HCG15 is a hypoxia-responsive lncRNA and facilitates hepatocellular carcinoma cell proliferation and invasion by enhancing ZNF641 transcription

Hypoxia, one of the key features of the hepatocellular carcinoma (HCC) microenvironment, transcriptionally regulates the expression of mRNAs and non-coding RNAs via hypoxia-inducible factors (HIFs), thereby promoting tumor progression. However, hypoxia-responsive long non-coding RNAs (lncRNAs) in HCC required further investigation. We found that HLA complex group 15 (HCG15) was a new hypoxia-related lncRNA in HCC cells. Both hypoxia and HIF prolyl-hydroxylase inhibitor significantly increased HCG15 expression in HCC cells. At the same time, HIF-1α knockdown blocked hypoxia-induced the upregulation of HCG15. TCGA data revealed that HCG15 was markedly overexpressed and closely associated with the poor prognosis of HCC. HCG15 knockdown prominently suppressed the migration, invasion and proliferation of Hep3B and Huh7 cells. HCG15 overexpression markedly enhanced the proliferation and mobility of Huh7 cells. Zinc finger protein 641 (ZNF641) mRNA was frequently overexpressed and positively associated with HCG15 level in HCC samples from the TCGA database. Either HCG15 or upstream transcription factor 1 (USF1) silencing markedly reduced the ZNF641 level in HCC cells. RNA immunoprecipitation assay confirmed the interaction between HCG15 and USF1. Either HCG15 or USF1 knockdown prominently reduced the luciferase activity of reporter plasmid containing ZNF642 promoter. HCG15 knockdown remarkably abolished USF1-activated ZNF641 transcription in Hep3B cells. Finally, we confirmed that restoring ZNF641 expression remarkably abolished the effects of HCG15 knockdown on HCC cell migration, invasion and proliferation. Collectively, our study demonstrated that HCG15 was a new HIF-1 target gene and played a tumor-promoting role in HCC cells by enhancing USF1-mediated ZNF641 transcription.