Characterization of nuclear RNases that cleave hepatitis B virus RNA near the La protein binding site

Non-cytotoxic functions of CD8 T cells: “repentance of a serial killer”

Cytotoxic CD8 T cells (CTLs) are classically described as the “serial killers” of the immune system, where they play a pivotal role in protective immunity against a wide spectrum of pathogens and tumors. Ironically, they are critical drivers of transplant rejection and autoimmune diseases, a scenario very similar to the famous novel “The strange case of Dr. Jekyll and Mr. Hyde”. Until recently, it has not been well-appreciated whether CTLs can also acquire non-cytotoxic functions in health and disease. Several investigations into this question revealed their non-cytotoxic functions through interactions with various immune and non-immune cells. In this review, we will establish a new classification for CD8 T cell functions including cytotoxic and non-cytotoxic. Further, we will discuss this novel concept and speculate on how these functions could contribute to homeostasis of the immune system as well as immunological responses in transplantation, cancer, and autoimmune diseases.

Host RNA quality control as a hepatitis B antiviral target

Inhibition of the host RNA polyadenylating polymerases, PAPD5 and PAPD7 (PAPD5/7), with dihydroquinolizinone, a small orally available, molecule, results in a rapid and selective degradation of hepatitis B virus (HBV) RNA, and hence reduction in the amounts of viral gene products. DHQ, is a first in class investigational agent and could represent an entirely new category of HBV antivirals. PAPD5 and PAPD7 are non-canonical, cell specified, polyadenylating polymerases, also called terminal nucleotidyl transferases 4B and 4A (TENT4B/A), respectively. They are involved in the degradation of poor-quality cell transcripts, mostly non-coding RNAs and in the maturation of a sub-set of transcripts. They also appear to play a role in shielding some mRNA from degradation. The results of studies with DHQ, along with other recent findings, provide evidence that repression of the PAPD5/7 arm of the cell "RNA quality control" pathway, causes a profound (multi-fold) reduction rather than increase, in the amount of HBV pre-genomic, pre-core and HBsAg mRNA levels in tissue culture and animal models, as well. In this review we will briefly discuss the need for new HBV therapeutics and provide background about HBV transcription. We also discuss cellular degradation of host transcripts, as it relates to a new family of anti-HBV drugs that interfere with these processes. Finally, since HBV mRNA maturation appears to be selectively sensitive to PAPD5/7 inhibition in hepatocytes, we discuss the possibility of targeting host RNA "quality control" as an antiviral strategy.

Role of the RNA-binding protein La in cancer pathobiology

RNA-binding proteins are important regulators of RNA metabolism and are of critical importance in all steps of the gene expression cascade. The role of aberrantly expressed RBPs in human disease is an exciting research field and the potential application of RBPs as a therapeutic target or a diagnostic marker represents a fast-growing area of research.Aberrant overexpression of the human RNA-binding protein La has been found in various cancer entities including lung, cervical, head and neck, and chronic myelogenous leukaemia. Cancer-associated La protein supports tumour-promoting processes such as proliferation, mobility, invasiveness and tumour growth. Moreover, the La protein maintains the survival of cancer cells by supporting an anti-apoptotic state that may cause resistance to chemotherapeutic therapy.The human La protein represents a multifunctional post-translationally modified RNA-binding protein with RNA chaperone activity that promotes processing of non-coding precursor RNAs but also stimulates the translation of selective messenger RNAs encoding tumour-promoting and anti-apoptotic factors. In our model, La facilitates the expression of those factors and helps cancer cells to cope with cellular stress. In contrast to oncogenes, able to initiate tumorigenesis, we postulate that the aberrantly elevated expression of the human La protein contributes to the non-oncogenic addiction of cancer cells. In this review, we summarize the current understanding about the implications of the RNA-binding protein La in cancer progression and therapeutic resistance. The concept of exploiting the RBP La as a cancer drug target will be discussed.

Salt-Dependent Modulation of the RNA Chaperone Activity of RNA-Binding Protein La

It is well established that the RNA-binding protein La has RNA chaperone activity. Recent work suggests that the La protein has two distinct RNA chaperone domains (RCD-A and RCD-B) assisting structural changes in diverse groups of RNA molecules such as RNA polymerase III transcripts (e.g., pre-tRNA, U6 snRNA), cellular messenger, and viral RNAs. In this protocol we focus on the RNA chaperone domain RCD-B, which is located in the carboxy-terminal domain of La. It has been shown that this RNA chaperone domain assists structural changes in predicted RNA hairpins folded in the 5'-untranslated regions of cyclin D1 and Bcl2 mRNAs. Besides RNA helicases, which are implicated in melting RNA hairpin structures in an ATP-dependent manner, RNA chaperones fulfil a similar function in an ATP-independent manner. Aiming to study the RNA chaperon activity of La, we established a La-dependent molecular beacon-based RNA chaperone assay and systematically tested the various salt conditions. Herein we describe the assay format and design to study the salt dependency of RNA chaperones. This protocol can be easily adapted to test the RNA chaperone activity of other RNA-binding proteins and to optimize assay conditions.

Study on the structure optimization and anti-hepatitis B virus activity of novel human La protein inhibitor HBSC11

In our previous study, Methyl pyrazolo[1,5‐a] pyridine‐2‐carboxylate (HBSC11) was shown to combine with La protein, which conferred anti‐hepatitis B virus (HBV) effects. The purpose of this study was to optimize, synthesize, and evaluate the anti‐HBV activity of HBSC11. The methyl group of HBSC11 was substituted with hydrophobic, hydrophilic, and tricyclic groups to generate novel HBV inhibitors with desirable potency. On in vitro evaluation, several derivatives exhibited good anti‐HBV activity compared with control. In particular, compound 5a reduced the level of HBV antigen by approximately 50%, which was similar to the activity of entecavir. In a mouse model, 5a showed 98.9% inhibition rate for HBV DNA, 57.4% for HBsAg, and 46.4% for HBeAg; the corresponding rates in the control group were 90.8, 3.8, and 9.8%, respectively. In addition, prediction of binding modes and physicochemical properties showed that 5a formed hydrogen bonds with La protein and conformed well to the Lipinski's rule of five. Our results suggest that 5a is a potential new anti‐HBV drug.

La protein protects HBV RNA from destruction by combining with HBV RNA and covers up the RNA cleavage site.

HBSC11 (Methyl pyrazolo[1,5‐a] pyridine‐2‐carboxylate) is a novel La protein inhibitor which we identified as previous.

10 derivatives (3a‐3f, 5a‐5d) were obtained by 2 sections‐scaffold and kept the active site form leading compound HBSC11.

Candidate compound 5a exhibited potent anti‐HBV activity with safety concentration and satisfied physicochemical properties.

