title: HBx-induced NF-κB signaling in liver cells is potentially mediated by the ternary complex of HBx with p22-FLIP and NEMO.
abstract: Sustained activation of NF-κB is one of the causative factors for various liver diseases, including liver inflammation and hepatocellular carcinoma (HCC). It has been known that activating the NF-κB signal by hepatitis B virus X protein (HBx) is implicated in the development of HCC. However, despite numerous studies on HBx-induced NF-κB activation, the detailed mechanisms still remain unsolved. Recently, p22-FLIP, a cleavage product of c-FLIPL, has been reported to induce NF-κB activation through interaction with the IκB kinase (IKK) complex in primary immune cells. Since our previous report on the interaction of HBx with c-FLIPL, we explored whether p22-FLIP is involved in the modulation of HBx function. First, we identified the expression of endogenous p22-FLIP in liver cells. NF-κB reporter assay and electrophoretic mobility shift assay (EMSA) revealed that the expression of p22-FLIP synergistically enhances HBx-induced NF-κB activation. Moreover, we found that HBx physically interacts with p22-FLIP and NEMO and potentially forms a ternary complex. Knock-down of c-FLIP leading to the downregulation of p22-FLIP showed that endogenous p22-FLIP is involved in HBx-induced NF-κB activation, and the formation of a ternary complex is necessary to activate NF-κB signaling. In conclusion, we showed a novel mechanism of HBx-induced NF-κB activation in which ternary complex formation is involved among HBx, p22-FLIP and NEMO. Our findings will extend the understanding of HBx-induced NF-κB activation and provide a new target for intervention in HBV-associated liver diseases and in the development of HCC.
authors.affiliation: Department of Pharmacology, and Center for Cancer Research and Diagnostic Medicine, IBST, Konkuk University School of Medicine, Seoul, Republic of Korea.
authors.forename: Keo-Heun
authors.initials: KH
authors.lastname: Lim
authors.forename: Hyo Sun
authors.initials: HS
authors.lastname: Choi
authors.forename: Yong Kwang
authors.initials: YK
authors.lastname: Park
authors.forename: Eun-Sook
authors.initials: ES
authors.lastname: Park
authors.forename: Gu Choul
authors.initials: GC
authors.lastname: Shin
authors.forename: Doo Hyun
authors.initials: DH
authors.lastname: Kim
authors.forename: Sung Hyun
authors.initials: SH
authors.lastname: Ahn
authors.forename: Kyun-Hwan
authors.initials: KH
authors.lastname: Kim
mesh_terms: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D055785:Gene Knockdown Techniques; D006515:Hepatitis B virus / Q000502:physiology; D022781:Hepatocytes / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism*; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008113:Liver Neoplasms / Q000378:metabolism / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism*; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins; D014779:Virus Replication
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; C491731:IKBKG protein, human; D016328:NF-kappa B; D034741:RNA, Small Interfering; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D051550:I-kappa B Kinase