Hepatitis B virus(HBV)X protein(HBx)is an important effector for HBV associated pathogenesis.In this study,we identified hepsin as an HBx-interacting protein and investigated the effects of hepsin on HBx-mediated complement component 3(C3)secretion in hepatocytes.In vivo and in vitro binding between HBx and hepsin was confirmed by coimmunoprecipitation and Glutathione S-transferase pull-down assays.HBx synergized with hepsin to promote C3 production by potentiating interleukin-6(IL-6)secretion.Knockdown of endogenous hepsin attenuated C3 and IL-6 secretion induced by HBx in hepatic cells.In addition,levels of hepsin protein correlated positively with C3 expression in human non-tumor liver tissues.Further exploration revealed that HBx and hepsin increased C3 promoter activity by up-regulating the expression and phosphorylation of the transcription factor CAAT/enhancer binding protein beta(C/EBP-β)w,hich binds to the IL-6/IL-1 response element in the C3 promoter.HBx and hepsin synergistically enhanced IL-6 mRNA levels and promoter activity by increasing the nuclear translocation of nuclear factor kappaB(NF-κB).Our findings show for the first time that binding between HBx and hepsin promotes C3 production by inducing IL-6 secretion in hepatocytes.