The Long Non-Coding RNA TMPO-AS1 Promotes Bladder Cancer Growth and Progression via OTUB1-Induced E2F1 Deubiquitination

Background: Increasing evidence indicates long non-coding RNAs (lncRNAs) play crucial roles in cancer tumorigenesis and progression. TMPO antisense RNA 1 (TMPO-AS1) has been found to be involved in several cancers by acting as an competing endogenous RNA. However, the potential roles of TMPO-AS1 interacting with proteins in bladder cancer (BC) remain poorly understood. Methods: The lncRNA TMPO-AS1 expression was evaluated by bioinformatics analysis and was validated by qRT-PCR. Loss- and gain-of- function assays were performed to determine the biological functions of TMPO-AS1 in BC carcinogenesis. Chromatin immunoprecipitation, luciferase reporter assays, western blotting, RNA pull-down, RNA immunoprecipitation assays, and fluorescence in situ hybridization were conducted to explore the molecular mechanisms of TMPO-AS1/E2F transcription factor 1 (E2F1) loop. Findings: TMPO-AS1 is upregulated in bladder cancer and is associated with poor prognosis of BC patients. Functional experiments demonstrated that TMPO-AS1 promotes bladder cancer cell proliferation, migration, invasion, and inhibits cell apoptosis in vivo and in vitro. Mechanically, E2F1 is responsible for the TMPO-AS1 upregulation. Overexpression of TMPO-AS1 facilitates the interaction of E2F1 with OTU domain-containing ubiquitin aldehyde binding 1 (OTUB1), leads to E2F1 deubiquitination and stabilization, and finally promotes BC malignant phenotypes.  Interpretation: Our study is the first to uncover a novel positive regulatory loop of TMPO-AS1/E2F1 important for the promotion of BC malignant phenotypes. The TMPO-AS1/E2F1 loop should be considered in the quest for new BC therapeutic options. Funding Statement: This work was financially supported by the National Natural Science Foundation of China (81874137), Outstanding Youth Foundation of Hunan Province (2018JJ1047), Hunan Province Science and Technology Talent Promotion Project (2019TJ-Q10), and Independent Exploration and Innovation Project of Central South University(2019zzts825). Declaration of Interests: The authors declare no conflicts of interest relevant to this study. Ethics Approval Statement: This study was approved by the ethics committee of the Third Xiangya Hospital, Central South University, and written informed consent were obtained from each patients.