DNMT1 mediated promoter methylation of GNAO1 in hepatoma carcinoma cells

Hepatocellular carcinoma (HCC) is one of the most lethal and prevalent cancers worldwide and has recently become the second most common cause of cancer-related deaths in men of developing countries. Guanine nucleotide-binding protein (G protein) has been reported to be associated with the early process of HCC. In our previous study, GNAO1, one of members of G protein, was found to be down-regulated in HCC. Thus, the present study aimed to throw light upon the mechanism of the abnormal expression of GNAO1 in HCC. First, qPCR results from two HCC cell lines (SMMC-7721 and QGY-7703) confirmed the down-expression of GNAO1, followed by the validation of the methylation status of the promoter region by bisulfite sequence PCR (BSP). Moreover, 5-Aza-2′-deoxycytidine (DAC) with Trichostatin A (TSA) treatment made it much clear that GNAO1 transcription was inhibited by promoter hypermethylation, contributing to its low expression. It was further revealed that the silencing effect was regulated by methyltransferase 1 (DNMT1), and was further enhanced by transforming growth factor β (TGF-β). In addition, the up-regulation of GNAO1 with the help of recombinant plasmid was also found to accelerate cell apoptosis, confirmed by flow cytometry and western blotting analysis. All these results above indicated that the promoter hypermethylation of GNAO1 might play an important role in HCC, suggesting that it might be used as a promising biomarker for HCC diagnosis and targeted therapy.