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Biomedical subjects

Takayuki Komatsu

Publications and source records attributed to Takayuki Komatsu.

7 recordsLinked to original sources
PubMed2004

C and V proteins of Sendai virus target signaling pathways leading to IRF-3 activation for the negative regulation of interferon-beta production.

We here report a molecular basis for downregulation of interferon (IFN)-beta production by V and C proteins of Sendai virus (SeV). The infection of HeLa cells with SeV poorly induced IFN-beta even if the expression of C/C' was disrupted. In contrast, when the expression of C/C'/Y1/Y2 or V/W was disrupted, SeV infection strongly induced IFN-beta production and significantly activated the interferon regulatory factor (IRF)-3 pathway. The independent expression of C or V inhibited the double-stranded (ds) RNA- or Newcastle disease virus (NDV)-induced activation of IRF-3 and NF-kappa B, as well as the IFN-beta promoter. This inhibitory effect was also observed when Y1, Y2, or a C-terminal half fragment (aa 85-204) of C was independently expressed. Phosphorylation and homodimer formation of IRF-3 were suppressed not only in cells infected with SeV capable of expressing both C/C'/Y1/Y2 (or Y1/Y2) and V/W, but also in HeLa cells constitutively expressing Y1. These results suggest that C, Y1, Y2, and V block signaling pathways leading to IRF-3 activation to downregulate IFN-beta production.

Animals↗
PubMed2004

Inhibition of the gamma interferon response by a Sendai virus C protein mutant with no STAT1-binding ability.

Sendai virus C protein interacts with the signal transducer and activator of transcription (STAT) 1. This interaction is believed to be essential for the Sendai virus inhibition of the interferon (IFN) response. We here analyzed C(F170S) (a C protein mutant with the F170S mutation) with no STAT1-binding ability. C(F170S) lacked the ability to inhibit the IFN-alpha response, but retained the ability to inhibit the IFN-gamma response. IFN-gamma stimulation caused STAT1 phosphorylation, formation of the gamma-activated factor capable of binding to a gamma-activated sequence DNA probe, and STAT1 nuclear translocation, even in the presence of C(F170S). These results suggest that C protein has the STAT1-binding-independent anti-IFN-gamma mechanism, which targets processes after the STAT1 nuclear translocation event.

Amino Acid Substitution↗
PubMed2003

The C-terminal half-fragment of the Sendai virus C protein prevents the gamma-activated factor from binding to a gamma-activated sequence site.

Sendai virus C protein associates with the signal transducer and activator of transcription (STAT) 1 and inhibits the interferon (IFN) response. We report a molecular basis for the anti-IFN-gamma mechanism of Sendai virus. The C-terminal half-fragment of the C protein (D1) retains both the STAT1-binding and the anti-IFN-gamma abilities comparable to those of the full-size C. IFN-gamma stimulation generates phosphorylated-STAT1 even in the presence of the C or the D1. The phosphorylated-STAT1 generated in the D1-expressing cells forms an aberrant complex, which does not bind to a gamma-activated sequence (GAS) probe. Purified D1, indeed, inhibits in vitro the binding of the phosphorylated-STAT1 dimer to the GAS probe. The D1, however, binds to the STAT1 N-terminal domain, but not the DNA binding domain. These results suggest the possibility that the C protein prevents the gamma-activated factor from binding to GAS elements through its interaction with the STAT1 N-terminal domain.

DNA-Binding Proteins↗
PubMed2003

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.

Cell Line↗
PubMed2002

Sendai virus C protein impairs both phosphorylation and dephosphorylation processes of Stat1.

Sendai virus expresses C protein that blocks interferon (IFN) signaling. We previously reported suppression of IFN-stimulated tyrosine phosphorylation of signal transducers and activators of transcription (Stats) in infected cells. However this conclusion has remained controversial. To settle it, we re-examined the effect of C protein expression on phosphorylation of Stat1 in detail. IFN-stimulated tyrosine phosphorylation of Stat1 was doubtlessly suppressed early in infection, but the suppression was incomplete, suggesting the importance of the unknown blocking mechanism that inactivates the tyrosine-phosphorylated (pY)-Stat1 generated as the signaling leak. Interestingly, the dephosphorylation process of pY-Stat1 was also impaired. These effects on both phosphorylation and dephosphorylation processes were attributable to the function of the C protein.

Blotting, Western↗
PubMedDate not supplied

Paramyxovirus strategies for evading the interferon response.

Two genera, the Respirovirus (Sendai virus (SeV) and human parainfluenza virus (hPIV3) and the Rubulavirus (simian virus (SV) 5, SV41, mumps virus and hPIV2), of the three in the subfamily Paramyxovirinae inhibit interferon (IFN) signalling to circumvent the IFN response. The viral protein responsible for the inhibition is the C protein for respirovirus SeV and the V protein for the rubulaviruses, both of which are multifunctional accessory proteins expressed from the P gene. SeV suppresses IFN-stimulated tyrosine phosphorylation of signal transducers and activators of transcription (STATs) at an early phase of infection and further inhibits the downstream signalling without degrading any of the signalling components in most cell lines. On the contrary, the Rubulavirus V protein targets Stat1 or Stat2 for degradation. Proteasome-mediated degradation appears to be involved in most cases. Studies on the molecular mechanisms by which paramyxoviruses evade the IFN response will offer important information for modulating the JAK-STAT pathway, designing novel antiviral drugs and recombinant live vaccines, and improving paramyxovirus expression vectors for gene therapy.

Antiviral Agents↗