Phosphorylation and specific ubiquitin acceptor sites are required for ubiquitination and degradation of the IFNAR1 subunit of type I interferon receptor

Ubiquitination is involved in PKC-mediated degradation of cell surface Kv1.5 channels

The voltage-gated Kv1.5 potassium channel, conducting the ultra-rapid delayed rectifier K+ current (IKur) in human cells, plays important roles in the repolarization of atrial action potentials and regulation of the vascular tone. We previously reported that activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) induces endocytic degradation of cell-surface Kv1.5 channels, and a point mutation removing the phosphorylation site, T15A, in the N terminus of Kv1.5 abolished the PMA-effect. In the present study, using mutagenesis, patch clamp recording, Western blot analysis, and immunocytochemical staining, we demonstrate that ubiquitination is involved in the PMA-mediated degradation of mature Kv1.5 channels. Since the expression of the Kv1.4 channel is unaffected by PMA treatment, we swapped the N- and/or C-termini between Kv1.5 and Kv1.4. We found that the N-terminus alone did not but both N- and C-termini of Kv1.5 did confer PMA sensitivity to mature Kv1.4 channels, suggesting the involvement of Kv1.5 C-terminus in the channel ubiquitination. Removal of each of the potential ubiquitination residue Lysine at position 536, 565, and 591 by Arginine substitution (K536R, K565R, and K591R) had little effect, but removal of all three Lysine residues with Arginine substitution (3K-R) partially reduced PMA-mediated Kv1.5 degradation. Furthermore, removing the cysteine residue at position 604 by Serine substitution (C604S) drastically reduced PMA-induced channel degradation. Removal of the three Lysines and Cys604 with a quadruple mutation (3K-R/C604S) or a truncation mutation (Δ536) completely abolished the PKC activation-mediated degradation of Kv1.5 channels. These results provide mechanistic insight into PKC activation-mediated Kv1.5 degradation.

Virus versus host: influenza A virus circumvents the immune responses

Influenza A virus (IAV) is a highly contagious pathogen causing dreadful losses to humans and animals around the globe. As is known, immune escape is a strategy that benefits the proliferation of IAVs by antagonizing, blocking, and suppressing immune surveillance. The HA protein binds to the sialic acid (SA) receptor to enter the cytoplasm and initiate viral infection. The conserved components of the viral genome produced during replication, known as the pathogen-associated molecular patterns (PAMPs), are thought to be critical factors for the activation of effective innate immunity by triggering dependent signaling pathways after recognition by pattern recognition receptors (PRRs), followed by a cascade of adaptive immunity. Viral infection-induced immune responses establish an antiviral state in the host to effectively inhibit virus replication and enhance viral clearance. However, IAV has evolved multiple mechanisms that allow it to synthesize and transport viral components by "playing games" with the host. At its heart, this review will describe how host and viral factors interact to facilitate the viral evasion of host immune responses.

The ATR inhibitor ceralasertib potentiates cancer checkpoint immunotherapy by regulating the tumor microenvironment

The Ataxia telangiectasia and Rad3-related (ATR) inhibitor ceralasertib in combination with the PD-L1 antibody durvalumab demonstrated encouraging clinical benefit in melanoma and lung cancer patients who progressed on immunotherapy. Here we show that modelling of intermittent ceralasertib treatment in mouse tumor models reveals CD8+ T-cell dependent antitumor activity, which is separate from the effects on tumor cells. Ceralasertib suppresses proliferating CD8+ T-cells on treatment which is rapidly reversed off-treatment. Ceralasertib causes up-regulation of type I interferon (IFNI) pathway in cancer patients and in tumor-bearing mice. IFNI is experimentally found to be a major mediator of antitumor activity of ceralasertib in combination with PD-L1 antibody. Improvement of T-cell function after ceralasertib treatment is linked to changes in myeloid cells in the tumor microenvironment. IFNI also promotes anti-proliferative effects of ceralasertib on tumor cells. Here, we report that broad immunomodulatory changes following intermittent ATR inhibition underpins the clinical therapeutic benefit and indicates its wider impact on antitumor immunity.

TNF-α-induced down-regulation of type I interferon receptor contributes to acquired resistance of cervical squamous cancer to Cisplatin

We aimed to investigate the effects of tumor necrosis factor (TNF)-α on the expression of interferon α/β receptor subunit 1 (IFNAR1) and cervical squamous cancer (CSCC) resistance to Cisplatin, as well as the underlying mechanisms. Kaplan-Meier analysis was used to plot the overall survival curves. SiHa cells were treated with 20 ng/ml TNF-α to determine cell proliferation in human CSCC cells and the expression of IFNAR1. The effects of TNF-α on the downstream signaling pathway, including casein kinase 1α (CK1α), were investigated using the caspase protease inhibitor FK009, the c-Jun kinase inhibitor SP600125, and the nuclear factor kappa-B inhibitor ammonium pyrrolidinedithiocarbamate (PDTC). TNF-α induced down-regulation of IFNAR1 in human CSCC cells and promoted proliferation of SiHa cells. SiHa cells were transfected with the catalytic inactive mutant CK1α K49A, and the ability of TNF-α to induce down-regulation of IFNAR1 expression was found to be significantly diminished in this context. FK009 and PDTC had no obvious effect on the expression of CK1α, however, SP600125 significantly reduced the expression of CK1α in the presence of TNF-α. SiHa cells treated with TNF-α showed reduced sensitivity to Cisplatin and exhibited higher cell viability, while the sensitivity of SiHa cells to Cisplatin was restored after treatment with CK1α inhibitor D4476. Additionally, we constructed a TNF-α overexpressing SiHa cell line and a transplanted tumor model. The results were similar to those of in vitro efficacy. We demonstrate that TNF-α-induced down-regulation of type I interferon receptor contributes to acquired resistance of cervical squamous cancer to Cisplatin.

Roles and functions of IAV proteins in host immune evasion

Influenza A viruses (IAVs) evade the immune system of the host by several regulatory mechanisms. Their genomes consist of eight single-stranded segments, including nonstructural proteins (NS), basic polymerase 1 (PB1), basic polymerase 2 (PB2), hemagglutinin (HA), acidic polymerase (PA), matrix (M), neuraminidase (NA), and nucleoprotein (NP). Some of these proteins are known to suppress host immune responses. In this review, we discuss the roles, functions and underlying strategies adopted by IAV proteins to escape the host immune system by targeting different proteins in the interferon (IFN) signaling pathway, such as tripartite motif containing 25 (TRIM25), inhibitor of nuclear factor κB kinase (IKK), mitochondrial antiviral signaling protein (MAVS), Janus kinase 1 (JAK1), type I interferon receptor (IFNAR1), interferon regulatory factor 3 (IRF3), IRF7, and nuclear factor-κB (NF-κB). To date, the IAV proteins NS1, NS2, PB1, PB1-F2, PB2, HA, and PA have been well studied in terms of their roles in evading the host immune system. However, the detailed mechanisms of NS3, PB1-N40, PA-N155, PA-N182, PA-X, M42, NA, and NP have not been well studied with respect to their roles in immune evasion. Moreover, we also highlight the future perspectives of research on IAV proteins.

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.

