Use of baculovirus expression vectors

An efficient method for multigene co-interference by recombinant Bombyx mori nucleopolyhedrovirus

Bombyx mori Nucleopolyhedrovirus (BmNPV), which is a member of the Baculoviridae family, is a significant pathogen of the silkworm. The infection of BmNPV is often lethal and causes about 20% loss of cocoon in the silk industry annually. To explore the effects of different gene inhibition strategies on the replication cycle of baculovirus, we constructed the mutant virus to infect BmN cells directly and further identified ie0, ie1, and gp64 as the essential viral genes of BmNPV. To elucidate the significance of the inhibition effect of different interference strategies, we characterized and constructed the recombinant BmNPV that carried a single or multigene-interfering cassette. The results showed that the inhibition effect of dsie1 on target gene expression, virus titer, and silkworm mortality was significantly better than that of dsie0 and dsgp64. It also showed that the dsie1 interference produced fewer progeny virions and was less lethal, which indicates that ie1 played a more critical role in the BmNPV replication cycle. Furthermore, the inhibitory effect of the virus titer and mortality indicated that the multigene co-interference constructed by the baculovirus expression system was significantly better than the interference of any single-gene (p < 0.05). In summary, the strategy of multigene synergy can achieve the function of continuous interference and provide a new platform for the breeding of silkworm disease resistant. In addition, this strategy improves the various traits of the silkworm.

Structure and Regulation of the Movement of Human Myosin VIIA

Human myosin VIIA (HM7A) is responsible for human Usher syndrome type 1B, which causes hearing and visual loss in humans. Here we studied the regulation of HM7A. The actin-activated ATPase activity of full-length HM7A (HM7AFull) was lower than that of tail-truncated HM7A (HM7AΔTail). Deletion of the C-terminal 40 amino acids and mutation of the basic residues in this region (R2176A or K2179A) abolished the inhibition. Electron microscopy revealed that HM7AFull is a monomer in which the tail domain bends back toward the head-neck domain to form a compact structure. This compact structure is extended at high ionic strength or in the presence of Ca(2+). Although myosin VIIA has five isoleucine-glutamine (IQ) motifs, the neck length seems to be shorter than the expected length of five bound calmodulins. Supporting this observation, the IQ domain bound only three calmodulins in Ca(2+), and the first IQ motif failed to bind calmodulin in EGTA. These results suggest that the unique IQ domain of HM7A is important for the tail-neck interaction and, therefore, regulation. Cellular studies revealed that dimer formation of HM7A is critical for its translocation to filopodial tips and that the tail domain (HM7ATail) markedly reduced the filopodial tip localization of the HM7AΔTail dimer, suggesting that the tail-inhibition mechanism is operating in vivo. The translocation of the HM7AFull dimer was significantly less than that of the HM7AΔTail dimer, and R2176A/R2179A mutation rescued the filopodial tip translocation. These results suggest that HM7A can transport its cargo molecules, such as USH1 proteins, upon release of the tail-dependent inhibition.

Tightly regulated expression of Autographa californica multicapsid nucleopolyhedrovirus immediate early genes emerges from their interactions and possible collective behaviors

To infect their hosts, DNA viruses must successfully initiate the expression of viral genes that control subsequent viral gene expression and manipulate the host environment. Viral genes that are immediately expressed upon infection play critical roles in the early infection process. In this study, we investigated the expression and regulation of five canonical regulatory immediate-early (IE) genes of Autographa californica multicapsid nucleopolyhedrovirus: ie0, ie1, ie2, me53, and pe38. A systematic transient gene-expression analysis revealed that these IE genes are generally transactivators, suggesting the existence of a highly interactive regulatory network. A genetic analysis using gene knockout viruses demonstrated that the expression of these IE genes was tolerant to the single deletions of activator IE genes in the early stage of infection. A network graph analysis on the regulatory relationships observed in the transient expression analysis suggested that the robustness of IE gene expression is due to the organization of the IE gene regulatory network and how each IE gene is activated. However, some regulatory relationships detected by the genetic analysis were contradictory to those observed in the transient expression analysis, especially for IE0-mediated regulation. Statistical modeling, combined with genetic analysis using knockout alleles for ie0 and ie1, showed that the repressor function of ie0 was due to the interaction between ie0 and ie1, not ie0 itself. Taken together, these systematic approaches provided insight into the topology and nature of the IE gene regulatory network.

Baculovirus transduction of chondrocytes elicits interferon-alpha/beta and suppresses transgene expression

BACKGROUND

Baculovirus is an effective vector for gene delivery into primary chondrocytes and repeated baculovirus transduction (i.e. supertransduction) appears to be promising for prolonging transgene expression, but how supertransduction may influence baculovirus-mediated gene delivery is unknown.