HBsAg mRNA degradation induced by a dihydroquinolizinone compound depends on the HBV posttranscriptional regulatory element

In pursuit of novel therapeutics targeting the hepatitis B virus (HBV) infection, we evaluated a dihydroquinolizinone compound (DHQ-1) that in the nanomolar range reduced the production of virion and surface protein (HBsAg) in tissue culture. This compound also showed broad HBV genotype coverage, but was inactive against a panel of DNA and RNA viruses of other species. Oral administration of DHQ-1 in the AAV-HBV mouse model resulted in a significant reduction of serum HBsAg as soon as 4 days following the commencement of treatment. Reduction of HBV markers in both in vitro and in vivo experiments was related to the reduced amount of viral RNA including pre-genomic RNA (pgRNA) and 2.4/2.1 kb HBsAg mRNA. Nuclear run-on and subcellular fractionation experiments indicated that DHQ-1 mediated HBV RNA reduction was the result of accelerated viral RNA degradation in the nucleus, rather than the consequence of inhibition of transcription initiation. Through mutagenesis of HBsAg gene sequences, we found induction of HBsAg mRNA decay by DHQ-1 required the presence of the HBV posttranscriptional regulatory element (HPRE), with a 109 nucleotides sequence within the central region of the HPRE alpha sub-element being the most critical. Taken together, the current study shows that a small molecule can reduce the overall levels of HBV RNA, especially the HBsAg mRNA, and viral surface proteins. This may shed light on the development of a new class of HBV therapeutics.

Alteration of microRNA profiles by a novel inhibitor of human La protein in HBV-transformed human hepatoma cells

A pyrazolopyridine HBSC11 was previously identified as a novel inhibitor of human La protein with anti‐hepatitis B virus (HBV) activity. However, the underlying mechanism(s) of HBV inhibition by HBSC11 remains unclear. This study aimed to examine the regulation of microRNA (miRNA) by HBSC11 in HBV‐transformed human hepatoma HepG2.2.15 cells using microarray and quantitative real‐time PCR. Target genes of the differentially expressed miRNAs were predicted and subjected to bioinformatics analysis. Results showed that HBSC11 significantly upregulated the expression of miR‐3912‐5p, miR‐6793‐5p, and miR‐7159‐5p in HepG2.2.15 cells. Target genes of the three miRNAs were mainly involved in the regulation of nucleic acid‐templated transcription, negative regulation of gene expression, nucleic acid binding transcription factor activity and regulation of phosphorylation. In addition, target genes were enriched in certain regulatory pathways related to HBV infection and HBV‐associated disease progression, such as the transforming growth factor (TGF)‐β, Wnt, and p53 signaling. Our study demonstrates the involvement of miR‐3912‐5p, miR‐6793‐5p, and miR‐7159‐5p and the potential modulation of specific pathways (TGF‐β, Wnt, and p53 signaling) in HBSC11‐mediated inhibition of HBV replication. This study provides insight into the molecular mechanism of the action of HBSC11 against HBV infection and will support the development of antiviral drugs targeting La protein.

Chronic hepatitis B surface antigen seroclearance-related immune factors

The ultimate aims of the treatment of hepatitis B virus infection are the loss of hepatitis B surface antigen (HBsAg) and hepatitis B surface antibody seroconversion. Unfortunately, these goals are rarely reached. Many factors are associated with HBsAg seroconversion, including genetic, immune, and viral factors. However, the mechanism of HBsAg seroclearance, and particularly the immune mechanism, is still difficult to elucidate. The immune factor interferon-α is currently the main antiviral therapy for chronic hepatitis B virus infection. However, a sustained shift from response of HBsAg to hepatitis B surface antibody seroconversion is rarely obtained. Recent studies have revealed that several of the newly identified immune factors are closely related to the removal of HBsAg. In this article, we review recent studies on these immune factors, their influence on hepatitis B progression, and HBsAg seroconversion.

Viral DNA-Dependent Induction of Innate Immune Response to Hepatitis B Virus in Immortalized Mouse Hepatocytes

Hepatitis B virus (HBV) infects hundreds of millions of people worldwide and causes acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. HBV is an enveloped virus with a relaxed circular (RC) DNA genome. In the nuclei of infected human hepatocytes, conversion of RC DNA from the incoming virion or cytoplasmic mature nucleocapsid (NC) to the covalently closed circular (CCC) DNA, which serves as the template for producing all viral transcripts, is essential to establish and sustain viral replication. A prerequisite for CCC DNA formation is the uncoating (disassembly) of NCs to expose their RC DNA content for conversion to CCC DNA. We report here that in an immortalized mouse hepatocyte cell line, AML12HBV10, in which RC DNA exposure is enhanced, the exposed viral DNA could trigger an innate immune response that was able to modulate viral gene expression and replication. When viral gene expression and replication were low, the innate response initially stimulated these processes but subsequently acted to shut off viral gene expression and replication after they reached peak levels. Inhibition of viral DNA synthesis or cellular DNA sensing and innate immune signaling diminished the innate response. These results indicate that HBV DNA, when exposed in the host cell cytoplasm, can function to trigger an innate immune response that, in turn, modulates viral gene expression and replication.

IMPORTANCE

Chronic infection by hepatitis B virus (HBV) afflicts hundreds of millions worldwide and is sustained by the episomal covalently closed circular (CCC) DNA in the nuclei of infected hepatocytes. Release of viral genomic DNA from cytoplasmic nucleocapsids (NCs) (NC disassembly or uncoating) is a prerequisite for its conversion to CCC DNA, which can also potentially expose the viral DNA to host DNA sensors and trigger an innate immune response. We have found that in an immortalized mouse hepatocyte cell line in which efficient CCC DNA formation was associated with enhanced exposure of nucleocapsid-associated DNA, the exposed viral DNA indeed triggered host cytoplasmic DNA sensing and an innate immune response that was able to modulate HBV gene expression and replication. Thus, HBV can, under select conditions, be recognized by the host innate immune response through exposed viral DNA, which may be exploited therapeutically to clear viral persistence.

Anti-HBV Drugs: Progress, Unmet Needs, and New Hope

Approximately 240 million people worldwide are chronically infected with hepatitis B virus (HBV), which represents a significant challenge to public health. The current goal in treating chronic HBV infection is to block progression of HBV-related liver injury and inflammation to end-stage liver diseases, including cirrhosis and hepatocellular carcinoma, because we are unable to eliminate chronic HBV infection. Available therapies for chronic HBV infection mainly include nucleos/tide analogues (NAs), non-NAs, and immunomodulatory agents. However, none of them is able to clear chronic HBV infection. Thus, a new generation of anti-HBV drugs is urgently needed. Progress has been made in the development and testing of new therapeutics against chronic HBV infection. This review aims to summarize the state of the art in new HBV drug research and development and to forecast research and development trends and directions in the near future.

Mouse Models of Hepatitis B Virus Pathogenesis

The host range of hepatitis B virus (HBV) is limited to humans and chimpanzees. As discussed in the literature, numerous studies in humans and chimpanzees have generated a great deal of information on the mechanisms that cause viral clearance, viral persistence, and disease pathogenesis during acute or chronic HBV infection. Relevant pathogenetic studies have also been performed in those few species representing natural hosts of hepadnaviruses that are related to HBV, such as the woodchuck hepatitis virus and the duck hepatitis virus. Further insight has been gained from multidisciplinary studies in transgenic or humanized chimeric mouse models expressing and/or replicating HBV to varying degrees. We provide here a concise summary of the available HBV mouse models as well as of the contributions of these models to our understanding of HBV pathogenesis.

