Background: As the seventh most common urologic carcinoma worldwide, approximately 430,000 patients are diagnosed with bladder cancer (BC) every year. Increasing evidence indicates that long noncoding RNAs (IncRNAs) play crucial roles in the progression of BC. Objectives: This study is aimed to explore the function and mechanism of CASC9 in BC. Methods: Bioinformatics analysis and experiments including RT-qPCR, luciferase reporter, Cell Counting Kit-8 assay, Western blot, RNA immunoprecipitation assay, and TU-NEL staining were applied to explore the function and mechanism of CASC9 in BC tissues and cell lines. Results: Our study demonstrated that CASC9 was upregulated in BC tissues and cell lines. Moreover, we found that CASC9 knockdown notably decreased proliferation while increased apop-totic rate in BC cells. Mechanistically, bioinformatics prediction andfollowing experiments indicated that CASC9 worked as a competing endogenous RNA (ceRNA) of CBX2 through sponging miR-497-5p. Meanwhile, we recognized that CASC9 and miR-497-5p negatively regulated each other in a mutual way. Furthermore, we found that miR-497-5p shared binding site with CBX2. In addition, miR-497-5p could negatively regulated CBX2, while CASC9 could positively regulated CBX2. Rescue assays reveled that CBX2 overexpression could reversed the reduction of cell proliferation or the enhancement of cell apoptosis induced by CASC9 suppression. Conclusions: Our study manifests the first evidence that CASC9 serves as an oncogene in BC and accelerates cell proliferation by modulating miR-497-5p/CBX2 axis. The present study may provide a cogitable target for BC therapy
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