The STAT2 activation process is a crucial target of Sendai virus C protein for the blockade of alpha interferon signaling.
Sendai virus (SeV) C protein functions as an interferon (IFN) antagonist and renders cells unresponsive to both alpha/beta IFN (IFN-alpha/beta) and IFN-gamma. We have recently found the physical association of the C protein with signal transducer and activator of transcription 1 (STAT1) in infected cells. However, involvement of the C-STAT1 interaction in the blockade of IFN signaling has remained unclear. We generated here a series of C mutant proteins that retained or lost the STAT1-binding capacity and examined their effects on IFN-alpha signaling. All of the C mutant proteins with no STAT1-binding capacity lost the ability to inhibit the IFN-alpha response. In contrast, the C mutant proteins retaining the STAT1-binding capacity suppressed IFN-alpha-stimulated tyrosine phosphorylation of both STAT2 and STAT1 to various degrees. Remarkably, their anti-IFN-alpha capacities correlated well with the inhibitory effect on phosphorylation of STAT2 rather than STAT1. In infected cells, the levels of tyrosine-phosphorylated (pY) STAT2 were below the detection level irrespective of duration of IFN-alpha stimulation, whereas the levels of pY-STAT1 strikingly increased after long-term IFN-alpha stimulation. These results suggest that the STAT2 activation process is a crucial target for the blockade of IFN-alpha signaling. An in vitro binding assay with extracts from (STAT1-deficient) U3A and (STAT1-expressing) U3A-ST1 cells suggested the requirement of STAT1 for the C-STAT2 interaction. Furthermore, expression of STAT1 enhanced the inhibitory effect of the C protein on STAT2 activation in U3A cells. The C protein thus appears to participate in the inhibitory process for STAT2 activation through the STAT1 interaction.
Gotoh
Bin
B
Department of Microbiology, Fukui Medical University School of Medicine, Yoshida-gun, Fukui 910-1193, Japan. bin@fmsrsa.fukui-med.ac.jp
Takeuchi
Kenji
K
Komatsu
Takayuki
T
Yokoo
Junko
J
D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D016898:Interferon-alpha / Q000378:metabolism / Q000494:pharmacology*; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; D029082:Sendai virus; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D004268:DNA-Binding Proteins; D016898:Interferon-alpha; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D015534:Trans-Activators; D014764:Viral Proteins; C051221:nonstructural C protein, Sendai virus