Pathogenesis of chronic viral hepatitis: differential roles of T cells and NK cells

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections account for 57% of cases of liver cirrhosis and 78% of cases of primary liver cancer worldwide and cause a million deaths per year. Although HBV and HCV differ in their genome structures, replication strategies and life cycles, they have common features, including their noncytopathic nature and their capacity to induce chronic liver disease, which is thought to be immune mediated. However, the rate of disease progression from chronic hepatitis to cirrhosis varies greatly among infected individuals, and the factors that regulate it are largely unknown. This review summarizes our current understanding of the roles of antigen-specific and nonspecific immune cells in the pathogenesis of chronic hepatitis B and C and discusses recent findings that identify natural killer cells as regulators of T cell function and liver inflammation.

A systematic analysis of the predicted human La protein targets identified a hepatitis B virus infection signature

The human La (hLa) protein functions in RNA metabolism and is activated by casein kinase 2 (CK2) phosphorylation. Hepatitis B virus (HBV) can exploit hLa to stabilize its RNA and promote its pathogenesis. To enhance our knowledge of host molecular pathways involved in HBV pathogenesis, a bioinformatic approach was used to generate an expression profile of all predicted target genes of CK2-activated hLa in HBV-infected cells. A computerized literature search was performed to identify English language studies of HBV-, hLa- and CK2-related molecules. The data were pooled and the genes were classified in three functional groups by gene ontology (GO) analysis. HBV, hLa and CK2 targets were predicted, respectively, by a computational method, followed by screening for matching gene symbols in the NCBI human sequences, GO, pathway and network analyses. hLa targets and respective networks in the viral mechanisms of HBV were obtained by the final integrative analysis. Thirty-seven hub genes were identified by overlap calculation, suggesting that hLa may play an important role in the development and progression of HBV through cytokine-cytokine receptor interaction, hematopoietic cell lineage, cell adhesion molecules (CAMs), antigen processing and presentation, Jak-STAT signalling pathway, natural killer cell-mediated cytotoxicity, apoptosis, T-cell receptor signalling pathway, complement and coagulation cascades, protein export and other pathways. Our data may help researchers to predict the molecular mechanisms of hLa in the development and progression of HBV through CK2 comprehensively. Moreover, the present data indicate that hLa targets may be a series of promising candidates for HBV.

Phosphorylation of human La protein at Ser 366 by casein kinase II contributes to hepatitis B virus replication and expression in vitro

Human La protein (hLa) is a multifunctional RNA-binding protein involved in the regulation of hepatitis B virus (HBV) expression. Casein kinase II (CK2), a protein kinase, is known to activate hLa by phosphorylating Ser(366). Tetrabromobenzimidazole (TBBz) has been shown to be a specific inhibitor of CK2 activity, which suggests that TBBz may be useful for reducing HBV gene expression. The aim of our study was to determine whether inhibition of CK2 by TBBz and decreased phosphorylation of hLa Ser(366) (pLa) would reduce HBV gene expression. pLa and total La expression levels were evaluated by immunohistochemistry in human liver tissues with or without HBV infection. HepG2.2.15 cells (an HBV-expressing cell line) were treated with TBBz, and cell viability and pLa levels were evaluated. Knockdown of hLa and CK2 levels by specific siRNA and mutant hLa Ala(366) were utilized to establish the roles of pLa and CK2 in HBV gene expression. HBV DNA replication and HBsAg and HBeAg levels were analysed in HepG2.2.15 cell supernatants by standard methods. pLa was significantly overexpressed in HBV-infected human liver samples. TBBz decreased the phosphorylation of hLa, which coincided with decreased HBV expression. Mutant hLa Ala(366) had reduced viral expression compared with hLa Ser(366) treatment in hLa siRNA knockdown cells. Knockdown of CK2 also decreased the HBV parameters. hLa plays a key role in the regulation of HBV gene expression in a CK2-dependent mechanism via phosphorylation of hLa at Ser(366).

Immunoregulation of hepatitis B virus infection--rationale and clinical application

Hepatitis B virus (HBV) is susceptible to the cellular immune responses, especially to the signal of interferon (IFN)-gamma. The action of IFN-gamma is pleiotropic, and causes downregulation of HBV in protein, RNA, and possibly DNA levels. Therefore, therapeutic vaccination to induce cellular immune responses to HBV is a promising approach for controlling chronic HBV infection. A number of clinical trials with this approach have been conducted to date, however, they have not been as successful as initially expected. T-cell exhaustion induced by the excessive HBV antigens caused by persistent infection is thought to be one of the main causes of poor responses to therapeutic vaccination. In this review, the mechanisms behind immunoregulation of HBV replication and immunodysfunction during chronic HBV infection are summarized, and novel approaches to improve the efficacy of therapeutic vaccination, from basic research to clinical trials, are introduced.

A novel inhibitor of human La protein with anti-HBV activity discovered by structure-based virtual screening and in vitro evaluation

BACKGROUND

Over 350 million people worldwide are infected with hepatitis B virus (HBV), a major cause of liver failure and hepatocellular carcinoma. Current therapeutic agents are highly effective, but are also associated with development of viral resistance. Therefore, strategies for identifying other anti-HBV agents with specific, but distinctive mechanisms of action are needed. The human La (hLa) protein, which forms a stabilizing complex with HBV RNA ribonucleoprotein to promote HBV replication, is a promising target of molecular therapy.

AIMS

This study aimed to discover novel inhibitors of hLa that could inhibit HBV replication and expression.

METHODS

A multistage molecular docking approach was used to screen a Specs database and an in-house library against hLa binding sites. Sequential in vitro evaluations were performed to detect potential compounds with high scores in HepG2.2.15 cells.

RESULTS

Of the 26 potential compounds with high scores chosen for experimental verification, 12 had HBV DNA inhibition ratios of less than 50% with P<0.05. Six had significant inhibition of HBV e antigen (HBeAg) levels, and 13 had significant inhibition of HBV surface antigen (HBsAg) levels by in vitro assays. Compounds HBSC-11, HBSC-15 and HBSC-34 (HBSC is system prefix for active compounds screened by the library) were selected for evaluation. HBSC-11 was found to have an obvious inhibitory effect on hLa transcription and expression.

CONCLUSIONS

Our findings suggest that anti-HBV activity of HBSC-11 may be mediated by a reduction in hLa levels. In addition, our data suggest the potential clinical use of hLa inhibitors, such as HBSC-11, for treating HBV infection.

Anti-hepatitis B virus activities of cinobufacini and its active components bufalin and cinobufagin in HepG2.2.15 cells

Cinobufacini (Huachansu) is a Chinese medicine prepared from the skin of Bufo bufo gargarizans Cantor (Bufonidae), which has long been used in traditional Chinese medicine (TCM). The aim of present study was to examine the anti-hepatitis B virus (HBV) activities of cinobufacini and its active components bufalin and cinobufagin in the human HBV-transfected cell line HepG2.2.15. The hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), and hepatitis B core-related antigen (HBcrAg) concentrations in cell culture medium were determined by chemiluminescent enzyme immunoassay after HepG2.2.15 cells were respectively treated with different concentrations of cinobufacini, bufalin, and cinobufagin for 3 or 6 d. HBV DNA and mRNA were determined using transcription-mediated amplification and real-time polymerase chain reaction (PCR), respectively. On d 3, cinobufacini at a concentration of 1 µg/ml had no activity against HBV virological markers. However, on d 6, cinobufacini at 1 µg/ml effectively inhibited the secretion of HBsAg, HBeAg, and HBcrAg by 29.58, 32.87, and 42.52%. It was more potent than the positive control lamivudine (100 µg/ml). Bufalin and cinobufagin slightly inhibited HBV antigen secretion. Treatment with cinobufacini, bufalin, or cinobufagin had no anti-HBV effect on DNA in cell culture medium. Consistent with the HBV antigen reduction, HBV mRNA expression was markedly inhibited in comparison to the control when HepG2.2.15 cells were treated with cinobufacini, bufalin, or cinobufagin. Results suggested that cinobufacini had more potent activity against HBV antigen secretion than its components bufalin and cinobufagin and this inhibitory role was attributed to the specific inhibition of HBV mRNA expression.

