To establish infections, viruses use various strategies to suppress the host defense mechanism, such as interferon (IFN)-induced antiviral state. We found that cells infected with a wild strain of measles virus (MeV) displayed nearly complete suppression of IFN-alpha-induced antiviral state, but not IFN-gamma-induced state. This phenomenon is due to the suppression of IFN-alpha-inducible gene expression at a transcriptional level. In the IFN-alpha signal transduction pathway, Jak1 phosphorylation induced by IFN-alpha is dramatically suppressed in MeV-infected cells; however, phosphorylation induced by IFN-gamma is not. We performed immunoprecipitation experiments using antibodies against type 1 IFN receptor chain 1 (INFAR1) and antibody against RACK1, which is reported to be a scaffold protein interacting with type I IFN receptor chain 2 and STAT1. These experiments indicated that IFNAR1 forms a complex containing the MeV-accessory proteins C and V, RACK1, and STAT1 in MeV-infected cells but not in uninfected cells. Composition of this complex in the infected cells altered little by IFN-alpha treatment. These results indicate that MeV suppresses the IFN-alpha, but not IFN-gamma, signaling pathway by inhibition of Jak1 phosphorylation. Our data suggest that functional disorder of the type I IFN receptor complex is due to "freezing" of the receptor through its association with the C and/or V proteins of MeV.

The pathogenesis of severe acute respiratory syndrome (SARS) is poorly understood and cytokine dysregulation has been suggested as one relevant mechanism to be explored. We compared the cytokine profile in Caco2 cells after infection of SARS coronavirus (SARS-CoV) with other respiratory viruses including respiratory syncytial virus (RSV), influenza A virus (FluAV), and human parainfluenza virus type 2 (hPIV2). Interferon (IFN) system (production and response) was not suppressed by SARS-CoV infection. Therefore, SARS-CoV replication was suppressed by pretreatment with IFN. SARS-CoV and RSV induced high levels of IL-6 and RANTES compared with FluAV and hPIV2. Induction level of suppressor of cytokine signaling-3 (SOCS3) by SARS-CoV was significantly lower than that by RSV in spite of the significant production of IL-6. Toll-like receptors 4 and 9, which correlate with the induction of inflammatory response, were upregulated by SARS-CoV infection. Collectively, overinduction of inflammatory cytokine and dysregulation of cytokine signaling may contribute to the immunopathology associated with "severe" inflammation in SARS.

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We showed previously that herpes simplex virus type 1 (HSV-1) suppresses the interferon (IFN) signaling pathway during the early infection stage in the human amnion cell line FL. HSV-1 inhibits the IFN-induced phosphorylation of Janus kinases (JAK) in infected FL cells. In the present study, we showed that the suppressor of cytokine signaling-3 (SOCS3), a host negative regulator of the JAK/STAT pathway, is rapidly induced in FL cells after HSV-1 infection. Maximal levels of SOCS3 protein were detected at around 1 to 2 h after infection. This is consistent with the occurrence of HSV-1-mediated inhibition of IFN-induced JAK phosphorylation. The HSV-1 wild-type strain VR3 induced SOCS3 more efficiently than did mutants that are defective in UL41 or UL13 and that are hyperresponsive to IFN. Induction of the IRF-7 protein and transcriptional activation of IFN-␣4, which occur in a JAK/STAT pathway-dependent manner, were poorly induced by VR3 but efficiently induced by the mutant viruses. In contrast, phosphorylation of IRF-3 and transcriptional activation of IFN-␤, which are JAK/STAT pathway-independent process, were equally well induced by the wild-type strain and the mutants. In conclusion, the SOCS3 protein appears to be mainly responsible for the suppression of IFN signaling and IFN production that occurs during HSV-1 infection.Cells have various defense mechanisms that protect them from viral infection. In turn, viruses suppress or escape host responses by a variety of strategies. Interferon (IFN) is induced by viral infection and plays an important role in the defense of the host cell from viral attack. When IFN binds to specific cell surface receptors on the host cells, it promotes the antiviral state through induction or activation of the 2Ј,5Ј-oligoadenylate synthetase (2-5AS)/RNase L system, the double-stranded RNA-activated protein kinase, and the MxA protein (10,30,35). The signal transduction pathway of IFN consists of Janus kinases (JAK), tyrosine protein kinases that interact with the intracellular domains of the receptors, and the STAT family proteins, transcription factors that are activated by their phosphorylation by JAK. This pathway, which is designated the JAK/STAT pathway, also transduces various cytokine signals. There are four JAK proteins (Jak1, Jak2, Jak3, and Tyk2) and seven STAT proteins (STAT1 to 4, STAT5a, STAT5b, and STAT6) (1, 9, 17, 25). Each cytokine employs a particular combination of the JAK and STAT proteins, which determines the specificity of the cytokine responses. For instance, Jak1 and Tyk2 are associated with the IFN-␣/␤ receptor complex. These JAK proteins are activated by phosphorylation after IFN-␣/␤ binds to the receptor, and they then phosphorylate STAT1 and STAT2. The transcription factor ISGF3, which consists of phosphorylated STAT1, phosphorylated STAT2, and IRF-9/ p48/ISGF3␥, forms and then translocates into the nucleus and binds to IFN-stimulated response elements in the promoters of IFN-inducible genes (9, 12).DNA and RNA viruses use various strategies to countera...