IGF2BP family of RNA-binding proteins regulate innate and adaptive immune responses in cancer cells and tumor microenvironment

Insulin-like growth factor 2 mRNA-binding proteins (IGF2BP1, IGF2BP2, and IGF2BP3) are a family of RNA-binding proteins that play an essential role in the development and disease by regulating mRNA stability and translation of critical regulators of cell division and metabolism. Genetic and chemical inhibition of these proteins slows down cancer cell proliferation, decreases invasiveness, and prolongs life span in a variety of animal models. The role of RNA-binding proteins in the induction of tissues' immunogenicity is increasingly recognized, but, the impact of the IGF2BPs family of proteins on the induction of innate and adaptive immune responses in cancer is not fully understood. Here we report that downregulation of IGF2BP1, 2, and 3 expression facilitates the expression of interferon beta-stimulated genes. IGF2BP1 has a greater effect on interferon beta and gamma signaling compared to IGF2BP2 and IGF2BP3 paralogs. We demonstrate that knockdown or knockout of IGF2BP1, 2, and 3 significantly potentiates inhibition of cell growth induced by IFNβ and IFNγ. Mouse melanoma cells with Igf2bp knockouts demonstrate increased expression of MHC I (H-2) and induce intracellular Ifn-γ expression in syngeneic T-lymphocytes in vitro. Increased immunogenicity, associated with Igf2bp1 inhibition, "inflames" mouse melanoma tumors microenvironment in SM1/C57BL/6 and SW1/C3H mouse models measured by a two-fold increase of NK cells and tumor-associated myeloid cells. Finally, we demonstrate that the efficiency of anti-PD1 immunotherapy in the mouse melanoma model is significantly more efficient in tumors that lack Igf2bp1 expression. Our retrospective data analysis of immunotherapies in human melanoma patients indicates that high levels of IGF2BP1 and IGF2BP3 are associated with resistance to immunotherapies and poor prognosis. In summary, our study provides evidence of the role of IGF2BP proteins in regulating tumor immunogenicity and establishes those RBPs as immunotherapeutic targets in cancer.

Molecular and cellular factors determining the functional pleiotropy of cytokines

Cytokines are soluble factors vital for mammalian physiology. Cytokines elicit highly pleiotropic activities, characterized by their ability to induce a wide spectrum of functional responses in a diverse range of cell subsets, which makes their study very challenging. Cytokines activate signalling via receptor dimerization/oligomerization, triggering activation of the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling pathway. Given the strong crosstalk and shared usage of key components of cytokine signalling pathways, a long-standing question in the field pertains to how functional diversity is achieved by cytokines. Here, we discuss how biophysical - for example, ligand-receptor binding affinity and topology - and cellular - for example, receptor, JAK and STAT protein levels, endosomal compartment - parameters contribute to the modulation and diversification of cytokine responses. We review how these parameters ultimately converge into a common mechanism to fine-tune cytokine signalling that involves the control of the number of Tyr residues phosphorylated in the receptor intracellular domain upon cytokine stimulation. This results in different kinetics of STAT activation, and induction of specific gene expression programs, ensuring the generation of functional diversity by cytokines using a limited set of signalling intermediaries. We describe how these first principles of cytokine signalling have been exploited using protein engineering to design cytokine variants with more specific and less toxic responses for immunotherapy.

ADP-Ribosylation in Antiviral Innate Immune Response

Adenosine diphosphate (ADP)-ribosylation is a reversible post-translational modification catalyzed by ADP-ribosyltransferases (ARTs). ARTs transfer one or more ADP-ribose from nicotinamide adenine dinucleotide (NAD⁺) to the target substrate and release the nicotinamide (Nam). Accordingly, it comes in two forms: mono-ADP-ribosylation (MARylation) and poly-ADP-ribosylation (PARylation). ADP-ribosylation plays important roles in many biological processes, such as DNA damage repair, gene regulation, and energy metabolism. Emerging evidence demonstrates that ADP-ribosylation is implicated in host antiviral immune activity. Here, we summarize and discuss ADP-ribosylation modifications that occur on both host and viral proteins and their roles in host antiviral response.

A Comparison of the Immunometabolic Effect of Antibiotics and Plant Extracts in a Chicken Macrophage-like Cell Line during a Salmonella Enteritidis Challenge

Immunometabolic modulation of macrophages can play an important role in the innate immune response of chickens triggered with a multiplicity of insults. In this study, the immunometabolic role of two antibiotics (oxytetracycline and gentamicin) and four plant extracts (thyme essential oil, grape seed extract, garlic oil, and capsicum oleoresin) were investigated on a chicken macrophage-like cell line (HD11) during a Salmonella Enteritidis infection. To study the effect of these substances, kinome peptide array analysis, Seahorse metabolic assay, and gene expression techniques were employed. Oxytetracycline, to which the bacterial strain was resistant, thyme essential oil, and capsicum oleoresin did not show any noteworthy immunometabolic effect. Garlic oil affected glycolysis, but this change was not detected by the kinome analysis. Gentamicin and grape seed extract showed the best immunometabolic profile among treatments, being able to both help the host with the activation of immune response pathways and with maintaining a less inflammatory status from a metabolic point of view.

Mechanisms regulating transitory suppressive activity of neutrophils in newborns: PMNs-MDSCs in newborns

Transitory appearance of immune suppressive polymorphonuclear neutrophils (PMNs) defined as myeloid-derived suppressor cells (PMNs-MDSCs) in newborns is important for their protection from inflammation associated with newly established gut microbiota. Here, we report that inhibition of the type I IFN (IFN1) pathway played a major role in regulation of PMNs-MDSCs-suppressive activity during first weeks of life. Expression of the IFN1 receptor IFNAR1 was markedly lower in PMNs-MDSCs. However, in newborn mice, down-regulation of IFNAR1 was not sufficient to render PMNs immune suppressive. That also required the presence of a positive signal from lactoferrin via its receptor low-density lipoprotein receptor-related protein 2. The latter effect was mediated via NF-κB activation, which was tempered by IFN1 in a manner that involved suppressor of cytokine signaling 3. Thus, we discovered a mechanism of tight regulation of immune suppressive PMNs-MDSCs in newborns, which may be used in the development of therapies of neonatal pathologies.

CK1α upregulates the IFNAR1 expression to prompt the anti-HBV effect of type I IFN in hepatoma carcinoma cells

Casein kinase 1α (CK1α) mediates the phosphorylation and degradation of interferon-α/β receptor 1 (IFNAR1) in response to viral infection. However, how CK1α regulates hepatitis B virus (HBV) replication and the anti-HBV effects of IFN-α are less reported. Here we show that CK1α can interact with IFNAR1 in hepatoma carcinoma cells and increased the abundance of IFNAR1 by reducing the ubiquitination levels in the presence of HBV. Furthermore, CK1α promotes the IFN-α triggered JAK-STAT signaling pathway and consequently enhances the antiviral effects of IFN-α against HBV replication. Our results collectively provide evidence that CK1α positively regulates the anti-HBV activity of IFN-α in hepatoma carcinoma cells, which would be a promising therapeutic target to improve the effectiveness of IFN-α therapy to cure CHB.

Targeting PARP11 to avert immunosuppression and improve CAR T therapy in solid tumors

Evasion of antitumor immunity and resistance to therapies in solid tumors are aided by an immunosuppressive tumor microenvironment (TME). We found that TME factors, such as regulatory T cells and adenosine, downregulated type I interferon receptor IFNAR1 on CD8⁺ cytotoxic T lymphocytes (CTLs). These events relied upon poly-ADP ribose polymerase-11 (PARP11), which was induced in intratumoral CTLs and acted as a key regulator of the immunosuppressive TME. Ablation of PARP11 prevented loss of IFNAR1, increased CTL tumoricidal activity and inhibited tumor growth in an IFNAR1-dependent manner. Accordingly, genetic or pharmacologic inactivation of PARP11 augmented the therapeutic benefits of chimeric antigen receptor T cells. Chimeric antigen receptor CTLs engineered to inactivate PARP11 demonstrated a superior efficacy against solid tumors. These findings highlight the role of PARP11 in the immunosuppressive TME and provide a proof of principle for targeting this pathway to optimize immune therapies.

Role of Hypoxia in the Interferon Response

In solid tumors, as the tumor grows and the disease progresses, hypoxic regions are often generated, but in contrast to most normal cells which cannot survive under these conditions, tumour cells adapt to hypoxia by HIF-driven mechanisms. Hypoxia can further promote cancer development by generating an immunosuppressive environment within the tumour mass, which allows tumour cells to escape the immune system recognition. This is achieved by recruiting immunosuppressive cells and by upregulating molecules which block immune cell activation. Hypoxia can also confer resistance to antitumor therapies by inducing the expression of membrane proteins that increase drug efflux or by inhibiting the apoptosis of treated cells. In addition, tumor cells require an active interferon (IFN) signalling pathway for the success of many anticancer therapies, such as radiotherapy or chemotherapy. Therefore, hypoxic effects on this pathway needs to be addressed for a successful treatment.