Active lytic infection of human primary tonsillar B cells by KSHV and its noncytolytic control by activated CD4+ T cells

Kaposi sarcoma-associated herpesvirus (KSHV) is a B-lymphotropic virus whose primary site of replication is the oropharynx. KSHV can infect both T and B cells from primary tonsillar explant cultures. However, T cells do not support lytic replication, while B cells spontaneously produce substantial amounts of infectious virus. Here, we provide evidence for a mechanism by which activated T cells may promote or stabilize latency of KSHV infection in B cells. When mixed cultures of B cells and activated T cells were exposed to KSHV, little spontaneous virus production was observed. Removing T cells from the mix or treating the mixed culture with immune suppressants enhanced virus production. Adding back activated T cells to purified infected B cells efficiently suppressed KSHV production, primarily due to CD4(+) T cells. This suppressive activity required T cell activation and direct cell-cell contact, but not prior exposure to KSHV antigen. Suppression was not MHC restricted and did not result in killing of the target cell. We therefore propose that oropharyngeal T cells activated by a variety of stimuli can recognize ligands on infected target B cells, leading to signaling events that prevent spontaneous lytic activation and promote latent infection in this compartment.

Conserved and divergent features of the structure and function of La and La-related proteins (LARPs)

Genuine La proteins contain two RNA binding motifs, a La motif (LAM) followed by a RNA recognition motif (RRM), arranged in a unique way to bind RNA. These proteins interact with an extensive variety of cellular RNAs and exhibit activities in two broad categories: i) to promote the metabolism of nascent pol III transcripts, including precursor-tRNAs, by binding to their common, UUU-3'OH containing ends, and ii) to modulate the translation of certain mRNAs involving an unknown binding mechanism. Characterization of several La-RNA crystal structures as well as biochemical studies reveal insight into their unique two-motif domain architecture and how the LAM recognizes UUU-3'OH while the RRM binds other parts of a pre-tRNA. Recent studies of members of distinct families of conserved La-related proteins (LARPs) indicate that some of these harbor activity related to genuine La proteins, suggesting that their UUU-3'OH binding mode has been appropriated for the assembly and regulation of a specific snRNP (e.g., 7SK snRNP assembly by hLARP7/PIP7S). Analyses of other LARP family members suggest more diverged RNA binding modes and specialization for cytoplasmic mRNA-related functions. Thus it appears that while genuine La proteins exhibit broad general involvement in both snRNA-related and mRNA-related functions, different LARP families may have evolved specialized activities in either snRNA or mRNA-related functions. In this review, we summarize recent progress that has led to greater understanding of the structure and function of La proteins and their roles in tRNA processing and RNP assembly dynamics, as well as progress on the different LARPs.

Pathogenesis of hepatitis B virus infection

The adaptive immune response is thought to be responsible for viral clearance and disease pathogenesis during hepatitis B virus infection. It is generally acknowledged that the humoral antibody response contributes to the clearance of circulating virus particles and the prevention of viral spread within the host while the cellular immune response eliminates infected cells. The T cell response to the hepatitis B virus (HBV) is vigorous, polyclonal and multispecific in acutely infected patients who successfully clear the virus and relatively weak and narrowly focussed in chronically infected patients, suggesting that clearance of HBV is T cell dependent. The pathogenetic and antiviral potential of the cytotoxic T lymphocyte (CTL) response to HBV has been proven by the induction of a severe necroinflammatory liver disease following the adoptive transfer of HBsAg specific CTL into HBV transgenic mice. Remarkably, the CTLs also purge HBV replicative intermediates from the liver by secreting type 1 inflammatory cytokines thereby limiting virus spread to uninfected cells and reducing the degree of immunopathology required to terminate the infection. Persistent HBV infection is characterized by a weak adaptive immune response, thought to be due to inefficient CD4+ T cell priming early in the infection and subsequent development of a quantitatively and qualitatively ineffective CD8+ T cell response. Other factors that could contribute to viral persistence are immunological tolerance, mutational epitope inactivation, T cell receptor antagonism, incomplete down-regulation of viral replication and infection of immunologically privileged tissues. However, these pathways become apparent only in the setting of an ineffective immune response, which is, therefore, the fundamental underlying cause. Persistent infection is characterized by chronic liver cell injury, regeneration, inflammation, widespread DNA damage and insertional deregulation of cellular growth control genes, which, collectively, lead to cirrhosis of the liver and hepatocellular carcinoma.

Identification of Apurinic/apyrimidinic endonuclease 1 (APE1) as the endoribonuclease that cleaves c-myc mRNA

Endonucleolytic cleavage of the coding region determinant (CRD) of c-myc mRNA appears to play a critical role in regulating c-myc mRNA turnover. Using (32)P-labeled c-myc CRD RNA as substrate, we have purified and identified two endoribonucleases from rat liver polysomes that are capable of cleaving the transcript in vitro. A 17-kDa enzyme was identified as RNase1. Apurinic/apyrimidinic (AP) DNA endonuclease 1 (APE1) was identified as the 35-kDa endoribonuclease that preferentially cleaves in between UA and CA dinucleotides of c-myc CRD RNA. APE1 was further confirmed to be the 35-kDa endoribonuclease because: (i) the endoribonuclease activity of the purified 35-kDa native enzyme was specifically immuno-depleted with APE1 monoclonal antibody, and (ii) recombinant human APE1 generated identical RNA cleavage patterns as the native liver enzyme. Studies using E96A and H309N mutants of APE1 suggest that the endoribonuclease activity for c-myc CRD RNA shares the same active center with the AP-DNA endonuclease activity. Transient knockdown of APE1 in HeLa cells led to increased steady-state level of c-myc mRNA and its half-life. We conclude that the ability to cleave RNA dinucleotides is a previously unidentified function of APE1 and it can regulate c-myc mRNA level possibly via its endoribonuclease activity.

Increase of Plasma IL-12/p40 Ratio Induced by the Combined Therapy of DNA Vaccine and Lamivudine Correlates with Sustained Viremia Control in CHB Carriers

Background

We previously reported that IFN-γ producing T cell responses induced by the combined therapy of DNA vaccine and lamivudine for one year are important for the induction of sustained virological response (SVR). However, IFN-γ production is not sufficient to predict sustained viremia control in chronic hepatitis B (CHB) carriers treated.

Methods

Twelve CHB carriers were intramuscularly immunized 12 times at a 4-week interval with 8 mg of HBV DNA vaccine during the standard lamivudine treatment (100 mg/daily/1 year). The level of cytokines during and after the combined therapy in plasma of all 12 CHB carriers treated was determined by each ELISA kit. Six out of 12 CHB carriers revisited the clinic, and their HBV DNA levels were examined.