METHODS

We first investigated whether prior baculovirus transduction suppressed the ensuing transgene expression mediated by the supertransduced baculovirus, and then examined whether baculovirus triggered the expression of various cytokines. Whether interferon-alpha and -beta (IFN-alpha/beta) suppressed the transgene expression as well as the pivotal step responsible for the attenuated transgene expression were examined.

RESULTS

Baculovirus transduction of chondrocytes elicited an immediate yet transient expression of IFN-alpha/beta, which repressed the transgene expression in a dose-dependent manner. The attenuation was observed for transgene expression driven by different promoters and resulted neither from internalization or nuclear import of baculovirus. Moreover, the attenuation was alleviated if supertransduction was performed when IFN-alpha/beta responses diminished. Baculovirus transduction also triggered the expression of tumor necrosis factor-alpha and interleukin (IL)-6, but not IL-1beta. Despite the induction of these responses, supertransduction of chondrocytes with a baculovirus expressing bone morphogenetic protein-2 successfully enhanced the chondrogenic differentiation and matrix synthesis.

CONCLUSIONS

Baculovirus transduction of primary chondrocytes elicits antiviral effects that suppress transgene expression. Nonetheless, baculovirus supertransduction comprises a feasible approach to extend transgene expression for cartilage engineering.

Hepatitis B virus (HBV)-specific short hairpin RNA is capable of reducing the formation of HBV covalently closed circular (CCC) DNA but has no effect on established CCC DNA in vitro

Hepatitis B virus (HBV) covalently closed circular (CCC) DNA is the source of HBV transcripts and persistence in chronically infected patients. The novel aspect of this study was to determine the effect of RNA interference (RNAi) on HBV CCC DNA when administered prior to establishment of HBV replication or during chronic HBV infection. HBV replication was initiated in HepG2 cells by transduction with HBV baculovirus. Subculture of HBV-expressing HepG2 cells at 10 days post-transduction generates a system in which HBV replication is ongoing and HBV is expressed largely from CCC DNA, thus simulating chronic HBV infection. HepG2 cells were transduced with short hairpin RNA (shRNA)-expressing baculovirus prior to initiation of HBV replication or during chronic HBV replication, and the levels of HBV RNA, HBV surface antigens (HBsAg) and replicative intermediates (RI), extracellular (EC) and CCC DNA species were measured. HBsAg, HBV RNA and DNA levels were markedly reduced until day 8 whether cells were transduced with shRNA prior to or during a chronic infection; however, the CCC DNA species were only affected when shRNA was administered prior to initiation of infection. We conclude that RNAi may have a therapeutic value for controlling HBV replication at the level of RI and EC DNA and for reducing establishment of CCC DNA during HBV infection. Our data support previous findings demonstrating the stability of HBV CCC DNA following antiviral therapy. This study also reports the development of a novel HBV baculovirus subculture system that can be used to evaluate antiviral effects on chronic HBV replication.

In vitro study of the effects of precore and lamivudine-resistant mutations on hepatitis B virus replication

Understanding the consequences of mutation in the hepatitis B virus (HBV) genome on HBV replication is critical for treating chronic HBV infection. In this study, HBV replication in HepG2 cells initiated by transduction with precore (PC), rtM204I, and wild-type (wt) HBV recombinant baculoviruses was compared. The pattern and magnitude of HBV replication initiated by the PC HBV recombinant baculovirus were similar to those observed for wt HBV throughout the time course examined. In contrast, when the rtM204I mutation was introduced into wt HBV, by day 10 postinfection the levels of intra- and extracellular HBV DNA were markedly reduced compared to those for wt HBV. Although the rtM204I mutation reduced the production of HBV replicative intermediates, no effect on the level of covalently closed circular DNA or HBV transcripts was observed at late time points. Coinfection studies with different ratios of wt and rtM204I baculoviruses showed that the rtM204I variant did not produce a product that inhibited HBV replication. However, the combination of the wt and rtM204I baculoviruses yielded HBV DNA levels at late time points that were greater than those for the wt alone, suggesting that wt polymerase may function in trans to boost rtM204I replication. We concluded that the rtM204I mutation generates a polymerase that is not only resistant to lamivudine but also replicates nucleic acids to lower levels in vitro.

