The replication and transcription activator of murine gammaherpesvirus 68 cooperatively enhances cytokine-activated, STAT3-mediated gene expression.

Gammaherpesviruses (γHVs) have a dynamic strategy for lifelong persistence, involving productive infection, latency, and intermittent reactivation. In latency reservoirs, such as B lymphocytes, γHVs exist as viral episomes and express few viral genes. Although the ability of γHV to reactivate from latency and re-enter the lytic phase is challenging to investigate and control, it is known that the γHV replication and transcription activator (RTA) can promote lytic reactivation. In this study, we provide first evidence that RTA of murine γΗV68 (MHV68) selectively binds and enhances the activity of tyrosine-phosphorylated host STAT3. STAT3 is a transcription factor classically activated by specific tyrosine 705 phosphorylation (pTyr705-STAT3) in response to cytokine stimulation. pTyr705-STAT3 forms a dimer that avidly binds a consensus target site in the promoters of regulated genes, and our results indicate that RTA cooperatively enhances the ability of pTyr705-STAT3 to induce expression of a STAT3-responsive reporter gene. As indicated by coimmunoprecipitation, in latently infected B cells that are stimulated to reactivate MHV68, RTA bound specifically to endogenous pTyr705-STAT3. An in vitro binding assay confirmed that RTA selectively recognizes pTyr705-STAT3 and indicated that the C-terminal transactivation domain of RTA was required for enhancing STAT3-directed gene expression. The cooperation of these transcription factors may influence both viral and host genes. During MHV68 de novo infection, pTyr705-STAT3 promoted the temporal expression of ORF59, a viral replication protein. Our results demonstrate that MHV68 RTA specifically recognizes and recruits activated pTyr705-STAT3 during the lytic phase of infection.

Determination of variable region sequences from hybridoma immunoglobulins that target Mycobacterium tuberculosis virulence factors.

Mycobacterium tuberculosis (Mtb) infects one-quarter of the world's population. Mtb and HIV coinfections enhance the comorbidity of tuberculosis (TB) and AIDS, accounting for one-third of all AIDS-associated mortalities. Humoral antibody to Mtb correlates with TB susceptibility, and engineering of Mtb antibodies may lead to new diagnostics and therapeutics. The characterization and validation of functional immunoglobulin (Ig) variable chain (IgV) sequences provide a necessary first step towards developing therapeutic antibodies against pathogens. The virulence-associated Mtb antigens SodA (Superoxide Dismutase), KatG (Catalase), PhoS1/PstS1 (regulatory factor), and GroES (heat shock protein) are potential therapeutic targets but lacked IgV sequence characterization. Putative IgV sequences were identified from the mRNA of hybridomas targeting these antigens and isotype-switched into a common immunoglobulin fragment crystallizable region (Fc region) backbone, subclass IgG2aκ. Antibodies were validated by demonstrating recombinant Ig assembly and secretion, followed by the determination of antigen-binding specificity using ELISA and immunoblot assay.

RNA-guided gene editing of the murine gammaherpesvirus 68 genome reduces infectious virus production.

Epstein-Barr virus (EBV) and Kaposi sarcoma herpesvirus (KSHV) are cancer-causing viruses that establish lifelong infections in humans. Gene editing using the Cas9-guideRNA (gRNA) CRISPR system has been applied to decrease the latent load of EBV in human Burkitt lymphoma cells. Validating the efficacy of Cas9-gRNA system in eradicating infection in vivo without off-target effects to the host genome will require animal model systems. To this end, we evaluated a series of gRNAs against individual genes and functional genomic elements of murine gammaherpesvirus 68 (MHV68) that are both conserved with KSHV and important for the establishment of latency or reactivation from latency in the host. gRNA sequences against ORF50, ORF72 and ORF73 led to insertion, deletion and substitution mutations in these target regions of the genome in cell culture. Murine NIH3T3 fibroblast cells that stably express Cas9 and gRNAs to ORF50 were most resistant to replication upon de novo infection. Latent murine A20 B cell lines that stably express Cas9 and gRNAs against MHV68 were reduced in their reactivation by approximately 50%, regardless of the viral gene target. Lastly, co-transfection of HEK293T cells with the vector expressing the Cas9-MHV68 gRNA components along with the viral genome provided a rapid read-out of gene editing and biological impact. Combinatorial, multiplex MHV68 gRNA transfections in HEK293T cells led to near complete ablation of infectious particle production. Our findings indicate that Cas9-gRNA editing of the murine gammaherpesvirus genome has a deleterious impact on productive replication in three independent infection systems.

