CircTLK1 Promotes the Proliferation and Metastasis of Renal Cell Carcinoma by Sponging miR-136-5p

Abstract

Background: Circular RNAs (circRNAs), a novel type of ncRNAs, are covalently linked to make up circular configuration via a loop structure. Accumulating evidence indicate that circRNAs are potential biomarkers and key regulators in the development and progression of tumors. However, the precise role of circRNAs in renal cell carcinoma (RCC) remains unknown. Methods: Though circRNA high-throughput sequencing from RCC cell lines, we determined circRNA TLK1 (circTLK1) as a novel candidate circRNA derived from TLK1 gene. Quantitative real-time PCR (qRT-PCR) was performed to detect the expression levels of mRNAs, circRNAs and miRNAs in RCC tissues and cells. Loss-of function experiments were executed to detect the biological roles of circTLK1 on the phenotypes of RCC cells in vitro and in vivo. RNA-FISH, RNA-pull down, dual-luciferase reporter, western blot and immunohistochemistry assay were used to investigate the molecular mechanisms underlying the functions of circTLK1. Findings: CircTLK1 is overexpressed in RCC and positively corelated with distant metastasis and unfavorable prognosis. Silence of circTLK1 significantly inhibits the proliferation, migration and invasion of RCC cells in vitro and in vivo. Mechanistically, circTLK1 is mainly distributed in the cytoplasm and positively regulates CBX4 expression by sponging miR-136-5p. In addition, forced expression of CBX4 reverses the phenotypes inhibition of RCC cells induced by circTLK1 suppression. Moreover, CBX4 expression is positively corelated with VEGF expression in renal cancer tissues. Knockdown of CBX4 significantly inhibited VEGF expression in RCC cells. Interpretation: Collectively, our findings demonstrate that circTLK1 plays a critical role in RCC progression by sponging miR-136-5p to increase CBX4 expression. CircTLK1 may act as a diagnostic biomarker and therapeutic target for RCC. Funding Statement: This study was supported by grants from Guangdong Key Laboratories (2017B030314074) and the Shenzhen Project of Science and Technology (JCYJ20170413100245260). Declaration of Interests: The authors declare that they have no competing interests. Ethics Approval Statement: The present study was approved the Institutional Review Board of Peking University Shenzhen Hospital. In vivo assay was approved by the animal management committee of Perking University Shenzhen Hospital, and all experimental procedures and animal care were in line with the institutional ethics guidelines for animal experiments.