Regulation of P53 signaling in breast cancer by the E3 ubiquitin ligase RNF187. Regulation of P53 signaling in breast cancer by the E3 ubiquitin ligase RNF187

The tumor suppressor P53 plays critical roles in prohibiting cancer. P53 is rarely mutated and still functional in luminal types of breast cancer. According to current knowledge, wild type P53 function is tightly controlled by post-translational modification, such as ubiquitination. Several ubiquitin ligases were shown to regulate P53 ubiquitination and protein stability. Here, we report RNF187, a RING family ubiquitin ligase, facilitates breast cancer growth and inhibits apoptosis via modulating P53 signaling. RNF187 is elevated in breast cancer and correlates with breast cancer survival only in P53 wild type groups. The bio-informatics analysis shows that RNF187 negatively correlates P53 target gene expression, such as IGFBP3 and FAS in breast cancer. RNF187 depletion inhibits breast cancer growth and facilitates cell death. RNA sequencing analysis indicates that RNF187 could be an important modifier for P53 signaling. Further experiments show that RNF187 interacts with P53 and promotes P53 degradation via facilitating P53 poly-ubiquitination in breast cancer cells. Interesting, the in vitro ubiquitin assay shows that RNF187 could directly ubiquitinate P53, which is independent of MDM2. These finding reveals a novel direct P53 regulator and a potential therapeutic target for breast cancer. Overall design: Breast cancer cell mRNA samples were summarized in six samples, divided into two groups, siControl and siRNF187

抑癌蛋白P53（tumor suppressor P53）在抑制肿瘤发生发展中发挥关键作用。在管腔型乳腺癌中，P53极少发生突变且仍保持正常功能。目前已知，野生型P53的功能严格受泛素化（ubiquitination）等翻译后修饰调控。已有研究表明，多种泛素连接酶（ubiquitin ligase）可调控P53的泛素化修饰与蛋白稳定性。本研究发现，属于RING家族泛素连接酶（RING family ubiquitin ligase）的RNF187可通过调控P53信号通路促进乳腺癌增殖并抑制细胞凋亡。RNF187在乳腺癌组织中表达升高，且仅在P53野生型亚组中与乳腺癌患者的生存情况相关。生物信息学分析显示，在乳腺癌中RNF187的表达与P53靶基因（如IGFBP3、FAS）的表达呈负相关。敲低RNF187可抑制乳腺癌增殖并促进细胞死亡。RNA测序分析表明，RNF187可作为P53信号通路的重要调控因子。进一步实验证实，RNF187可与P53结合，并通过促进乳腺癌细胞中P53的多聚泛素化修饰加速其降解。值得注意的是，体外泛素化实验显示，RNF187可直接对P53进行泛素化修饰，且该过程不依赖于MDM2。上述研究发现了一种全新的P53直接调控因子，同时也为乳腺癌治疗提供了潜在的靶点。实验整体设计：本研究共纳入6例乳腺癌细胞mRNA样本，分为两组，分别为阴性对照siRNA组（siControl）与RNF187靶向敲低siRNA组（siRNF187）