Interleukin-17A pretreatment attenuates the anti-hepatitis B virus efficacy of interferon-alpha by reducing activation of the interferon-stimulated gene factor 3 transcriptional complex in hepatitis B virus-expressing HepG2 cells

Background

Some cytokine signaling pathways can interact with interferon (IFN)-α pathway and thus regulate cell responses to IFN-α. Levels of the pro-inflammatory cytokine interleukin-17A (IL-17A) were found to be elevated in both the peripheral blood and liver in chronic hepatitis B (CHB) patients. However, how IL-17A affects the anti-HBV activity of IFN-α remains unclear.

Methods

The effects of IL-17A on anti-HBV activity of IFN-α were evaluated in HBV-expressing HepG2 cells (HepG2-HBV1.3) with IL-17A pretreatment and IFN-α stimulation. Culture supernatant levels of HBsAg, HBeAg, and HBV DNA, or intracellular expression of HBsAg and HBcAg were detected by ELISA, real-time quantitative PCR (RT-qPCR), or western blotting (WB). The expression of canonical IFN-α signaling pathway components, including the interferon-α/β receptor (IFNAR), Janus Kinase 1 (JAK1), Tyrosine Kinase 2 (TYK2), the Interferon Stimulated Gene Factor 3 complex (ISGF3) and IFN-stimulated genes (ISGs), was also examined by RT-qPCR, Immunofluorescence or WB. The effects of IL-17A were further investigated by the suppression of the IL-17A pathway with a TRAF6 inhibitor.

Results

Compared to IFN-α stimulation alone, IL-17A pretreatment followed by IFN-α stimulation increased the levels of HBsAg, HBeAg, and HBV DNA, and decreased the levels of ISGF3 complex (phosphorylated (p)-signal transducer and activator of transcription (STAT1)/p-STAT2/IRF9) and antiviral-related ISGs (ISG15, ISG20 and Mx1). Interestingly, IL-17A pretreatment increased the expression of suppressor of cytokine signaling (SOCS) 1, SOCS3 and USP18, which were also the ISGs negatively regulating activity of ISGF3. Moreover, IFNAR1 protein expression declined more sharply in the group with IL-17A pretreatment than in the group with IFN-α stimulation alone. Blocking the IL-17A pathway reversed the effects of IL-17A on the IFN-α-induced activation of ISGF3 and anti-HBV efficacy.

Conclusions

Our results demonstrate that IL-17A pretreatment could attenuate IFN-α-induced anti-HBV activity by upregulating negative regulators of the critical transcriptional ISGF3 complex. Thus, this might be a potential target for improving response to IFN-α therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01753-x.

UBX Domain Protein 6 Positively Regulates JAK-STAT1/2 Signaling

Type I/III IFNs induce expression of hundreds of IFN-stimulated genes through the JAK/STAT pathway to combat viral infections. Although JAK/STAT signaling is seemingly straightforward, it is nevertheless subjected to complex cellular regulation. In this study, we show that an ubiquitination regulatory X (UBX) domain-containing protein, UBXN6, positively regulates JAK-STAT1/2 signaling. Overexpression of UBXN6 enhanced type I/III IFNs-induced expression of IFN-stimulated genes, whereas deletion of UBXN6 inhibited their expression. RNA viral replication was increased in human UBXN6-deficient cells, accompanied by a reduction in both type I/III IFN expression, when compared with UBXN6-sufficient cells. Mechanistically, UBXN6 interacted with tyrosine kinase 2 (TYK2) and inhibited IFN-β-induced degradation of both TYK2 and type I IFNR. These results suggest that UBXN6 maintains normal JAK-STAT1/2 signaling by stabilizing key signaling components during viral infection.

Negative Regulation of the Innate Immune Response through Proteasomal Degradation and Deubiquitination

The rapid and dynamic activation of the innate immune system is achieved through complex signaling networks regulated by post-translational modifications modulating the subcellular localization, activity, and abundance of signaling molecules. Many constitutively expressed signaling molecules are present in the cell in inactive forms, and become functionally activated once they are modified with ubiquitin, and, in turn, inactivated by removal of the same post-translational mark. Moreover, upon infection resolution a rapid remodeling of the proteome needs to occur, ensuring the removal of induced response proteins to prevent hyperactivation. This review discusses the current knowledge on the negative regulation of innate immune signaling pathways by deubiquitinating enzymes, and through degradative ubiquitination. It focusses on spatiotemporal regulation of deubiquitinase and E3 ligase activities, mechanisms for re-establishing proteostasis, and degradation through immune-specific feedback mechanisms vs. general protein quality control pathways.

Immune suppressive activity of myeloid-derived suppressor cells in cancer requires inactivation of the type I interferon pathway

Myeloid-derived suppressor cells (MDSC) are pathologically activated neutrophils and monocytes with potent immune suppressive activity. These cells play an important role in accelerating tumor progression and undermining the efficacy of anti-cancer therapies. The natural mechanisms limiting MDSC activity are not well understood. Here, we present evidence that type I interferons (IFN1) receptor signaling serves as a universal mechanism that restricts acquisition of suppressive activity by these cells. Downregulation of the IFNAR1 chain of this receptor is found in MDSC from cancer patients and mouse tumor models. The decrease in IFNAR1 depends on the activation of the p38 protein kinase and is required for activation of the immune suppressive phenotype. Whereas deletion of IFNAR1 is not sufficient to convert neutrophils and monocytes to MDSC, genetic stabilization of IFNAR1 in tumor bearing mice undermines suppressive activity of MDSC and has potent antitumor effect. Stabilizing IFNAR1 using inhibitor of p38 combined with the interferon induction therapy elicits a robust anti-tumor effect. Thus, negative regulatory mechanisms of MDSC function can be exploited therapeutically.

Interferon Receptor Trafficking and Signaling: Journey to the Cross Roads

Like most plasma membrane proteins, type I interferon (IFN) receptor (IFNAR) traffics from the outer surface to the inner compartments of the cell. Long considered as a passive means to simply control subunits availability at the plasma membrane, an array of new evidence establishes IFNAR endocytosis as an active contributor to the regulation of signal transduction triggered by IFN binding to IFNAR. During its complex journey initiated at the plasma membrane, the internalized IFNAR complex, i.e. IFNAR1 and IFNAR2 subunits, will experience post-translational modifications and recruit specific effectors. These finely tuned interactions will determine not only IFNAR subunits destiny (lysosomal degradation vs. plasma membrane recycling) but also the control of IFN-induced signal transduction. Finally, the IFNAR system perfectly illustrates the paradigm of the crosstalk between membrane trafficking and intracellular signaling. Investigating the complexity of IFN receptor intracellular routes is therefore necessary to reveal new insight into the role of IFNAR membrane dynamics in type I IFNs signaling selectivity and biological activity.

BRCA1-A and BRISC: Multifunctional Molecular Machines for Ubiquitin Signaling

The K63-linkage specific deubiquitinase BRCC36 forms the core of two multi-subunit deubiquitination complexes: BRCA1-A and BRISC. BRCA1-A is recruited to DNA repair foci, edits ubiquitin signals on chromatin, and sequesters BRCA1 away from the site of damage, suppressing homologous recombination by limiting resection. BRISC forms a complex with metabolic enzyme SHMT2 and regulates the immune response, mitosis, and hematopoiesis. Almost two decades of research have revealed how BRCA1-A and BRISC use the same core of subunits to perform very distinct biological tasks.

Stat2 stability regulation: an intersection between immunity and carcinogenesis

Signal transducer and activator of transcription (STAT2) is a member of the STAT family that plays an essential role in immune responses to extracellular and intracellular stimuli, including inflammatory reactions, invasion of foreign materials, and cancer initiation. Although the majority of STAT2 studies in the last few decades have focused on interferon (IFN)-α/β (IFNα/β) signaling pathway-mediated host defense against viral infections, recent studies have revealed that STAT2 also plays an important role in human cancer development. Notably, strategic research on STAT2 function has provided evidence that transient regulatory activity by homo- or heterodimerization induces its nuclear localization where it to forms a ternary IFN-stimulated gene factor 3 (ISGF3) complex, which is composed of STAT1 and/or STAT2 and IFN regulatory factor 9 (IEF9). The molecular mechanisms of ISGF3-mediated ISG gene expression provide the basic foundation for the regulation of STAT2 protein activity but not protein quality control. Recently, previously unknown molecular mechanisms of STAT2-mediated cell proliferation via STAT2 protein quality control were elucidated. In this review, we briefly summarize the role of STAT2 in immune responses and carcinogenesis with respect to the molecular mechanisms of STAT2 stability regulation via the proteasomal degradation pathway.

