The non‐enveloped fusogenic avian and Nelson Bay reoviruses encode homologous 10 kDa non‐structural transmembrane proteins. The p10 proteins localize to the cell surface of transfected cells in a type I orientation and induce efficient cell–cell fusion. Mutagenic studies revealed the importance of conserved sequence‐predicted structural motifs in the membrane association and fusogenic properties of p10. These motifs included a centrally located transmembrane domain, a conserved cytoplasmic basic region, a small hydrophobic motif in the N‐terminal domain and four conserved cysteine residues. Functional analysis indicated that the extreme C‐terminus of p10 functions in a sequence‐independent manner to effect p10 membrane localization, while the N‐terminal domain displays a sequence‐dependent effect on the fusogenic property of p10. The small size, unusual arrangement of structural motifs and lack of any homologues in previously described membrane fusion proteins suggest that the fusion‐associated small transmembrane (FAST) proteins of reovirus represent a new class of membrane fusion proteins.

Reovirus, a potential cancer therapy, replicates more efficiently in Ras-transformed cells than in non-transformed cells. It was presumed that increased translation was the mechanistic basis of reovirus oncolysis. Analyses of each step of the reovirus life cycle now show that cellular processes deregulated by Ras transformation promote not one but three viral replication steps. First, in Ras-transformed cells, proteolytic disassembly (uncoating) of the incoming virions, required for onset of infection, occurs more efficiently. Consequently, threefold more Ras-transformed cells become productively infected with reovirus than non-transformed cells, which accounts for the observed increase of reovirus proteins in Ras-transformed cells. Second, Ras transformation increases the infectious-to-noninfectious virus particle ratio, as virions purified from Ras-transformed cells are fourfold more infectious than those purified from non-transformed cells. Progeny assembled in non- and Ras-transformed cells appear similar by electron microscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis, suggesting that Ras transformation introduces a subtle change necessary for virus infectivity. Finally, reovirus release, mediated by caspase-induced apoptosis, is ninefold more efficient in Ras-transformed cells. The combined effects of enhanced virus uncoating, infectivity, and release result in >100-fold differences in virus titers within one round of replication. Our analysis reveals previously unrecognized mechanisms by which Ras transformation mediates selective viral oncolysis.

Human mast cells are found in skin and mucosal surfaces and next to blood vessels. They play a sentinel cell role in immunity, recognizing invading pathogens and producing proinflammatory mediators. Mast cells can recruit granulocytes, and monocytes in allergic disease and bacterial infection, but their ability to recruit antiviral effector cells such as natural killer (NK) cells and T cells has not been fully elucidated. To investigate the role of human mast cells in response to virus-associated stimuli, human cord blood-derived mast cells (CBMCs) were stimulated with polyinosinic⅐polycytidylic acid, a double-stranded RNA analog, or infected with the double-stranded RNA virus, reovirus serotype 3 Dearing for 24 hours. CBMCs responded to stimulation with polyinosinic⅐polycytidylic acid by producing a distinct chemokine profile, including CCL4, CXCL8, and CXCL10. CBMCs produced significant amounts of CXCL8 in response to low levels of reovirus infection, while both skin-and lungderived fibroblasts were unresponsive unless higher doses of reovirus were used. Supernatants from CBMCs infected with reovirus induced substantial NK cell chemotaxis that was highly dependent on CXCL8 and CXCR1. These results sug- IntroductionMast cells are long-lived resident tissue cells found close to blood vessels, and are numerous at sites in close proximity to the external environment such as the skin and airways (reviewed in Galli et al 1 and Metz and Maurer 2 ). From these strategic locations they can quickly recognize and respond to invading pathogens. They are also relatively resistant to ultraviolet (UV) and gamma irradiation. [3][4][5] Upon activation, mast cells produce a wide array of mediators, including granule-associated products, such as histamine, and preformed and de novo synthesized cytokines, chemokines, and lipid mediators. They can activate and recruit effector cells, including eosinophils, 6 neutrophils, 7 and monocytes. 8 Their role in innate immune responses to bacterial infections has been clearly delineated, however their involvement in viral infections is not well understood. Mast cells express Toll-like receptor 3 (TLR3), which recognizes viral double-stranded RNA (dsRNA), 9 and they can produce type I interferons when activated through this receptor. 10 Studies examining the permissiveness of mast cells to viruses show that they can be infected by, and respond to, dengue virus, 11,12 HIV, 13,14 and respiratory syncytial virus. 15 Human mast cells produce the chemokines CCL3, CCL4, and CCL5 when infected with dengue virus, 16 and mouse mast cells produce CCL4 and CCL5 when infected with Newcastle disease virus, all of which are known natural killer (NK) cell and T-cell chemoattractants. 17 NK cells are large granular lymphocytes that can kill virally infected cells, and are crucial for the clearance of viruses during infections (reviewed in Lodoen and Lanier 18 ). The chemokines and chemokine receptors necessary for the infiltration of NK cells into virally infected tissues have recently begun to be uncover...

