Background: Circular RNAs (circRNAs) are novel clusters of endogenous noncoding RNAs (ncRNAs) that are involved in the regulation of multiple biological processes in diverse types of cancers. However, the roles and precise mechanisms of circRNAs in renal cell carcinoma (RCC) occurrence and progression have not been clearly elucidated.
Methods: We identified the aberrantly expressed circRNAs in RCC by high-throughput RNA-seq assay and used qRT-PCR to test the expression level of circRNAs in RCC tissues. Loss-of-function experiments were executed to detect the biological roles of circPDK1  in the RCC cells both in vivo and in vitro. RNA Fish, luciferase reporter assays and Western blotting were used to explore the molecular mechanism of circPDK1 function. All data were expressed as the means ± standard error of the mean (SEM). Student’s t -test, one-way ANOVA, Cox regression, an LSD-t -test, Pearson’s chi-squared test, a Log-rank test, and linear regression analyses were used to evaluate the group differences. P <  0.05 was considered significant.
Results: CircPDK1 was overexpressed in RCC tissues and positively associated with patient tumor metastasis and renal cell invasion. The in vivo functional assays also revealed that circPDK1 drove RCC xenograft metastasis. CircPDK1  was mainly located in the cytoplasm, serving as a sponge of miR-377-3P  to regulate RCC invasion and metastasis through NOTCH1  (Notch Homolog 1). Ectopic express of NOTCH1  in RCC cell lines will block the metastasis inhibition effect after circPDK1  knockdown.
Conclusion: CircPDK1 is aberrantly expressed in RCC and promotes the metastasis of RCC cells mainly through sponging miR-377-3P  and reducing its negative regulation of NOTCH1 . Thus, circPDK1  may act as a therapeutic target and biomarker for RCC.
Keywords: circPDK1 , miR-377-3P , NOTCH1, renal cell carcinoma, metastasis