Results

The combined therapy increased plasma IL-12 and IL-12/p40 ratio during the treatment (baseline vs. peak level: 41.8±8.3 vs. 163.1±29.2 pg/ml; p<0.01 and 0.96±0.25 vs. 3.58±0.86; p<0.01, espectively), and the peak level of plasma IL-12 and IL-12/p40 ratio was evoked at 6 to 10 months during the combined therapy. In particular, CHB carriers with SVR had two and three-fold higher level of the peak plasma IL-12 and plasma IL-12/p40 ratio than non-virological responders (NVRs), respectively (218.0±41.4 vs. 108.1±28.6 pg/ml; p=0.09 and 5.35±1.38 vs. 1.80±0.29; p<0.05, respectively), while p40 level was consistent during the combined therapy. In addition, there was no significant temporal correlation between the peak IL-12/p40 ratio and the elevation of serum alanine aminotransferase (ALT) in this study, contrast to IFN-α therapy which induced peak IL-12 level following ALT flares.

Conclusion

Our results indicate that the combined therapy induces the increase of plasma IL-12 and IL-12/p40 ratio, which are associated with long-term SVR in CHB carriers.

Correlation of virus and host response markers with circulating immune complexes during acute and chronic woodchuck hepatitis virus infection

Woodchuck hepatitis virus (WHV) is an established model for human hepatitis B virus. The kinetics of virus and host responses in serum and liver during acute, self-limited WHV infection in adult woodchucks were studied. Serum WHV DNA and surface antigen (WHsAg) were detected as early as 1 to 3 weeks following experimental infection and peaked between 1 and 5 weeks postinfection. Thereafter, serum WHsAg levels declined rapidly and became undetectable, while WHV DNA levels became undetectable much later, between 4 and 20 weeks postinfection. Decreasing viremia correlated with transient liver injury marked by an increase in serum sorbitol dehydrogenase (SDH) levels. Clearance of WHV DNA from serum was associated with the normalization of serum SDH. Circulating immune complexes (CICs) of WHsAg and antibodies against WHsAg (anti-WHs) that correlated temporarily with the peaks in serum viremia and WHs antigenemia were detected. CICs were no longer detected in serum once free anti-WHs became detectable. The detection of CICs around the peak in serum viremia and WHs antigenemia in resolving woodchucks suggests a critical role for the humoral immune response against WHsAg in the early elimination of viral and subviral particles from the peripheral blood. Individual kinetic variation during WHV infections in resolving woodchucks infected with the same WHV inoculum and dose is likely due to the outbred nature of the animals, indicating that the onset and magnitude of the individual immune response determine the intensity of virus inhibition and the timing of virus elimination from serum.

Biological and clinical implications of HBV infection in peripheral blood mononuclear cells

The liver is the main site of HBV replication, however extrahepatic organs, such as the lymphoid system, are an important reservoir of the virus. Viral DNA into different mononuclear cell subsets has been mainly detected in monocytes and B lymphocytes. The attachment site of the virus has been identified in the preS1 encoded protein of the virus envelope, the same involved in hepatocyte infection. The risk of HBV transmission by infected lymphocytes has been clearly documented in the setting of liver transplantation where de novo HBV infection has been found in up to about 80% of liver grafts from HBsAg negative but anti-HBc positive donors. In the hemodialysis setting the percentage of HBV DNA detection in mononuclear cells of HBsAg negative patients has been described in up to 54% of the cases. Vertical transmission studies indicate that HBV-infected mononuclear cells of the mother may result in viral infection of mononuclear cells of the newborns and possible HBV vaccine response failure. HBV can also infect bone marrow cells and in vitro studies demonstrate a block of hematopoiesis by HBV, supporting clinical observations of isolate cases of aplastic anemia associated to the infection.

Cellular La protein shields nonsegmented negative-strand RNA viral leader RNA from RIG-I and enhances virus growth by diverse mechanisms

The La antigen (SS-B) associates with a wide variety of cellular and viral RNAs to affect gene expression in multiple systems. We show that La is the major cellular protein found to be associated with the abundant 44-nucleotide viral leader RNA (leRNA) early after infection with respiratory syncytial virus (RSV), a nonsegmented negative-strand RNA virus. Consistent with this, La redistributes from the nucleus to the cytoplasm in RSV-infected cells. Upon RNA interference knockdown of La, leRNA is redirected to associate with the RNA-binding protein RIG-I, a known activator of interferon (IFN) gene expression, and this is accompanied by the early induction of IFN mRNA. These results suggest that La shields leRNA from RIG-I, abrogating the early viral activation of type I IFN. We mapped the leRNA binding function to RNA recognition motif 1 of La and showed that while wild-type La greatly enhanced RSV growth, a La mutant defective in RSV leRNA binding also did not support RSV growth. Comparative studies of RSV and Sendai virus and the use of IFN-negative Vero cells indicated that La supports the growth of nonsegmented negative-strand RNA viruses by both IFN suppression and a potentially novel IFN-independent mechanism.

Immunobiology and pathogenesis of viral hepatitis

Among the many viruses that are known to infect the human liver, hepatitis B virus (HBV) and hepatitis C virus (HCV) are unique because of their prodigious capacity to cause persistent infection, cirrhosis, and liver cancer. HBV and HCV are noncytopathic viruses and, thus, immunologically mediated events play an important role in the pathogenesis and outcome of these infections. The adaptive immune response mediates virtually all of the liver disease associated with viral hepatitis. However, it is becoming increasingly clear that antigen-nonspecific inflammatory cells exacerbate cytotoxic T lymphocyte (CTL)-induced immunopathology and that platelets enhance the accumulation of CTLs in the liver. Chronic hepatitis is characterized by an inefficient T cell response unable to completely clear HBV or HCV from the liver, which consequently sustains continuous cycles of low-level cell destruction. Over long periods of time, recurrent immune-mediated liver damage contributes to the development of cirrhosis and hepatocellular carcinoma.

HBV pathogenesis in animal models: recent advances on the role of platelets

Hepatitis B virus (HBV) causes acute and chronic necroinflammatory liver diseases and hepatocellular carcinoma (HCC). HBV replicates noncytopathically in the hepatocyte, and most of the liver injury associated with this infection reflects the immune response. While the innate immune response may not contribute significantly to the pathogenesis of liver disease or viral clearance, the adaptive immune response, particularly the cytotoxic T lymphocyte (CTL) response, contributes to both. Recent observations also reveal that antigen-nonspecific inflammatory cells enhance CTL-induced liver pathology and, more surprisingly, that platelets facilitate the intrahepatic accumulation of CTLs, suggesting that the host response to HBV infection is a highly complex but coordinated process. The notion that platelets contribute to liver disease and viral clearance by promoting the recruitment of virus-specific CTLs into the liver is a new concept in viral pathogenesis, which may prove useful to implement treatments of chronic HBV infection in man.

