Amino acid substitutions in the region between RpoB clusters II and III on rifampin susceptibility in Haemophilus influenzae.

BACKGROUND: Rifampin is a potent chemoprophylactic antibiotic for Haemophilus influenzae infection, and the resistance rate in H. influenzae is low. In this study, we assessed rifampin resistance-related genetic variations in H. influenzae. METHODS: Rifampin susceptibility testing and whole-genome sequencing were performed in 51 H. influenzae isolates. Variations associated with rifampin resistance were identified using Fisher's exact tests. Functional assays were performed to evaluate the effect of RpoB substitutions on rifampin susceptibility. RESULTS: Using the genome of the Rd KW20 H. influenzae strain as the reference, we detected 40 genetic variations in rpoB, which resulted in 39 deduced amino acid substitutions among the isolates. Isolate A0586 was resistant to rifampin, with a minimum inhibitory concentration (MIC) = 8 µg/mL. Phylogenetic analyses revealed that the RpoB sequence of isolate A0586 was distinct from other isolates. Five substitutions, including H526N located in cluster I and L623F, R628C, L645F, and L672F in the region between clusters II and III, were unique to isolate A0586. In two rifampin-susceptible H. influenzae isolates, RpoB-H526N alone and in combination with RpoB-L672F increased the MICs of rifampin to 4 and 8 µg/mL, respectively. RpoB-L672F did not affect cell growth and transcription in H. influenzae isolates. No amino acid substitutions in the AcrAB-TolC efflux pump or outer membrane proteins were found to be associated with rifampin resistance in H. influenzae. CONCLUSIONS: Our findings indicate that L672F substitution in the region between RpoB clusters II and III has an aggravating effect on rifampin resistance in H. influenzae.

Molecular characterization of multidrug-resistant non-typeable Haemophilus influenzae with high-level resistance to cefuroxime, levofloxacin, and trimethoprim-sulfamethoxazole.

BACKGROUND: Non-typeable Haemophilus influenzae (NTHi) has become the major cause of invasive H. influenzae diseases in the post-H. influenzae type b vaccine era. The emergence of multidrug-resistant (MDR) NTHi is a growing public health problem. Herein, we investigated the molecular basis of MDR in NTHi. The isolated NTHi were subjected to antimicrobial susceptibility testing for 12 agents. Whole genome and plasmid sequencing were conducted and analyzed to identify significant genetic variations and plasmid-encoded genes conferred antibiotic resistance. RESULTS: Thirteen (50%) MDR NTHi isolates were obtained; of these, 92.3% were non-susceptible to ampicillin, 30.8% to amoxicillin-clavulanate, 61.5% to cefuroxime, 61.5% to ciprofloxacin/levofloxacin, 92.3% to trimethoprim-sulfamethoxazole, 30.8% to tetracycline, and 7.7% to azithromycin. Eight ampicillin-resistant isolates were ß-lactamase positive; of these, 6 carried blaTEM-1 and 2 carried blaROB-1, whereas 4 were ß-lactamase negative. Genetic variations in mrdA, mepA, and pbpG were correlated with amoxicillin-clavulanate non-susceptibility, whereas variations in ftsI and lpoA conferred cefuroxime resistance. Five variations in gyrA, 2 in gyrB, 3 in parC, 1 in parE, and 1 in the parC-parE intergenic region were associated with levofloxacin/ciprofloxacin non-susceptibility. Among these genes, 8 variations were linked to high-level levofloxacin resistance. Six variations in folA were associated with trimethoprim-sulfamethoxazole resistance. Plasmid-bearing tet(B) and mef(A) genes were responsible for tetracycline and azithromycin resistance in 4 and 1 MDR isolates, respectively. CONCLUSIONS: This study clarified the molecular epidemiology of MDR in NTHi. This can benefit the monitoring of drug resistance trends in NTHi and the adequate medical management of patients with NTHi infection.

Molecular characterization of cefepime and aztreonam nonsusceptibility in Haemophilus influenzae.

