Non-structural and nucleocapsid proteins of Punta Toro virus induce apoptosis of hepatocytes through both intrinsic and extrinsic pathways.
Punta Toro virus (PTV; family Bunyaviridae, genus Phlebovirus) causes severe hepatic damage through brisk apoptosis of hepatocytes. In the present study, two viral proteins encoded by the S segment of the viral genome, non-structural (NSs) and nucleocapsid protein (N), were examined for their roles in apoptosis. Expression of NSs in HepG2 cells led to apoptosis in 45% of transfected cells, and with N, 28%, on average. These levels represent a four- to an eightfold increase over cells transfected with the mutated protein vectors. Caspase-3, -8 and -9 activities were increased by N protein when compared with the control NC (P < 0.05), and by NSsA and NSsB, as compared to control NSsC (P < 0.01). Treatment of the transfected cells with caspase-8 or -9 inhibitors markedly decreased apoptosis. Neutralization of TNF-alpha or Fas ligand had no effect on apoptosis. These results indicate that both NSs and N are responsible for causing hepatocyte apoptosis by triggering the extrinsic caspase-8 and intrinsic caspase-9 pathways.
Li
Guangyu
G
Department of Internal Medicine and Center for Biodefense and Emerging Infectious Diseases, University of Texas Medical Branch, Galveston, Texas 77550-0609, USA. guli@utmb.edu
Ren
Junping
J
Xu
Fangling
F
Ferguson
Monique R
MR
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D015153:Blotting, Western; D053181:Caspase 8 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002522:Chlorocebus aethiops; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D019590:Nucleocapsid Proteins / Q000235:genetics / Q000502:physiology*; D016856:Phlebovirus / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D014709:Vero Cells; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000502:physiology*
D019590:Nucleocapsid Proteins; D017361:Viral Nonstructural Proteins; D053181:Caspase 8; D053453:Caspase 9