Palmitoylation of interferon-alpha (IFN-alpha) receptor subunit IFNAR1 is required for the activation of Stat1 and Stat2 by IFN-alpha

The anti-inflammatory role of zDHHC23 through the promotion of macrophage M2 polarization and macrophage necroptosis in large yellow croaker (Larimichthys crocea)

Zinc finger Asp-His-His-Cys motif-containing (zDHHC) proteins, known for their palmitoyltransferase (PAT) activity, play crucial roles in diverse cellular processes, including immune regulation. However, their non-palmitoyltransferase immunomodulatory functions and involvement in teleost immune responses remain underexplored. In this study, we systematically characterized the zDHHC family in the large yellow croaker (Larimichthys crocea), identifying 22 members. Phylogenetic analysis unveiled that each of the 22 LczDHHCs formed distinct clusters with their orthologues from other teleost species. Furthermore, all LczDHHCs exhibited a highly conserved DHHC domain, as confirmed by tertiary structure prediction. Notably, LczDHHC23 exhibited the most pronounced upregulation following Pseudomonas plecoglossicida (P. plecoglossicida) infection of macrophage/monocyte cells (MO/MΦ). Silencing LczDHHC23 led to heightened pro-inflammatory cytokine expression and diminished anti-inflammatory cytokine levels in MO/MΦ during infection, indicating its anti-inflammatory role. Functionally, LczDHHC23 facilitated M2-type macrophage polarization, as evidenced by a significant skewing of MO/MΦ towards the pro-inflammatory M1 phenotype upon LczDHHC23 knockdown, along with the inhibition of MO/MΦ necroptosis induced by P. plecoglossicida infection. These findings highlight the non-PAT immunomodulatory function of LczDHHC23 in teleost immune regulation, broadening our understanding of zDHHC proteins in host-pathogen interactions, suggesting LczDHHC23 as a potential therapeutic target for immune modulation in aquatic species.

Sciellin promotes the development and progression of thyroid cancer through the JAK2/STAT3 signaling pathway

Thyroid cancer (TC) is one of the most common endocrine tumors worldwide. Sciellin (SCEL) is involved in various disease processes, including burn wound healing and neutrophil extracellular traps (NETs); it is highly expressed in TC. However, its biological impact on TC and related mechanisms remain unclear. This study aimed to investigate the effect of SCEL on the function of human TC cell lines B-CPAP and OCUT-2C (cancer cell lines with BRAF V600E mutations). Analyses of data sets and clinical samples revealed enhanced expression of SCEL in TC than in adjacent normal tissue. SCEL knockout suppresses proliferation and cell cycle progression in TC cells, and these results were reversed by the upregulated SCEL expression in TC. SCEL knockout inhibited tumor development in xenograft mouse models. Western blot (WB) demonstrated that the expression of p-JAK2 and p-STAT3 was reduced in SCEL-knockdown TC. These results suggest that SCEL plays a key role in TC progression through the JAK2-STAT3 pathway. Therefore, SCEL can be considered a potential diagnostic biomarker and therapeutic target for TC.

Protein lipidation in cancer: mechanisms, dysregulation and emerging drug targets

Protein lipidation describes a diverse class of post-translational modifications (PTMs) that is regulated by over 40 enzymes, targeting more than 1,000 substrates at over 3,000 sites. Lipidated proteins include more than 150 oncoproteins, including mediators of cancer initiation, progression and immunity, receptor kinases, transcription factors, G protein-coupled receptors and extracellular signalling proteins. Lipidation regulates the physical interactions of its protein substrates with cell membranes, regulating protein signalling and trafficking, and has a key role in metabolism and immunity. Targeting protein lipidation, therefore, offers a unique approach to modulate otherwise undruggable oncoproteins; however, the full spectrum of opportunities to target the dysregulation of these PTMs in cancer remains to be explored. This is attributable in part to the technological challenges of identifying the targets and the roles of protein lipidation. The early stage of drug discovery for many enzymes in the pathway contrasts with efforts for drugging similarly common PTMs such as phosphorylation and acetylation, which are routinely studied and targeted in relevant cancer contexts. Here, we review recent advances in identifying targetable protein lipidation pathways in cancer, the current state-of-the-art in drug discovery, and the status of ongoing clinical trials, which have the potential to deliver novel oncology therapeutics targeting protein lipidation.

Potential therapies targeting nuclear metabolic regulation in cancer

The interplay between genetic alterations and metabolic dysregulation is increasingly recognized as a pivotal axis in cancer pathogenesis. Both elements are mutually reinforcing, thereby expediting the ontogeny and progression of malignant neoplasms. Intriguingly, recent findings have highlighted the translocation of metabolites and metabolic enzymes from the cytoplasm into the nuclear compartment, where they appear to be intimately associated with tumor cell proliferation. Despite these advancements, significant gaps persist in our understanding of their specific roles within the nuclear milieu, their modulatory effects on gene transcription and cellular proliferation, and the intricacies of their coordination with the genomic landscape. In this comprehensive review, we endeavor to elucidate the regulatory landscape of metabolic signaling within the nuclear domain, namely nuclear metabolic signaling involving metabolites and metabolic enzymes. We explore the roles and molecular mechanisms through which metabolic flux and enzymatic activity impact critical nuclear processes, including epigenetic modulation, DNA damage repair, and gene expression regulation. In conclusion, we underscore the paramount significance of nuclear metabolic signaling in cancer biology and enumerate potential therapeutic targets, associated pharmacological interventions, and implications for clinical applications. Importantly, these emergent findings not only augment our conceptual understanding of tumoral metabolism but also herald the potential for innovative therapeutic paradigms targeting the metabolism-genome transcriptional axis.

