Posttranscriptional clearance of hepatitis B virus RNA by cytotoxic T lymphocyte-activated hepatocytes.

Abstract

Using transgenic mice that replicate the hepatitis B virus (HBV) genome, we recently demonstrated that class I-restricted, hepatitis B surface antigen-specific cytotoxic T lymphocytes (CTLs) can noncytolytically eliminate HBV pregenomic and envelope RNA transcripts from the hepatocyte. We now demonstrate that the steady-state content of these viral transcripts is profoundly reduced in the nucleus and cytoplasm of CTL-activated hepatocytes, but their transcription rates are only slightly reduced. Additionally, we demonstrate that transcripts covering the HBV X coding region are resistant to downregulation by the CTL. These results imply the existence of CTL-inducible hepatocellular factors that interact with a discrete element(s) between nucleotides 3157 and 1239 within the viral pregenomic and envelope transcripts and mediate their degradation, thus converting the hepatocyte from a passive victim to an active participant in the host response to HBV infection.Hepatitis B virus (HBV) infection causes acute and chronic hepatitis and hepatocellular carcinoma. Clearance of HBV is thought to be mediated by the destruction of infected cells by a major histocompatibility complex class I-restricted cytotoxic T lymphocyte (CTL) response to HBV-encoded antigens (1). Using HBV transgenic mice, we have recently shown that the cytodestructive properties of the CTL response may not be the only mechanism for HBV clearance from the liver. In particular, we have shown that HBV envelope transcripts are specifically degraded in the cytoplasm by a posttranscriptional mechanism when the hepatocytes are activated by the administration or activation of tumor necrosis factor a (TNF-a) (2). We have also shown that injection of hepatitis B surface antigen (HBsAg)-specific CTLs into HBV transgenic mice causes a much more profound reduction in hepatocellular HBV gene expression than TNF-a (3). Furthermore, we have demonstrated that this effect is noncytolytic and that it is mediated by interferon 'y (IFN--y) as well as by TNF-a, both of which are secreted by the CTLs after antigen activation (3).Recently, we have produced transgenic mouse lineages that express high levels of the HBV 3.5-kb pregenomic RNA as well as HBV envelope transcripts. These animals replicate the HBV genome in the liver and secrete HBV virions into the blood (4). Administration of HBsAg-specific CTLs into these mice causes a profound reduction of all of these HBV products in the liver and serum by a process that is inhibitable by the prior administration of antibodies to IFN-,y and TNF-a (L.G.G. and F.V.C., unpublished results). This suggests that the CTLs deliver one or more cytokine-mediated signals to the hepatocyte that induce or activate specific cellular gene products that either inhibit the synthesis, destabilize, or actively degrade these viral gene products, including the viral mRNA, thereby precluding viral replication.We now report that the HBV pregenomic and envelope RNAs are profoundly reduced in the nucleus, as well as the The publication costs of...

Quantitative analysis of the peripheral blood cytotoxic T lymphocyte response in patients with chronic hepatitis C virus infection.

“…Along these lines, based on evidence from a transgenic mouse model, we have recently suggested that hepatitis B virus (HBV)-specific CTL may control HBV infection not only by killing infected hepatocytes but also by inhibiting HBV replication by secreting certain antiviral cytokines when they recognize antigen (30,31). If this or related potentially curative antiviral pathways are required for viral clearance to be complete in an organ with as many infectible cells as the liver, viruses that are either intrinsically resistant to noncytolytic control or that induce an immune response that does not produce the corresponding antiviral cytokines would have a survival advantage.…”

Viruses, Immunity, and Cancer: Lessons from Hepatitis B

“…At the moment, we know that the cytokines inhibit viral gene expression by a posttranscriptional mechanism that destabilizes the viral mRNA in the nucleus of the cell, 51 and we have shown that this is associated with the cytokine-induced proteolytic cleavage of a cellular HBV RNA-binding protein that stabilizes the viral RNA under baseline conditions. 52,53 We also know that the cytokines inhibit viral replication by posttranslationally eliminating viral nucleocapsid particles, within which replication occurs, from the cytoplasm of the hepatocyte (Wieland S, Guidotti LG, Chisari FV, J Virol, in press).…”

Viral cross talk: intracellular inactivation of the hepatitis B virus during an unrelated viral infection of the liver.

“…Recently, however, we have shown that adoptively transferred hepatitis B surface antigen (HBsAg)-specific CTL can abolish HBV gene expression (2) and replication (3) in HBV transgenic mice by secreting interferon y (IFN-'y) and tumor necrosis factor a (TNF-a) after antigen recognition. Further, we have reported that these cytokines deliver two noncytopathic antiviral signals to the hepatocyte: one that activates the hepatocyte to degrade HBV RNA posttranscriptionally in a sequence-specific manner (4) and one that causes the hepatocytes to eliminate HBV nucleocapsid particles and their cargo of replicating viral genomes (3). It is possible, therefore, that these noncytopathic antiviral processes may exert an important but previously unsuspected influence on the outcome of HBV infection in man.…”