FHIT overexpression in HepG2 hepatoma cells affects growth and cyclin D1 expression in vitro

The aim of this study was to investigate the methylation status of fragile histidine triad (FHIT) and the effects of FHIT on cell growth and cyclin D1 expression in hepatoma cells. The total proteins from the human hepatoma cell lines HepG2, Hep3B and Huh7 were collected and the expression levels of FHIT were analyzed. The methylation status in the promoter region of FHIT in the hepatoma cells was measured using methylation-specific polymerase chain reaction (PCR). The HepG2, Hep3B and Huh7 cells were subsequently treated with 5-aza-2'-deoxycytidine (5-azadc) and the restoration of FHIT expression was then examined. A p-hemagglutinin (HA)-FHIT plasmid was constructed and used to transfect the HepG2 cells, and the inhibitory effects of the transfection on cell growth were then assessed. In addition, HepG2 cells were cotransfected with the pHA-FHIT plasmid and a cyclin D1 luciferase reporter plasmid, and the effects of FHIT on the activity of cyclin D1 transcription factor were analyzed using a luciferase assay. FHIT was observed to be expressed at a low level in Hep3B and HepG2 cells; however, it was expressed at a relatively high level in Huh7 cells. The promoter region of FHIT in the Hep3B and HepG2 cells was partially methylated, and 5-azadc treatment induced an increased expression of FHIT. The increased expression of FHIT inhibited the growth of HepG2 cells. Cotransfection with the pHA-FHIT plasmid significantly inhibited the transcriptional activity of the cyclin D1 promoter and decreased the expression of cyclin D1 in HepG2 cells. In conclusion, FHIT was partially methylated in the HepG2 and Hep3B hepatoma cells. The overexpression of FHIT inhibited cell growth and decreased the expression of cyclin D1 in HepG2 cells.