ABSTRACT
Latent signal transducers and activators of transcription (STATs) reside in the cytoplasm but rapidly accumulate in the nucleus following cytokine stimulation. Nuclear accumulation requires specific tyrosine phosphorylation and STAT dimerization. The presence of STATs in the nucleus is transient, however, and within hours the STATs reappear in the cytoplasm. Results indicate that STAT1 can be dephosphorylated in the nucleus and actively exported by the chromosome region maintenance 1 (CRM1) export receptor. CRM1 recognizes a specific amino acid sequence located within the DNA-binding domain of STAT1. This region shares sequence and functional properties of characterized nuclear export signals. The location of this sequence within STAT1 suggests that it is not accessible to CRM1 when STAT1 is bound to DNA. Evidence is presented to support a model in which STAT1 is tyrosine dephosphorylated in the nucleus and dissociates from DNA, allowing recognition by CRM1 and nuclear export. The regulated export of STAT1 may contribute to silencing of the signal pathway and/or to re-establish STAT1 in the cytoplasm to monitor activity of receptor-kinase signals.
Subject(s)
DNA-Binding Proteins/chemistry , DNA-Binding Proteins/metabolism , Karyopherins , Receptors, Cytoplasmic and Nuclear , Trans-Activators/chemistry , Trans-Activators/metabolism , Amino Acid Sequence , Animals , Base Sequence , Carrier Proteins/metabolism , Cell Line , Cell Nucleus/metabolism , DNA/metabolism , DNA-Binding Proteins/genetics , Dimerization , Green Fluorescent Proteins , Humans , Luminescent Proteins/chemistry , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Models, Molecular , Nuclear Localization Signals , Oligonucleotide Probes/genetics , Protein Structure, Quaternary , Protein Structure, Tertiary , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , STAT1 Transcription Factor , Signal Transduction , Trans-Activators/genetics , Exportin 1 ProteinABSTRACT
Viral double-stranded RNA (dsRNA) generated during the course of infection leads to the activation of a latent transcription factor, dsRNA-activated factor 1 (DRAF1). DRAF1 binds to a DNA target containing the type I interferon-stimulated response element and induces transcription of responsive genes. DRAF1 is a multimeric transcription factor containing the interferon regulatory factor 3 (IRF-3) protein and one of the histone acetyl transferases, CREB binding protein (CBP) or p300 (CBP/p300). In uninfected cells, the IRF-3 component of DRAF1 resides in the cytoplasm. The cytoplasmic localization of IRF-3 is dependent on a nuclear export signal, and we demonstrate IRF-3 recognition by the chromosome region maintenance 1 (CRM1) (also known as exportin 1) shuttling receptor. Following infection and specific phosphorylation, IRF-3 accumulates in the nucleus where it associates with CBP and p300. We identify a nuclear localization signal (NLS) in IRF-3 that is critical for nuclear accumulation. Mutation of the NLS abrogates nuclear localization even following infection. The NLS appears to be active constitutively, but it is recognized by only a subset of importin-alpha shuttling receptors. Evidence is presented to support a model in which IRF-3 normally shuttles between the nucleus and the cytoplasm but cytoplasmic localization is dominant prior to infection. Following infection, phosphorylated IRF-3 can bind to the CBP/p300 proteins resident in the nucleus. We provide the evidence of a role for CBP/p300 binding in the nuclear sequestration of a transcription factor that normally resides in the cytoplasm.
Subject(s)
DNA-Binding Proteins/metabolism , Transcription Factors/metabolism , Cell Nucleus/metabolism , Cytoplasm/metabolism , DNA-Binding Proteins/genetics , Humans , Interferon Regulatory Factor-3 , Nuclear Localization Signals , Nuclear Proteins/metabolism , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Trans-Activators/metabolism , Transcription Factors/genetics , Tumor Cells, CulturedABSTRACT
Clinical and radiographic examinations were performed preoperatively and an average of 18 1/2 months postoperatively on 33 patients who had undergone TMJ disk plication surgery because of significant TMJ dysfunction symptoms that had not been resolved by previous conservative therapy. The results indicated that the disk plication procedure reduced the overall frequency of symptoms by 75%. The frequency of TMJ intracapsular, otologic, and head and shoulder symptoms was reduced by more than 80% after surgery whereas dental symptoms such as bruxing and clenching showed only a 28% reduction in incidence. Of the sample 77% were either free of pain or experiencing only mild symptoms at their postoperative recall, with only nine joints still experiencing moderate or severe symptoms, compared with the 31 joints that were in this category before surgery.
