 TAM 抗性促进作用至少部分是由于 β-连环蛋白的稳定，并且抑制 UBR5/β-连环蛋白信号使抗性乳腺癌细胞对他莫昔芬重新敏感。活体。