STAT3 activation by type I interferons is dependent on specific tyrosines located in the cytoplasmic domain of interferon receptor chain 2c. Activation of multiple STATS proceeds through the redundant usage of two tyrosine residues

Capsaicin functions as a selective degrader of STAT3 to enhance host resistance to viral infection

Although STAT3 has been reported as a negative regulator of type I interferon (IFN) signaling, the effects of pharmacologically inhibiting STAT3 on innate antiviral immunity are not well known. Capsaicin, approved for the treatment of postherpetic neuralgia and diabetic peripheral nerve pain, is an agonist of transient receptor potential vanilloid subtype 1 (TRPV1), with additional recognized potencies in anticancer, anti-inflammatory, and metabolic diseases. We investigated the effects of capsaicin on viral replication and innate antiviral immune response and discovered that capsaicin dose-dependently inhibited the replication of VSV, EMCV, and H1N1. In VSV-infected mice, pretreatment with capsaicin improved the survival rate and suppressed inflammatory responses accompanied by attenuated VSV replication in the liver, lung, and spleen. The inhibition of viral replication by capsaicin was independent of TRPV1 and occurred mainly at postviral entry steps. We further revealed that capsaicin directly bound to STAT3 protein and selectively promoted its lysosomal degradation. As a result, the negative regulation of STAT3 on the type I IFN response was attenuated, and host resistance to viral infection was enhanced. Our results suggest that capsaicin is a promising small-molecule drug candidate, and offer a feasible pharmacological strategy for strengthening host resistance to viral infection.

Ubiquitination network in the type I IFN-induced antiviral signaling pathway

Type I IFN (IFN-I) is the body's first line of defense against pathogen infection. IFN-I can induce cellular antiviral responses and therefore plays a key role in driving antiviral innate and adaptive immunity. Canonical IFN-I signaling activates the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, which induces the expression of IFN-stimulated genes and eventually establishes a complex antiviral state in the cells. Ubiquitin is a ubiquitous cellular molecule for protein modifications, and the ubiquitination modifications of protein have been recognized as one of the key modifications that regulate protein levels and/or signaling activation. Despite great advances in understanding the ubiquitination regulation of many signaling pathways, the mechanisms by which protein ubiquitination regulates IFN-I-induced antiviral signaling have not been explored until very recently. This review details the current understanding of the regulatory network of ubiquitination that critically controls the IFN-I-induced antiviral signaling pathway from three main levels, including IFN-I receptors, IFN-I-induced cascade signals, and effector IFN-stimulated genes.

E3 ubiquitin ligase MID1 ubiquitinates and degrades type-I interferon receptor 2

Type I interferon (IFN-I) is a common biological molecule used for the treatment of viral diseases. However, the clinical antiviral efficacy of IFN-I needs to be greatly improved. In this study, IFN-I receptor 2 (IFNAR2) was revealed to undergo degradation at the protein level in cells treated with IFN-I for long periods of time. Further studies found a physical interaction between the E3 ubiquitin ligase Midline-1 (MID1) and IFNAR2. As a consequence, MID1 induced both K48-linked and K63-linked polyubiquitination of IFNAR2, which promoted IFNAR2 protein degradation in a lysosome-dependent manner. Conversely, knockdown of MID1 largely restricted IFN-I-induced degradation of IFNAR2. Importantly, MID1 regulated the strength of IFN-I signaling and IFN-I-induced antiviral activity. These findings reveal a regulatory mechanism of IFNAR2 ubiquitination and protein stability in IFN-I signaling, which could provide a potential target for improving the antiviral efficacy of IFN-I.