Quantitative analysis of HBV cccDNA from clinical specimens: correlation with clinical and virological response during antiviral therapy

Attempts to investigate changes in various forms of intrahepatic hepatitis B virus (HBV) DNA during antiviral therapy have been hampered by limitations in technologies and scarcity of adequate tissue for analysis. We used a sensitive, specific assay to detect and quantitate covalently closed circular DNA (cccDNA) from total intrahepatic HBV DNA in clinical liver specimens. Total HBV DNA and cccDNA from 21 needle-biopsy specimens were quantified, with levels ranging from 0.1 to 9.8 copies/cell and 0.3 to 491.0 copies/cell, respectively. Then, we performed the same determinations on baseline and week-52 liver needle-biopsy specimens from eight patients enrolled in a clinical trial and evaluated the association between intrahepatic HBV DNA levels and serological and virological endpoints. In most patients, levels of intrahepatic HBV DNA, including cccDNA, decreased over the 52-week study, regardless of therapy or serological outcome. Higher ratios of cccDNA to total HBV DNA were detected at week 52 than at baseline indicating a shift in predominance of nonreplicating virus in posttreatment specimens. In patients who achieved treatment-related or spontaneous hepatitis B e antigen (HBeAg) responses, including those harbouring tyrosine-methionine-aspartate-aspartate-mutant HBV, levels of intrahepatic and serum HBV DNA suppression were greater than those in patients without HBeAg responses. In conclusion, this pilot study of intrahepatic HBV replicative forms in patients with chronic hepatitis B indicated that total intrahepatic and, specifically, cccDNA levels are not static but change as a reflection of serological and virological events.

Identification of c-myc coding region determinant RNA sequences and structures cleaved by an RNase1-like endoribonuclease

The coding region of c-myc mRNA encompassing the coding region determinant (CRD) nucleotides (nts) 1705-1792 is critical in regulating c-myc mRNA stability. This is in part due to the susceptibility of c-myc CRD RNA to attack by an endoribonuclease. We have previously purified and characterized a mammalian endoribonuclease that cleaves c-myc CRD RNA in vitro. This enzyme is tentatively identified as a 35 kDa RNase1-like endonuclease. In an effort to understand the sequence and secondary structure requirements for RNA cleavage by this enzyme, we have determined the secondary structure of the c-myc CRD RNA nts 1705-1792 using RNase probing technique. The secondary structure of c-myc CRD RNA possesses five stems; two of which contain 4 base pairs (stems I and V) and three consisting of 3 base pairs (stems II, III, and IV). Endonucleolytic assays using the c-myc CRD and several c-myc CRD mutants as substrates led to the following conclusions: (i) the enzyme prefers to cleave in between the dinucleotides UA, CA, and UG in single-stranded regions; (ii) the enzyme is more specific towards UA dinucleotides. These properties further distinguish the enzyme from previously described mammalian endonuclease that cleaves c-myc mRNA in vitro.

IFNgamma expression inhibits LHBs storage disease and ground glass hepatocyte appearance, but exacerbates inflammation and apoptosis in HBV surface protein-accumulating transgenic livers

BACKGROUND/AIMS

Interferon gamma (IFNgamma) controls hepatitis B virus replication. As systemic application may cause severe adverse effects, approaches of liver-directed IFNgamma gene therapy may represent an attractive alternative for treatment of chronic viral hepatitis B and thus needs testing in vivo in suitable animal models.

METHODS

We therefore crossbred Alb-1HBV transgenic mice overexpressing the large HBV surface protein (LHBs) in their livers and developing LHBs storage disease and ground glass hepatocyte appearance with SAP-IFNgamma transgenic animals previously shown to exhibit constitutive hepatic IFNgamma expression, and analyzed the resulting double-transgenic offspring.

RESULTS

We found that IFNgamma coexpression significantly reduced hepatic LHBs expression and thereby inhibited hepatocellular LHBs storage disease and ground glass hepatocyte appearance. The beneficial antiviral IFNgamma effects as observed in Alb1-HBV SAP-IFNgamma double-transgenic livers were associated with significantly elevated serum ALT concentrations, massive mononuclear cell infiltrates, appearance of Councilman bodies, and increased alpha-PARP (poly(ADP-ribose) polymerase cleavage).

CONCLUSIONS

Exacerbation of hepatic necroinflammation and increased hepatocellular apoptosis rate in IFNgamma-expressing Alb1-HBV transgenic livers suggest that special precautions be taken for testing approaches of liver-specific IFNgamma expression in patients with chronic hepatitis B.

Purification and characterization of a novel mammalian endoribonuclease

Endonuclease-mediated mRNA decay appears to be a common mode of mRNA degradation in mammalian cells, but yet only a few mRNA endonucleases have been described. Here, we report the existence of a second mammalian endonuclease that is capable of cleaving c-myc mRNA within the coding region in vitro. This study describes the partial purification and biochemical characterization of this enzyme. Five major proteins of approximately 10-35 kDa size co-purified with the endonuclease activity, a finding supported by gel filtration and glycerol gradient centrifugation analysis. The enzyme is an RNA-specific endonuclease that degrades single-stranded RNA, but not double-stranded RNA, DNA or DNA-RNA duplexes. It preferentially cleaves RNA in between the pyrimidine and purine dinucleotides UA, UG, and CA, at the coding region determinant (CRD) of c-myc RNA. The enzyme generates products with a 3'hydroxyl group, and it appears to be a protein-only endonuclease. It does not possess RNase A-like activity. The enzyme is capable of cleaving RNAs other than c-myc CRD RNA in vitro. It is Mg(2+)-independent and is resistant to EDTA. The endonuclease is inactivated at and above 70 degrees C. These properties distinguished the enzyme from other previously described vertebrate endonucleases.

The clinical virology of hepatitis B

Hepatitis B virus (HBV) is a major human health problem as approximately 8% of the world’s population are chronic carriers and there are over a million HBV-related deaths annually. Treatment of HBV is extremely difficult, as the unique viral replication strategy results in both a continual source of stable DNA molecules that are the template for viral replication and gene expression, and a pool of viral quasispecies from which different isolates may emerge as selection pressures alter. Although the use of antiviral therapies has improved outcomes significantly for many chronically infected individuals, the emergence of drug-resistant and immune/vaccine-escape viruses ensures there is a continuing need for the development of new and imaginative approaches to control and eventually eradicate HBV.

Pathogenetic and antiviral immune responses against hepatitis B virus

Hepatitis B virus (HBV) is a noncytopathic virus that causes liver disease of variable duration and severity. It is widely assumed that during HBV infection the host immune response is responsible for both hepatocellular damage and viral clearance. Whereas there is considerable evidence that the innate immune response does not play a significant role in these processes, the adaptive immune response, particularly virus-specific cytotoxic T lymphocytes (CTLs), seems to contribute to nearly all of the liver injury associated with HBV infection. By killing infected cells and producing antiviral cytokines capable of purging HBV from viable hepatocytes, CTLs are also thought to eliminate the virus. Although liver damage is initiated and mediated by the CTLs, antigen-nonspecific inflammatory cells can worsen CTL-induced immunopathology and platelets may facilitate the accumulation of CTLs in the liver. The mechanisms responsible for disease pathogenesis and viral clearance during HBV infection are the subject of this review.

