O030 Evasion of the OAS-RNase L pathway by murine coronavirus ns2 protein is required for viral replication and hepatitis

Introduction

The 2′,5′-oligoadenylate synthetase-ribonuclease L (OAS-RNase L) system is a potent IFN induced antiviral pathway. Following infection, IFNs induce a group of OAS genes whose products are activated by viral double-stranded RNA. OAS uses ATP to generate 2′,5′-linked oligoadenylates (2-5A). 2-5A binds to and activates the ubiquitous cellular endoribonuclease RNase L causing cleavages of single stranded regions of both viral and cellular RNA thus inhibiting viral replication. In addition, detection of the newly generated short RNAs by cellular pattern recognition receptors, MDA5 and RIG-I, further enhances IFN production and the ensuing antiviral activities. The intracellular concentration of 2-5A is believed to be the primary factor controlling RNase L activation. The liver contains abundant innate immune cells, which provide the first line of defense against pathogens. However, the factors that determine whether a virus can bypass this defense to access and infect the liver parenchyma are not well understood. The murine coronavirus, mouse hepatitis virus (MHV), strain A59, infection of mice provides a model for virus induced hepatitis. The MHV accessory protein, ns2, antagonizes the type I IFN response in macrophages and promotes the induction of hepatitis. Here we will describe how the ns2 protein facilitates the development of viral hepatitis by blocking OAS-RNase L pathway.

Methods

Bone marrow macrophages (BMM) from wild type (wt) and RNase L−/− mice were infected with A59 and ns2 mutant MHV. Viral titers were determined by plaque assays. RNase L activity was monitored by rRNA integrity in RNA chips. Intracellular levels of 2-5A were measured using RNase L activation assays. Effects of ns2 on 2-5A levels in cells were determined by transfecting ns2 or mutant ns2 cDNAs into HEK-293T cells. Recombinant ns2 and mutant ns2H126R proteins were purified and incubated with 2-5A in vitro and the 2-5A breakdown products were measured by HPLC. Hepatitis was determined by histology following inoculation A59 or ns2 mutant MHV into wt and RNase L−/− mice.

Results

We found evidence for a new molecular mechanism of subversion of the RNase L pathway in macrophages that regulates acute hepatitis during MHV infection. Coronavirus ns2 belongs to the LigT-like protein family, within the 2H phosphoesterase superfamily, some of which possess cyclophosphodiesterase activity (CPD). We have found that ns2 is not a CPD, but instead is a 2′,5′-phosphodiesterase (PDE) that cleaves, and thus eliminates 2-5A, the activator of RNase L. We observed that ns2 blocks the IFN inducible OAS-RNase L pathway to facilitate hepatitis development. Ns2 prevents activation of RNase L and consequently limits viral RNA degradation. An ns2 mutant virus was unable to replicate in the liver or induce hepatitis in wt mice, but was highly pathogenic in RNase L−/− mice. Thus, RNase L is a critical cellular factor for protection against viral infection of the liver and the resulting hepatitis.

Conclusion

MHV accessory protein ns2 is a 2′,5′-PDE which degrades 2-5A and limits RNase L activation thus facilitating virus-induced hepatitis in mice.

Early changes in cerebral oxidative stress and apoptotic neuronal injury after various flows for selective cerebral perfusion in piglets

BACKGROUND

The impact of various flows for selective cerebral perfusion (SCP) on cerebral oxidative stress in the immature brain is unknown. We examined early changes in cerebral markers of oxidative damage, apoptotic protein activation and histological outcome after different flows for SCP in a piglet model of deep hypothermic circulatory arrest (DHCA).

METHODS

Twenty piglets, randomly divided into four groups (each n = 5), were placed on cardiopulmonary bypass (CPB) at 20°C, then underwent DHCA for 60 minutes. SCP was conducted at flow rates of 0, 25, 50 and 80 ml·kg(-1)·min(-1) through the innominate artery in the DHCA, SCP 25, SCP 50, and SCP 80 groups, respectively. The animals were killed at 2 hours off CPB. Brain tissues were examined for the activity of SOD, MDA and caspase-3, and histological damage was quantitatively assayed by light microscopic examinations.

RESULTS

There were no significant differences in the activities of SOD, MDA and the SOD/MDA index between the groups. Caspase-3 activity significantly decreased in the SCP 25, SCP 50 and SCP 80 groups compared with the DHCA group. However, the caspase-3 level was higher in the SCP 80 group than in the SCP 25 and SCP 50 group. There were no significant correlations between MDA, SOD, SOD/MDA index and caspase-3.

