SUMMARY The cytoplasmic pattern recognition receptor RIG-I is activated by viral RNA and induces type I IFN responses to control viral replication. The cellular dsRNA binding protein PACT can also activate RIG-I. To counteract innate antiviral responses, some viruses, including Ebola virus (EBOV), encode proteins that antagonize RIG-I signaling. Here, we show that EBOV VP35 inhibits PACT-induced RIG-I ATPase activity in a dose-dependent manner. The interaction of PACT with RIG-I is disrupted by wild-type VP35, but not by VP35 mutants that are unable to bind PACT. In addition, PACT-VP35 interaction impairs the association between VP35 and the viral polymerase, thereby diminishing viral RNA synthesis and modulating EBOV replication. PACT-deficient cells are defective in IFN induction and are insensitive to VP35 function. These data support a model in which the VP35-PACT interaction is mutually antagonistic and plays a fundamental role in determining the outcome of EBOV infection.

BackgroundMetabolically active cells require robust mechanisms to combat oxidative stress. The cytoplasmic thioredoxin reductase/thioredoxin (Txnrd1/Txn1) system maintains reduced protein dithiols and provides electrons to some cellular reductases, including peroxiredoxins.Principal FindingsHere we generated mice in which the txnrd1 gene, encoding Txnrd1, was specifically disrupted in all parenchymal hepatocytes. Txnrd1-deficient livers exhibited a transcriptome response in which 56 mRNAs were induced and 12 were repressed. Based on the global hybridization profile, this represented only 0.3% of the liver transcriptome. Since most liver mRNAs were unaffected, compensatory responses were evidently effective. Nuclear pre-mRNA levels indicated the response was transcriptional. Twenty-one of the induced genes contained known antioxidant response elements (AREs), which are binding sites for the oxidative and chemical stress-induced transcription factor Nrf2. Txnrd1-deficient livers showed increased accumulation of nuclear Nrf2 protein and chromatin immunoprecipitation on the endogenous nqo1 and aox1 promoters in fibroblasts indicated that Txnrd1 ablation triggered in vivo assembly of Nrf2 on each.ConclusionsChronic deletion of Txnrd1 results in induction of the Nrf2 pathway, which contributes to an effective compensatory response.

Summary The albCre transgene, having Cre recombinase driven by the serum albumin (alb) gene promoter, is commonly used to generate adult mice having reliable hepatocyte-specific recombination of loxP-flanked (“floxed”) alleles. Based on previous studies, it has been unclear whether albCre transgenes are also reliable in fetal and juvenile mice. Perinatal liver undergoes a dynamic transition from being predominantly hematopoietic to predominantly hepatic. We evaluated Cre activity during this transition in albCre mice using a sensitive two-color fluorescent reporter system. From fetal through adult stages, in situ patterns of Cre-dependent recombination of the reporter closely matched expression of endogenous Alb mRNA or protein, indicating most or all hepatocytes, including those in fetal and juvenile livers, had expressed Cre and recombined the reporter. Our results indicate the albCre transgene is effective at converting simple floxed alleles in fetal and neonatal mice and is an appropriate tool for studies on hepatocyte development.

The rotavirus nonstructural protein NSP1 is the least conserved protein in the rotavirus genome, and its function in the replication cycle is not known. We employed NSP1 as bait in the yeast two-hybrid interaction trap to identify candidate cellular partners of NSP1 that may provide clues to its function. Interferon regulatory factor 3 (IRF-3) was identified as an NSP1 interactor. NSP1 synthesized in rotavirus-infected cells bound IRF-3 in a glutathione S-transferase pull-down assay, indicating that the interaction was not unique to the two-hybrid system. NSP1 of murine rotavirus strain EW also interacted with IRF-3. NSP1 deletion and point mutants were constructed to map domains important in the interaction between NSP1 and IRF-3. The data suggest that a binding domain resides in the C terminus of NSP1 and that the N-terminal conserved zinc finger is important but not sufficient to mediate binding to IRF-3. We predict that a role for NSP1 in rotavirus-infected cells is to inhibit activation of IRF-3 and diminish the cellular interferon response.Rotaviruses are the most important cause of severe, often life-threatening gastroenteritis in infants and children under 2 years of age (33). These viruses are ubiquitous in nature and are also responsible for a significant proportion of neonatal diarrheal illness in domestic animals, particularly in bovine and porcine species (18,40). Substantial research efforts have thus focused on understanding the correlates of a protective immune response to rotavirus infection and the molecular mechanisms of virus replication so that efficacious vaccines can be developed.The rotavirus segmented double-stranded RNA genome encodes six structural proteins (VP) and six nonstructural proteins (NSP) (reviewed in reference 17). The structural proteins VP1, VP2, VP3, VP4, VP6, and VP7 are well characterized in terms of their antigenic, structural, and biochemical properties. The functions of the rotavirus nonstructural proteins NSP1 to NSP6 are less well defined with regard to the roles that these proteins play in the rotavirus replication cycle. Intriguing functions have recently been described for some. NSP3 binds the 3Ј consensus sequence of viral mRNAs (37) and acts as a functional analog of poly(A) binding protein through its interaction with eIF4GI (36). NSP4 is both an intracellular glycoprotein receptor for maturating rotavirus particles that bud through the endoplasmic reticulum (3, 32) and a viral enterotoxin that induces diarrhea in mice in the absence of any other viral protein (5). Functions of the remaining nonstructural proteins, NSP1, NSP2, NSP5, and NSP6, have been proposed based predominately on biochemical properties and activities of recombinant proteins (reviewed in reference 17).NSP1 displays several interesting properties that warrant investigation. NSP1 has a calculated molecular weight of approximately 54,000 and is the least conserved protein encoded by the rotavirus genome when NSP1s of different strains are compared (23,34). The N terminus contains a conserved ...