circCEP128 Knockdown Suppresses Bladder Cancer Progression via Regulating microRNA-515-5p/SDC1 Axis

BACKGROUND: Dysregulation of circular RNAs (circRNAs) is associated with bladder cancer progression. Nevertheless, the mechanisms of circRNA centrosomal protein 128 (circCEP128) underlying bladder cancer progression remain poorly understood. METHODS: The levels of circCEP128, microRNA-515-5p (miR-515-5p) and syndecan-1 (SDC1) were determined via reverse transcription-quantitative polymerase chain reaction or Western blot. The effects of circCEP128, miR-515-5p and SDC1 on bladder cancer progression were investigated via MTT and colony formation assays, flow cytometry and transwell analysis and subcutaneous xenograft experiments. The interactions between miR-515-5p and circCEP128 or SDC1 were examined through bioinformatics prediction and luciferase reporter assay. RESULTS: circCEP128 and SDC1 were highly expressed and miR-515-5p was low expressed in bladder cancer tissues and cells. circCEP128 knockdown hindered cell proliferation, migration and invasion and promoted cell apoptosis in bladder cancer. circCEP128 loss increased miR-515-5p expression through direct interaction in bladder cancer cells. MiR-515-5p depletion mitigated the influences of circCEP128 knockdown on bladder cancer cell phenotypes. SDC1 was a direct target of miR-515-5p. circCEP128 positively regulated SDC1 expression via miR-515-5p. MiR-515-5p restrained the malignant progression of bladder cancer cells by decreasing SDC1 expression. circCEP128 knockdown hindered the growth of bladder cancer xenograft tumors by up-regulating miR-515-5p and down-regulating SDC1. CONCLUSION: circCEP128 knockdown hampered the tumorigenesis and progression of bladder cancer by regulating miR-515-5p/SDC1 axis in vitro and in vivo, deepening our understanding on the molecular mechanisms of circCEP128 in bladder cancer.