BACKGROUND: Cefepime and aztreonam are highly efficacious against H. influenzae, and resistant strains are rare. In this study, we isolated cefepime- and aztreonam-nonsusceptible H. influenzae strains and addressed the molecular basis of their resistance to cefepime and aztreonam. METHODS: Two hundred and 28 specimens containing H. influenzae were screened, of which 32 isolates were enrolled and applied to antimicrobial susceptibility testing and whole-genome sequencing. Genetic variations that were detected in all nonsusceptible isolates with statistical significance by Fisher's exact tests were identified as cefepime or aztreonam nonsusceptibility related. Functional complementation assays were conducted to assess the in vitro effects of proteins with sequence substitutions on drug susceptibility. RESULTS: Three H. influenzae isolates were nonsusceptible to cefepime, one of which was also nonsusceptible to aztreonam. Genes encoding TEM, SHV and CTX-M extended-spectrum ß-lactamases were not detected in the cefepime- and aztreonam-nonsusceptible isolates. Five genetic variations in four genes and 10 genetic variations in five genes were associated with cefepime and aztreonam nonsusceptibility, respectively. Phylogenetic analyses revealed that changes in FtsI were correlated strongly with the MIC of cefepime and moderately with aztreonam. FtsI Thr532Ser-Tyr557His cosubstitution linked to cefepime nonsusceptibility and Asn305Lys-Ser385Asn-Glu416Asp cosubstitution to aztreonam nonsusceptibility. Functional complementation assays revealed that these cosubstitutions increased MICs of cefepime and aztreonam in susceptible H. influenzae isolates, respectively. CONCLUSIONS: Genetic variations relevant to resistant phenotypes of cefepime and aztreonam nonsusceptibility in H. influenzae were identified. Moreover, the effects of FtsI cosubstitutions on increasing MICs of cefepime and aztreonam in H. influenzae were demonstrated.

Hepatitis B virus virion secretion is a CRM1-spike-mediated late event.

BACKGROUND: Hepatitis B virus (HBV) is a major human pathogen worldwide. To date, there is no curative treatment for chronic hepatitis B. The mechanism of virion secretion remains to be investigated. Previously, we found that nuclear export of HBc particles can be facilitated via two CRM1-specific nuclear export signals (NES) at the spike tip. METHODS: In this study, we used site-directed mutagenesis at the CRM1 NES, as well as treatment with CRM1 inhibitors at a low concentration, or CRM1-specific shRNA knockdown, in HBV-producing cell culture, and measured the secretion of various HBV viral and subviral particles via a native agarose gel electrophoresis assay. Separated HBV particles were characterized by Western blot analysis, and their genomic DNA contents were measured by Southern blot analysis. Secreted extracellular particles were compared with intracellular HBc capsids for DNA synthesis and capsid formation. Virion secretion and the in vivo interactions among HBc capsids, CRM1 and microtubules, were examined by proximity ligation assay, immunofluorescence microscopy, and nocodazole treatment. RESULTS: We report here that the tip of spike of HBV core (HBc) particles (capsids) contains a complex sensor for secretion of both HBV virions and naked capsids. HBV virion secretion is closely associated with HBc nuclear export in a CRM1-dependent manner. At the conformationally flexible spike tips of HBc particles, NES motifs overlap extensively with motifs important for secretion of HBV virions and naked capsids. CONCLUSIONS: We provided experimental evidence that virions and naked capsids can egress via two distinct, yet overlapping, pathways. Unlike the secretion of naked capsids, HBV virion secretion is highly CRM1- and microtubule-dependent. CRM1 is well known for its involvement in nuclear transport in literature. To our knowledge, this is the first report that CRM1 is required for virion secretion. CRM1 inhibitors could be a promising therapeutic candidate for chronic HBV patients in clinical medicine.

Rapid, reliable, and reproducible cell fusion assay to quantify SARS-Cov-2 spike interaction with hACE2.