Gene delivery to mammalian cells using a graphene nanoribbon platform.

We have developed a novel oxidized graphene nanoribbon-based platform (O-GNR) for gene delivery of double-stranded DNA into mammalian cells. O-GNRs, synthesized via longitudinal unzipping of multi-walled carbon nanotubes (MWCNTs), exhibited efficient DNA loading of small dsDNA fragments. Fourier Transform Infrared Spectroscopy identified stretching peaks in the O-P-O and DNA sugar phosphate backbone that were consistent with DNA loading onto O-GNRs. The presence of salts in the loading buffer promoted DNA loading and effective dispersion of O-GNRs. DNA:O-GNR complexes were stable upon treatment with surfactants Tween 20 and Triton-X100. O-GNRs did not impact the viability of mammalian cells. Last, the detection of GFP expression upon transfection of the DNA:O-GNR complex indicated that the cargo DNA is expressed in the nucleus. Taken together, O-GNRs function as a platform for gene delivery to mammalian cells.

Ablation of STAT3 in the B Cell Compartment Restricts Gammaherpesvirus Latency In Vivo.

UNLABELLED: A challenging property of gammaherpesviruses is their ability to establish lifelong persistence. The establishment of latency in B cells is thought to involve active virus engagement of host signaling pathways. Pathogenic effects of these viruses during latency or following reactivation can be devastating to the host. Many cancers, including those associated with members of the gammaherpesvirus family, Kaposi's sarcoma-associated herpesvirus and Epstein-Barr virus, express elevated levels of active host signal transducer and activator of transcription-3 (STAT3). STAT3 is activated by tyrosine phosphorylation in response to many cytokines and can orchestrate effector responses that include proliferation, inflammation, metastasis, and developmental programming. However, the contribution of STAT3 to gammaherpesvirus pathogenesis remains to be completely understood. This is the first study to have identified STAT3 as a critical host determinant of the ability of gammaherpesvirus to establish long-term latency in an animal model of disease. Following an acute infection, murine gammaherpesvirus 68 (MHV68) established latency in resident B cells, but establishment of latency was dramatically reduced in animals with a B cell-specific STAT3 deletion. The lack of STAT3 in B cells did not impair germinal center responses for immunoglobulin (Ig) class switching in the spleen and did not reduce either total or virus-specific IgG titers. Although ablation of STAT3 in B cells did not have a global effect on these assays of B cell function, it had long-term consequences for the viral load of the host, since virus latency was reduced at 6 to 8 weeks postinfection. Our findings establish host STAT3 as a mediator of gammaherpesvirus persistence. IMPORTANCE: The insidious ability of gammaherpesviruses to establish latent infections can have detrimental consequences for the host. Identification of host factors that promote viral latency is essential for understanding latency mechanisms and for therapeutic interventions. We provide the first evidence that STAT3 expression is needed for murine gammaherpesvirus 68 to establish latency in primary B cells during an active immune response to infection. STAT3 deletion in B cells does not impair adaptive immune control of the virus, but loss of STAT3 in B cells has a long-lasting impact on viral persistence. These results indicate a potential therapeutic benefit of STAT3 inhibitors for combating gammaherpesvirus latency and, thereby, associated pathologies.