Functional analysis of hepatitis B virus reactivating in hepatitis B surface antigen-negative individuals

The biological properties of latent or occult hepatitis B virus (HBV) have been poorly characterized as a result of the extremely low virus concentration. This report describes the phenotype of HBV reactivating in two patients after an HBsAg-negative latency period. One patient had latent HBV infection for at least 12 years without detectable viremia and symptoms of liver disease. Several full-length HBV genomes were cloned at reactivation, sequenced, and functionally tested by transfection into HuH7 cells. Genomes from both patients showed a low replication phenotype. It was caused at the level of RNA encapsidation or HBV DNA synthesis, but was not attributable to uncommon mutations in the terminal protein domain of P protein. A substantial subpopulation ( approximately 50%) of genomes from one patient did not express pre-S2/S mRNA and HBsAg. Site-directed mutagenesis identified a single G-A mutation within the S gene (position 458) to be responsible for this effect. The G458A mutation was also effective if the S gene was placed under control of a heterologous promoter. Furthermore, nuclear run-on transcription showed that the G458A mutation acts at the posttranscriptional level. The mutation affected a 5' splice site and prevented splicing of the pre-S2/S mRNA from position 458 to 1305. In conclusion, HBV latency may be characterized by viruses with reduced replication competence and antigen expression. In one patient, HBsAg expression was terminated by an as yet undescribed posttranscriptional mechanism. A single mutation inactivated a 5' splice site that is obviously essential for pre-S2/S mRNA accumulation. Supplementary material for this article can be found on the HEPATOLOGY website (http://www.interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Immunology of hepatitis B virus and hepatitis C virus infection

More than 500 million people worldwide are persistently infected with the hepatitis B virus (HBV) and/or hepatitis C virus (HCV) and are at risk of developing chronic liver disease, cirrhosis and hepatocellular carcinoma. Despite many common features in the pathogenesis of HBV- and HCV-related liver disease, these viruses markedly differ in their virological properties and in their immune escape and survival strategies. This review assesses recent advances in our understanding of viral hepatitis, contrasts mechanisms of virus-host interaction in acute hepatitis B and hepatitis C, and outlines areas for future studies.

Functional characterization of the interaction between human La and hepatitis B virus RNA

The La protein is a multifunctional RNA-binding protein and has also been suggested to be involved in the stabilization of hepatitis B virus (HBV) RNA. Here we demonstrate that antibodies against the human La protein specifically precipitate HBV RNA from HBV ribonucleoprotein-containing mammalian cell extracts, providing evidence for the association between human La and HBV RNA. Moreover, we report that the turnover of HBV RNA depends on structural features and less on the primary sequence of the La-binding site on the viral RNA. In addition we show that the interaction between human La and HBV RNA in vitro is modulated by accessory factor(s) in a phosphorylation-dependent manner. Taken together these data indicate that both structural features, the composition of La/HBV ribonucleoprotein particles as well as interacting cellular factors, are critical determinants in the regulation of the stability of the HBV RNA.

Inhibition of human La protein by RNA interference downregulates hepatitis B virus mRNA in 2.2.15 cells

AIM

To investigate the role of human La protein in HBV mRNA expression.

METHODS

Three human La protein (hLa) specific siRNA expression cassettes (SECs) containing U6+1 promoter were prepared via one-step overlapping extension PCR. After transfection with SECs into HepG2 cells, inhibition effects on hLa expression were analyzed by semi-quantitative RT-PCR and Western blotting. Then, effective SECs were screened out and transfected into 2.2.15 cells, a stable HBV-producing cell line. HBV surface antigen (HBsAg) and e antigen (HBeAg) secretions into culture media were detected by microparticle enzyme immunoassay (MEIA) and HBs and HBe mRNA levels were analyzed by semi-quantitative RT-PCR.

RESULTS

SEC products containing U6+1 snRNA promoter, and 3 sites of hLa mRNA specific siRNA were obtained successfully by one-step overlapping extension PCR and could be directly transfected into HepG2 cells, resulting in inhibition of La protein expression in both mRNA and protein levels, among which U6+1-hLa833 was the most efficient, which reduced 18.6-fold mRNA and 89% protein level respectively. In 2.2.15 cells, U6+1-hLa833 was also efficient on inhibition of hLa expression. Furthermore, semi-quantitative RT-PCR showed that HBs and HBe mRNA levels were significantly decreased by 8- and 66-fold in U6+1-hLa833 transfected cells compared to control. Accordingly, HBsAg and HBeAg secretions were decreased partly posttransfection with SECs.

CONCLUSION

PCR-based SECs can be used to mediate RNAi in mammalian cells and provide a novel approach to study the function of La protein. The inhibition of La protein expression can result in a significant decrease of HBV mRNA, which implies that the hLa protein is also involved HBV RNA metabolism as one of the HBV RNA-stabilizing factors in human cells.

Hepatitis B virus: pathogenesis, viral intermediates, and viral replication

Although HBV has the potential to generate an almost limitless spectrum of quasispecies during chronic infection, the viability of the majority of these quasispecies is almost certainly impaired due to constraints imposed by the remarkably compact organization of the HBV genome. On the other hand, single mutations may affect more than one gene and result in complex and unpredictable effects on viral phenotype. Better understanding of the constraints imposed by gene overlap and of genotype-phenotype relationships should help in the development of improved antiviral strategies and management approaches. Although the probability of developing viral resistance is directly proportional to the intensity of selection pressure and the diversity of quasispecies, potent inhibition of HBV replication should be able to prevent development of drug resistance because mutagenesis is replication dependent. If viral replication can be suppressed for a sufficient length of time, viral load should decline to a point where the continued production of quasispecies with the potential to resist new drug treatments no longer occurs. Clinical application of this concept will require optimization of combination therapies analogous to highly active antiretroviral therapy (HAART) for HIV infection. Total cure of hepatitis B will require elimination of the intranuclear pool of viral minichromosomes, which will probably only be achieved by normal cell turnover, reactivation of host immunity, or elucidation of the antiviral mechanisms operating during cytokine clearance in acute hepatitis B (see Fig. 1).

Cloning of genes differentially expressed in Jurkat cells treated with glycyrrhizin using cDNA microarray

AIM: To study the difference in gene expression profile in human lymphoma cell line Jurkat cells treated with glycyrrhizin (GL), and to further elucidate the molecular immune mechanism of glycyrrhizin against T lymphocyte.

METHODS: cDNA microarray technology was employed to detect the mRNA from Jurkat cells treated with GL and 0.9 percent sodium chloride, respectively.

RESULTS: The results indicated that among 1 152 genes which were obtained from gene expression profile analysis, there were 30 genes different from those in GenBank in which 12 genes were up-regulated and 18 genes were down-regulated in Jurkat cells treated with GL, compared to those treated with 0.9 percent sodium chloride. These genes differentially regulated by GL included human genes encoding proteins involved in immune regulation, cell signal transduction, cell proliferation and differentiation.

CONCLUSION: cDNA microarray technology is successfully used to screen the genes differentially expressed in Jurkat cells treated with GL, which brings some new clues for studying the immune regulation mechanism of GL.