Reovirus is the first naturally occurring human virus reported to exploit activated Ras signaling in the host cell for infection, and is currently undergoing clinical trials as a cancer therapeutic. Recent evidence suggests that Ras transformation promotes three reoviral replication steps during the first round of infection: uncoating of the incoming virion, generation of progeny viruses with enhanced infectivity, and virus release through enhanced apoptosis. Whether oncogenic Ras also enhances reovirus spread in subsequent rounds of infection through other mechanisms has not been examined. Here, we show that compared with nontransformed cells, Ras-transformed cells are severely compromised not only in their response to IFN-β, but also in the induction of IFN-β mRNA following reovirus infection. Defects in both IFN-β production and response allow for efficient virus spread in Ras-transformed cells. We show that the MEK/ERK pathway downstream of Ras is responsible for inhibiting IFN-β expression by blocking signaling from the retinoic acid-inducible gene I (RIG-I) which recognizes viral RNAs. Overexpression of wild-type RIG-I restores INF-β expression in reovirus-infected Rastransformed cells. In vitro-synthesized viral mRNAs also invoke robust RIG-I-mediated IFN-β production in transfected nontransformed cells, but not in Ras-transformed cells. Collectively, our data suggest that oncogenic Ras promotes virus spread by suppressing viral RNA-induced IFN-β production through negative regulation of RIG-I signaling. Cancer Res; 70(12); 4912-21. ©2010 AACR.

Immunosuppression associated with ovarian cancer (OC) and resultant peritoneal carcinomatosis (PC) hampers the efficacy of many promising treatment options, including immunotherapies. It is hypothesized that oncolytic virus-based therapies can simultaneously kill OC and mitigate immunosuppression. Currently, reovirus-based anticancer therapy is undergoing phase I/II clinical trials for the treatment of OC. Hence, this study was focused on characterizing the effects of reovirus therapy on OC and associated immune microenvironment. Our data shows that reovirus efficiently killed OC cells and induced higher expression of the molecules involved in antigen presentation including major histocompatibility complex (MHC) class I, β2-microglobulin (β2M), TAP-1, and TAP-2. In addition, in the presence of reovirus, dendritic cells (DCs) overcame the OC-mediated phenotypic suppression and successfully stimulated tumor-specific CD8+ T cells. In animal studies, reovirus targeted local and distal OC, alleviated the severity of PC and significantly prolonged survival. These therapeutic effects were accompanied by decreased frequency of suppressive cells, e.g., Gr1.1+, CD11b+ myeloid derived suppressor cells (MDSCs), and CD4+, CD25+, FOXP3+ Tregs, tumor-infiltration of CD3+ cells and higher expression of Th1 cytokines. Finally, reovirus therapy during early stages of OC also resulted in the postponement of PC development. This report elucidates timely information on a therapeutic approach that can target OC through clinically desired multifaceted mechanisms to better the outcomes.

Reovirus has an inherent preference for replicating in cells with dysregulated growth factor signaling cascades that comprise Ras activation. Precisely how reovirus exploits the host cell Ras pathway is unclear, but there is evidence suggesting that activated Ras signaling is important for efficient viral protein synthesis. Defining the molecular mechanism of reovirus oncolysis will shed light on reovirus replication and important aspects of cellular transformation, Ras signaling cascades and regulation of protein translation. Oncogene (2005) 24, 7720-7728.