EMT alterations in the solute carrier landscape uncover SLC22A10/A15 imposed vulnerabilities in pancreatic cancer

The involvement of membrane-bound solute carriers (SLCs) in neoplastic transdifferentiation processes is poorly defined. Here, we examined changes in the SLC landscape during epithelial-mesenchymal transition (EMT) of pancreatic cancer cells. We show that two SLCs from the organic anion/cation transporter family, SLC22A10 and SLC22A15, favor EMT via interferon (IFN) α and γ signaling activation of receptor tyrosine kinase-like orphan receptor 1 (ROR1) expression. In addition, SLC22A10 and SLC22A15 allow tumor cell accumulation of glutathione to support EMT via the IFNα/γ-ROR1 axis. Moreover, a pan-SLC22A inhibitor lesinurad reduces EMT-induced metastasis and gemcitabine chemoresistance to prolong survival in mouse models of pancreatic cancer, thus identifying new vulnerabilities for human PDAC.

Role of collagen regulators in cancer treatment: A comprehensive review

Abstract:

Collagen is the most important structural protein and also a main component of extra-cellular matrix (ECM). It plays a role in tumor progression. Collagen can be regulated by altering it’s biosynthesis pathway through various signaling pathways, receptors and genes. Activity of cancer cells can also be regulated by other ECM components like metalloproteinases, hyaluronic acid, fibronectin and so on. Hypoxia is also one of the condition which leads to cancer progression by stimulating the expression of procollagen lysine as a collagen crosslinker, which increases the size of collagen fibres promoting cancer spread. The collagen content in cancerous cells leads to resistance in chemotherapy. So, to reduce this resistance, some of the collagen regulating therapies are introduced, which include inhibiting its biosynthesis, disturbing cancer cell signaling pathway, mediating ECM components and directly utilizing collagenase. This study is an effort to compile the strategies reported to control the collagen level and different collagen inhibitors reported so far. More research is needed in this area, growing understandings of collagen’s structural features and its role in cancer progression will aid in the advancement of newer chemotherapies.

JAK/STAT: Why choose a classical or an alternative pathway when you can have both?

A subset of cytokines triggers the JAK‐STAT pathway to exert various functions such as the induction of inflammation and immune responses. The receptors for these cytokines are dimers/trimers of transmembrane proteins devoid of intracellular kinase activity. Instead, they rely on Janus kinases (JAKs) for signal transduction. Classical JAK‐STAT signalling involves phosphorylation of cytokine receptors' intracellular tyrosines, which subsequently serve as docking sites for the recruitment and activation of STATs. However, there is evidence to show that several cytokine receptors also use a noncanonical, receptor tyrosine‐independent path to induce activation of STAT proteins. We identified two main alternative modes of STAT activation. The first involves an association between a tyrosine‐free region of the cytokine receptor and STATs, while the second seems to depend on a direct interaction between JAK and STAT proteins. We were able to identify the use of noncanonical mechanisms by almost a dozen cytokine receptors, suggesting they have some importance. These alternative pathways and the receptors that employ them are discussed in this review.

Profiling transcription factor sub-networks in type I interferon signaling and in response to SARS-CoV-2 infection

Type I interferons (IFN α/β) play a central role in innate immunity to respiratory viruses, including coronaviruses. In this study, transcription factor profiling in the transcriptome was used to gain novel insights into the role of inducible transcription factors in response to type I interferon signaling in immune cells and in lung epithelial cells after SARS-CoV-2 infection. Modeling the interferon-inducible transcription factor mRNA data in terms of distinct sub-networks based on biological functions such as antiviral response, immune modulation, and cell growth revealed enrichment of specific transcription factors in mouse and human immune cells. Interrogation of multiple microarray datasets revealed that SARS-CoV-2 induced high levels of IFN-beta and interferon-inducible transcription factor mRNA in human lung epithelial cells. Transcription factor mRNA of the three sub-networks were differentially regulated in human lung epithelial cell lines after SARS-CoV-2 infection and in COVID-19 patients. A subset of type I interferon-inducible transcription factors and inflammatory mediators were specifically enriched in the lungs and neutrophils of Covid-19 patients. The emerging complex picture of type I IFN transcriptional regulation consists of a rapid transcriptional switch mediated by the Jak-Stat cascade and a graded output of the inducible transcription factor activation that enables temporal regulation of gene expression.

