CircBRWD3 promotes non-small cell lung cancer progression through enhancing the stability of TRIM25 to increase p53 ubiquitin degradation and upregulating SPTBN2

Circular RNAs (circRNAs) play crucial roles in cancer progression and metastasis. However, the expression profiles and biological roles of circRNAs in non-small cell lung cancer (NSCLC) remain unclear. In this study, we found a novel circRNA, hsa_circ_0001936(circBRWD3), in NSCLC and investigated the biological role of circBRWD3 in NSCLC progression in vitro and in vivo. qRT-PCR was used to quantify the expression of circBRWD3 in NSCLC tissues, serum and cells. Cell growth curves, colony formation, Edu assay and transwell assays were conducted to study the function of circBRWD3. Finally, the molecular mechanism of circBRWD3 was revealed by Bioinformatic analyses, RNA pull-down analysis, RNA Fluorescence in situ hybridization (FISH), RNA-Binding Protein Immunoprecipitation (RIP), western blot, dual-luciferase reporter gene assays and rescue experiments. Our results showed that circBRWD3 was upregulated in NSCLC tumor tissues, patient serum and cell lines. CircBRWD3 knockdown inhibited NSCLC cells' growth and metastasis both in vitro and in vivo, while circBRWD3 overexpression had the opposite effect. Mechanistically, circBRWD3 binds to the TRIM25 protein to enhance its stability and mediate ubiquitin degradation of the p53 protein. In addition, circBRWD3 acted as a sponge for miR-135a-5p and miR-135b-5p to regulate the expression of SPTBN2, which promoted NSCLC progression. Our findings uncovered a tumor oncogenic function of circBRWD3 in NSCLC through the regulation of TRIM25 protein stability and miR-135a-5p/miR-135b-5p/SPTBN2 axis. CircBRWD3 may act as a promising oncogenic biomarker and therapeutic target for NSCLC.