Signal transduction pathways that inhibit hepatitis B virus replication

Abstract

The replication of hepatitis B virus (HBV) in hepatocytes is strongly inhibited in response to IFN-␣͞␤ and IFN-␥. Although it has been previously demonstrated that IFN-␣͞␤ eliminates HBV RNA-containing capsids from the cell in a proteasome-dependent manner, the precise cellular pathway that mediates this antiviral effect has not been identified. Because IFN-induced signal transduction involves kinase-mediated activation of gene expression, we used an immortalized hepatocyte cell line that replicates HBV in an IFNsensitive manner to investigate the role of cellular kinase activity and the cellular transcription and translation machinery in the antiviral effect. Our results indicate that Janus kinase activity is required for the antiviral effect of IFN against HBV, but that phosphatidylinositol 3-kinase, cyclin-dependent kinase, mitogenactivated protein kinase, and NF-B activity are not. Additionally, we found that inhibitors of cellular transcription and translation completely abolish the antiviral effect, which also appears to require cellular kinase activity downstream of signal transduction and gene expression. Collectively, these results identify IFN-regulated pathways that interrupt the HBV replication cycle by eliminating viral RNA-containing capsids from the cell, and they provide direction for discovery of the terminal effector molecules that ultimately mediate this antiviral effect.

Interferon prevents formation of replication-competent hepatitis B virus RNA-containing nucleocapsids

“…Importantly, IFN-␤ and -␥ inhibit HBV replication in immortalized hepatocyte cell lines derived from HBV transgenic mice (14), confirming that these cytokines mediate noncytolytic inhibition of HBV replication. Furthermore, the antiviral activity is induced within the first 3 h of IFN-␤ signaling (15), consistent with the rapid clearance kinetics of HBV RNA-containing capsids in HBV transgenic mice (13) and immortalized HBV transgenic hepatocytes (14). However, our previous studies did not reveal whether the antiviral effect of IFN-␤ prevented the formation of replication-competent HBV RNAcontaining capsids or degraded existing capsids.…”

Functional Characterization of the Interaction between Human La and Hepatitis B Virus RNA

“…Furthermore, it will be interesting to find out which cellular signaling pathway affects the proposed phosphorylation-dependent composition of HBV RNPs thereby potentially regulating the turnover of viral RNAs. Most importantly, it has been shown recently that Janus kinase activity is required for the antiviral effect of interferons on HBV replication (35), indicating that cell signaling pathways and thereby phosphorylation/dephosphorylation events are required. This might also apply for cytokine-induced degradation of HBV RNA decay as supported by our finding that binding of mouse and human La to HBV RNA is modulated by accessory factors in a phosphorylation-dependent manner.…”

“…Therefore, it is reasonable to consider that additional regulatory elements within the viral RNA and cellular factors interacting with HBV RNA and/or the La protein have to be integrated to fully understand the decay of HBV RNA under steady state conditions like in our experiments. Furthermore, the variety and remarkable changes in gene expression profiles observed after CTL injection into HBV transgenic mice (34,35), probably inducing the inhibition of viral replication and inducing HBV RNA decay, suggest that additional cellular factors and cellular events have to be identified in order to understand the induced decay mechanism specific for the HBV RNA. It is reasonable to speculate that structural features of the La-binding site determine the interaction with trans-acting factors, and it might therefore be possible that mutation M2 leads to disruption of hLa containing RNPs normally protecting HBV RNA against endoribonucleolytic cleavage.…”

Interferon-inducible expression of APOBEC3 editing enzymes in human hepatocytes and inhibition of hepatitis B virus replication

“…2 Interferons restrict the replication of HBV by inducing the expression of antiviral proteins that inhibit the formation of replication-competent HBV nucleocapsids, and ultimately can result in the resolution of the chronic HBV infection. [2][3][4][5][6][7] HBV and other hepadnaviruses replicate their partially double-stranded DNA genome within cytoplasmic core particles by reverse transcription of encapsidated pregenomic RNA and thus are related to retroviruses. 8,9 The cytidine deaminase APOBEC3G (A3G), which is encoded within a cluster of seven related editing enzymes (APOBEC3A-G) on chromosome 22, provides broad innate immunity against exogenous and endogenous retroelements.…”