The covalently closed circular DNA (cccDNA) of the hepatitis B virus (HBV) plays an essential role in chronic hepatitis. The cellular repair system is proposed to convert cytoplasmic nucleocapsid (NC) DNA (partially double-stranded DNA) into cccDNA in the nucleus. Recently, antiviral cytidine deaminases, AID/APOBEC proteins, were shown to generate uracil residues in the NC-DNA through deamination, resulting in cytidine-to-uracil (C-to-U) hypermutation of the viral genome. We investigated whether uracil residues in hepadnavirus DNA were excised by uracil-DNA glycosylase (UNG), a host factor for base excision repair (BER). When UNG activity was inhibited by the expression of the UNG inhibitory protein (UGI), hypermutation of NC-DNA induced by either APOBEC3G or interferon treatment was enhanced in a human hepatocyte cell line. To assess the effect of UNG on the cccDNA viral intermediate, we used the duck HBV (DHBV) replication model. Sequence analyses of DHBV DNAs showed that cccDNA accumulated G-to-A or C-to-T mutations in APOBEC3G-expressing cells, and this was extensively enhanced by UNG inhibition. The cccDNA hypermutation generated many premature stop codons in the P gene. UNG inhibition also enhanced the APOBEC3G-mediated suppression of viral replication, including reduction of NC-DNA, pre-C mRNA, and secreted viral particle-associated DNA in prolonged culture. Enhancement of APOBEC3G-mediated suppression by UNG inhibition was not observed when the catalytic site of APOBEC3G was mutated. Transfection experiments of recloned cccDNAs revealed that the combination of UNG inhibition and APOBEC3G expression reduced the replication ability of cccDNA. Taken together, these data indicate that UNG excises uracil residues from the viral genome during or after cccDNA formation in the nucleus and imply that BER pathway activities decrease the antiviral effect of APOBEC3-mediated hypermutation.

Activation-induced cytidine deaminase (AID) is essential for the somatic hypermutation (SHM) and class-switch recombination (CSR) of Ig genes. The mechanism by which AID triggers SHM and CSR has been explained by two distinct models. In the DNA deamination model, AID converts cytidine bases in DNA into uridine. The uridine is recognized by the DNA repair system, which produces DNA strand breakages and point mutations. In the alternative model, RNA edited by AID is responsible for triggering CSR and SHM. However, RNA deamination by AID has not been demonstrated. Here we found that C-to-T and G-to-A mutations accumulated in hepatitis B virus (HBV) nucleocapsid DNA when AID was expressed in HBVreplicating hepatic cell lines. AID expression caused C-to-T mutations in the nucleocapsid DNA of RNase H-defective HBV, which does not produce plus-strand viral DNA. Furthermore, the RT-PCR products of nucleocapsid viral RNA from AID-expressing cells exhibited significant C-to-T mutations, whereas viral RNAs outside the nucleocapsid did not accumulate C-to-U mutations. Moreover, AID was packaged within the nucleocapsid by forming a ribonucleoprotein complex with HBV RNA and the HBV polymerase protein.The encapsidation of the AID protein with viral RNA and DNA provides an efficient environment for evaluating AID's RNA and DNA deamination activities. A bona fide RNA-editing enzyme, apolipoprotein B mRNA editing catalytic polypeptide 1, induced a similar level of C-to-U mutations in nucleocapsid RNA as AID. Taken together, the results indicate that AID can deaminate the nucleocapsid RNA of HBV.3D-PCR | RNA binding | viral particle | hepadnavirus | pgRNA A ntigen-induced Ig diversification is the basis of antibody memory, which is critical for effective vaccination. Activation-induced cytidine deaminase (AID) is required for somatic hypermutation (SHM) and class-switch recombination (CSR), both of which are initiated by DNA cleavage induced by AID (1-4). The molecular mechanism by which AID triggers DNA cleavage specifically in Ig loci is a key question for understanding acquired immunity. There are two hypotheses for explaining how AID initiates DNA cleavage at the Ig locus: the DNA deamination model and the RNA editing hypothesis.The DNA deamination model is based on the observation that AID induces mutations in the genomic DNA of Escherichia coli and deaminates dC in single-stranded DNA in vitro (5-8). The resulting dU/dG mismatches are proposed to be recognized by enzymes in the base excision repair pathway, which cleave the DNA phosphodiester bond. However, it has not been directly demonstrated that AID generates dU specifically in the Ig locus. By contrast, in the RNA editing hypothesis, AID deaminates RNA, and the edited RNA is involved in DNA cleavage at the Ig genes (4, 9). This model was initially based on the structural similarity of AID to apolipoprotein B mRNA editing catalytic polypeptide 1 (APOBEC1), which is a bona fide RNA-editing enzyme (3, 4). Subsequently, various AID mutants were shown to have distinct defec...

