title: Hepatitis B virus X protein targets Bcl-2 proteins to increase intracellular calcium, required for virus replication and cell death induction.
abstract: Infection with the hepatitis B virus (HBV) promotes the development of hepatitis, cirrhosis, and hepatocellular carcinoma (HCC) and is a leading cause of morbidity and mortality worldwide. HBV X protein (HBx) is an important effector for HBV pathogenesis, but its cellular targets and acting mechanisms remain elusive. We show here that HBx interacts with the anti-apoptotic proteins Bcl-2 and Bcl-xL through a Bcl-2 homology 3 (BH3)-like motif in mammalian cells. Importantly, mutations in the BH3-like motif that prevent HBx binding to Bcl-2 and Bcl-xL abrogate cytosolic calcium elevation and cell death induced by HBx expression in hepatocytes and severely impair HBV viral replication, which can be substantially rescued by restoring cytosolic calcium. These results suggest that HBx binding to Bcl-2 family members and subsequent elevation of cytosolic calcium are important for HBV viral replication. Consistently, RNAi knockdown of Bcl-2 or Bcl-xL results in reduced calcium elevation by HBx and decreased viral replication in hepatocytes. Our results suggest that HBx targets Bcl-2 proteins through its BH3-like motif to promote cytosolic calcium elevation, cell death, and viral replication during HBV pathogenesis, which presents an excellent therapeutic intervention point in treating patients with chronic HBV.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Geng
authors.forename: Chenghao
authors.initials: C
authors.lastname: Huang
authors.forename: Yan
authors.initials: Y
authors.lastname: Qin
authors.forename: Janet E
authors.initials: JE
authors.lastname: McCombs
authors.forename: Quan
authors.initials: Q
authors.lastname: Yuan
authors.forename: Brian L
authors.initials: BL
authors.lastname: Harry
authors.forename: Amy E
authors.initials: AE
authors.lastname: Palmer
authors.forename: Ning-Shao
authors.initials: NS
authors.lastname: Xia
authors.forename: Ding
authors.initials: D
authors.lastname: Xue
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death; D003600:Cytosol / Q000378:metabolism; D056945:Hep G2 Cells; D006515:Hepatitis B virus / Q000502:physiology; D022781:Hepatocytes / Q000378:metabolism / Q000473:pathology* / Q000821:virology*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D011485:Protein Binding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins; D014779:Virus Replication / Q000502:physiology*; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; D051020:bcl-X Protein; C057628:hepatitis B virus X protein; D002118:Calcium