The activity of STAT2, a protein stimulated by molecular signalling systems to activate selected genes in ways that can lead to cancer, is regulated by factors controlling its rate of degradation. Yong-Yeon Cho and colleagues at The Catholic University of Korea in South Korea review the role of STAT2 in links between molecular signals of the immune response and the onset of cancer. They focus on the significance of factors that regulate the stability of STAT2. One key factor appears to be the molecular mechanisms controlling the degradation of STAT2 by cellular structures called proteasomes. These structures break down proteins as part of routine cell maintenance. Deeper understanding of the stimulation, action and degradation of STAT2 will assist efforts to treat the many cancers in which STAT2 activity is involved.

PARP1 Enhances Influenza A Virus Propagation by Facilitating Degradation of Host Type I Interferon Receptor

Influenza A virus (IAV) utilizes multiple strategies to confront or evade host type I interferon (IFN)-mediated antiviral responses in order to enhance its own propagation within the host. One such strategy is to induce the degradation of type I IFN receptor 1 (IFNAR1) by utilizing viral hemagglutinin (HA). However, the molecular mechanism behind this process is poorly understood. Here, we report that a cellular protein, poly(ADP-ribose) polymerase 1 (PARP1), plays a critical role in mediating IAV HA-induced degradation of IFNAR1. We identified PARP1 as an interacting partner for IAV HA through mass spectrometry analysis. This interaction was confirmed by coimmunoprecipitation analyses. Furthermore, confocal fluorescence microscopy showed altered localization of endogenous PARP1 upon transient IAV HA expression or during IAV infection. Knockdown or inhibition of PARP1 rescued IFNAR1 levels upon IAV infection or HA expression, exemplifying the importance of PARP1 for IAV-induced reduction of IFNAR1. Notably, PARP1 was crucial for the robust replication of IAV, which was associated with regulation of the type I IFN receptor signaling pathway. These results indicate that PARP1 promotes IAV replication by controlling viral HA-induced degradation of host type I IFN receptor. Altogether, these findings provide novel insight into interactions between influenza virus and the host innate immune response and reveal a new function for PARP1 during influenza virus infection.IMPORTANCE Influenza A virus (IAV) infections cause seasonal and pandemic influenza outbreaks, which pose a devastating global health concern. Despite the availability of antivirals against influenza, new IAV strains continue to persist by overcoming the therapeutics. Therefore, much emphasis in the field is placed on identifying new therapeutic targets that can more effectively control influenza. IAV utilizes several tactics to evade host innate immunity, which include the evasion of antiviral type I interferon (IFN) responses. Degradation of type I IFN receptor (IFNAR) is one known method of subversion, but the molecular mechanism for IFNAR downregulation during IAV infection remains unclear. Here, we have found that a host protein, poly(ADP-ribose) polymerase 1 (PARP1), facilitates IFNAR degradation and accelerates IAV replication. The findings reveal a novel cellular target for the potential development of antivirals against influenza, as well as expand our base of knowledge regarding interactions between influenza and the host innate immunity.

Age-Dependent Effects of Type I and Type III IFNs in the Pathogenesis of Bordetella pertussis Infection and Disease

Type I and III IFNs play diverse roles in bacterial infections, being protective for some but deleterious for others. Using RNA-sequencing transcriptomics we investigated lung gene expression responses to Bordetella pertussis infection in adult mice, revealing that type I and III IFN pathways may play an important role in promoting inflammatory responses. In B. pertussis-infected mice, lung type I/III IFN responses correlated with increased proinflammatory cytokine expression and with lung inflammatory pathology. In mutant mice with increased type I IFN receptor (IFNAR) signaling, B. pertussis infection exacerbated lung inflammatory pathology, whereas knockout mice with defects in type I IFN signaling had lower levels of lung inflammation than wild-type mice. Curiously, B. pertussis-infected IFNAR1 knockout mice had wild-type levels of lung inflammatory pathology. However, in response to infection these mice had increased levels of type III IFN expression, neutralization of which reduced lung inflammation. In support of this finding, B. pertussis-infected mice with a knockout mutation in the type III IFN receptor (IFNLR1) and double IFNAR1/IFNLR1 knockout mutant mice had reduced lung inflammatory pathology compared with that in wild-type mice, indicating that type III IFN exacerbates lung inflammation. In marked contrast, infant mice did not upregulate type I or III IFNs in response to B. pertussis infection and were protected from lethal infection by increased type I IFN signaling. These results indicate age-dependent effects of type I/III IFN signaling during B. pertussis infection and suggest that these pathways represent targets for therapeutic intervention in pertussis.

Quantitative Proteome Analysis of Atg5-Deficient Mouse Embryonic Fibroblasts Reveals the Range of the Autophagy-Modulated Basal Cellular Proteome

Autophagy performs housekeeping functions for cells and maintains a functional mode by degrading damaged proteins and organelles and providing energy under starvation conditions. The process is tightly regulated by the evolutionarily conserved Atg genes, of which Atg5 is one such crucial mediator. Here, we have done a comprehensive quantitative proteome analysis of mouse embryonic fibroblasts that lack a functional autophagy pathway (Atg5 knockout). We observe that 14% of the identified cellular proteome is remodeled, and several proteins distributed across diverse cellular processes with functions in signaling, cell adhesion, development, and immunity show either higher or lower levels under autophagy-deficient conditions. These cells have lower levels of crucial immune proteins that are required to mount a protective inflammatory response. This study will serve as a valuable resource to determine the role of autophagy in modulating specific protein levels in cells.

Basal autophagy is crucial for maintenance of cellular homeostasis. ATG5 is an essential protein for autophagosome formation, and its depletion has been extensively used as a tool to disrupt autophagy. Here, we characterize the impact of Atg5 deficiency on the cellular proteome of mouse embryonic fibroblasts (MEFs). Using a tandem mass tagging (TMT)-based quantitative proteomics analysis, we observe that 14% of identified proteins show dysregulated levels in atg5^−/− MEFs. These proteins were distributed across diverse biological processes, such as cell adhesion, development, differentiation, transport, metabolism, and immune responses. Several of the upregulated proteins were receptors involved in transforming growth factor β (TGF-β) signaling, JAK-STAT signaling, junction adhesion, and interferon/cytokine-receptor interactions and were validated as autophagy substrates. Nearly equal numbers of proteins, including several lysosomal proteins and enzymes, were downregulated, suggesting a complex role of autophagy/ATG5 in regulating their levels. The atg5^−/− MEFs had lower levels of key immune sensors and effectors, including Toll-like receptor 2 (TLR2), interferon regulatory factor 3 (IRF3), IRF7, MLKL, and STAT1/3/5/6, which were restored by reexpression of ATG5. While these cells could efficiently mount a type I interferon response to the double-stranded RNA (dsRNA) mimic poly(I·C), they were compromised in their inflammatory response to the bacterial pathogen-associated molecular patterns (PAMPs) lipopolysaccharide (LPS) and Pam3CSK4. Transcriptional activation and secretion of interleukin-6 (IL-6) in these cells could be recovered by ATG5 expression, supporting the role of autophagy in the TLR2-induced inflammatory response. This study provides a key resource for understanding the effect of autophagy/ATG5 deficiency on the fibroblast proteome.

IMPORTANCE Autophagy performs housekeeping functions for cells and maintains a functional mode by degrading damaged proteins and organelles and providing energy under starvation conditions. The process is tightly regulated by the evolutionarily conserved Atg genes, of which Atg5 is one such crucial mediator. Here, we have done a comprehensive quantitative proteome analysis of mouse embryonic fibroblasts that lack a functional autophagy pathway (Atg5 knockout). We observe that 14% of the identified cellular proteome is remodeled, and several proteins distributed across diverse cellular processes with functions in signaling, cell adhesion, development, and immunity show either higher or lower levels under autophagy-deficient conditions. These cells have lower levels of crucial immune proteins that are required to mount a protective inflammatory response. This study will serve as a valuable resource to determine the role of autophagy in modulating specific protein levels in cells.

