ABSTRACT
The transcription factor, interferon regulatory Factor 3 (IRF-3) plays a critical role in the activation of an antiviral innate immune response. However the transcriptional activity of IRF-3 is tightly regulated by a proteosome mediated degradation. We describe here a novel mechanism by which the activity of IRF-3 is stabilized in infected cells. We have shown that both interferon treatment and NDV infection profoundly increase conjugation of interferon induced ubiquitin- like protein ISG15 to cellular proteins. ISGylated IRF-3 could be detected both in interferon treated and virus-infected cells. ISG15, subverts the ubiquitin mediated degradation of IRF-3 in NDV infected 2fTGH cells and enhances the NDV mediated transactivation of interferonbeta promoter and the translocation of activated IRF-3 to the nucleus. The relative levels of IRF-3 were significantly lower in NDV infected ISG15 null MEF, than in wt MEF. While ISG15 null MEF were more permissive to VSV replication their sensitivity to the antiviral effect of interferon was not modulated. These results reveal that virus mediated subversion of the antiviral response by proteolysis of IRF-3 is counteracted by induction of ISG15 expression and that ISGylation provides a feedback mechanism, which enhances the host innate antiviral response via IRF-3 stabilization.
Subject(s)
Cytokines/physiology , Immunity, Innate/physiology , Interferon Regulatory Factor-3/metabolism , Proteasome Inhibitors , Active Transport, Cell Nucleus , Animals , Avulavirus Infections/immunology , Cells, Cultured , Cytokines/deficiency , Endopeptidases/metabolism , Gene Expression , Humans , Interferon-beta/genetics , Mice , Newcastle disease virus/immunology , Promoter Regions, Genetic , Protein Binding , Protein Denaturation , Protein Transport , Proteins/metabolism , Rhabdoviridae Infections/immunology , Transfection , Ubiquitin/metabolism , Ubiquitin Thiolesterase , Ubiquitins/deficiency , Ubiquitins/physiology , Vesicular stomatitis Indiana virus/immunology , Virus Activation , Virus ReplicationABSTRACT
All-trans-retinoic acid (RA)-based differentiation therapy induces clinical remissions in acute promyelocytic leukemia (APL). This has propelled interest in elucidating the molecular mechanisms responsible for these remissions. The t(15;17) rearrangement results in the expression of the PML/RARalpha fusion transcript that is paradoxically linked to the etiology and clinical retinoid response in APL. PML/RARalpha expression blocks terminal myeloid differentiation in APL. Treatment with pharmacological RA dosages overcomes the dominant-negative effects of PML/RARalpha to activate transcription of retinoid target genes. This regulation is linked directly to RA effects in APL, including PML/RARalpha degradation and induction of differentiation. Identifying retinoid target genes is an important step in developing a mechanistic understanding of RA effects in APL. RA target genes have been uncovered through the use of molecular genetic approaches as well as unique cellular and transgenic APL models. Recent developments in the proteomic and functional genomic fields are providing useful tools for elucidating mechanisms of RA response or resistance in APL. These target genes represent potential therapeutic targets in APL and other retinoid-responsive diseases. Previous spotlights in Leukemia have highlighted the importance of cytokine effects and signal transduction crosstalk in retinoid response in APL and in normal hematopoiesis. This review builds on prior work by addressing the role of retinoid target genes in mediating retinoid response or resistance in APL.
Subject(s)
Antineoplastic Agents/pharmacology , Gene Expression Regulation, Neoplastic/drug effects , Leukemia, Promyelocytic, Acute/genetics , Tretinoin/pharmacology , Animals , Cell Differentiation , Gene Targeting , Humans , Receptors, Retinoic Acid/metabolism , Retinoic Acid Receptor alphaABSTRACT
Mycobacterial infections are critically controlled by interferon-gamma (IFN-gamma) and the cellular responses it elaborates, as shown by patients with mutations in the IFN-gamma receptor ligand-binding chain (IFN-gamma R1) who have disseminated nontuberculous mycobacterial infections. The immunologic sequelae of IFN-gamma R1 deficiency were characterized in 2 unrelated patients from the Indian subcontinent with novel homozygous recessive IFN-gamma R1 mutations. In vitro, these patients' peripheral blood mononuclear cells produced 10% of normal IFN-gamma and interleukin-12 (IL-12) in response to phytohemagglutinin (PHA) but normal amounts of IFN-gamma in response to PHA plus IL-12. Tumor necrosis factor-alpha (TNF-alpha) production was normal in response to endotoxin and to PHA but was not augmented by the addition of IFN-gamma. An abnormal phenotype was not found in heterozygous patient relatives. These patients demonstrate the critical role that the IFN-gamma receptor plays in the regulation of IFN-gamma, IL-12, and TNF-alpha.
