Induction of manganese-superoxide dismutase in MRC-5 cells persistently infected with an alphavirus, sindbis

Effect of IL-10 Deficiency on TGFβ Expression during Fatal Alphavirus Encephalomyelitis in C57Bl/6 Mice

Sindbis virus (SINV) causes viral encephalitis in mice with strain-dependent virulence. Fatal encephalomyelitis in C57Bl/6 mice infected with a neuroadapted strain of SINV (NSV) is an immunopathogenic process that involves Th17 cells modulated by the regulatory cytokine IL-10. To further characterize the pathogenic immune response to NSV, we analyzed the regulation of transforming growth factor (TGF)-b in both wild-type (WT) and IL-10-deficient mice. NSV infection upregulated the expression of TGFb1 and TGFb3 in the central nervous system (CNS). In the absence of IL-10, levels of brain Tgfb1 mRNA and brain and spinal cord mature active TGFβ1 and TGFβ3 proteins were higher than in WT mice. Compared to WT mice, IL-10-deficient mice had more TGFβ1-expressing type 3 innate lymphoid cells (ILC3s) and CD4+ T cells infiltrating the CNS, but similar numbers in the cervical lymph nodes. Expression of glycoprotein A repetitions predominant protein (GARP) that binds pro-TGFb on the surface of regulatory T cells was decreased on CNS cells from IL-10-deficient mice. Higher CNS TGFb was accompanied by more expression of TGFbRII receptor, activation of SMAD transcription factors, increased PCKα mRNA, and more RORγt-positive and IL-17A-expressing cells. These results suggest a compensatory role for TGFβ in the absence of IL-10 that fosters Th17-related immunopathology and more rapid death after NSV infection.

Infection of Mammals and Mosquitoes by Alphaviruses: Involvement of Cell Death

Alphaviruses, such as the chikungunya virus, are emerging and re-emerging viruses that pose a global public health threat. They are transmitted by blood-feeding arthropods, mainly mosquitoes, to humans and animals. Although alphaviruses cause debilitating diseases in mammalian hosts, it appears that they have no pathological effect on the mosquito vector. Alphavirus/host interactions are increasingly studied at cellular and molecular levels. While it seems clear that apoptosis plays a key role in some human pathologies, the role of cell death in determining the outcome of infections in mosquitoes remains to be fully understood. Here, we review the current knowledge on alphavirus-induced regulated cell death in hosts and vectors and the possible role they play in determining tolerance or resistance of mosquitoes.

Increased mitochondrial functions in human glioblastoma cells persistently infected with measles virus

Measles virus (MV) is known for its ability to cause an acute infection with a potential of development of persistent infection. However, knowledge of how viral genes and cellular factors interact to cause or maintain the persistent infection has remained unclear. We have previously reported the possible involvement of mitochondrial short chain enoyl-CoA hydratase (ECHS), which is localized at mitochondria, in the regulation of MV replication. In this study we found increased functions of mitochondria in MV-persistently infected cells compared with uninfected or acutely infected cells. Furthermore, impairment of mitochondrial functions by treatment with mitochondrial inhibitors such as ethidium bromide (EtBr) or carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) induced the cytopathic effects of extensive syncytial formation in persistently infected cells. These findings suggest that mitochondria are one of the subcellular organelles contributing to regulate persistent infection of MV. Recent studies showed mitochondria provide an integral platform for retinoic acid-inducible protein (RIG-I)-like cytosolic receptors (RLRs) signaling and participate in cellular innate antiviral immunity. Our findings not only reveal a role of mitochondria in RLR mediated antiviral signaling but also suggest that mitochondria contribute to the regulation of persistent viral infection.