Rotavirus is a segmented double-stranded RNA (dsRNA) virus that causes severe gastroenteritis in young children. We have established an efficient simplified rotavirus reverse genetics (RG) system that uses 11 T7 plasmids, each expressing a unique simian SA11 (+)RNA, and a cytomegalovirus support plasmid for the African swine fever virus NP868R capping enzyme. With the NP868R-based system, we generated recombinant rotavirus (rSA11/NSP3-FL-UnaG) with a genetically modified 1.5-kb segment 7 dsRNA encoding full-length nonstructural protein 3 (NSP3) fused to UnaG, a 139-amino-acid green fluorescent protein (FP). Analysis of rSA11/NSP3-FL-UnaG showed that the virus replicated efficiently and was genetically stable over 10 rounds of serial passaging. The NSP3-UnaG fusion product was well expressed in rSA11/NSP3-FL-UnaG-infected cells, reaching levels similar to NSP3 levels in wild-type recombinant SA11-infected cells. Moreover, the NSP3-UnaG protein, like functional wild-type NSP3, formed dimers in vivo. Notably, the NSP3-UnaG protein was readily detected in infected cells via live-cell imaging, with intensity levels ∼3-fold greater than those of the NSP1-UnaG fusion product of rSA11/NSP1-FL-UnaG. Our results indicate that FP-expressing recombinant rotaviruses can be made through manipulation of the segment 7 dsRNA without deletion or interruption of any of the 12 open reading frames (ORFs) of the virus. Because NSP3 is expressed at higher levels than NSP1 in infected cells, rotaviruses expressing NSP3-based FPs may be more sensitive tools for studying rotavirus biology than rotaviruses expressing NSP1-based FPs. This is the first report of a recombinant rotavirus containing a genetically engineered segment 7 dsRNA. IMPORTANCE Previous studies generated recombinant rotaviruses that express FPs by inserting reporter genes into the NSP1 ORF of genome segment 5. Unfortunately, NSP1 is expressed at low levels in infected cells, making viruses expressing FP-fused NSP1 less than ideal probes of rotavirus biology. Moreover, FPs were inserted into segment 5 in such a way as to compromise NSP1, an interferon antagonist affecting viral growth and pathogenesis. We have identified an alternative approach for generating rotaviruses expressing FPs, one relying on fusing the reporter gene to the NSP3 ORF of genome segment 7. This was accomplished without interrupting any of the viral ORFs, yielding recombinant viruses that likely express the complete set of functional viral proteins. Given that NSP3 is made at moderate levels in infected cells, rotaviruses encoding NSP3-based FPs should be more sensitive probes of viral infection than rotaviruses encoding NSP1-based FPs.

Previous studies of the avian reovirus strain S1133 (ARV-S1133) S1 genome segment revealed that the open reading frame (ORF) encoding the C viral cell attachment protein initiates over 600 nucleotides distal from the 5 end of the S1 mRNA and is preceded by two predicted small nonoverlapping ORFs. To more clearly define the translational properties of this unusual polycistronic RNA, we pursued a comparative analysis of the S1 genome segment of the related Nelson Bay reovirus (NBV). Sequence analysis indicated that the 3-proximal ORF present on the NBV S1 genome segment also encodes a C homolog, as evidenced by the presence of an extended N-terminal heptad repeat characteristic of the coiled-coil region common to the cell attachment proteins of reoviruses. Most importantly, the NBV S1 genome segment contains two conserved ORFs upstream of the C coding region that are extended relative to the predicted ORFs of ARV-S1133 and are arranged in a sequential, partially overlapping fashion. Sequence analysis of the S1 genome segments of two additional strains of ARV indicated a similar overlapping tricistronic gene arrangement as predicted for the NBV S1 genome segment. Expression analysis of the ARV S1 genome segment indicated that all three ORFs are functional in vitro and in virus-infected cells. In addition to the previously described p10 and C gene products, the S1 genome segment encodes from the central ORF a 17-kDa basic protein (p17) of no known function. Optimizing the translation start site of the ARV p10 ORF lead to an approximately 15-fold increase in p10 expression with little or no effect on translation of the downstream C ORF. These results suggest that translation initiation complexes can bypass over 600 nucleotides and two functional overlapping upstream ORFs in order to access the distal C start site.The orthoreoviruses consist of a number of diverse virus species, all of which have a similar capsid structure and a genome composed of 10 double-stranded RNA (dsRNA) segments (38). For the most part, the genome segments of reoviruses are monocistronic, each encoding a single unique polypeptide. The mammalian reovirus (MRV) S1 genome segment, however, is bicistronic and encodes two unrelated polypeptides from overlapping open reading frames (ORFs). The 1 viral cell attachment protein is encoded by a large ORF that originates near the 5Ј end of the mRNA and spans almost the complete length of the S1 mRNA (12, 37). A second small ORF, beginning at nucleotide position 71, is nested within the 1 ORF in a ϩ1 reading frame and encodes the small nonstructural 1NS protein of MRV (14,23).Since the translation start site for 1 is in a nonpreferred context (a pyrimidine at position Ϫ3), leaky scanning by the preinitiation complex most likely accounts for translation of the downstream 1NS ORF from the MRV S1 mRNA (28). In addition to leaky scanning, there is evidence suggesting that translation of the 1 protein from the bicistronic S1 mRNA is modulated by ribosomal pausing at the downstream 1NS start site (7, 15).As wit...