IFNAR1 and IFNAR2 play distinct roles in initiating type I interferon-induced JAK-STAT signaling and activating STATs

[Figure: see text].

Germline STAT3 gain-of-function mutations in primary immunodeficiency: Impact on the cellular and clinical phenotype

Signal transducer and activator of transcription 3 (STAT3) is a key transcription factor involved in regulation of immune cell activation and differentiation. Recent discoveries highlight the role of germline activating STAT3 mutations in inborn errors of immunity characterized by early-onset multi-organ autoimmunity and lymphoproliferation. Much progress has been made in defining the clinical spectrum of STAT3 GOF disease and unraveling the molecular and cellular mechanisms underlying this disease. In this review, we summarize our current understanding of the disease and discuss the clinical phenotype, diagnostic approach, cellular and molecular effects of STAT3 GOF mutations and therapeutic concepts for these patients.

The Role of Type I Interferons in the Pathogenesis and Treatment of COVID-19

Type I interferons (IFN-I) were first discovered over 60 years ago in a classical experiment by Isaacs and Lindenman, who showed that IFN-Is possess antiviral activity. Later, it became one of the first approved protein drugs using heterologous protein expression systems, which allowed its large-scale production. It has been approved, and widely used in a pleiotropy of diseases, including multiple-sclerosis, hepatitis B and C, and some forms of cancer. Preliminary clinical data has supported its effectiveness against potential pandemic pathogens such as Ebola and SARS. Still, more efficient and specific drugs have taken its place in treating such diseases. The COVID-19 global pandemic has again lifted the status of IFN-Is to become one of the more promising drug candidates, with initial clinical trials showing promising results in reducing the severity and duration of the disease. Although SARS-CoV-2 inhibits the production of IFNβ and thus obstructs the innate immune response to this virus, it is sensitive to the antiviral activity of externally administrated IFN-Is. In this review I discuss the diverse modes of biological actions of IFN-Is and how these are related to biophysical parameters of IFN-I-receptor interaction and cell-type specificity in light of the large variety of binding affinities of the different IFN-I subtypes towards the common interferon receptor. Furthermore, I discuss how these may guide the optimized use IFN-Is in combatting COVID-19.

A STAT3 of Addiction: Adipose Tissue, Adipocytokine Signalling and STAT3 as Mediators of Metabolic Remodelling in the Tumour Microenvironment

Metabolic remodelling of the tumour microenvironment is a major mechanism by which cancer cells survive and resist treatment. The pro-oncogenic inflammatory cascade released by adipose tissue promotes oncogenic transformation, proliferation, angiogenesis, metastasis and evasion of apoptosis. STAT3 has emerged as an important mediator of metabolic remodelling. As a downstream effector of adipocytokines and cytokines, its canonical and non-canonical activities affect mitochondrial functioning and cancer metabolism. In this review, we examine the central role played by the crosstalk between the transcriptional and mitochondrial roles of STAT3 to promote survival and further oncogenesis within the tumour microenvironment with a particular focus on adipose-breast cancer interactions.

Viral manipulation of STAT3: Evade, exploit, and injure

Signal transducer and activator of transcription 3 (STAT3) is a key regulator of numerous physiological functions, including the immune response. As pathogens elicit an acute phase response with concerted activation of STAT3, they are confronted with two evolutionary options: either curtail it or employ it. This has important consequences for the host, since abnormal STAT3 function is associated with cancer development and other diseases. This review provides a comprehensive outline of how human viruses cope with STAT3-mediated inflammation and how this affects the host. Finally, we discuss STAT3 as a potential target for antiviral therapy.