COVID-19 is a global crisis of unimagined dimensions. Currently, Remedesivir is only fully licensed FDA therapeutic. A major target of the vaccine effort is the SARS-CoV-2 spike-hACE2 interaction, and assessment of efficacy relies on time consuming neutralization assay. Here, we developed a cell fusion assay based upon spike-hACE2 interaction. The system was tested by transient co-transfection of 293T cells, which demonstrated good correlation with standard spike pseudotyping for inhibition by sera and biologics. Then established stable cell lines were very well behaved and gave even better correlation with pseudotyping results, after a short, overnight co-incubation. Results with the stable cell fusion assay also correlated well with those of a live virus assay. In summary we have established a rapid, reliable, and reproducible cell fusion assay that will serve to complement the other neutralization assays currently in use, is easy to implement in most laboratories, and may serve as the basis for high throughput screens to identify inhibitors of SARS-CoV-2 virus-cell binding and entry.

Extensively drug-resistant Haemophilus influenzae - emergence, epidemiology, risk factors, and regimen.

BACKGROUND: Concern about Haemophilus influenzae infection has been increasing over recent decades. Given the emergence of H. influenzae with severe drug resistance, we assessed the prevalence of as well as risk factors and potential therapies for extensively drug-resistant (XDR) H. influenzae infection in Taiwan. RESULTS: In total, 2091 H. influenzae isolates with disk diffusion-based antibiotic susceptibility testing from 2007 to 2018 were enrolled. H. influenzae strains resistant to ampicillin, chloramphenicol, levofloxacin, and trimethoprim-sulfamethoxazole tended to be isolated from patient wards (≧41%), whereas those resistant to amoxicillin-clavulanate, cefotaxime, and cefuroxime were more likely to be isolated from intensive care units (approximately 50%). XDR H. influenzae was first identified in 2007, and its incidence did not significantly change thereafter. Overall prevalence of single, multiple, and extensively drug-resistant H. influenzae over 2007-2018 was 21.5% (n = 450), 26.6% (n = 557), and 2.5% (n = 52), respectively. A stepwise logistic regression analysis revealed that blood culture (odds ratio: 4.069, 95% confidence intervals: 1.339-12.365, P = 0.013) was an independent risk factor for XDR H. influenzae infection. No nosocomial transmission of XDR H. influenzae observed. Antibiotic susceptibility testing results demonstrated that cefotaxime was effective against 78.8% (n = 41) of the XDR strains. CONCLUSIONS: The presence of XDR H. influenzae strains was identified in Taiwan, and cefotaxime was efficacious against most of these strains.

Critical Role of Mortalin/GRP75 in Endothelial Cell Dysfunction Associated with Acute Lung Injury.

Mortalin/GRP75 (glucose regulated protein 75), a member of heat shock protein 70 family of chaperones, is involved in several cellular processes including proliferation and signaling, and plays a pivotal role in cancer and neurodegenerative disorders. In this study, we sought to determine the role of mortalin/GRP75 in mediating vascular inflammation and permeability linked to the pathogenesis of acute lung injury (ALI). In an aerosolized bacterial lipopolysaccharide inhalation mouse model of ALI, we found that administration of mortalin/GRP75 inhibitor mean kinetic temperature-077, both prophylactically and therapeutically, protected against polymorphonuclear leukocytes influx into alveolar airspaces, microvascular leakage, and expression of pro-inflammatory mediators such as interleukin-1ß, E-selectin, and tumor necrosis factor TNFα. Consistent with this, thrombin-induced inflammation in cultured human endothelial cells (EC) was also protected upon before and after treatment with mean kinetic temperature-077. Similar to pharmacological inhibition of mortalin/GRP75, siRNA-mediated depletion of mortalin/GRP75 also blocked thrombin-induced expression of proinflammatory mediators such as intercellular adhesion molecule-1 and vascular adhesion molecule-1. Mechanistic analysis in EC revealed that inactivation of mortalin/GRP75 interfered with the binding of the liberated NF-κB to the DNA, thereby leading to inhibition of downstream expression of adhesion molecules, cytokines, and chemokines. Importantly, thrombin-induced Ca signaling and EC permeability were also prevented upon mortalin/GRP75 inactivation/depletion. Thus, this study provides evidence for a novel role of mortalin/GRP75 in mediating EC inflammation and permeability associated with ALI.

