HBx inhibits proliferation and induces apoptosis via Fas/FasL upregulation in rat renal tubular epithelial cells

The hepatitis B virus X protein (HBx) regulates numerous signaling pathways, including those that modulate apoptosis. However, previous research has indicated different effect of HBx on apoptosis, possibly because of differences in the experimental conditions and cell types. The purpose of this study was to investigate the mechanism of HBx-induced apoptosis of rat renal tubular epithelial (NRK-52E) cells. An HBx expression vector (pc-DNA3.1(+)-HBx) was used to transfect NRK-52E cells to establish an HBx overexpression model. One control group was not transfected and the other control group was transfected with plasmid lacking the HBx-encoding insert. Cell proliferation was measured using the MTT assay, and the rate of apoptosis was determined by flow cytometry and fluorescence microscopy. The expressions of Fas, FasL, Bcl-2 and Bax were determined by Western blotting and reverse transcription polymerase chain reaction, and the activity of caspase-8 was measured by spectrophotometry. Transfection of NRK-52E cells with pc-DNA3.1(+)-HBx led to inhibition of proliferation and increased apoptosis relative to the controls. Transfected cells had increased mRNA and protein expression of Fas, FasL and Bax and decreased mRNA and protein expression of Bcl-2 relative to the controls. In addition, transfected cells had increased caspase-8 activity relative to the controls. Our results suggest that HBx induces apoptosis in NRK-52E cells, at least in part through activation of the Fas/FasL pathway. The activation of caspase-8 appears to mediate the induction of apoptosis.