The important roles of type I interferon and interferon-inducible genes in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease that causes multiple-organ dysfunction mainly affecting women in their childbearing years. Type I IFN synthesis is usually triggered by viruses, and its production is tightly regulated and limited in time in health individuals. However, many patients with systemic autoimmune diseases including SLE have signs of aberrant production of type I interferon (IFN) and display an increased expression of IFN-inducible genes. Continuous type I IFNs derived from activated plasmacytoid dendritic cells (pDCs) by interferogenic immune complexes (ICs) and migration of these cells to tissues both break immune tolerance and promote an on-going autoimmune reaction in human body. By the means of detecting type I IFNs and IFN-inducible genes, it can help with diagnosis and evaluation of SLE in early stage and more efficiently. Anti-IFN-α monoclonal antibodies in SLE patients were recently reported and is now being investigated in phase II clinical trails. In this review, we focus on recent research progress in type I IFN and IFN-inducible genes. Possible mechanisms behind the dysregulated type I IFN system in SLE and how they contribute to the development of an autoimmune process, and act as a biomarker and therapeutic target will be reviewed.

A point mutation, E95D, in the mumps virus V protein disengages STAT3 targeting from STAT1 targeting

Mumps virus, like other paramyxoviruses in the Rubulavirus genus, encodes a V protein that can assemble a ubiquitin ligase complex from cellular components, leading to the destruction of cellular signal transducer and activator of transcription (STAT) proteins. While many V proteins target the interferon-activated STAT1 or STAT2 protein, mumps virus V protein is unique in its ability to also target STAT3 for ubiquitin modification and proteasome-mediated degradation. Here we report that a single amino acid substitution in the mumps virus V protein, E95D, results in defective STAT3 targeting while maintaining the ability to target STAT1. Results indicate that the E95D mutation disrupts the ability of the V protein to associate with STAT3. A recombinant mumps virus carrying the E95D mutation in its P and V proteins replicates normally in cultured cells but fails to induce targeting of STAT3. Infection with the recombinant virus results in the differential regulation of a number of cellular genes compared to wild-type mumps virus and increases cell death in infected cells, producing a large-plaque phenotype.

A conserved IFN-alpha receptor tyrosine motif directs the biological response to type I IFNs

Mammalian type I IFNs (IFN-Is) mediate their potent biological activities through an evolutionarily conserved IFN-alpha receptor (IFNAR), consisting of IFNAR1 and IFNAR2. These two chains direct the rapid activation of two founding members of the STAT family of transcription factors, STAT1 and STAT2. To understand how IFN-Is direct the recruitment and activation of STATs, a series of mutant murine IFNAR1 and IFNAR2 receptors were generated and evaluated in IFNAR1 and IFNAR2 knockout cells. These studies reveal that a single conserved IFNAR2 tyrosine, Y(510), plays a critical role in directing the IFN-I-dependent activation of STAT1 and STAT2, both in murine fibroblasts and macrophages. A second IFNAR2 tyrosine, Y(335), plays a more minor role. Likewise, Y(510) > Y(335) play a critical role in the induction of genes and antiviral activity traditionally associated with IFN-Is.

Regulation of interferon-gamma during innate and adaptive immune responses

Interferon-gamma (IFN-gamma) is crucial for immunity against intracellular pathogens and for tumor control. However, aberrant IFN-gamma expression has been associated with a number of autoinflammatory and autoimmune diseases. This cytokine is produced predominantly by natural killer (NK) and natural killer T (NKT) cells as part of the innate immune response, and by Th1 CD4 and CD8 cytotoxic T lymphocyte (CTL) effector T cells once antigen-specific immunity develops. Herein, we briefly review the functions of IFN-gamma, the cells that produce it, the cell extrinsic signals that induce its production and influence the differentiation of naïve T cells into IFN-gamma-producing effector T cells, and the signaling pathways and transcription factors that facilitate, induce, or repress production of this cytokine. We then review and discuss recent insights regarding the molecular regulation of IFN-gamma, focusing on work that has led to the identification and characterization of distal regulatory elements and epigenetic modifications with the IFN-gamma locus (Ifng) that govern its expression. The epigenetic modifications and three-dimensional structure of the Ifng locus in naive CD4 T cells, and the modifications they undergo as these cells differentiate into effector T cells, suggest a model whereby the chromatin architecture of Ifng is poised to facilitate either rapid opening or silencing during Th1 or Th2 differentiation, respectively.