Adding a C-terminal Cysteine (CTC) Can Enhance the Bactericidal Activity of Three Different Antimicrobial Peptides.

The emergence of antibiotic-resistant bacteria has threatened our health worldwide. There is an urgent need for novel antibiotics. Previously, we identified a novel 37-mer antimicrobial peptide (AMP), HBcARD, with broad spectrum antimicrobial activity. Here, we improved the efficacy of HBcARD, by re-engineering the peptide, including the addition of a new cysteine to its C-terminus (CTC). The new 28-mer derivative, D-150-177C, contains all D-form arginines, in addition to a C-terminal cycteine. This peptide can kill antibiotic-resistant clinical isolates of Gram-negative bacteria, and is more potent than the parental HBcARD peptide in a mouse sepsis model. In another lung infection mouse model, D-150-177C showed protection efficacy against colistin-resistant Acinetobacter baumannii. Unlike colistin, we observed no acute toxicity of D-150-177C in vivo. Interestingly, we found that CTC modification could enhance the antibacterial activity of several other AMPs, such as buforinII and lysin. The potential application and mechanism of this CTC method as a general approach to improving drug efficacy, warrants further investigation in the future.

HBV maintains electrostatic homeostasis by modulating negative charges from phosphoserine and encapsidated nucleic acids.

Capsid assembly and stability of hepatitis B virus (HBV) core protein (HBc) particles depend on balanced electrostatic interactions between encapsidated nucleic acids and an arginine-rich domain (ARD) of HBc in the capsid interior. Arginine-deficient ARD mutants preferentially encapsidated spliced viral RNA and shorter DNA, which can be fully or partially rescued by reducing the negative charges from acidic residues or serine phosphorylation of HBc, dose-dependently. Similarly, empty capsids without RNA encapsidation can be generated by ARD hyper-phosphorylation in insect, bacteria, and human hepatocytes. De-phosphorylation of empty capsids by phosphatase induced capsid disassembly. Empty capsids can convert into RNA-containing capsids by increasing HBc serine de-phosphorylation. In an HBV replicon system, we observed a reciprocal relationship between viral and non-viral RNA encapsidation, suggesting both non-viral RNA and serine-phosphorylation could serve as a charge balance buffer in maintaining electrostatic homeostasis. In addition, by comparing the biochemistry assay results between a replicon and a non-replicon system, we observed a correlation between HBc de-phosphorylation and viral replication. Balanced electrostatic interactions may be important to other icosahedral particles in nature.

Improvement of in vivo antimicrobial activity of HBcARD peptides by D-arginine replacement.

We previously identified a novel antimicrobial peptide with a broad spectrum bactericidal activity from human hepatitis B virus (HBV) core protein (HBc) arginine-rich domain (ARD). We compared the antimicrobial activities of HBcARD peptides from different hepadnaviruses which share similar amino acid sequences. In general, mammalian HBcARD peptides exhibited stronger antimicrobial activity than avian peptides. Using the strategy of D-amino acid substitutions, we improved the antimicrobial efficacy of human HBcARD peptide. This D-HBcARD peptide was much more resistant than L-HBcARD peptide to proteolytic degradation in vitro. Moreover, this D-HBcARD peptide maintained similar minimal bactericidal concentrations (MBC) against tested bacteria, and showed very low hemolytic activity. In the Staphylococcus aureus-infected mouse model, this D-HBcARD peptide was more protective than the L-HBcARD peptide. Repeated treatments with either L- or D-HBcARD peptides induced no significant immunogenicity. New derivatives of HBcARD peptides could serve as alternatives to the conventional antibiotics in clinical medicine in the future.

Functional polymorphisms of the TLR7 and TLR8 genes contribute to Mycobacterium tuberculosis infection.

