Circular RNA circ‐TNPO3 inhibits clear cell renal cell carcinoma metastasis by binding to IGF2BP2 and destabilizing SERPINH1 mRNA

BACKGROUND: Clear cell renal cell carcinoma (ccRCC) is a common malignant tumour of the urinary tract. The major causes of poor prognosis are the lack of early diagnosis and metastasis. Accumulating research reveals that circular RNAs (circRNAs) can play key roles in the development and the progression of cancer. However, the role of circRNAs in ccRCC is still uncertain. METHODS: The circRNAs microarray (n = 4) was performed to investigate the circRNAs with differential expression in ccRCC tissues. The candidate circRNA was selected based on the cut‐off criteria, such as circRNA expression abundance, circRNA size and the design of divergent primers. The circ‐transportin‐3 (TNPO3) levels in ccRCC tissues were tested by quantitative real‐time (qRT)‐PCR (n = 110). The characteristics and subcellular localization of circ‐TNPO3 were identified via RNase R assay, qRT‐PCR and fluorescence in situ hybridization (FISH). Then, we explored the biological roles of circ‐TNPO3 in ccRCC via the function experiments in vitro and in vivo. RNA pull‐down, RNA immunoprecipitation, bioinformatic analysis, RNA‐FISH assays and rescue assays were applied to validate the interactions between circ‐TNPO3, insulin‐like growth factor 2 mRNA‐binding protein 2 (IGF2BP2) and serpin family H member 1 (SERPINH1) to uncover the underlying molecular mechanisms of circ‐TNPO3. RESULTS: We detected the obvious downregulation of circ‐TNPO3 in ccRCC compared to matched adjacent normal tissues (n = 110). The lower circ‐TNPO3 expression was found in ccRCC patients with distant metastasis, higher World Health Organization/International Society of Urologic Pathologists (WHO/ISUP) grade and more advanced tumour T stage. In vitro and in vivo, circ‐TNPO3 significantly suppressed the proliferation and migration of ccRCC cells. Mechanistically, we elucidated that circ‐TNPO3 directly bound to IGF2BP2 protein and then destabilized SERPINH1 mRNA. Moreover, IGF2BP2/SERPINH1 axis was responsible for circ‐TNPO3's function of inhibiting ccRCC metastasis. Epithelial splicing regulatory protein 1 (ESRP1) was probably involved in the biogenesis of circ‐TNPO3. CONCLUSIONS: Circ‐TNPO3 can suppress ccRCC progression and metastasis via directly binding to IGF2BP2 protein and destabilizing SERPINH1 mRNA. Circ‐TNPO3 may act as a potential target for ccRCC treatment.