Cinobufotalin, a Small Chemical Drug, Suppresses Nasopharyngeal Carcinoma Metastasis by Inducing ENKUR to Depress β-Catenin/C-Jun/MYH9 Signal-Mediated p53 Ubiquitination

Background: Clinically, the metastasis of tumor cells is the key factor of death in patients with cancer.  Methods: In this study, we used a model of metastatic nasopharyngeal carcinoma (NPC) to explore the effects of a new chemical, cinobufotalin (CB), combined with cisplatin (DDP).  Findings: We observed that chemically synthesized CB strongly decreased the metastasis of NPC. Furthermore, a better therapeutic effect was shown when CB was combined with DDP. Molecular analysis revealed that CB induced ENKUR expression by deregulating the PI3K/AKT pathway and suppressing c-Jun, an oncogenic transcriptional factor that binds to the ENKUR promoter. ENKUR as a tumor suppressor binds to MYH9 and decreases its expression by recruiting β-catenin via its enkurin domain to prevent its nuclear accumulation, which therefore suppresses c-Jun-induced MYH9 expression. Subsequently, downregulated MYH9 reduces the enlistment of E3 ligase UBE3A and thus decreases the UBE3A-mediated ubiquitination degradation of p53, a key tumor suppressor that decreases epithelial-mesenchymal transition (EMT). Clinical sample analysis demonstrated that the ENKUR expression level was significantly reduced in NPC tissues. Its decreased expression substantially promoted clinical progression and reflected poor prognosis for patients with NPC.  Interpretation: This study demonstrated that CB induced ENKUR to repress the β-catenin/c-Jun/MYH9 signal and thus decreased UBE3A-mediated p53 ubiquitination degradation. As a result, the EMT signal was inactivated to suppress NPC metastasis.  Funding: This study was supported by the National Natural Science Foundation of China(81974460, 81572649), the Scientific Research Project of Guangdong Provincial Bureau of Traditional Chinese Medicine (No. 20193010), the People’s Livelihood Science and Technology grant of Guangzhou Municipal Science and Technology Project (No. 201803010023), Nature Science Fund of Guangdong Province (2021A1515012430, 2020A1515010176)，Discipline construction project of Guangdong Medical University(4SG21011G). Declaration of Interest: Prof. Fang has a pending patent on Cinobufotalin (No. 201910399834.7). All authors declare no conflicts. Ethical Approval: All in vivo experiments were approved by the Animal Care and Use Committee of Southern Medical University.