Tuberculosis (TB) has recently re-emerged as a major global public health threat and Mycobacterium tuberculosis (MTB) is a highly successful pathogen that evolved remarkable strategies to establish persistent infection. There is strong evidence that host genetic factors influence individual susceptibility to TB. In this study, we evaluated the associations between the TLR7 and TLR8 genetic polymorphisms and TB susceptibility in Chinese individuals. The results demonstrated that the frequency of the TLR8-129C allele was higher in male patients with pulmonary TB than in healthy controls (22.9% vs. 6.8%, p < 0.001). Based on haplotype analysis, the frequency of the TLR7 IVS2-151A/TLR8 -129C haplotype increased the risk for TB infection compared to the wild-type allele (TLR7 IVS2-151A/TLR8 -129G), with OR = 3.23 (95% CI = 1.58-6.61; p = 0.001). An ex vivo phagocytosis assay that examined the functional effects of these polymorphisms on the defense against MTB revealed higher phagocytosis in monocytes from males with the TLR7 IVS2-151A/TLR8 -129C genotype than in those with the wild-type allele (73.0 ± 20.3% versus 34.6 ± 8.1%; p = 0.03). In addition, mRNA expression and cytokine production were analyzed in the whole blood of male healthy volunteers stimulated with inactivated MTB ex vivo. TNFα production was lower in TLR7 IVS2-151A/TLR8 -129C subjects than in those with the wild-type allele (578.4 ± 90.3 pg/ml versus 1043 ± 136 pg/ml; p = 0.03), and the expression of TLR7 was significantly impaired (0.8 ± 0.1 folds, p = 0.05) after MTB stimulation. In conclusion, these findings provide evidence that TLR7 and TLR8 genetic polymorphisms are associated with susceptibility to MTB infection, and the link is shaped by less effective MTB phagocytosis and impaired TLR signaling.

Cell surface nucleolin facilitates enterovirus 71 binding and infection.

UNLABELLED: Because the pathogenesis of enterovirus 71 (EV71) remains mostly ambiguous, identifying the factors that mediate viral binding and entry to host cells is indispensable to ultimately uncover the mechanisms that underlie virus infection and pathogenesis. Despite the identification of several receptors/attachment molecules for EV71, the binding, entry, and infection mechanisms of EV71 remain unclear. Herein, we employed glycoproteomic approaches to identify human nucleolin as a novel binding receptor for EV71. Glycoproteins purified by lectin chromatography from the membrane extraction of human cells were treated with sialidase, followed by immunoprecipitation with EV71 particles. Among the 16 proteins identified by tandem mass spectrometry analysis, cell surface nucleolin attracted our attention. We found that EV71 interacted directly with nucleolin via the VP1 capsid protein and that an antinucleolin antibody reduced the binding of EV71 to human cells. In addition, the knockdown of cell surface nucleolin decreased EV71 binding, infection, and production in human cells. Furthermore, the expression of human nucleolin on the cell surface of a mouse cell line increased EV71 binding and conferred EV71 infection and production in the cells. These results strongly indicate that human nucleolin can mediate EV71 binding to and infection of cells. Our findings also demonstrate that the use of glycoproteomic approaches is a reliable methodology to discover novel receptors for pathogens. IMPORTANCE: Outbreaks of EV71 have been reported in Asia-Pacific countries and have caused thousands of deaths in young children during the last 2 decades. The discovery of new EV71-interacting molecules to understand the infection mechanism has become an emergent issue. Hence, this study uses glycoproteomic approaches to comprehensively investigate the EV71-interacting glycoproteins. Several EV71-interacting glycoproteins are identified, and the role of cell surface nucleolin in mediating the attachment and entry of EV71 is characterized and validated. Our findings not only indicate a novel target for uncovering the EV71 infection mechanism and anti-EV71 drug discovery but also provide a new strategy for virus receptor identification.

Nuclear export of human hepatitis B virus core protein and pregenomic RNA depends on the cellular NXF1-p15 machinery.

