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. Breast cancer cell mRNA samples were summarized in six samples, divided into two groups, siControl and siRNF187

肿瘤抑制因子P53（tumor suppressor P53）在抑制癌症发生中发挥关键作用。在腔面型乳腺癌（luminal types of breast cancer）中，P53鲜有突变且仍保持正常功能。现有研究表明，野生型P53的功能严格受泛素化等翻译后修饰（post-translational modification）调控。已有多种泛素连接酶（ubiquitin ligase）被证实可调控P53的泛素化修饰与蛋白质稳定性。
本研究报道了RING家族泛素连接酶（RING family ubiquitin ligase）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生存率相关。生物信息学分析显示，RNF187与P53靶基因（如IGFBP3、FAS）的表达呈负相关。敲低RNF187可抑制乳腺癌细胞增殖并促进细胞死亡。RNA测序（RNA sequencing）分析表明，RNF187可作为P53信号通路的重要调控修饰因子。
进一步实验证实，RNF187可与P53相互作用，并通过促进乳腺癌细胞内P53的多聚泛素化（poly-ubiquitination）介导P53降解。有趣的是，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MDM2。上述发现揭示了一种全新的直接P53调控因子，同时也为乳腺癌提供了潜在的治疗靶点。
本研究纳入6例乳腺癌细胞mRNA样本，分为两组：siControl组与siRNF187组。