Hepatitis B virus core/capsid protein induces hepatocellular carcinoma progression via long non-coding RNA KCNQ1OT1/miR-335-5p/CDC7 axis.

BACKGROUND: Hepatocellular carcinoma (HCC) is the sixth most common malignancy and the fourth leading cause of cancer-related deaths worldwide. Long non-coding RNAs (lncRNAs) are dysregulated in various malignancies. However, the mechanisms by which lncRNA influences HCC remain unclear. The aim of this study was to reveal a novel mechanism of lncRNA in HCC progression. METHODS: Differentially expressed (DE) analyses were performed to identify DE lncRNAs, DE microRNAs (miRNAs), and DE messenger RNAs (mRNAs) in HCC and normal tissues from The Cancer Genome Atlas (TCGA) database. The competing endogenous RNA (ceRNA) network of DE genes was constructed using the ENCORI/starBase database. The potential binding sites among the components of the ceRNA regulatory axis were predicted using RNAhybrid. The combination and regulatory effects among them were identified by luciferase reporter assay. Additionally, cell counting kit-8 (CCK-8) and colony formation assay confirmed the effect on HCC proliferation, whereas the wound healing assay demonstrated the impact on HCC migration. Expression levels of DE genes were determined via quantitative real-time polymerase chain reaction (qRT-PCR), western blotting (WB), and immunofluorescence. An immunohistochemistry assay was used to verify cell division cycle 7 (CDC7) expression in HCC tissues and adjacent normal tissues (ANT). Finally, to investigate the effects of hepatitis B virus (HBV) and its encoded proteins on this axis, SMMC-7721 cells were transfected with HBV whole genome plasmids, as well as HBV X protein (HBx), HBV surface protein (HBs), and HBV core/capsid protein (HBc) recombinant plasmids. Expression level post-transfection was measured via qRT-PCR and WB. RESULTS: Our findings found that the KCNQ1OT1/miR-335-5p/CDC7 axis has a unique regulatory role in the network. Functional analyses revealed that KCNQ1OT1 is a key lncRNA associated with HCC proliferation and migration. The study further indicated that KCNQ1OT1 has binding sites with miR-335-5p. Furthermore, miR-335-5p overexpression can reverse the inhibiting effect of KCNQ1OT1 knockdown on malignant progression in HCC cells. Moreover, we confirmed that CDC7 is negatively regulated by miR-335-5p, and its upregulation enhances HCC proliferation and migration. Notably, our results demonstrated that HBV and its encoded protein HBc significantly induce the KCNQ1OT1/miR-335-5p/CDC7 axis, thereby promoting HCC progression. CONCLUSIONS: Consequently, we confirmed that HBc promotes the malignant progression of HCC by inducing the KCNQ1OT1/miR-335-5p/CDC7 axis. This axis may provide a novel and promising therapeutic target for improving malignant progression in HCC, particularly in patients with HBV infection.