Hepatitis B virus (HBV) core protein (HBc) can shuttle between nucleus and cytoplasm. Cytoplasm-predominant HBc is clinically associated with severe liver inflammation. Previously, we found that HBc arginine-rich domain (ARD) can associate with a host factor NXF1 (TAP) by coimmunoprecipitation. It is well known that NXF1-p15 heterodimer can serve as a major export receptor of nuclear mRNA as a ribonucleoprotein complex (RNP). In the NXF1-p15 pathway, TREX (transcription/export) complex plays an important role in coupling nuclear pre-mRNA processing with mRNA export in mammalian cells. Here, we tested the hypothesis whether HBc and HBV specific RNA can be exported via the TREX and NXF1-p15 mediated pathway. We demonstrated here that HBc can physically and specifically associate with TREX components, and the NXF1-p15 export receptor by coimmunoprecipitation. Accumulation of HBc protein in the nucleus can be induced by the interference with TREX and NXF1-p15 mediated RNA export machinery. HBV transcripts encodes a non-spliced 3.5 kb pregenomic RNA (pgRNA) which can serve as a template for reverse transcription. Cytoplasmic HBV pgRNA appeared to be reduced by siRNA treatment specific for the NXF1-p15 complex by quantitative RT-qPCR and Northern blot analyses. This result suggests that the pgRNA was also exported via the NXF1-p15 machinery. We entertain the hypothesis that HBc protein can be exported as an RNP cargo via the mRNA export pathway by hijacking the TREX and NXF1-p15 complex. In our current and previous studies, HBc is not required for pgRNA accumulation in the cytoplasm. Furthermore, HBc ARD can mediate nuclear export of a chimeric protein containing HBc ARD in a pgRNA-independent manner. Taken together, it suggests that while both pgRNA and HBc protein exports are dependent on NXF1-p15, they are using the same export machinery in a manner independent of each other.

Nucleic acid chaperone activity associated with the arginine-rich domain of human hepatitis B virus core protein.

UNLABELLED: Hepatitis B virus (HBV) DNA replication occurs within the HBV icosahedral core particles. HBV core protein (HBc) contains an arginine-rich domain (ARD) at its carboxyl terminus. This ARD domain of HBc 149-183 is known to be important for viral replication but not known to have a structure. Recently, nucleocapsid proteins of several viruses have been shown to contain nucleic acid chaperone activity, which can facilitate structural rearrangement of viral genome. Major features of nucleic acid chaperones include highly basic amino acid residues and flexible protein structure. To test the nucleic acid chaperone hypothesis for HBc ARD, we first used the disassembled full-length HBc from Escherichia coli to analyze the nucleic acid annealing and strand displacement activities. To exclude the potential contamination of chaperones from E. coli, we designed synthetic HBc ARD peptides with different lengths and serine phosphorylations. We demonstrated that HBc ARD peptide can behave like a bona fide nucleic acid chaperone and that the chaperone activity depends on basic residues of the ARD domain. The loss of chaperone activity by arginine-to-alanine substitutions in the ARD can be rescued by restoring basic residues in the ARD. Furthermore, the chaperone activity is subject to regulation by phosphorylation and dephosphorylation at the HBc ARD. Interestingly, the HBc ARD can enhance in vitro cleavage activity of RNA substrate by a hammerhead ribozyme. We discuss here the potential significance of the HBc ARD chaperone activity in the context of viral DNA replication, in particular, at the steps of primer translocations and circularization of linear replicative intermediates. IMPORTANCE: Hepatitis B virus is a major human pathogen. At present, no effective treatment can completely eradicate the virus from patients with chronic hepatitis B. We report here a novel chaperone activity associated with the viral core protein. Our discovery could lead to a new drug design for more effective treatment against hepatitis B virus in the future.

Identification of a novel antimicrobial peptide from human hepatitis B virus core protein arginine-rich domain (ARD).