Increased mitochondrial superoxide dismutase expression and lowered production of reactive oxygen species during rotavirus infection

Rotaviruses are responsible for severe diarrhea in infants and substantial economic losses in animal husbandry worldwide. We investigated the oxidant/antioxidant status in rotavirus-infected human colon adenocarcinoma (Caco-2) cell line. Our results show that within the initial 48 h of infection the expression of the mitochondrial superoxide dismutase (MnSOD) is significantly increased, which correlates with a decrease in reactive oxygen species production, and with a lack of cellular glutathione depletion. During this period the mitochondria display a hyperpolarization of the inner membrane, which leads to an increased mitochondrial membrane potential. No increase in apoptosis was detected in the infected cultures. In contrast to many viral infections which cause redox imbalance in host cells, the described virus-host interaction suggests that rotavirus infection does not lead to an induction of oxidative stress, possibly to prolong cell survival and to allow for accumulation of viral particles before cell destruction and virus release.

Utilization of host SR protein kinases and RNA-splicing machinery during viral replication

Although the viral genome is often quite small, it encodes a broad series of proteins. The virus takes advantage of the host-RNA-processing machinery to provide the alternative splicing capability necessary for the expression of this proteomic diversity. Serine-arginine-rich (SR) proteins and the kinases that activate them are central to this alternative splicing machinery. In studies reported here, we use the HIV genome as a model. We show that HIV expression decreases overall SR protein/activity. However, we also show that HIV expression is significantly increased (20-fold) when one of the SR proteins, SRp75 is phosphorylated by SR protein kinase (SRPK)2. Thus, inhibitors of SRPK2 and perhaps of functionally related kinases, such as SRPK1, could be useful antiviral agents. Here, we develop this hypothesis and show that HIV expression down-regulates SR proteins in Flp-In293 cells, resulting in only low-level HIV expression in these cells. However, increasing SRPK2 function up-regulates HIV expression. In addition, we introduce SR protein phosphorylation inhibitor 340 (SRPIN340), which preferentially inhibits SRPK1 and SRPK2 and down-regulates SRp75. Although an isonicotinamide compound, SPRIN340 (or its derivatives) remain to be optimized for better specificity and lower cytotoxicity, we show here that SRPIN340 suppresses propagation of Sindbis virus in plaque assay and variably suppresses HIV production. Thus, we show that SRPK, a well known kinase in the cellular RNA-processing machinery, is used by at least some viruses for propagation and hence suggest that SRPIN340 or its derivatives may be useful for curbing viral diseases.

Induction of alternatively spliced spermidine/spermine N1-acetyltransferase mRNA in the human kidney cells infected by venezuelan equine encephalitis and tick-borne encephalitis viruses

293 and RH cells derived from human embryo kidney were infected by Venezuelan equine encephalitis and tick-borne encephalitis viruses and cDNA libraries representing cellular mRNAs induced or suppressed due to the infection were prepared using suppressive subtractive hybridization. Among the up-regulated clones the RT-PCR and Northern analyses revealed an unusual transcript of the spermidine/spermine N1-acetyltransferase (SSAT) gene that was shown to be an alternatively spliced form containing an additional 110-bp exon. The alternatively spliced transcript is polyadenylated and can be expected to yield only a truncated 71 amino acid polypeptide. This first evidence of the host gene alternatively spliced mRNA induction by RNA viruses raises the questions of its biological role, regulation mechanisms of alternative splicing, and significance for the virus life cycle.

Japanese encephalitis virus stimulates superoxide dismutase activity in rat glial cultures

Japanese encephalitis virus (JEV) infection is commonly associated with inflammatory reaction and neurological disease that occurs in the infected animals. Reactive oxygen species have been implicated as a critical mediator for inflammation and diseases. The present study investigated the change of redox potential in glial cells following JEV infection. JEV infection induced the generation of superoxide anion and nitric oxide in rat cortical glial cells. Manganese superoxide dismutase, but not copper/zinc superoxide dismutase was activated by JEV infection, and this activation was blocked by pyrrolidine dithiocarbamate. In addition, the increased superoxide dismutase activity was also apparent in JEV acutely, or persistently infected continuous cell lines. These results suggest that cellular factors regulating oxidative pathway might play roles in responding to JEV infection.