Hepatitis Research Today is a free monthly online journal that collates and summarizes the latest research about Hepatitis, including details on hepatitis a, b, c, causes, symptoms.

Viral and therapeutic control of IFN-beta promoter stimulator 1 during hepatitis C virus infection.

Loo YM, Owen DM, Li K, Erickson AK, Johnson CL, Fish PM, Carney DS, Wang T, Ishida H, Yoneyama M, Fujita T, Saito T, Lee WM, Hagedorn CH, Lau DT, Weinman SA, Lemon SM, Gale M

Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.

Viral signaling through retinoic acid-inducible gene-I (RIG-I) and its adaptor protein, IFN promoter-stimulator 1 (IPS-1), activates IFN regulatory factor-3 (IRF-3) and the host IFN-alpha/beta response that limits virus infection. The hepatitis C virus (HCV) NS3/4A protease cleaves IPS-1 to block RIG-I signaling, but how this regulation controls the host response to HCV is not known. Moreover, endogenous IPS-1 cleavage has not been demonstrated in the context of HCV infection in vitro or in vivo. Here, we show that HCV infection transiently induces RIG-I- and IPS-1-dependent IRF-3 activation. This host response limits HCV production and constrains cellular permissiveness to infection. However, HCV disrupts this response early in infection by NS3/4A cleavage of IPS-1 at C508, releasing IPS-1 from the mitochondrial membrane. Cleavage results in subcellular redistribution of IPS-1 and loss of interaction with RIG-I, thereby preventing downstream activation of IRF-3 and IFN-beta induction. Liver tissues from chronically infected patients similarly demonstrate subcellular redistribution of IPS-1 in infected hepatocytes and IPS-1 cleavage associated with a lack of ISG15 expression and conjugation of target proteins in vivo. Importantly, small-molecule inhibitors of NS3/4A prevent cleavage and restore RIG-I signaling of IFN-beta induction. Our results suggest a dynamic model in which early activation of IRF-3 and induction of antiviral genes are reversed by IPS-1 proteolysis and abrogation of RIG-I signaling as NS3/4A accumulates in newly infected cells. HCV protease inhibitors effectively prevent IPS-1 proteolysis, suggesting they may be capable of restoring this innate host response in clinical practice.

Published 12 April 2006 in Proc Natl Acad Sci U S A, 103(15): 6001-6.
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