Author Video: An author video summary of this article is available.

The PKR-Like Endoplasmic Reticulum Kinase Promotes the Dissemination of Myc-Induced Leukemic Cells

Hyperactive oncogenic Myc stimulates protein synthesis that induces the unfolded protein response, which requires the function of the eukaryotic translation initiation factor 2-alpha kinase 3, also known as protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK). Activated PERK acts to limit mRNA translation, enable proper protein folding, and restore the homeostasis in the endoplasmic reticulum. Given that Myc activation contributes to many types of lymphoid and myeloid human leukemias, we used a mouse model to examine the importance of PERK in development and progression of Myc-induced leukemias. We found that genetic ablation of Perk does not suppress the generation of the leukemic cells in the bone marrow. However, the cell-autonomous Perk deficiency restricts the dissemination of leukemic cells into peripheral blood, lymph nodes, and vital peripheral organs. Whereas the loss of the IFNAR1 chain of type I IFN receptor stimulated leukemia, Perk ablation did not stabilize IFNAR1, suggesting that PERK stimulates the leukemic cells' dissemination in an IFNAR1-independent manner. We discuss the rationale for using PERK inhibitors against Myc-driven leukemias. IMPLICATIONS: The role of PERK in dissemination of Myc-induced leukemic cells demonstrated in this study argues for the use of PERK inhibitors against leukemia progression.

Viral dedication to vigorous destruction of interferon receptors

Interferons (IFNs) exhibit forceful inhibitory activities against numerous viruses by inducing synthesis of anti-viral proteins or promoting immune cell functions, which help eradicate the vicious microbes. Consequently, the degree to which viruses evade or counterattack IFN responses influences viral pathogenicity. Viruses have developed many strategies to interfere with the synthesis of IFNs or IFN receptor signaling pathway. Furthermore, multiple viruses decrease levels of IFN receptors via diverse tactics, which include decreasing type I IFN receptor mRNA expression, blocking post-translational modification of the receptor, and degrading IFN receptors. Recently, influenza virus was found to induce CK1α-induced phosphorylation and subsequent degradation of the receptor for type I and II IFNs. In this review, viral mechanisms that remove IFN receptors are summarized with an emphasis on the mechanisms for virus-induced degradation of IFN receptors.

Ten Strategies of Interferon Evasion by Viruses

Viruses infecting vertebrate hosts must overcome the interferon (IFN)-mediated antiviral response to replicate and propagate to new hosts. The complex regulation of the IFN response allows viruses to antagonize IFN at multiple levels. However, no single strategy appears to be the golden ticket, and viruses have adopted multiple means to dampen this host defense. This Review does not exhaustively cover all mechanisms of viral IFN antagonism. Rather it examines the ten most common strategies that viruses use to subvert the IFN response with examples from publications appearing in the last 10 years of Cell Host & Microbe. The virus-host interactions involved in induction and evasion of IFN represent a fertile area of research due to the significant large number of host and viral products that regulate this response, resulting in an intricate dance between hosts and their pathogens to achieve an optimal balance between virus replication, host disease, and survival.

Casein Kinase 1α Mediates the Degradation of Receptors for Type I and Type II Interferons Caused by Hemagglutinin of Influenza A Virus

Although influenza A virus (IAV) evades cellular defense systems to effectively propagate in the host, the viral immune-evasive mechanisms are incompletely understood. Our recent data showed that hemagglutinin (HA) of IAV induces degradation of type I IFN receptor 1 (IFNAR1). Here, we demonstrate that IAV HA induces degradation of type II IFN (IFN-γ) receptor 1 (IFNGR1), as well as IFNAR1, via casein kinase 1α (CK1α), resulting in the impairment of cellular responsiveness to both type I and II IFNs. IAV infection or transient HA expression induced degradation of both IFNGR1 and IFNAR1, whereas HA gene-deficient IAV failed to downregulate the receptors. IAV HA caused the phosphorylation and ubiquitination of IFNGR1, leading to the lysosome-dependent degradation of IFNGR1. Influenza viral HA strongly decreased cellular sensitivity to type II IFNs, as it suppressed the activation of STAT1 and the induction of IFN-γ-stimulated genes in response to exogenously supplied recombinant IFN-γ. Importantly, CK1α, but not p38 MAP kinase or protein kinase D2, was proven to be critical for HA-induced degradation of both IFNGR1 and IFNAR1. Pharmacologic inhibition of CK1α or small interfering RNA (siRNA)-based knockdown of CK1α repressed the degradation processes of both IFNGR1 and IFNAR1 triggered by IAV infection. Further, CK1α was shown to be pivotal for proficient replication of IAV. Collectively, the results suggest that IAV HA induces degradation of IFN receptors via CK1α, creating conditions favorable for viral propagation. Therefore, the study uncovers a new immune-evasive pathway of influenza virus.IMPORTANCE Influenza A virus (IAV) remains a grave threat to humans, causing seasonal and pandemic influenza. Upon infection, innate and adaptive immunity, such as the interferon (IFN) response, is induced to protect hosts against IAV infection. However, IAV seems to be equipped with tactics to evade the IFN-mediated antiviral responses, although the detailed mechanisms need to be elucidated. In the present study, we show that IAV HA induces the degradation of the type II IFN receptor IFNGR1 and thereby substantially attenuates cellular responses to IFN-γ. Of note, a cellular kinase, casein kinase 1α (CK1α), is crucial for IAV HA-induced degradation of both IFNGR1 and IFNAR1. Accordingly, CK1α is proven to positively regulate IAV propagation. Thus, this study unveils a novel strategy employed by IAV to evade IFN-mediated antiviral activities. These findings may provide new insights into the interplay between IAV and host immunity to impact influenza virus pathogenicity.

Understanding the Unfolded Protein Response in the Pathogenesis of Asthma

Asthma is a heterogeneous, chronic inflammatory disease of the airways. It is a complex disease with different clinical phenotypes and results in a substantial socioeconomic burden globally. Poor understanding of pathogenic mechanisms of the disease hinders the investigation into novel therapeutics. Emerging evidence of the unfolded protein response (UPR) in the endoplasmic reticulum (ER) has demonstrated previously unknown functions of this response in asthma development. A worsening of asthmatic condition can be brought on by stimuli such as oxidative stress, pathogenic infections, and allergen exposure. All of which can induce ER stress and activate UPR leading to activation of different inflammatory responses and dysregulate the innate immune functions in the airways. The UPR as a central regulator of asthma pathogenesis may explain several unknown mechanism of the disease onset, which leads us in new directions for future asthma treatments. In this review, we summarize and discuss the causes and impact of ER–UPR in driving the pathogenesis of asthma and highlight its importance in clinical implications.

Post-translational modification of the interferon-gamma receptor alters its stability and signaling

The IFN gamma receptor 1 (IFNGR1) binds IFN-γ and activates gene transcription pathways crucial for controlling bacterial and viral infections. Although decreases in IFNGR1 surface levels have been demonstrated to inhibit IFN-γ signaling, little is known regarding the molecular mechanisms controlling receptor stability. Here, we show in epithelial and monocytic cell lines that IFNGR1 displays K48 polyubiquitination, is proteasomally degraded, and harbors three ubiquitin acceptor sites at K277, K279, and K285. Inhibition of glycogen synthase kinase 3 beta (GSK3β) destabilized IFNGR1 while overexpression of GSK3β increased receptor stability. We identified critical serine and threonine residues juxtaposed to ubiquitin acceptor sites that impacted IFNGR1 stability. In CRISPR-Cas9 IFNGR1 generated knockout cell lines, cellular expression of IFNGR1 plasmids encoding ubiquitin acceptor site mutations demonstrated significantly impaired STAT1 phosphorylation and decreased STAT1-dependent gene induction. Thus, IFNGR1 undergoes rapid site-specific polyubiquitination, a process modulated by GSK3β. Ubiquitination appears to be necessary for efficient IFNGR1-dependent gamma gene induction and represents a relatively uncharacterized regulatory mechanism for this receptor.