Increased interferon alpha receptor 2 mRNA levels is associated with renal cell carcinoma metastasis

Background

Interferon-α (IFN-α) is one of the central agents in immunotherapy for renal cell carcinoma (RCC) and binds to the IFN-α receptor (IFNAR). We investigated the role of IFNAR in RCC.

Methods

We quantified IFNAR mRNA expression in paired tumor and non-tumor samples from the surgical specimens of 103 consecutive patients with RCC using a real-time reverse transcription polymerase chain reaction (RT-PCR), and IFNAR2 protein using Western blotting.

Results

The absolute level of IFNAR1 and IFNAR2 mRNAs in tumor and non-tumor tissues did not correlate with the malignant and metastatic profiles. The relative yields of the PCR product from the tumor tissue to that from the corresponding non-tumor tissue (T/N) for the expression of IFNAR mRNAs were calculated. While the T/N ratio of IFNAR1 did not correlate with any factor, a high T/N ratio of IFNAR2 correlated with poor differentiation (P < 0.05), local invasion (P < 0.001), and metastasis (P < 0.0001). By multivariate analysis, a high T/N ratio of IFNAR2 predicted a shortened overall survival in all cases (P < 0.05) and a shorter disease-free survival in those without metastasis (M0; 68 cases, P < 0.05). Impressively, patients with a poorer response to IFN-α treatment had a higher IFNAR2 T/N ratio than those who had a good response (P < 0.05). IFNAR2c protein expression was higher in the primary tumors in patients with metastases (M1; 35 cases) compared to those without ( P < 0.0001).

Conclusion

IFNAR2 is associated with the progression of RCC.

Stats: multifaceted regulators of transcription

The high-affinity binding interactions between interferons (IFNs) and their cognate cell surface receptors lead to the activation of receptor-associated Janus protein tyrosine kinases (Jaks) and subsequent phosphorylation and activation of a group of transcription factors, the signal transducers and activators of transcription (Stats). Upon IFN-induced activation, these Stat proteins form homodimeric and heterodimeric complexes that translocate to the nucleus and bind specific elements within the promoters of IFN-stimulated genes (ISGs). In addition to the well-studied IFN-induced ISG factor 3 (ISGF3) and Stat1:1 complexes, IFNs induce the formation of a number of other Stat-containing complexes, including Stat3:3 and Stat5:5 homodimers, as well as Stat2:1 and Stat5:CrkL heterodimers, that also mediate gene transcription. Moreover, emerging evidence suggests that particular amino acid residues within the individual Stat proteins contribute to different aspects of Stat function. These residues modulate the transcriptional activation potential of Stat-containing complexes and thereby influence the expression of ISGs. Indeed, the Stat proteins function in a multifaceted manner to regulate the expression of proteins that mediate IFN responses.

The production of IL-1 receptor antagonist in IFN-beta-stimulated human monocytes depends on the activation of phosphatidylinositol 3-kinase but not of STAT1

IFN-beta induces the production of secreted IL-1R antagonist (sIL-1Ra) without triggering synthesis of the agonist IL-1beta in human monocytes. This might account for its anti-inflammatory properties. Canonically, IFN-beta signals through activation of JAK/STAT pathway, although PI3K and MAPK have also been involved. In this study, the role of PI3K, MEK1, and STAT1 in IFN-beta-induced sIL-1Ra production is investigated in freshly isolated human blood monocytes. PI3K, but not MEK1 activation is essential for sIL-1Ra production in monocytes treated with IFN-beta, as demonstrated by using the respective inhibitors of PI3K and MEK1, Ly294002 and PD98059. The use of cycloheximide and actinomycin D shows that sIL-1Ra was an immediate early gene induced by IFN-beta and that PI3K was controlling sIL-1Ra gene transcription. Although both inhibitors of PI3K and MEK1 diminished the Ser(727) phosphorylation of STAT1 induced by IFN-beta, only Ly294002 inhibited sIL-1Ra production. Furthermore, the inhibition of STAT1-Ser(727) phosphorylation by Ly294002 did not affect STAT1 translocation, suggesting that STAT1 was not involved in sIL-1Ra gene induction. This was confirmed in monocytes that were transfected with small interfering RNA specifically targeting STAT1. Indeed, monocytes in which effective STAT1 gene knockdown was achieved were fully responsive to IFN-beta in terms of sIL-1Ra production. Taken together, the present data demonstrate that the induction of sIL-1Ra transcription and production by IFN-beta in human monocytes involved PI3K, but not STAT1 activation.

