Silencing circ-BIRC6 inhibits the proliferation, invasion, migration and epithelial-mesenchymal transition of bladder cancer cells by targeting the miR-495-3p/XBP1 signaling axis

Circular RNAs (circRNAs) regulate gene expression by acting as a ‘sponge’ for microRNAs (miRs) and play crucial roles in tumorigenesis, including in bladder cancer (BC). circRNA-baculoviral IAP repeat-containing 6 (circ-BIRC6) has been reported to participate in the pathogenesis of several cancer types. The present study aimed to elucidate the roles and potential mechanisms of circ-BIRC6 in the progression of BC. circ-BIRC6 expression levels in BC cell lines were determined using reverse transcription-quantitative PCR. Following circ-BIRC6 knockdown, cell proliferation, invasion and migration were detected using Cell Counting Kit-8, colony formation, Transwell and wound healing assays, respectively. Western blotting was also conducted to evaluate the expression levels of X-box binding protein 1 (XBP1) and epithelial-mesenchymal transition (EMT)-associated proteins. In addition, rescue experiments were performed using by transfecting a miR-495-3p inhibitor into T24 cells following circ-BIRC6 knockdown. The interactions between circ-BIRC6, miR-495-3p and XBP1 was verified using dual luciferase reporter assays. Moreover, T24 cells with circ-BIRC6 knockdown and miR-495-3p inhibitor transfection were used for the tumor-bearing experiment. Tumor growth was observed and Ki-67 expression was determined using immunohistochemistry. The results demonstrated that circ-BIRC6 expression was upregulated in BC cell lines. Moreover, circ-BIRC6 knockdown notably attenuated the proliferation, invasion, migration and EMT of BC cells, which was blocked by the miR-495-3p inhibitor. It was also identified that circ-BIRC6 sponged miR-495-3p to regulate XBP1 expression. In addition, results from the xenograft experiments indicated that the knockdown of circ-BIRC6 and miR-495-3p expression significantly inhibited tumor growth. It was also found that the expression levels of XBP1, Ki-67 and EMT-associated proteins in tumor tissues of the co-transfection group were markedly restored compared with the circ-BIRC6 knockdown group. In conclusion, these findings demonstrated that circ-BIRC6 knockdown suppressed BC tumorigenesis and progression via regulation of the miR-495-3p/XBP1 signaling axis, offering a promising therapeutic target for the treatment of BC.