The rise of multidrug-resistant (MDR) pathogens causes an increasing challenge to public health. Antimicrobial peptides are considered a possible solution to this problem. HBV core protein (HBc) contains an arginine-rich domain (ARD) at its C-terminus, which consists of 16 arginine residues separated into four clusters (ARD I to IV). In this study, we demonstrated that the peptide containing the full-length ARD I-IV (HBc147-183) has a broad-spectrum antimicrobial activity at micro-molar concentrations, including some MDR and colistin (polymyxin E)-resistant Acinetobacter baumannii. Furthermore, confocal fluorescence microscopy and SYTOX Green uptake assay indicated that this peptide killed Gram-negative and Gram-positive bacteria by membrane permeabilization or DNA binding. In addition, peptide ARD II-IV (HBc153-176) and ARD I-III (HBc147-167) were found to be necessary and sufficient for the activity against P. aeruginosa and K. peumoniae. The antimicrobial activity of HBc ARD peptides can be attenuated by the addition of LPS. HBc ARD peptide was shown to be capable of direct binding to the Lipid A of lipopolysaccharide (LPS) in several in vitro binding assays. Peptide ARD I-IV (HBc147-183) had no detectable cytotoxicity in various tissue culture systems and a mouse animal model. In the mouse model by intraperitoneal (i.p.) inoculation with Staphylococcus aureus, timely treatment by i.p. injection with ARD peptide resulted in 100-fold reduction of bacteria load in blood, liver and spleen, as well as 100% protection of inoculated animals from death. If peptide was injected when bacterial load in the blood reached its peak, the protection rate dropped to 40%. Similar results were observed in K. peumoniae using an IVIS imaging system. The finding of anti-microbial HBc ARD is discussed in the context of commensal gut microbiota, development of intrahepatic anti-viral immunity and establishment of chronic infection with HBV. Our current results suggested that HBc ARD could be a new promising antimicrobial peptide.

Cell surface sialylation affects binding of enterovirus 71 to rhabdomyosarcoma and neuroblastoma cells.

BACKGROUND: Enterovirus 71 (EV71) is a major causative agent of hand-foot-and-mouth disease (HFMD), and infection of EV71 to central nerve system (CNS) may result in a high mortality in children less than 2 years old. Although there are two highly glycosylated membrane proteins, SCARB2 and PSGL-1, which have been identified as the cellular and functional receptors of EV71, the role of glycosylation in EV71 infection is still unclear. RESULTS: We demonstrated that the attachment of EV71 to RD and SK-N-SH cells was diminished after the removal of cell surface sialic acids by neuraminidase. Sialic acid specific lectins, Maackia amurensis (MAA) and Sambucus Nigra (SNA), could compete with EV71 and restrained the binding of EV71 significantly. Preincubation of RD cells with fetuin also reduced the binding of EV71. In addition, we found that SCARB2 was a sialylated glycoprotein and interaction between SCARB2 and EV71 was retarded after desialylation. CONCLUSIONS: In this study, we demonstrated that cell surface sialic acids assist in the attachment of EV71 to host cells. Cell surface sialylation should be a key regulator that facilitates the binding and infection of EV71 to RD and SK-N-SH cells.

Nuclear export and import of human hepatitis B virus capsid protein and particles.

It remains unclear what determines the subcellular localization of hepatitis B virus (HBV) core protein (HBc) and particles. To address this fundamental issue, we have identified four distinct HBc localization signals in the arginine rich domain (ARD) of HBc, using immunofluorescence confocal microscopy and fractionation/Western blot analysis. ARD consists of four tight clustering arginine-rich subdomains. ARD-I and ARD-III are associated with two co-dependent nuclear localization signals (NLS), while ARD-II and ARD-IV behave like two independent nuclear export signals (NES). This conclusion is based on five independent lines of experimental evidence: i) Using an HBV replication system in hepatoma cells, we demonstrated in a double-blind manner that only the HBc of mutant ARD-II+IV, among a total of 15 ARD mutants, can predominantly localize to the nucleus. ii) These results were confirmed using a chimera reporter system by placing mutant or wild type HBc trafficking signals in the heterologous context of SV40 large T antigen (LT). iii) By a heterokaryon or homokaryon analysis, the fusion protein of SV40 LT-HBc ARD appeared to transport from nuclei of transfected donor cells to nuclei of recipient cells, suggesting the existence of an NES in HBc ARD. This putative NES is leptomycin B resistant. iv) We demonstrated by co-immunoprecipitation that HBc ARD can physically interact with a cellular factor TAP/NXF1 (Tip-associated protein/nuclear export factor-1), which is known to be important for nuclear export of mRNA and proteins. Treatment with a TAP-specific siRNA strikingly shifted cytoplasmic HBc to nucleus, and led to a near 7-fold reduction of viral replication, and a near 10-fold reduction in HBsAg secretion. v) HBc of mutant ARD-II+IV was accumulated predominantly in the nucleus in a mouse model by hydrodynamic delivery. In addition to the revised map of NLS, our results suggest that HBc could shuttle rapidly between nucleus and cytoplasm via a novel TAP-dependent NES.

