HBV Promotes CHOP MRNA Expression During Thapsigargin Induced ER Stress

BackgroundsHepatocellular carcinoma (HCC) is a major public health challenges that resulting in enormous global burden. High incidence of HCC is mainly distributed in developing country. Many factors have contributed to the occurrence of the disease, while hepatitis B virus (HBV) infection is a very important aspect. More than 350 million people are chronic carriers of hepatitis B virus in the worldwide context and at least one million people die of the infection each year. In China, HCC is usually caused by HBV infection. HBV infection causes massive viral replication and produces a large number of viral proteins in a short period of time which result in perturbation of the endoplasmic reticulum homeostasis and protein misfolding. Accumulation of the unfolded or misfolded proteins leads to the endoplasmic reticulum stress (ERs), followed by unfolded protein response (UPR). UPR consists of many signal transduction pathways. In mammals, UPR is initiated by three transmembrane receptor proteins, PERK, IRE1, ATF6, developing a series reaction to relieve stress in the ER. But if the stress continues, can’t be alleviated, the cell starts apoptotic program, which plays an important role in the progression of HCC. This study detected the different expression tendency of UPR molecules between HepG2 (HBV") and HepG2.2.15 cells (HBV+) to explore the impact of HBV on genes expression in UPR signaling pathways of HCC cells.MethodsEukaryotic expression ATF6-spliced plasmids, tunicamycin (tm) and thapsigargin (tg) were used to treat HepG2 (HBV-) and HepG2.2.15 cells (HBV+) Total RNA extraction was conducted after 4 hours,8 hours,12 hours,24 hours,48 hours,72 hours,96 hours. RT-PCR and qPCR was used to detect the expression change of CHOP mRNA, Xbp-1s mRNA, ATF6 mRNA in the three UPR pathways (PERK, IRE 1,ATF6).ResultsIn HepG2.2.15 cells (HBV+), CHOP mRNA expression increased at first and stayed abundant at last; Xbp-1s mRNA expression increased after four hours and continued to decline; ATF6 mRNA expression levels have been low with slightly fluctuating. In HepG2 cells (HBV), CHOP mRNA expression increased first, then followed by a decrease; Xbp-1s mRNA increased after four hours and changed little until 96 hours; ATF6 mRNA expression levels have been low. The change tendencies of CHOP mRNA (P<0.05) and Xbp-1s mRNA (P<0.05) were significantly different. While in the tm and eukaryotic expression ATF6-spliced plasmids treated group, change tendencies of the molecules in the two cell lines were not significantly different.ConclusionAfter exposure to tg, HepG2.2.15 cells (HBV+) and HepG2 cells (HBV-) developed ERs. The expression change tendency of CHOP mRNA and Xbp-1s mRNA were different between the two cell lines, respectively. The conclusion is that HBV can promote apoptosis by stimulating the expression of CHOP mRNA and inhibiting expression of Xbp-1s mRNA.