Circular RNA hsa_circ_0005239 contributes to hepatocellular carcinoma cell migration, invasion, and angiogenesis by targeting the miR‐34a‐5p/PD‐L1 axis

Circular RNAs (circRNAs) may be involved in tumorigenesis. Recently, the role of circRNAs in hepatocellular carcinoma (HCC) has drawn wide attention. Herein, we aimed to explore the regulation and function of hsa_circ_0005239 in the malignant biological behavior and angiogenesis of HCC, as well as the link between hsa_circ_0005239 and programmed cell death ligand 1 (PD-L1) in HCC. Quantitative real-time polymerase chain reaction (qRT-PCR) assays revealed that hsa_circ_0005239 was upregulated in HCC tumor samples and cell lines. Furthermore, a series of in vitro and in vivo assays explored the effects of hsa_circ_0005239 on biological processes involved in the development of HCC. Knockdown of hsa_circ_0005239 significantly inhibited cell migration, cell invasion, and angiogenesis in HCC, while overexpression showed the opposite effect. In the in vivo assays, hsa_circ_0005239 downregulation suppressed the growth of xenograft tumors in nude mice, which supported that hsa_circ_0005239 is a tumor promoter in HCC. Mechanistically, hsa_circ_0005239 binds to miR-34a-5p and functions as a competing endogenous RNA to modulate the expression of PD-L1. Further experiments revealed that the hsa_circ_0005239/PD-L1 axis regulates the malignant phenotypes of HCC cells through the phosphoinositide-3 kinase/protein kinase B (PI3K/Akt) signaling pathway. These results revealed the role of hsa_circ_0005239 and the hsa_circ_0005239/miR-34a-5p/PD-L1 axis in HCC, providing a potential diagnostic biomarker and therapeutic target for HCC.