The down-regulation of casein kinase 1 alpha as a host defense response against infectious bursal disease virus infection

Infectious bursal disease virus (IBDV) is an important immunosuppressive virus of chickens. Although the gene functions of IBDV have been well characterized, the host responses during IBDV infection remain much poor. In the present study, casein kinase 1 alpha (CK1α), a novel VP2-associated protein, was down-regulated during IBDV replication in DF1 cells. Further experiments showed that siRNA-mediated knockdown of CK1α inhibited IBDV replication, while overexpression of CK1α promoted IBDV growth. Finally, we revealed that the effects of CK1α expression level on IBDV replication were involved in the negative regulation of CK1α on type I interferon receptor (IFNAR1), because ubiquitination assay analyses demonstrated that CK1α could promote the ubiquitination of IFNAR1, thereby affecting the stability of this receptor. In conclusion, down-regulation of CK1α during IBDV infection as a host defense response increased abundance of IFNAR1, which in turn enhanced an inhibitory effect on IBDV replication.

Downregulation of the IFNAR1 chain of type 1 interferon receptor contributes to the maintenance of the haematopoietic stem cells

Recent studies demonstrated that prolonged exposure of haematopoietic stem cells (HSCs) to type I interferons (IFN) stimulates HSCs entrance into cell cycle, continuous proliferation and eventual exhaustion, which could be prevented by ablation of the Ifnar1 chain of IFN receptor. Given that levels IFNAR1 expression can be robustly affected by IFN-independent ubiquitination and downregulation of IFNAR1 in response to activation of protein kinases such as protein kinase R-like endoplasmic reticulum kinase (PERK) and casein kinase 1α (CK1α), we aimed to determine the role of IFNAR1 downregulation in the maintenance of HSCs. Mice harboring the ubiquitination-deficient Ifnar1^S526A allele displayed greater levels of haematopoietic cell progenitors but reduced numbers of the long-term HSCs compared with wild type mice and animals lacking Ifnar1. Studies using competitive bone marrow repopulation assays showed that CK1α (but not PERK) is essential for the long-term HSCs function. Concurrent ablation of Ifnar1 led to a modest attenuation of the CK1α-null phenotype indicating that, although other CK1α targets are likely to be important, IFNAR1 downregulation can contribute to the maintenance of the HSCs function.

Ubiquitin C-terminal hydrolase-L3 promotes interferon antiviral activity by stabilizing type I-interferon receptor

Type-I interferons (IFN-I) are important antiviral drugs which are widely used in clinical therapy of diverse viral infections. However, understanding the detailed mechanisms for IFN-I antiviral signaling remains a major challenge, and may provide novel targets for IFN-based antiviral therapy. So far, the roles of deubiquitinases (DUBs) in regulating IFN-I antiviral activity are still largely unexplored. Here, we find that Ubiquitin C-terminal hydrolase-L3 (UCHL3) plays an important role in regulating type I-interferon (IFN-I) mediated antiviral response. Interestingly, we find that UCHL3 regulates COPS5-dependent deneddylation of Cullin1, which is an essential component of SCF^β-TrCP complex and associated with SCF^β-TrCP activities. Furthermore, we reveal that UCHL3 physically interacts with COPS5, and determines the level and protein stability of cellular COPS5 by deubiquitinating COPS5. We further demonstrate that UCHL3 upregulates the levels of SCF^β-TrCP substrates including IFN-I receptor IFNAR1, which enhances IFN-I mediated signaling pathway and antiviral activity. These findings identify COPS5 as a novel in vivo substrate of UCHL3, and uncover the deubiquitination-deneddylation mediated regulation for IFN-I signaling and antiviral function, which may provide a novel strategy for improving IFN-based antiviral therapy.

A Potent In Vivo Antitumor Efficacy of Novel Recombinant Type I Interferon

Purpose: Antiproliferative, antiviral, and immunomodulatory activities of endogenous type I IFNs (IFN1) prompt the design of recombinant IFN1 for therapeutic purposes. However, most of the designed IFNs exhibited suboptimal therapeutic efficacies against solid tumors. Here, we report evaluation of the in vitro and in vivo antitumorigenic activities of a novel recombinant IFN termed sIFN-I.Experimental Design: We compared primary and tertiary structures of sIFN-I with its parental human IFNα-2b, as well as affinities of these ligands for IFN1 receptor chains and pharmacokinetics. These IFN1 species were also compared for their ability to induce JAK-STAT signaling and expression of the IFN1-stimulated genes and to elicit antitumorigenic effects. Effects of sIFN-I on tumor angiogenesis and immune infiltration were also tested in transplanted and genetically engineered immunocompetent mouse models.Results: sIFN-I displayed greater affinity for IFNAR1 (over IFNAR2) chain of the IFN1 receptor and elicited a greater extent of IFN1 signaling and expression of IFN-inducible genes in human cells. Unlike IFNα-2b, sIFN-I induced JAK-STAT signaling in mouse cells and exhibited an extended half-life in mice. Treatment with sIFN-I inhibited intratumoral angiogenesis, increased CD8+ T-cell infiltration, and robustly suppressed growth of transplantable and genetically engineered tumors in immunodeficient and immunocompetent mice.Conclusions: These findings define sIFN-I as a novel recombinant IFN1 with potent preclinical antitumorigenic effects against solid tumor, thereby prompting the assessment of sIFN-I clinical efficacy in humans. Clin Cancer Res; 23(8); 2038-49. ©2016 AACR.

Mutation of a putative MAP kinase consensus site regulates NCAM endocytosis and NCAM-dependent neurite outgrowth

The cytoplasmic domain of the neural cell adhesion molecule NCAM contains several putative serine/threonine phosphorylation sites whose functions are largely unknown. Human NCAM140 (NCAM140) possesses a potential MAP kinase phosphorylation site at threonine (T) 803. The aim of this study was to analyze a possible phosphorylation of NCAM140 by MAP kinases and to identify the functional role of T803. We found that NCAM140 is phosphorylated by the MAP kinase ERK2 in vitro. Exchange of T803 to aspartic acid (D) which mimics constitutive phosphorylation at the respective position resulted in increased endocytosis compared to NCAM140 in neuroblastoma cells and primary neurons. Consistently, NCAM140 endocytosis was inhibited by the MEK inhibitor U0126 in contrast to NCAM140-T803D or NCAM140-T803A endocytosis supporting a role of a potential ERK2 mediated phosphorylation at this site in endocytosis. Furthermore, cells expressing NCAM140-T803D developed significantly shorter neurites than NCAM140 expressing cells indicating that a potential phosphorylation of NCAM by ERK2 also regulates NCAM-dependent neurite outgrowth.

Transcriptional Regulation of Antiviral Interferon-Stimulated Genes

Interferon-stimulated genes (ISGs) are a group of gene products that coordinately combat pathogen invasions, in particular viral infections. Transcription of ISGs occurs rapidly upon pathogen invasion, and this is classically provoked via activation of the Janus kinase/signal transducer and activator of transcription (JAK–STAT) pathway, mainly by interferons (IFNs). However, a plethora of recent studies have reported a variety of non-canonical mechanisms regulating ISG transcription. These new studies are extremely important for understanding the quantitative and temporal differences in ISG transcription under specific circumstances. Because these canonical and non-canonical regulatory mechanisms are essential for defining the nature of host defense and associated detrimental proinflammatory effects, we comprehensively review the state of this rapidly evolving field and the clinical implications of recently acquired knowledge in this respect.

Transcriptional regulation of ISGs defines the state of host anti-pathogen defense.

In light of the recently identified regulatory elements and mechanisms of the IFN–JAK–STAT pathway, new insights have been gained into this classical cascade in regulating ISG transcription.

A variety of non-canonical mechanisms have been recently revealed that coordinately regulate ISG transcription.

With regards to the adverse effects of IFNs in clinic, ISG-based antiviral strategy could be the next promising frontier in drug discovery.