We examined the influence on the interferon (IFN) signaling pathway of infection with herpes simplex virus type 1 (HSV-1) strain VR3. Data from reporter gene assays showed that expression of both type I and type II IFN-inducible genes was dramatically suppressed during the early stage of HSV-1 infection (2 to 3 h postinfection). During these periods, phosphorylation levels of janus kinases (JAKs) and STATs did not increase after treatment of HSV-1-infected FL cells with IFN-alpha or IFN-gamma, although cellular protein levels of the JAKs and the STATs were not significantly changed. In contrast, the inhibitory effect of HSV-1 on phosphorylation of STAT1 was not observed in U937 cells, which show resistance to steady-state accumulation of RNA for HSV-1 immediate-early genes. The phosphorylation of STAT1 in FL cells was not inhibited by infection with a UV-inactivated virus. These results indicate that viral gene expression or viral protein production is necessary for the inhibition of phosphorylation by HSV-1.

Viruses belonging to the Paramyxoviridae family block the IFN signal transduction pathway in order to circumvent host cellular defense activity. Mumps virus (MuV) and human parainfluenza virus type 2 (hPIV2) reduced the constitutive production of respectively (3,7,15,20,21,22,28,30). These proteins are components of the transcription factor IFN-stimulated gene factor 3 (ISGF3) or gamma IFN (IFN-␥)-activated factor (GAF). The ISGF3 complex is formed from STAT-1␣, STAT-2, and IFN regulatory factor-9 (IRF-9), and the GAF complex is a homodimer of STAT-1␣. ISGF3 and GAF bind to the IFN-responsive promoter elements alpha IFN (IFN-␣)-stimulated response element (ISRE) and IFN-␥-activated sequence (GAS), respectively. Didcock et al. reported that simian virus 5 (SV5) belongs to the same genus as MuV and induced the proteosome-mediated degradation of STAT-1 (1). The proteosome inhibitor MG132 prevented SV5-induced STAT-1 degradation. Moreover, our recent studies also noted that MG132 partly inhibited the degradation of STAT-1 in FL cells persistently infected with MuV (FLMT cells) and that basal levels of STAT-1 were detectable in the presence of the reagent (15). Therefore, it is reasonable to consider that the mechanism(s) of reduction of STAT-1 induced by MuV infection is the same as that found in SV5 infection. However, the detailed mechanism of STAT-1 degradation is not clearly understood, although it has been shown that SV5 protein V (SV5-V)-induced STAT-1 reduction seems to be mediated by a proteosome-mediated degradation pathway. These results are supported by one finding only from an experiment with the proteosome inhibitor MG132.It is important to clarify whether the MuV protein V (MuV-V)-induced decrease in STAT-1 production is mediated through the ubiquitination and proteosome degradation pathways. Kim and Maniatis reported that the carboxy-terminal region of STAT-1 is necessary for the degradation of its activated or phosphorylation form (13). In this study, we sought to evaluate the role of the C-terminal region of STAT-1 in its degradation caused by MuV-V and to examine the function of

We showed previously that infection of herpes simplex virus type 1 (HSV-1) rapidly induced the suppressor of cytokine signaling-3 (SOCS3), a host negative regulator of the JAK/STAT pathway, in the amnion cell line FL. Thus, HSV-1 suppresses the interferon (IFN) signaling pathway at the step of IFN-induced phosphorylation of janus kinases during an early infection stage. In the present study, we examined SOCS3 induction by HSV-1 infection in several types of human cell lines. FL cells and the T-cell line CCRF-CEM strongly induced SOCS3 during HSV-1 infection. The virus rapidly propagated in both cell lines and produced a lytic infection. On the other hand, the monocytic cell lines U937 and THP-1, and the B-cell line AKATA showed neither SOCS3 induction nor suppression of IFN-induced STAT1 phosphorylation during HSV-1 infection. These cell lines resulted in a persistent or prolonged infection, which continuously produced a low titer of infectious virus. The induction of SOCS3 by HSV-1 should occur via STAT3 activation immediately after HSV-1 infection. SOCS3 induction was inhibited by the addition of a Jak3 inhibitor WHI-P131. Treatment with WHI-P131 or transfection of antisense oligonucleotides specific for SOCS3 dramatically suppressed replication of HSV-1 in FL cells. The suppression of viral replication by WHI-P131 was released in the presence of neutralizing anti-IFN-alpha and anti-IFN-beta antibodies. In conclusion, suppression of IFN signaling by HSV-1-induced SOCS3 is required for efficient replication and lytic infection of HSV-1. The SOCS3 induction varied among cell lines, indicating that it is an important factor determining the cell type specificity of efficient HSV-1 replication.

Poor induction of interferon-induced 2',5'-oligoadenylate synthetase (2-5AS) has been demonstrated in cells persistently infected with mumps virus as compared with uninfected cells. As for the number of interferon (IFN) receptors and the level of IFN regulatory factors (IRF-1 and IRF-2) mRNAs, there was little difference between them. Therefore, it is suggested that the IFN-alpha signaling system is ineffective in the persistently infected cells. Components of IFN-stimulating gene factor 3 alpha (ISGF-3 alpha), STAT-1 alpha (p91) and STAT-2 (p113), were investigated in human amnion (FL), human nasopharyngeal cancer (KB), human T-lymphoid (HUT 78), and human B-lymphoid (Akata) cells persistently infected with mumps virus. STAT-1 alpha, but not STAT-2, disappeared in these persistently infected cells, and this factor was not restored by treatment of these cells with IFN. However, no difference was observed between the levels of STAT-1 alpha mRNA transcript in persistently infected and uninfected control cells. It is reasonable to infer that the poor induction of 2-5AS activity is due to the decrease of STAT-1 alpha in correlation with the IFN-signal transduction pathway. Furthermore, induction of other IFN-stimulated genes (ds-RNA activated protein kinase, PKR, and MxA protein) was also reduced in the cells persistently infected with mumps virus.