Identification of the cytoplasmic domains of CXCR4 involved in Jak2 and STAT3 phosphorylation

The chemokine SDF-1alpha transduces G(i)-dependent and -independent signals through CXCR4. Activation of Jak2/STAT3, a G(i)-independent signaling pathway, which plays a major role in survival signals, is known to be activated after SDF-1alpha binding to CXCR4 but the domains of CXCR4 involved in this signaling remain unexplored. Using human embryonic kidney HEK-293 cells stably expressing wild-type or mutated forms of CXCR4, we demonstrated that STAT3 phosphorylation requires the N-terminal part of the third intracellular loop (ICL3) and the tyrosine 157 present at the end of the second intracellular loop (ICL2) of CXCR4. In contrast, neither the conserved Tyr(135) in the DRY motif at the N terminus of ICL2 nor the Tyr(65) and Tyr(76) in the first intracellular loop (ICL1) are involved in this activation. ICL3, which does not contain any tyrosine residues, is needed to activate Jak2. These results demonstrate that two separate domains of CXCR4 are involved in Jak2/STAT3 signaling. The N-terminal part of ICL3 is needed to activate Jak2 after SDF-1alpha binding to CXCR4, leading to phosphorylation of only one cytoplasmic Tyr, present at the C terminus of ICL2, which triggers STAT3 activation. This work has profound implications for the understanding of CXCR4-transduced signaling.

Oxidized phospholipids increase interleukin 8 (IL-8) synthesis by activation of the c-src/signal transducers and activators of transcription (STAT)3 pathway

Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (Ox-PAPC) and its component phospholipids 1-palmitoyl-2-epoxyisoprostane-sn-glycero-3-phosphorylcholine (PEIPC) and 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine induce endothelial cells to synthesize chemotactic factors, such as interleukin 8 (IL-8). We have shown recently that Ox-PAPC-mediated induction of IL-8 transcription is independent of NF-kappaB activation, a major transcription factor utilized by cytokines and lipopolysaccharide for the induction of IL-8 transcription. In this study, we provide evidence for the role of c-src in Ox-PAPC and, specifically, PEIPC-mediated IL-8 induction. Ox-PAPC and its component phospholipids induced a rapid and transient phosphorylation of c-src Tyr418, a hallmark of c-src activation, in human aortic endothelial cells (HAEC). Ox-PAPC-mediated IL-8 protein synthesis in HAEC was inhibited by Src family kinase inhibitors, PP1 and PP2, but not by an inactive analog, PP3. Transient expression of plasmids containing C-terminal Src kinase or kinase-deficient dominant-negative c-src resulted in a 72 and 50% reduction in Ox-PAPC-induced IL-8 promoter activation in human microvascular endothelial cells, respectively. In contrast, overexpression of v-src kinase resulted in a 4-fold increase in IL-8 promoter activation, without inducing NF-kappaB promoter activation. Furthermore, treatment of HAEC with Ox-PAPC and its component PEIPC induced the activation of STAT3 by phosphorylating Tyr705, a feature of STAT3 activation. STAT3 is a known downstream effector of c-src. Ox-PAPC-induced activation of STAT3 resulted in the translocation of STAT3 from the cytoplasm of HAEC into their nuclear compartment. Transient expression of a dominant-negative STAT3beta construct in HMEC strongly inhibited IL-8 induction by Ox-PAPC. Taken together, these data demonstrate the role of the c-src kinase/STAT3 pathway in Ox-PAPC-mediated IL-8 expression in endothelial cells.