Acrylamide analog as a novel nitric oxide-independent soluble guanylyl cyclase activator

Soluble guanylyl cyclase (sGC) is a target enzyme for endogenous nitric oxide (NO), and it converts GTP to cyclic GMP (guanosine 3',5'-cyclic monophosphate) as part of a cascade that results in physiological processes such as smooth muscle relaxation, neurotransmission, and inhibition of platelet aggregation. Here we examine a representative of the novel class sCG activators, A-778935 ((+/-)-cis-3-[2-(2,2-dimethyl-propylsulfanyl)-pyridin-3-yl]-N-(3-hydroxy-cyclohexyl)-acrylamide). A-778935 activated sGC synergistically with sodium nitroprusside (SNP) over a wide range of concentration, inducing up to 420-fold activation. A specific inhibitor of sGC, ODQ (1H-[1,2,4]-oxadiazolo[4,3-alpha]quinoxalin-1-one), did not block basal sGC activity, but competitively inhibited the activation by A-778935. A-778935, with or without SNP, did not activate heme-deficient sGC, indicating that the activation of sGC by A-778935 is fully heme-dependent. A-778935 increased intracellular cGMP level dose-dependently in smooth muscle cells. In the presence of 1 microM SNP, a lower concentration of A-778935 increased cGMP than A-778935 alone, and the cGMP concentration reached the same level at 100 microM of A-778935. A-778935 relaxed cavernosum tissue strips in a dose-dependent manner; and in the presence of 1 microM SNP, A-778935 relaxed the strips more potently, shifting the dose-response curve to the left. This novel activator of sGC may have potential efficacy for the treatment of a variety of disorders associated with reduced NO signaling.

Kinetic analysis of wild-type and YMDD mutant hepatitis B virus polymerases and effects of deoxyribonucleotide concentrations on polymerase activity

Mutations in the YMDD motif of the hepatitis B virus (HBV) DNA polymerase result in reduced susceptibility of HBV to inhibition by lamivudine, at a cost in replication fitness. The mechanisms underlying the effects of YMDD mutations on replication fitness were investigated using both a cell-based viral replication system and an in vitro enzyme assay to examine wild-type (wt) and YMDD-mutant polymerases. We calculated the affinities of wt and YMDD-mutant polymerases for each natural deoxyribonucleoside triphosphate (dNTP) and determined the intracellular concentrations of each dNTP in HepG2 cells under conditions that support HBV replication. In addition, inhibition constants for lamivudine triphosphate were determined for wt and YMDD-mutant polymerases. Relative to wt HBV polymerase, each of the YMDD-mutant polymerases showed increased apparent K(m) values for the natural dNTP substrates, indicating decreased affinities for these substrates, as well as increased K(i) values for lamivudine triphosphate, indicating decreased affinity for the drug. The effect of the differences in apparent K(m) values between YMDD-mutant polymerase and wt HBV polymerase could be masked by high levels of dNTP substrates (>20 microM). However, assays using dNTP concentrations equivalent to those measured in HepG2 cells under physiological conditions showed decreased enzymatic activity of YMDD-mutant polymerases relative to wt polymerase. Therefore, the decrease in replication fitness of YMDD-mutant HBV strains results from the lower affinities (increased K(m) values) of the YMDD-mutant polymerases for the natural dNTP substrates and physiological intracellular concentrations of dNTPs that are limiting for the replication of YMDD-mutant HBV strains.

Cross-resistance testing of antihepadnaviral compounds using novel recombinant baculoviruses which encode drug-resistant strains of hepatitis B virus

Long-term nucleoside analog therapy for hepatitis B virus (HBV)-related disease frequently results in the selection of mutant HBV strains that are resistant to therapy. Molecular studies of such drug-resistant variants are clearly warranted but have been difficult to do because of the lack of convenient and reliable in vitro culture systems for HBV. We previously developed a novel in vitro system for studying HBV replication that relies on the use of recombinant baculoviruses to deliver greater than unit length copies of the HBV genome to HepG2 cells. High levels of HBV replication can be achieved in this system, which has recently been used to assess the effects of lamivudine on HBV replication and covalently closed circular DNA accumulation. The further development of this novel system and its application to determine the cross-resistance profiles of drug-resistant HBV strains are described here. For these studies, novel recombinant HBV baculoviruses which encoded the L526M, M550I, and L526M M550V drug resistance mutations were generated and used to examine the effects of these substitutions on viral sensitivity to lamivudine, penciclovir (the active form of famciclovir), and adefovir, three compounds of clinical importance. The following observations were made: (i) the L526M mutation confers resistance to penciclovir and partial resistance to lamivudine, (ii) the YMDD mutations M550I and L526M M550V confer high levels of resistance to lamivudine and penciclovir, and (iii) adefovir is active against each of these mutants. These findings are supported by the limited amount of clinical data currently available and confirm the utility of the HBV-baculovirus system as an in vitro tool for the molecular characterization of clinically significant HBV strains.