Hepatitis C virus core protein induces an anergic state characterized by decreased interleukin-2 production and perturbation of mitogen-activated protein kinase responses.

Alterations of cytokine responses are thought to favor the establishment of persistent hepatitis C virus (HCV) infections, enhancing the risk of liver cirrhosis and hepatocellular carcinoma. Here we demonstrate that the expression of the HCV core (C) protein in stably transfected T cells correlates with a selective reduction of interleukin-2 (IL-2) promoter activity and IL-2 production in response to T-cell receptor triggering, whereas the activation of IL-4, IL-10, gamma interferon, and tumor necrosis factor alpha was moderately increased. This altered cytokine expression profile was associated with a perturbation of mitogen-activated protein (MAP) kinase responses. Extracellular regulated kinase and p38 were constitutively phosphorylated in C-expressing cells, while triggering of the costimulatory c-Jun N-terminal kinase (JNK) signaling cascade and activation of the CD28 response element within the IL-2 promoter appeared to be impaired. The perturbations of MAP kinase phosphorylation could be eliminated by cyclosporine A-mediated inhibition of nuclear factor of activated T cells, suggesting that the inactivation of JNK signaling and hyporesponsiveness to IL-2 induction were downstream consequences of C-induced Ca(2+) flux in a manner that mimics the induction of clonal anergy.

The hepatitis C virus core protein modulates T cell responses by inducing spontaneous and altering T-cell receptor-triggered Ca2+ oscillations.

Alterations of cytokine responses are thought to favor the establishment of persistent hepatitis C virus (HCV) infection, enhancing the risk of liver cirrhosis and hepatocellular carcinoma. Expression of the HCV core (C) protein modulates transcription of the IL-2 promoter in T lymphocytes by activating the nuclear factor of activated T lymphocyte (NFAT) pathway. Here we report on the effect of HCV C on Ca2+ signaling, which is essential for activation of NFAT. Expression of HCV C correlated with increased levels of cytosolic Ca2+ and spontaneous Ca2+ oscillations in transfected Jurkat cells. Triggering of the T-cell receptor induced a prolonged Ca2+ response characterized by vigorous high frequent oscillations in a high proportion of the responding cells. This was associated with decreased sizes and accelerated emptying of the intracellular calcium stores. The effect of HCV C on calcium mobilization was not dependent on phospholipase C-gamma 1 (PLC-gamma) activity or increased inositol 1,4,5-trisphosphate (IP3) production and did not require functional IP3 receptors, suggesting that insertion of the viral protein in the endoplasmic reticulum membrane may be sufficient to promote Ca2+ leakage with dramatic downstream consequences on the magnitude and duration of the response. Our data suggest that expression of HCV C in infected T lymphocytes may contribute to the establishment of persistent infections by inducing Ca2+ oscillations that regulate both the efficacy and information content of Ca2+ signals and are ultimately responsible for induction of gene expression and functional differentiation.