STAT protein interference and suppression of cytokine signal transduction by measles virus V protein

Measles virus, a paramyxovirus of the Morbillivirus genus, is responsible for an acute childhood illness that infects over 40 million people and leads to the deaths of more than 1 million people annually (C. J. Murray and A. D. Lopez, Lancet 349:1269-1276, 1997). Measles virus infection is characterized by virus-induced immune suppression that creates susceptibility to opportunistic infections. Here we demonstrate that measles virus can inhibit cytokine responses by direct interference with host STAT protein-dependent signaling systems. Expression of the measles V protein prevents alpha, beta, and gamma interferon-induced transcriptional responses. Furthermore, it can interfere with signaling by interleukin-6 and the non-receptor tyrosine kinase, v-Src. Affinity purification demonstrates that the measles V protein associates with cellular STAT1, STAT2, STAT3, and IRF9, as well as several unidentified partners. Mechanistic studies indicate that while the measles V protein does not interfere with STAT1 or STAT2 tyrosine phosphorylation, it causes a defect in IFN-induced STAT nuclear accumulation. The defective STAT nuclear redistribution is also observed in measles virus-infected cells, where some of the STAT protein is detected in cytoplasmic bodies that contain viral nucleocapsid protein and nucleic acids. Interference with STAT-inducible transcription may provide a novel intracellular mechanism for measles virus-induced cytokine inhibition that links innate immune evasion to adaptive immune suppression.

STAT3 ubiquitylation and degradation by mumps virus suppress cytokine and oncogene signaling

Mumps virus is a common infectious agent of humans, causing parotitis, meningitis, encephalitis, and orchitis. Like other paramyxoviruses in the genus Rubulavirus, mumps virus catalyzes the proteasomal degradation of cellular STAT1 protein, a means for escaping antiviral responses initiated by alpha/beta and gamma interferons. We demonstrate that mumps virus also eliminates cellular STAT3, a protein that mediates transcriptional responses to cytokines, growth factors, nonreceptor tyrosine kinases, and a variety of oncogenic stimuli. STAT1 and STAT3 are independently targeted by a single mumps virus protein, called V, that assembles STAT-directed ubiquitylation complexes from cellular components, including STAT1, STAT2, STAT3, DDB1, and Cullin4A. Consequently, mumps virus V protein prevents responses to interleukin-6 and v-Src signals and can induce apoptosis in STAT3-dependent multiple myeloma cells and transformed murine fibroblasts. These findings demonstrate a unique cytokine and oncogene evasion property of mumps virus that provides a molecular basis for its observed oncolytic properties.

Involvement of the zinc-binding capacity of Sendai virus V protein in viral pathogenesis

The V protein of Sendai virus (SeV) is nonessential to virus replication in cell culture but indispensable to viral pathogenicity in mice. The highly conserved cysteine-rich zinc finger-like domain in its carboxyl terminus is believed to be responsible for this viral pathogenicity. In the present study, we showed that the cysteine-rich domain of the SeV V protein could actually bind zinc by using glutathione-S-transferase fusion proteins. When the seven conserved cysteine residues at positions 337, 341, 353, 355, 358, 362, and 365 were replaced individually, the zinc-binding capacities of the mutant proteins were greatly impaired, ranging from 22 to 68% of that of the wild type. We then recovered two mutant SeVs from cDNA, which have V-C(341)S and V-C(365)R mutations and represent maximal and minimal zinc-binding capacities among the corresponding mutant fusion proteins, respectively. The mutant viruses showed viral protein synthesis and growth patterns similar to those of wild-type SeV in cultured cells. However, the mutant viruses were strongly attenuated in mice in a way similar to that of SeV V(DeltaC), which has a truncated V protein lacking the cysteine-rich domain, by exhibiting earlier viral clearance from the mouse lung and less virulence to mice. We therefore conclude that the zinc-binding capacity of the V protein is involved in viral pathogenesis.