Binding of LINE-1 RNA to PSF transcriptionally promotes GAGE6 and regulates cell proliferation and tumor formation

Hepatocellular carcinoma (HCC) has one of the highest mortality rates among numerous types of cancer. It has been demonstrated that in hepatitis B (HBV)-associated HCC, the expression of chimeric fusion transcript HBx-long interspersed nuclear element-1 (LINE-1) initiated by HBV integration is correlated with hepatocarcinogenesis and poor patient survival rates. Furthermore, increased rates of LINE-1 hypomethylation have been detected in HCC tissues compared with adjacent tissues. This suggests that individual LINE-1 RNA (L1 RNA) serves an important role in the processes of hepatocarcinogenesis. The present study assessed the epigenic interaction between L1 RNA and polypyrimidine tract-binding protein-associated splicing factor (PSF) in the A549 human alveolar epithelial and 16HBE human bronchial epithelial cell lines. In addition, changes in the transcriptional regulatory activity of PSF on its target gene, proto-oncogene G antigen 6 (GAGE6), were investigated following overexpression of L1 RNA, as well as its impact on cell-proliferative capacity, carried out by plotting cell growth curves and 5-ethynyl-2'-deoxyuridine assay. It was observed that L1 RNA specifically bound to the RNA binding domain of PSF and released the GAGE6 promoter region from the DNA-binding domain of PSF. This increased the transcription of GAGE6 and led to the promotion of cell proliferation as well as colony formation. Furthermore, at least two binding sites specific for PSF were identified on L1 RNA. In conclusion, the transcriptional regulatory activity of L1 RNA may partially result in cell transformation, and endogenous L1 RNA may function as an important regulatory factor in the process of tumorigenesis.