Ty3 requires yeast La homologous protein for wild-type frequencies of transposition

The Saccharomyces cerevisiae retrovirus-like element Ty3 inserts specifically into the initiation sites of genes transcribed by RNA polymerase III (pol III). A strain with a disruption of LHP1, which encodes the homologue of autoantigen La protein, was recovered in a screen for mutants defective in Ty3 transposition. Transposition into a target composed of divergent tRNA genes was decreased eightfold. In lhp1 mutants, Ty3 polyproteins were produced at wild-type levels, assembled into virus-like particles (VLPs) and processed efficiently. The amount of cDNA associated with these particles was about half the amount in a wild-type control at early times, but approached the wild-type level after 48 h of induction. Ty3 integration was examined at two genomic tRNA gene families and two plasmid-borne tRNA promoters. Integration was significantly decreased at one of the tRNA gene families, but was only slightly decreased at the second tRNA gene family. These findings suggest that Lhp1p contributes to Ty3 cDNA synthesis, but might also act at a target-specific step, such as integration.

Effect of thymosin-α1 on immune function with chronic hepatitis B

AIM

To realize effect of thymosin-α1 (Tα1) on immune function with chronic hepatitis B (CHB) and to evaluate the efficacy of Tα1 in the treatment of CHB.

METHODS

Sixty patients with CHB were randomly chosen. Twenty-five cases were received Tα1 (1.6 mg, sc, twice a week, 3-6mo) and thirty-five were received Tα1 combined with Lamivudine (0.1 g, po, once a day, 3-6 mo). Hepatic function, virological analyses (HBeAg, HBsAg, HBV-DNA) and immunological analyses (periperal blood T lymphocytes subset, IFN-α and IL-4 levels) from patients in pretreatment and posttreatment were observed.

RESULTS

At the end of treatment, ALT and T-Bil were decreased in the group of Tα1 combined with Lamivudine (P<0.01), HBeAg/HBsAg remained negative (n = 9) and HBV-DNA levels were also low (n = 14) in the group of Tα1 combined with Lamivudine (P<0.01 and P<0.05, respectively) as compared with healthy individuals. CD₄⁺ T Cell (from 31.3±2.4 to 36.1±2.5), the level of IFN-α(from 71.3±21.0 to 83.7±21.4) and Th1/Th2 (from 0.79±0.2 to 0.98±0.3) increased in the group of Tα1 (P<0.01, P<0.05 and P<0.05, respectively).

CONCLUSION

Tα1 is efficient to treat patients with CHB because it can elevate the level of cellular immunity, which is beneficial to viral clearance.

Regulation of pathways of mRNA destabilization and stabilization

The level of an mRNA in the cytoplasm represents a balance between the rate at which the mRNA precursor is synthesized in the nucleus and the rates of nuclear RNA processing and export and cytoplasmic mRNA degradation. Although most studies of gene expression have focused on gene transcription and in the area of eukaryotic mRNA degradation, but to provide a short general discussion of the importance of mRNA degradation and its regulation and a brief overview of recent findings and present knowledge. The overview is followed by a more in-depth discussion of one of the several pathways for mRNA degradation. We concentrate on the pathway for regulated mRNA degradation mediated by mRNA-binding proteins and endonucleases that cleave within the body of mRNAs. As a potential example of this type of control, we focus on the regulated degradation of the egg yolk precursor protein vitellogenin on the mRNA-binding protein vigilin and the mRNA endonuclease polysomal ribonuclease 1 (PMR-1).

Molecular characterization of the human La protein.hepatitis B virus RNA.B interaction in vitro

The La protein was recently identified as a host factor potentially involved in the cytokine-induced post-transcriptional down-regulation of hepatitis B virus (HBV) RNA. The La binding site was mapped to a predicted stem-loop structure within a region shared by all HBV RNAs, and it was concluded that the La protein might be an HBV RNA-stabilizing factor. To characterize the RNA binding mediated by the different RNA recognition motifs (RRMs) of the human La protein, several La deletion mutants were produced and analyzed for HBV RNA binding ability. The data demonstrate that the first RRM is not required for binding, whereas the RNP-1 and RNP-2 consensus sequences of the RRM-2 and RRM-3 are separately required for binding, indicating a cooperative function of these two RRMs. Furthermore, the results suggest that multimeric La disassembles into monomeric La upon binding of HBV RNA.B. By gel retardation assay the affinity of the wild type human La.HBV RNA.B interaction was determined in the nanomolar range, comparable to the affinity determined for the mouse La.HBV RNA.B interaction. This study identified small regions within the human La protein mediating the binding of HBV RNA. Hence, these binding sites might represent targets for novel antiviral strategies based on the disruption of the human La.HBV RNA interaction, thereby leading to HBV RNA degradation.

Of the three tegument proteins that package mRNA in herpes simplex virions, one (VP22) transports the mRNA to uninfected cells for expression prior to viral infection

An earlier report has shown that herpes simplex virus 1 virions package RNA. Experiments designed to reveal the identity of the virion proteins capable of binding the RNA and to show whether the mRNA carried in the newly infected cells was expressed showed the following: (i) (32)P-labeled riboprobe generated by in vitro transcription of the U(S)8.5 ORF bound three proteins identified as the products of U(S)11, U(L)47, and U(L)49 (VP22) genes. (ii) Viral RNA was bound to U(L)47 or U(S)11 proteins immune precipitated from cells transduced with baculoviruses expressing U(L)47 or U(S)11 and then superinfected with HSV-1 under conditions that blocked DNA synthesis and assembly of virions. (iii) Virions were purified from cells transduced with a baculovirus encoding a U(S)8.5 protein fused to green fluorescent protein and superinfected with an HSV-1 mutant lacking the U(S)8-12 genes. HEp-2 cells infected with these virions expressed the chimeric protein in approximately 1% of infected cells. (iv) In mixed cultures, untreated Vero cells acquired the mRNA encoding the green fluorescent-U(S)8.5 chimeric protein from HEp-2 cells doubly transduced with the genes encoding VP22 and the chimeric protein. The transfer was RNase sensitive and VP22 dependent, indicating that the RNA encoded by the chimeric gene was transferred to Vero cells as mRNA. We conclude that (i) three virion proteins are capable of binding RNA; (ii) the packaged RNA can be expressed in newly infected cells; and (iii) the U(L)47 protein was earlier reported to shuttle from nucleus to the cytoplasm and may transport RNA. VP22 thus appears to be a member of a new class of viral proteins whose major function is to bind and transport infected cell mRNA to uninfected cells to create the environment for effective initiation of infection.

Characterization and purification of a mammalian endoribonuclease specific for the alpha -globin mRNA

The alpha-globin mRNA has previously been shown to be the target of an erythroid-enriched endoribonuclease (ErEN) activity which cleaves the mRNA within the 3'-untranslated region. We have currently undertaken a biochemical approach to purify this enzyme and have begun characterization of the enzyme to determine requirements for substrate recognition as well as optimal cleavage conditions. Through mutational analysis and truncations we show that a 26-nucleotide region of the alpha-globin 3'-untranslated region is an autonomous element that is both necessary and sufficient for cleavage by ErEN. Mutations throughout this region abolish cleavage activity by ErEN suggesting that the entire sequence is important for recognition and cleavage. ErEN is most active under biological salt concentrations and temperature and activity of the enzyme does not require cations. The size for ErEN was estimated by denaturing gel filtration analysis and is approximately 40 kDa. Interestingly, the exquisite specificity of ErEN cleavage became compromised with increased purity of the enzyme suggesting the involvement of other proteins in specificity of ErEN cleavage. Nondenaturing gel filtration of MEL extract demonstrated that ErEN is a component of an approximately 160 kDa complex implying that additional proteins may regulate ErEN activity and provide increased cleavage specificity.