Calpain activation by hepatitis C virus proteins inhibits the extrinsic apoptotic signaling pathway.
An unresolved question regarding the physiopathology of hepatitis C virus (HCV) infection is the remarkable efficiency with which host defenses are neutralized to establish chronic infection. Modulation of an apoptotic response is one strategy used by viruses to escape immune surveillance. We previously showed that HCV proteins down-regulate expression of BH3-only Bcl2 interacting domain (Bid) in hepatocytes of HCV transgenic mice. As a consequence, cells acquire resistance to Fas-mediated apoptosis, which in turn leads to increased persistence of experimental viral infections in vivo. This mechanism might participate in the establishment of chronic infections and the resulting pathologies, including hepatocellular carcinoma. We now report that Bid is also down-regulated in patients in the context of noncirrhotic HCV-linked tumorigenesis and in the HCV RNA replicon system. We show that the nonstructural HCV viral protein NS5A is sufficient to activate a calpain cysteine protease, leading to degradation of Bid. Moreover, pharmacological inhibitors of calpains restore both the physiological levels of Bid and the sensitivity of cells toward a death receptor-mediated apoptotic signal. Finally, human HCV-related tumors and hepatocytes from HCV transgenic mice that display low Bid expression contain activated calpains.


CONCLUSIONS
Calpains activated by HCV proteins degrade Bid and thus dampen apoptotic signaling. These results suggest that inhibiting calpains could lead to an improved efficiency of immune-mediated elimination of HCV-infected cells.
Simonin
Yannick
Y
Centre National de la Recherche Scientifique (CNRS), UMR 5535, Institut de Génétique Moléculaire de Montpellier, Montpellier, France.
Disson
Olivier
O
Lerat
Hervé
H
Antoine
Etienne
E
Binamé
Fabien
F
Rosenberg
Arielle R
AR
Desagher
Solange
S
Lassus
Patrice
P
Bioulac-Sage
Paulette
P
Hibner
Urszula
U
D000328:Adult; D000368:Aged; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005260:Female; D016174:Hepacivirus / Q000378:metabolism*; D019698:Hepatitis C, Chronic / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008113:Liver Neoplasms / Q000378:metabolism / Q000473:pathology*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008875:Middle Aged; D012093:Replicon / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D017361:Viral Nonstructural Proteins / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase
D051023:BH3 Interacting Domain Death Agonist Protein; D002154:Calpain; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase