C-terminal region of STAT-1alpha is not necessary for its ubiquitination and degradation caused by mumps virus V protein.
Constitutive levels of production of STAT-1 were reduced by 10 h postinfection (p.i.) and significantly lost by 24 h p.i. in FL cells acutely infected with mumps virus (MuV). This result was consistent with that observed in previous studies and experiments with cells persistently infected with MuV (FLMT cells). There was a marked decrease in the amount of STAT-1 in cells expressing MuV accessory protein V (MuV-V). Furthermore, single amino acid substitutions in the Cys-rich region of V protein (Vc189a, Vc207a, and Vc214a) showed that each cysteine residue plays an important role in the decrease in STAT-1 production, but substitution of a histidine residue at amino acid position 203 had no effect. These events and the resultant suppression of the alpha interferon (IFN-alpha) response were confirmed by a luciferase reporter gene assay with five tandem repeats of the IFN-alpha-stimulated response element as an enhancer element of the firely luciferase gene. STAT-1 production was restored and detectable in FLMT cells treated with a proteosome inhibitor, such as MG132 or lactacystin. In the presence of MG132, ubiquitination of STAT-1 and the interaction of MuV-V with STAT-1 were demonstrated in FLMT cells by immunoprecipitation with anti-STAT-1 antibody. The same results for the interaction and ubiquitination were obtained in experiments with an expression vector for a C-terminal deletion mutant of STAT-1. The truncated STAT-1 molecules were degraded in the presence of MuV-V. Therefore, the C-terminal region (transcriptional activation and Src homology 2 domains) of STAT-1 is not necessary for its degradation caused by MuV-V. Our data suggest that MuV-V promotes ubiquitination and degradation of STAT-1.
Yokosawa
Noriko
N
Department of Microbiology, School of Medicine, Sapporo Medical University, South 1 West 17, Chou-ku, Sapporo 060-8556, Hokkaido, Japan.
Yokota
Shin-Ichi
S
Kubota
Toru
T
Fujii
Nobuhiro
N
D000595:Amino Acid Sequence; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000502:physiology; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D053614:Janus Kinase 2; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000502:physiology; D009109:Mumps virus / Q000502:physiology*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D014764:Viral Proteins / Q000502:physiology*
D004268:DNA-Binding Proteins; D009097:Multienzyme Complexes; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; D015534:Trans-Activators; D025801:Ubiquitin; D014764:Viral Proteins; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex