ABSTRACT
Kaposi's sarcoma-associated herpesvirus encodes four genes with homology to the family of interferon regulatory factors (IRFs). At least one of these viral IRFs, vIRF-3, is expressed in latently Kaposi's sarcoma-associated herpesvirus-infected primary effusion lymphoma (PEL) cells and is essential for the survival of PEL cells. We now report that vIRF-3 interacts with cellular IRF-5, thereby inhibiting binding of IRF-5 to interferon-responsive promoter elements. Consequently, vIRF-3 blocked IRF-5-mediated promoter activation. A central double helix motif present in vIRF-3 was sufficient to abrogate both DNA binding and transcriptional transactivation by IRF-5. Upon DNA damage or activation of the interferon or Toll-like receptor pathways, cytoplasmic IRF-5 has been reported to be translocated to the nucleus, which results in induction of both p53-independent apoptosis and p21-mediated cell cycle arrest. We report here that IRF-5 is present in the nuclei of PEL cells without interferon stimulation. Silencing of vIRF-3 expression in PEL cells was accompanied by increased sensitivity to interferon-mediated apoptosis and up-regulation of IRF-5 target genes. In addition, vIRF-3 antagonized IRF-5-mediated activation of the p21 promoter. The data presented here indicate that vIRF-3 contributes to immune evasion and sustained proliferation of PEL cells by releasing IRF-5 from transcription complexes.
Subject(s)
Cell Nucleus/metabolism , Herpesvirus 8, Human/metabolism , Interferon Regulatory Factors/metabolism , Response Elements , Viral Proteins/metabolism , Active Transport, Cell Nucleus/genetics , Active Transport, Cell Nucleus/immunology , Amino Acid Motifs/genetics , Amino Acid Motifs/immunology , Apoptosis/genetics , Apoptosis/immunology , Cell Nucleus/genetics , Cell Nucleus/immunology , Cyclin-Dependent Kinase Inhibitor p21/genetics , Cyclin-Dependent Kinase Inhibitor p21/immunology , Cyclin-Dependent Kinase Inhibitor p21/metabolism , Gene Silencing , Herpesvirus 8, Human/genetics , Herpesvirus 8, Human/immunology , Humans , Interferon Regulatory Factors/genetics , Interferon Regulatory Factors/immunology , Lymphoma, Primary Effusion/genetics , Lymphoma, Primary Effusion/immunology , Lymphoma, Primary Effusion/metabolism , Protein Binding/genetics , Protein Binding/immunology , Receptors, Interferon/genetics , Receptors, Interferon/immunology , Receptors, Interferon/metabolism , Sarcoma, Kaposi/genetics , Sarcoma, Kaposi/immunology , Sarcoma, Kaposi/metabolism , Toll-Like Receptors/genetics , Toll-Like Receptors/immunology , Toll-Like Receptors/metabolism , Transcriptional Activation/genetics , Transcriptional Activation/immunology , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Protein p53/immunology , Tumor Suppressor Protein p53/metabolism , Up-Regulation/genetics , Up-Regulation/immunology , Viral Proteins/genetics , Viral Proteins/immunologyABSTRACT
A promising approach to protect susceptible individuals against severe diseases is the inoculation of plasmids. Such DNA vaccines against influenza virus infections were quite efficient in different animal models; but still this procedure is not in clinical use until today. The present study reports the generation and characterization of bicistronic plasmids which enables the expression of influenza A virus gene sequences together with immunostimulatory cytokines demonstrating that among these cytokines especially interleukin-2 (IL-2) was efficient to prevent a lethal influenza virus infection in mice.