Activation of the JAK-STAT Signaling Pathway after In Vitro Stimulation with IFNß in Multiple Sclerosis Patients According to the Therapeutic Response to IFNß

Interferon beta (IFNß) is a common treatment used for multiple sclerosis (MS) which acts through the activation of the JAK-STAT pathway. However, this therapy is not always effective and currently there are no reliable biomarkers to predict therapeutic response. We postulate that the heterogeneity in the response to IFNß therapy could be related to differential activation patterns of the JAK-STAT signaling pathway. Our aim was to evaluate the basal levels and the short term activation of this pathway after IFNß stimulation in untreated and IFNß treated patients, as well as according to therapeutic response. Therefore, cell surface levels of IFNAR subunits (IFNAR1 and IFNAR2) and the activated forms of STAT1 and STAT2 were assessed in peripheral blood mononuclear cells from MS patients by flow cytometry. Basal levels of each of the markers strongly correlated with the expression of the others in untreated patients, but many of these correlations lost significance in treated patients and after short term activation with IFNß. Patients who had undergone IFNß treatment showed higher basal levels of IFNAR1 and pSTAT1, but a reduced response to in vitro exposure to IFNß. Conversely, untreated patients, with lower basal levels, showed a greater ability of short term activation of this pathway. Monocytes from responder patients had lower IFNAR1 levels (p = 0.039) and higher IFNAR2 levels (p = 0.035) than non-responders just after IFNß stimulation. A cluster analysis showed that levels of IFNAR1, IFNAR2 and pSTAT1-2 in monocytes grouped 13 out of 19 responder patients with a similar expression pattern, showing an association of this pattern with the phenotype of good response to IFNß (p = 0.013). Our findings suggest that an activation pattern of the IFNß signaling pathway in monocytes could be associated with a clinical phenotype of good response to IFNß treatment and that a differential modulation of the IFNAR subunits in monocytes could be related with treatment effectiveness.

Spatiotemporal control of interferon-induced JAK/STAT signalling and gene transcription by the retromer complex

Type-I interferons (IFNs) play a key role in the immune defences against viral and bacterial infections, and in cancer immunosurveillance. We have established that clathrin-dependent endocytosis of the type-I interferon (IFN-α/β) receptor (IFNAR) is required for JAK/STAT signalling. Here we show that the internalized IFNAR1 and IFNAR2 subunits of the IFNAR complex are differentially sorted by the retromer at the early endosome. Binding of the retromer VPS35 subunit to IFNAR2 results in IFNAR2 recycling to the plasma membrane, whereas IFNAR1 is sorted to the lysosome for degradation. Depletion of VPS35 leads to abnormally prolonged residency and association of the IFNAR subunits at the early endosome, resulting in increased activation of STAT1- and IFN-dependent gene transcription. These experimental data establish the retromer complex as a key spatiotemporal regulator of IFNAR endosomal sorting and a new factor in type-I IFN-induced JAK/STAT signalling and gene transcription.

Emodin potentiates the antiproliferative effect of interferon α/β by activation of JAK/STAT pathway signaling through inhibition of the 26S proteasome

The 26S proteasome is a negative regulator of type I interferon (IFN-α/β) signaling. Inhibition of the 26S proteasome by small molecules may be a new strategy to enhance the efficacy of type I IFNs and reduce their side effects. Using cell-based screening assay for new 26S proteasome inhibitors, we found that emodin, a natural anthraquinone, was a potent inhibitor of the human 26S proteasome. Emodin preferably inhibited the caspase-like and chymotrypsin-like activities of the human 26S proteasome and increased the ubiquitination of endogenous proteins in cells. Computational modeling showed that emodin exhibited an orientation/conformation favorable to nucleophilic attack in the active pocket of the β1, β2, and β5 subunits of the 26S proteasome. Emodin increased phosphorylation of STAT1, decreased phosphorylation of STAT3 and increased endogenous gene expression stimulated by IFN-α. Emodin inhibited IFN-α-stimulated ubiquitination and degradation of type I interferon receptor 1 (IFNAR1). Emodin also sensitized the antiproliferative effect of IFN-α in HeLa cervical carcinoma cells and reduced tumor growth in Huh7 hepatocellular carcinoma-bearing mice. These results suggest that emodin potentiates the antiproliferative effect of IFN-α by activation of JAK/STAT pathway signaling through inhibition of 26S proteasome-stimulated IFNAR1 degradation. Therefore, emodin warrants further investigation as a new means to enhance the efficacy of IFN-α/β.

Therapeutic Elimination of the Type 1 Interferon Receptor for Treating Psoriatic Skin Inflammation

Phototherapy with UV light is a standard treatment for psoriasis, yet the mechanisms underlying the therapeutic effects are not well understood. Studies in human and mouse keratinocytes and in the skin tissues from human patients and mice showed that UV treatment triggers ubiquitination and downregulation of the type I IFN receptor chain IFNAR1, leading to suppression of IFN signaling and an ensuing decrease in the expression of inflammatory cytokines and chemokines. The severity of imiquimod-induced psoriasiform inflammation was greatly exacerbated in skin of mice deficient in IFNAR1 ubiquitination (Ifnar1(SA)). Furthermore, these mice did not benefit from UV phototherapy. Pharmacologic induction of IFNAR1 ubiquitination and degradation by an antiprotozoal agent halofuginone also relieved psoriasiform inflammation in wild-type but not in Ifnar1(SA) mice. These data identify downregulation of IFNAR1 by UV as a major mechanism of the UV therapeutic effects against the psoriatic inflammation and provide a proof of principle for future development of agents capable of inducing IFNAR1 ubiquitination and downregulation for the treatment of psoriasis.

Rotavirus Strategies Against the Innate Antiviral System

"Rotaviruses represent the most important etiological agents of acute, severe gastroenteritis in the young of many animal species, including humans." This statement, variations of which are a common beginning in articles about rotaviruses, reflects the fact that these viruses have evolved efficient strategies for evading the innate immune response of the host and for successfully replicating in the population. In this review, we summarize what is known about the defense mechanisms that host cells employ to prevent rotavirus invasion and the countermeasures that these viruses have successfully developed to surpass cellular defenses. Rotaviruses use at least two viral multifunctional proteins to directly interact with, and prevent the activation of, the interferon system, and they use at least one other protein to halt the protein synthesis machinery and prevent the expression of most of the transcriptional antiviral program of the cell. Characterization of the confrontation between rotaviruses and their host cells has allowed us to learn about the virus-host coevolution that prevents the damaging effects of the innate immune response.

Deubiquitinase USP2a Sustains Interferons Antiviral Activity by Restricting Ubiquitination of Activated STAT1 in the Nucleus

STAT1 is a critical transcription factor for regulating host antiviral defenses. STAT1 activation is largely dependent on phosphorylation at tyrosine 701 site of STAT1 (pY701-STAT1). Understanding how pY701-STAT1 is regulated by intracellular signaling remains a major challenge. Here we find that pY701-STAT1 is the major form of ubiquitinated-STAT1 induced by interferons (IFNs). While total STAT1 remains relatively stable during the early stages of IFNs signaling, pY701-STAT1 can be rapidly downregulated by the ubiquitin-proteasome system. Moreover, ubiquitinated pY701-STAT1 is located predominantly in the nucleus, and inhibiting nuclear import of pY701-STAT1 significantly blocks ubiquitination and downregulation of pY701-STAT1. Furthermore, we reveal that the deubiquitinase USP2a translocates into the nucleus and binds to pY701-STAT1, and inhibits K48-linked ubiquitination and degradation of pY701-STAT1. Importantly, USP2a sustains IFNs-induced pY701-STAT1 levels, and enhances all three classes of IFNs- mediated signaling and antiviral activity. To our knowledge, this is the first identified deubiquitinase that targets activated pY701-STAT1. These findings uncover a positive mechanism by which IFNs execute efficient antiviral signaling and function, and may provide potential targets for improving IFNs-based antiviral therapy.

