HBx-induced NF-κB signaling in liver cells is potentially mediated by the ternary complex of HBx with p22-FLIP and NEMO

• Published in: PloS one Vol. 8; no. 3; p. e57331
• Main Authors: Lim, Keo-Heun, Choi, Hyo Sun, Park, Yong Kwang, Park, Eun-Sook, Shin, Gu Choul, Kim, Doo Hyun, Ahn, Sung Hyun, Kim, Kyun-Hwan
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 04.03.2013; Public Library of Science (PLoS)
• Subjects: Activation; Apoptosis; Biology; c-FLIP protein; Carcinoma, Hepatocellular - metabolism; Carcinoma, Hepatocellular - pathology; CASP8 and FADD-Like Apoptosis Regulating Protein - metabolism; Cell growth; Cell Line, Tumor; Complex formation; Electrophoretic mobility; FLIP protein; Gene Knockdown Techniques; Genomics; HBX protein; Hepatitis; Hepatitis B; Hepatitis B virus - physiology; Hepatocellular carcinoma; Hepatocytes; Hepatocytes - metabolism; Hepatocytes - pathology; Herpes viruses; Humans; I-kappa B Kinase - metabolism; Immune system; Kinases; Liver; Liver - metabolism; Liver - pathology; Liver cancer; Liver diseases; Liver Neoplasms - metabolism; Liver Neoplasms - pathology; Medical research; Medicine; NF-kappa B - metabolism; NF-κB protein; Pharmacology; Protein Binding; Proteins; Recruitment; Regulation; RNA, Small Interfering - metabolism; Signal Transduction; Signaling; Trans-Activators - metabolism; Virus Replication; Viruses
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0057331

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.