Increased transcription of hsa_circ_0000644 upon RUNX family transcription factor 3 downregulation participates in the malignant development of bladder cancer

Background Studies are ongoing to examine the versatile functions of circular RNAs (circRNAs) in human diseases. This research investigates the effects of hsa_circ_0000644 (circ_644) and its related molecules on the malignant behavior of bladder cancer (BCa) cells. Methods Abundant bioinformatics analyses were performed to screen the key circRNA and its related molecules in BCa. Tumor tissues and the para-tumorous tissues were collected from 58 patients with BCa. Expression of RUNX family transcription factor 3 (RUNX3), circ_644, microRNA-143-3p (miR-143-3p), and musashi RNA binding protein 2 (MSI2) in BCa tissues or cells was determined. Molecular interactions were confirmed by chromatin immunoprecipitation, RNA pull-down, and luciferase assays. Gain and loss-of function assays were performed using two BCa cell lines (T24 and HT1376). Results Circ_644 was highly expressed whereas RUNX3 , which could suppress circ_644 transcription, was lowly expressed in BCa tissues and cells. Upregulation of RUNX3 suppressed proliferation, colony formation, migration and invasion, and tumorigenicity of BCa cells and induced cell cycle arrest . However, the tumor-suppressive effects of RUNX3 were blocked by circ_644 upregulation. Circ_644 served as a sponge for miR-143-3p, and miR-143-3p bound to MSI2 mRNA. The rescue experiments showed that miR-143-3p inhibition or MSI2 overexpression restored the malignant behaviors of BCa cells induced by circ_644 knockdown or RUNX3 overexpression. Conclusion This study demonstrates that transcriptional activation of circ_644 upon RUNX3 downregulation drives the malignant development of BCa through the miR-143-3p/MSI2 axis. RUNX3 restoration or specific inhibition of circ_644 or MSI2 may help block BCa progression.