Phosphorylated STAT1 at tyrosine 701 site (pY701-STAT1) is critical for regulating many cellular functions including antiviral immunity. Maintaining sufficient pY701-STAT1 levels in the nucleus is essential to sustain efficient interferons (IFNs) signaling and antiviral functions. Therefore, it is important to clarify how pY701-STAT1 levels are positively regulated in the nucleus. Here, we demonstrated for the first time that IFNs-induced pY701-STAT1 largely raised STAT1 ubiquitination, and ubiquitinated-pY701-STAT1 is located predominantly in the nucleus and regulated by proteasome-dependent degradation. In IFNs signaling, the deubiquitinase USP2a translocates into the nucleus and binds to pY701-STAT1. USP2a positively regulates pY701-STAT1 levels through inhibiting its K48-linked ubiquitination and degradation. Importantly, USP2a sustains all three classes of IFNs-mediated signaling and antiviral function. Our studies uncover an important positive mechanism in the nucleus by which IFNs can execute efficient antiviral signaling and functions.

Dietary apigenin potentiates the inhibitory effect of interferon-α on cancer cell viability through inhibition of 26S proteasome-mediated interferon receptor degradation

Background

Type I interferons (IFN-α/β) have broad and potent immunoregulatory and antiproliferative activities. However, it is still known whether the dietary flavonoids exhibit their antiviral and anticancer properties by modulating the function of type I IFNs.

Objective

This study aimed at determining the role of apigenin, a dietary plant flavonoid abundant in common fruits and vegetables, on the type I IFN-mediated inhibition of cancer cell viability.

Design

Inhibitory effect of apigenin on human 26S proteasome, a known negative regulator of type I IFN signaling, was evaluated in vitro. Molecular docking was conducted to know the interaction between apigenin and subunits of 26S proteasome. Effects of apigenin on JAK/STAT pathway, 26S proteasome-mediated interferon receptor stability, and cancer cells viability were also investigated.

Results

Apigenin was identified to be a potent inhibitor of human 26S proteasome in a cell-based assay. Apigenin inhibited the chymotrypsin-like, caspase-like, and trypsin-like activities of the human 26S proteasome and increased the ubiquitination of endogenous proteins in cells. Results from computational modeling of the potential interactions of apigenin with the chymotrypsin site (β5 subunit), caspase site (β1 subunit), and trypsin site (β2 subunit) of the proteasome were consistent with the observed proteasome inhibitory activity. Apigenin enhanced the phosphorylation of signal transducer and activator of transcription proteins (STAT1 and STAT2) and promoted the endogenous IFN-α-regulated gene expression. Apigenin inhibited the IFN-α-stimulated ubiquitination and degradation of type I interferon receptor 1 (IFNAR1). Apigenin also sensitized the inhibitory effect of IFN-α on viability of cervical carcinoma HeLa cells.

Conclusion

These results suggest that apigenin potentiates the inhibitory effect of IFN-α on cancer cell viability by activating JAK/STAT signaling pathway through inhibition of 26S proteasome-mediated IFNAR1 degradation. This may provide a novel mechanism for increasing the efficacy of IFN-α/β.

Suppression of Type I Interferon Signaling Overcomes Oncogene-Induced Senescence and Mediates Melanoma Development and Progression

Oncogene activation induces DNA damage responses and cell senescence. We report a key role of type I interferons (IFNs) in oncogene-induced senescence. IFN signaling-deficient melanocytes expressing activated Braf do not exhibit senescence and develop aggressive melanomas. Restoration of IFN signaling in IFN-deficient melanoma cells induces senescence and suppresses melanoma progression. Additional data from human melanoma patients and mouse transplanted tumor models suggest the importance of non-cell-autonomous IFN signaling. Inactivation of the IFN pathway is mediated by the IFN receptor IFNAR1 downregulation that invariably occurs during melanoma development. Mice harboring an IFNAR1 mutant, which is partially resistant to downregulation, delay melanoma development, suppress metastatic disease, and better respond to BRAF or PD-1 inhibitors. These results suggest that IFN signaling is an important tumor-suppressive pathway that inhibits melanoma development and progression and argue for targeting IFNAR1 downregulation to prevent metastatic disease and improve the efficacy of molecularly target and immune-targeted melanoma therapies.

Involvement of F-BOX proteins in progression and development of human malignancies

The Ubiquitin Proteasome System (UPS) is a core regulator with various protein components (ubiquitin-activating E1 enzymes, ubiquitin-conjugating E2 enzymes, ubiquitin-protein E3 ligases, and the 26S proteasome) which work together in a coordinated fashion to ensure the appropriate and efficient proteolysis of target substrates. E3 ubiquitin ligases are essential components of the UPS machinery, working with E1 and E2 enzymes to bind substrates and assist the transport of ubiquitin molecules onto the target protein. As the UPS controls the degradation of several oncogenes and tumor suppressors, dysregulation of this pathway leads to several human malignancies. A major category of E3 Ub ligases, the SCF (Skp-Cullin-F-box) complex, is composed of four principal components: Skp1, Cul1/Cdc53, Roc1/Rbx1/Hrt1, and an F-box protein (FBP). FBPs are the substrate recognition components of SCF complexes and function as adaptors that bring substrates into physical proximity with the rest of the SCF. Besides acting as a component of SCF complexes, FBPs are involved in DNA replication, transcription, cell differentiation and cell death. This review will highlight the recent literature on three well characterized FBPs SKP2, Fbw7, and beta-TRCP. In particular, we will focus on the involvement of these deregulated FBPs in the progression and development of various human cancers. We will also highlight some novel substrates recently identified for these FBPs.

Type I Interferons Control Proliferation and Function of the Intestinal Epithelium

Wnt pathway-driven proliferation and renewal of the intestinal epithelium must be tightly controlled to prevent development of cancer and barrier dysfunction. Although type I interferons (IFN) produced in the gut under the influence of microbiota are known for their antiproliferative effects, the role of these cytokines in regulating intestinal epithelial cell renewal is largely unknown. Here we report a novel role for IFN in the context of intestinal knockout of casein kinase 1α (CK1α), which controls the ubiquitination and degradation of both β-catenin and the IFNAR1 chain of the IFN receptor. Ablation of CK1α leads to the activation of both β-catenin and IFN pathways and prevents the unlimited proliferation of intestinal epithelial cells despite constitutive β-catenin activity. IFN signaling contributes to the activation of the p53 pathway and the appearance of apoptotic and senescence markers in the CK1α-deficient gut. Concurrent genetic ablation of CK1α and IFNAR1 leads to intestinal hyperplasia, robust attenuation of apoptosis, and rapid and lethal loss of barrier function. These data indicate that IFN play an important role in controlling the proliferation and function of the intestinal epithelium in the context of β-catenin activation.

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

Type I Interferon Signaling Is Decoupled from Specific Receptor Orientation through Lenient Requirements of the Transmembrane Domain

Type I interferons serve as the first line of defense against pathogen invasion. Binding of IFNs to its receptors, IFNAR1 and IFNAR2, is leading to activation of the IFN response. To determine whether structural perturbations observed during binding are propagated to the cytoplasmic domain, multiple mutations were introduced into the transmembrane helix and its surroundings. Insertion of one to five alanine residues near either the N or C terminus of the transmembrane domain (TMD) likely promotes a rotation of 100° and a translation of 1.5 Å per added residue. Surprisingly, the added alanines had little effect on the binding affinity of IFN to the cell surface receptors, STAT phosphorylation, or gene induction. Similarly, substitution of the juxtamembrane residues of the TMD with alanines, or replacement of the TMD of IFNAR1 with that of IFNAR2, did not affect IFN binding or activity. Finally, only the addition of 10 serine residues (but not 2 or 4) between the extracellular domain of IFNAR1 and the TMD had some effect on signaling. Bioinformatic analysis shows a correlation between high sequence conservation of TMDs of cytokine receptors and the ability to transmit structural signals. Sequence conservation near the TMD of IFNAR1 is low, suggesting limited functional importance for this region. Our results suggest that IFN binding to the extracellular domains of IFNAR1 and IFNAR2 promotes proximity between the intracellular domains and that differential signaling is a function of duration of activation and affinity of binding rather than specific conformational changes transmitted from the outside to the inside of the cell.