AIM:To investigate the molecular mechanism of the influenceof HBx protein on multidrug resistance associated genes:multidrug resistance 1(MDR-1),multidrug related protein(MRP-1),lung resistance related protein(LRP)in hepatomacells and the potential role of extracellular signal-regulatedkinase/mitogen-activated protein kinase(ERK/MAPK)pathwayin this process.METHODS:A cell model stably expressing the HBx proteinwas established by liposome-mediated transfection of HBxgene into HepG2 cell line.The expression of multidrugresistance associated genes and proteins was detected byRT-PCR and Westem blot.AnnexinV-FITC/PI assay was usedto confirm the multidrug resistance(MDR)phenotype oftransfected cells by fluorescence cytometry(FACS).TheERK/MAPK pathway activation was measured by Westernblot through comparing the ratio of phosphorylation ofERK/MAPK to total ERK/MAPK protein.After treated withthe ERK/MAPK pathway inhibitor U0126,the HBx-expressingcells were harvested.Then RT-PCR,Western blot and FACSwere used to analyze the alterations in the expression ofmultidrug resistance associated genes and the MDRphenotype after exposure.RESULTS:Compared with the control group,the transfectedcells showed a higher expression of MDR associated genesand proteins.Marked elevations in MDR-1(64.3%),MRP-1(87.5%)and LRP(90.8%)were observed in the transfectedcells(P<0.05).RT-PCR revealed that the over-expressionof MDR associated proteins was due to amplification ofsuch genes(MDR12.9 fold,MRP1 1.67 fold,LRP1.95 fold).Furthermore,we found that the ERK/MAPK activity wasremarkably high in the HBx-expressing cells.The activationof ERK/MAPK,as measured by the ratio of phosphorylatedERK bands normalized to the total ERK bands,was increasedby 2.3-fold in HBx-transfected cells compared with cellstransfected with the empty vector.After treated with theERK/MAPK pathway inhibitor,the level of MDR associatedgenes and proteins in the transfected cells decreased tosome extent.Compared with controls,a significant decreasein MDR-1 mRNA(53.3%),MRP-1 mRNA(59.7%)as well as LRP rnRNA(56.4%)was observed in the U0126 treatedtransfected cells after 12 h.Western blot also demonstratedthat the protein expression of these MDR associated genesslightly reduced after treated with U0126 for 12 h(MDR-140.1%,MRP-1 29.4%,LRP35.7%).This change wasaccompanied with the rise of cell apoptosis ratio confirmedby Annexin V-PI detection.The apoptosis index of U0126-treated cells increased by 1.28 fold,compared with that oftransfected cells.Obviously,the MDR phenotype of thesecells was obviously related with increased activities of theERK/MAPK pathway.CONCLUSION:HBx protein might be one of the causesfor the occurrence of MDR in HCC,and ERK/MAPK pathwaymight be involved in this change. To investigate the molecular mechanism of the influence of HBx protein on multidrug resistance associated genes: multidrug resistance 1 (MDR-1), multidrug related protein (MRP-1), lung resistance related protein (LRP) in hepatoma cells and the potential role of extracellular signal-regulated kinase / mitogen-activated protein kinase (ERK / MAPK) pathwayin this process. METHODS: A cell model stably expressing the HBx proteinwas established by liposome-mediated transfection of HBxgene into HepG2 cell line. The expression of multidrugresistance associated genes and proteins was detected by RT-PCR and Western blot. Annexin V-FITC / PI assay was used to confirm the multidrug resistance (MDR) phenotype of transfected cells by fluorescence cytometry (FACS). The ERK / MAPK pathway activation was measured by Western blot through comparing the ratio of phosphorylation of ERK / MAPK to total ERK / MAPK protein. After treated with the ERK / MAPK pathway inhibitor U0126, the HBx-expressing cells were harvested.Then RT-PCR, Western blot and FACSwere used to analyze the alterations in the expression of multidrug resistance associated genes and the MDR phenotype after exposure .RESULTS: Compared with the control group, the transfected cells showed a higher expression of MDR associated genes and proteins. Marked elevations in MDR-1 (64.3%), MR-1 (87.5%) and LRP (90.8%) were observed in the transfected cells (P <0.05) fold, LRP1.95 fold) .Furthermore, we found that the ERK / MAPK activity wasremarkably high in the HBx-expressing cells. activation of ERK / MAPK, as measured by the ratio of phosphorylated ERK bands normalized to the total ERK bands, was increasedby 2.3-fold in HBx-transfected cells compared with cellstransfected with the empty vector. After treatment with the ERK / MAPK pathway inhibitor, the level of MDR associated genes and proteins in the transfected cells decreased body extent. Compared with controls, a significantThe decrease in MDR-1 mRNA (53.3%), MRP-1 mRNA (59.7%) was observed in the U0126 treated transfected cells after 12 h. Western blot also demonstrated the protein expression of these MDR associated gene change was reduced after treated with U0126 for 12 h (MDR-140.1%, MRP-1 29.4%, LRP35.7%). This change was accompanied by the rise of cell apoptosis ratio confirmed by Annexin V-PI detection. The apoptosis index of U0126- treated cells increased by 1.28 fold, compared with that of transfected cells. Obviously, the MDR phenotype of these cells was obviously related with increased activities of the ERK / MAPK pathway. CONCLUSION: HBx protein might be one of the causes for the occurrence of MDR in HCC, and ERK / MAPK pathwaymight be involved in this change.