title: A CRM1-dependent nuclear export pathway is involved in the regulation of IRF-5 subcellular localization.
abstract: Interferon regulatory factors (IRFs) are involved in gene regulation in many biological processes including the antiviral, growth regulatory, and immune modulatory functions of the interferon system. Several studies have demonstrated that IRF-3, IRF-5, and IRF-7 specifically contribute to the innate antiviral response to virus infection. It has been reported that virus-specific phosphorylation leads to IRF-5 nuclear localization and up-regulation of interferon, cytokine, and chemokine gene expression. Two nuclear localization signals have been identified in IRF-5, both of which are sufficient for nuclear translocation and retention in virus-infected cells. In the present study, we demonstrate that a CRM1-dependent nuclear export pathway is involved in the regulation of IRF-5 subcellular localization. IRF-5 possesses a functional nuclear export signal (NES) that controls dynamic shuttling between the cytoplasm and the nucleus. The NES element is dominant in unstimulated cells and results in the predominant cytoplasmic localization of IRF-5. Mutation of two leucine residues in the NES motif to alanine, or three adjacent Ser/Thr residues to the phosphomimetic Asp, results in constitutively nuclear IRF-5 and suggests that phosphorylation of adjacent Ser/Thr residues may contribute to IRF-5 nuclear accumulation in virus-induced cells. IKK-related kinases TBK1 and IKKepsilon have been shown to phosphorylate and activate IRF-3 and IRF-7, leading to the production of type 1 interferons and the development of a cellular antiviral state. We examined the phosphorylation and activation of IRF-5 by TBK1 and IKKepsilon kinases. Although IRF-5 is phosphorylated by IKKepsilon and TBK1 in co-transfected cells, the phosphorylation of IRF-5 did not lead to IRF-5 nuclear localization or activation.
authors.affiliation: Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research, McGill University, Montreal, Quebec H3T 1E2, Canada. rongtuan.lin@mcgill.ca
authors.forename: Rongtuan
authors.initials: R
authors.lastname: Lin
authors.forename: Long
authors.initials: L
authors.lastname: Yang
authors.forename: Meztli
authors.initials: M
authors.lastname: Arguello
authors.forename: Claudia
authors.initials: C
authors.lastname: Penafuerte
authors.forename: John
authors.initials: J
authors.lastname: Hiscott
mesh_terms: D021581:Active Transport, Cell Nucleus; D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism*; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D050835:Interferon Regulatory Factors; D007372:Interferons / Q000378:metabolism; D028884:Karyopherins / Q000502:physiology*; D007930:Leucine / Q000737:chemistry; D008156:Luciferases / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000737:chemistry; D013912:Threonine / Q000737:chemistry; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D000097606:Exportin 1 Protein
chemical_list: D000409:Alanine; D004268:DNA-Binding Proteins; D049452:Green Fluorescent Proteins; D050835:Interferon Regulatory Factors; D007372:Interferons; D028884:Karyopherins; D007930:Leucine; D008156:Luciferases; D018160:Receptors, Cytoplasmic and Nuclear; D012694:Serine; D013912:Threonine; D014157:Transcription Factors; D000097606:Exportin 1 Protein; C431713:IRF5 protein, human