Combining antiangiogenic therapy with immunotherapy exerts better therapeutical effects on large tumors in a woodchuck hepatoma model.

Cytokine and antiangiogenic gene therapies have proved effective in implanted hepatocellular carcinoma (HCC) models in which small tumor burdens were established in small rodents. These models, however, may not reflect human HCCs, which are frequently detected at a stage when tumors are large and multifocal. In addition, HCC in patients is often associated with viral hepatitis. To investigate the effectiveness of a mixture type of gene therapy strategy on large tumor burdens, we used the woodchuck model in which woodchuck hepatitis virus-induced HCCs are large and multifocal, simulating the conditions in humans. Adenoviruses encoding antiangiogenic factors (pigment epithelium-derived factor and endostatin) or cytokines (GM-CSF and IL-12) were delivered via the hepatic artery separately or in combination into woodchuck livers bearing HCCs. Our results showed that the mixture type of strategy, which contained two cytokines and two antiangiogenic factors, had better antitumor effects on large tumors as compared with monotherapy either with antiangiogenic or cytokine genes. The immunotherapy recruited significant levels of CD3(+) T cells that infiltrated the tumors, whereas the antiangiogenesis-based therapy significantly reduced tumor vasculature. The mixture type of gene therapy achieved both effects. In addition, it induced high levels of natural killer cells and apoptotic cells and reduced the levels of immunosuppressive effectors in the tumor regions. Hence, antiangiogenic therapy may provide the advantage of reducing immune tolerance in large tumors, making them more vulnerable to the immune reactions. Our study implies that in the future, the combination therapy may prove effective for the treatment of patients with advanced HCC.

Testing an electrostatic interaction hypothesis of hepatitis B virus capsid stability by using an in vitro capsid disassembly/reassembly system.

To test a previously coined "charge balance hypothesis" of human hepatitis B virus (HBV) capsid stability, we established an in vitro disassembly and reassembly system using bacterially expressed HBV capsids. Capsid disassembly can be induced by micrococcal nuclease digestion of encapsidated RNA. HBV core protein (HBc) mutants containing various amounts of arginine were constructed by serial truncations at the C terminus. Capsids containing smaller amounts of arginine (HBc 149, 154, and 157) remained intact after micrococcal nuclease digestion by native gel electrophoresis. Capsids containing larger amounts of arginine (HBc 159, 164, 169, and 171) exhibited reduced and more diffuse banding intensity and slightly upshifted mobility (HBc 159 and 164). Capsids containing the largest amounts of arginine (HBc 173, 175, and 183), as well as HBc 167, exhibited no detectable banding signal, indicating loss of capsid integrity or stability. Interestingly, capsid reassembly can be induced by polyanions, including oligonucleotides, poly-glutamic acid, and nonbiological polymer (polyacrylic acid). In contrast, polycations (polylysine and polyethylenimine) and low-molecular-weight anions (inositol triphosphate) induced no capsid reassembly. Results obtained by gel assay were confirmed by electron microscopy. Reassembled capsids comigrated with undigested parental capsids on agarose gels and cosedimented with undigested capsids by sucrose gradient ultracentrifugation. Taken together, the results indicate that HBV capsid assembly and integrity depend on polyanions, which probably can help minimize intersubunit charge repulsion caused mainly by arginine-rich domain III or IV in close contact. The exact structure of polyanions is not important for in vitro capsid reassembly. A large amount of independent experimental evidence for this newly coined "electrostatic interaction hypothesis" is discussed.