CONCLUSIONS

In this acute model, under different flows for SCP, cerebral MDA and SOD activities show no change, whereas activated caspase-3 has a marked change. There was no relationship between oxidative stress, indicated by MDA and SOD, and apoptotic protein activation in the early phase after DHCA.

An engineered anti-CA19-9 cys-diabody for PET imaging of pancreas cancer and targeting of polymerized liposomal nanoparticles

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Background: Antibody-based therapeutics is a rapidly growing field. Small engineered antibody fragments, such as the cys-diabody demonstrate similar antigen affinity compared to the parental antibody but have a shorter serum half-life (4hrs) and possess the ability to be conjugated to nanoparticles. Our goal was to engineer an anti-CA19-9 cys-diabody fragment in hopes of imaging and targeting pancreatic cancer.

Methods: The anti-CA19-9 cys-diabody was created by cloning the variable region of the parental antibody, engineering a C-terminus cysteine, expressing in NS0 cells followed by protein purification utilizing HPLC. Maleimide chemistry was used to conjugate the cys-diabody to PLNs through the engineered cysteine residues. Immunofluorescence and flow cytometry were used to evaluate targeting of cys-diabody and diabody conjugated PLNs to human pancreatic cancer cell lines. The cys-diabody was evaluated in a mouse xenograft model harboring CA19-9 positive (BxPC3) and negative (MiaPaca) tumors. The cys-diabody was radiolabeled with a positron emitter (I-124) and microPET/CT were performed after tail vein injection. Percent of injected dose per gram (%ID/g) of radioactivity was measured in blood and tumor to provide objective confirmation of the microPET images.

Results: Immunofluorescence and flow cytometry showed specific binding of the anti-CA19-9 cys- diabody. Tumor xenograft imaging of the anti-CA19-9 cys-diabody demonstrated an average tumor:blood (%ID/g) ratio of 3.3 and positive:negative tumor ratio of 7.4. Successful conjugation of the cys-diabody to PLNs was indicated by immunofluorescence showing specific targeting of PLN-cys- diabody conjugate to human pancreatic cancer cells in vitro.

Conclusions: Our results show that the anti-CA19.9 cys- diabody targets pancreatic cancer providing specific molecular imaging in tumor xenograft models. Furthermore, the PLN-cys-diabody conjugate targets human pancreatic cancer cells with the potential to deliver targeted treatment. Further studies evaluating the in vivo ability of the PLN-cys-diabody conjugate to target pancreatic cancer need to be performed.

No significant financial relationships to disclose.

Innovative DNA vaccine for human papillomavirus (HPV)-associated head and neck cancer

Human papillomavirus (HPV), particularly type 16, has been associated with a subset of head and neck cancers. The viral-encoded oncogenic proteins E6 and E7 represent ideal targets for immunotherapy against HPV-associated head and neck cancers. DNA vaccines have emerged as attractive approaches for immunotherapy due to its simplicity, safety, and ease of preparation. Intradermal administration of DNA vaccine via gene gun represents an efficient method to deliver DNA directly into dendritic cells for priming antigen-specific T cells. We have previously shown that a DNA vaccine encoding an invariant chain (Ii), in which the class II-associated Ii peptide (CLIP) region has been replaced by a Pan-DR-epitope (PADRE) sequence to form Ii-PADRE, is capable of generating PADRE-specific CD4+ T cells in vaccinated mice. In the current study, we hypothesize a DNA vaccine encoding Ii-PADRE linked to E6 (Ii-PADRE-E6) will further enhance E6-specific CD8+ T cell immune responses through PADRE-specific CD4+ T helper cells. We found that mice vaccinated with Ii-PADRE-E6 DNA generated comparable levels of PADRE-specific CD4+ T cell immune responses as well as significantly stronger E6-specific CD8+ T cell immune responses and antitumor effects against the lethal challenge of E6-expressing tumor compared to mice vaccinated with Ii-E6 DNA. Taken together, our data indicates that vaccination with Ii-E6 DNA with PADRE replacing the CLIP region is capable of enhancing the E6-specific CD8+ T cell immune response generated by the Ii-E6 DNA. Thus, Ii-PADRE-E6 represents a novel DNA vaccine for the treatment of HPV-associated head and neck cancer and other HPV-associated malignancies.