Transforming growth factor (TGF)-β inhibits hepatitis B virus (HBV) replication although the intracellular effectors involved are not determined. Here, we report that reduction of HBV transcripts by TGF-β is dependent on AID expression, which significantly decreases both HBV transcripts and viral DNA, resulting in inhibition of viral replication. Immunoprecipitation reveals that AID physically associates with viral P protein that binds to specific virus RNA sequence called epsilon. AID also binds to an RNA degradation complex (RNA exosome proteins), indicating that AID, RNA exosome, and P protein form an RNP complex. Suppression of HBV transcripts by TGF-β was abrogated by depletion of either AID or RNA exosome components, suggesting that AID and the RNA exosome involve in TGF-β mediated suppression of HBV RNA. Moreover, AID-mediated HBV reduction does not occur when P protein is disrupted or when viral transcription is inhibited. These results suggest that induced expression of AID by TGF-β causes recruitment of the RNA exosome to viral RNP complex and the RNA exosome degrades HBV RNA in a transcription-coupled manner.

BackgroundEarly diagnosis of tuberculosis (TB) and involvement of the public-private partnership are critical to eradicate TB. Patients need to receive proper treatment through the National Tuberculosis Control Programme (NTP). This study describes various predictors for health seeking behaviour of TB patients and health system delay made by the different health care providers.MethodsA cross-sectional study was conducted in a public health facility of a rural area in Bangladesh. Newly diagnosed smear positive pulmonary TB (PTB) patients who were ≥ 15 years of age were sequentially enrolled in this study. The socio-demographic characteristics and proportion of health care utilization by the patients, and health system delay made by the health care providers were calculated. Multivariate analysis was conducted to determine the independent association of the risk factors with the time to seek medical care.ResultsTwo hundred and eighty patients were enrolled in this study. Among them, 73.6% were male and 26.4% were female. A hundred percent of patients primarily sought treatment for their cough, 170 (60.7%) first consulted a non-qualified practitioner while 110 patients (39.3%) first consulted with qualified practitioners about their symptoms. Pharmacy contact was the highest (27.9%) among the non-qualified practitioners, and 58.9% non-qualified practitioners prescribed treatment without any laboratory investigation. The average health system delay was 68.5 days. Multiple logistic regressions revealed a significant difference between uneducated and educated patients (OR 2.33; CI 1.39–3.92), and qualified and non-qualified practitioners (OR 2.34; CI 1.38–3.96) to be independent predictors of health system delay.ConclusionsCompared to men, fewer women sought TB treatment. Uneducated patients and questionably qualified practitioners made for a longer delay in detecting TB. Increasing public health awareness and improving health seeking behavior of females and uneducated patients, and greater participation of the qualified practitioners in the NTP are highly recommended.Electronic supplementary materialThe online version of this article (10.1186/s12879-018-3430-0) contains supplementary material, which is available to authorized users.

Background: Street children concern to millions of deprived boys and girls who have adopted the street as their residence. They grow up where tranquility and physical and emotional stability are frequently threatened. The purpose is to have an empathetic look into the lives of street children for identifying their health-related needs. Method: A cross sectional descriptive type of study was conducted among 125 street children between the ages 8 to 14 years who were available at different intercept points of Dhaka city, Bangladesh. The information was collected through face-to-face interview using a structured questionnaire. An attempt was made to relate their lifestyle, risk behavior and health impact upon the socio demographic characteristics. Result: According to the statement of street children, poverty (41%) is the main reason behind enforcing the children to stay and work on the street. They pass their leisure by playing games, roaming around by watching video/cinema but on the other side of the coin, they are frequently abused (80.8%) either physically or sexually. Regarding health, about 87.2% of street children were suffering from different type of diseases as accidental injury, skin infection, hepatitis, sexually transmitted diseases and warm infestation. Conclusion: A careful examination of the lives of these children will provide a clearer understanding of their disadvantageous life. A better diagnosis of the contributing factors will help to minimize the extent of the problems and also to develop innovative approaches and ensure a healthy lifestyle, protection and rehabilitation for those children.