S-palmitoylation regulates innate immune signaling pathways: molecular mechanisms and targeted therapies

S-palmitoylation is a reversible posttranslational lipid modification that targets cysteine residues of proteins and plays critical roles in regulating the biological processes of substrate proteins. The innate immune system serves as the first line of defense against pathogenic invaders and participates in the maintenance of tissue homeostasis. Emerging studies have uncovered the functions of S-palmitoylation in modulating innate immune responses. In this review, we focus on the reversible palmitoylation of innate immune signaling proteins, with particular emphasis on its roles in the regulation of protein localization, protein stability, and protein-protein interactions. We also highlight the potential and challenge of developing therapies that target S-palmitoylation or de-palmitoylation for various diseases.

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.

Positive Regulation of the Antiviral Activity of Interferon-Induced Transmembrane Protein 3 by S-Palmitoylation

The interferon-induced transmembrane protein 3 (IFITM3), a small molecule transmembrane protein induced by interferon, is generally conserved in vertebrates, which can inhibit infection by a diverse range of pathogenic viruses such as influenza virus. However, the precise antiviral mechanisms of IFITM3 remain unclear. At least four post-translational modifications (PTMs) were found to modulate the antiviral effect of IFITM3. These include positive regulation provided by S-palmitoylation of cysteine and negative regulation provided by lysine ubiquitination, lysine methylation, and tyrosine phosphorylation. IFITM3 S-palmitoylation is an enzymatic addition of a 16-carbon fatty acid on the three cysteine residues within or adjacent to its two hydrophobic domains at positions 71, 72, and 105, that is essential for its proper targeting, stability, and function. As S-palmitoylation is the only PTM known to enhance the antiviral activity of IFITM3, enzymes that add this modification may play important roles in IFN-induced immune responses. This study mainly reviews the research progresses on the antiviral mechanism of IFITM3, the regulation mechanism of S-palmitoylation modification on its subcellular localization, stability, and function, and the enzymes that mediate the S-palmitoylation modification of IFITM3, which may help elucidate the mechanism by which this IFN effector restrict virus replication and thus aid in the design of therapeutics targeted at pathogenic viruses.

Therapeutic targeting miR130b counteracts diffuse large B-cell lymphoma progression via OX40/OX40L-mediated interaction with Th17 cells

MicroRNAs (miRNAs) are involved in lymphoma progression by regulating the tumor microenvironment. Serum miR130b is overexpressed in diffuse large B-cell lymphoma (DLBCL), inducing Th17 cell alterations. To further illustrate its biological significance and therapeutic rationale, miR130b was detected by quantitative real-time PCR in the serum samples of 532 newly diagnosed DLBCL patients. The mechanism of miR130b on lymphoma progression and the tumor microenvironment was investigated both in vitro and in vivo. Therapeutic targeting miR130b was also evaluated, including OX40 agonistic antibody and lipid nanoparticles (LNPs)-miR130b antagomir. The results showed that serum miR130b significantly correlated with tumor miR130b and serum interleukin-17, indicating lymphoma relapse and inferior survival of DLBCL patients. MiR130b overexpression altered tumor microenvironment signaling pathways and increased Th17 cell activity. As mechanism of action, miR130b downregulated tumor OX40L expression by directly targeting IFNAR1/p-STAT1 axis, recruiting Th17 cells via OX40/OX40L interaction, thereby promoting immunosuppressive function of Th17 cells. In co-culture systems of B-lymphoma cells with immune cells, miR130b inhibited lymphoma cell autophagy, which could be counteracted by OX40 agonistic antibody and LNPs-miR130b antagomir. In murine xenograft model established with subcutaneous injection of A20 cells, both OX40 agonistic antibody and LNPs-miR130b antagomir remarkably inhibited Th17 cells and retarded miR130b-overexpressing tumor growth. In conclusion, as an oncogenic biomarker of DLBCL, miR130b was related to lymphoma progression through modulating OX40/OX40L-mediated lymphoma cell interaction with Th17 cells, attributing to B-cell lymphoma sensitivity towards OX40 agonistic antibody. Targeting miR130b using LNPs-miR130b antagomir could also be a potential immunotherapeutic strategy in treating OX40-altered lymphoid malignancies.

Protein Lipidation by Palmitate Controls Macrophage Function

Macrophages are present in all tissues within our body, where they promote tissue homeostasis by responding to microenvironmental triggers, not only through clearance of pathogens and apoptotic cells but also via trophic, regulatory, and repair functions. To accomplish these divergent functions, tremendous dynamic fine-tuning of their physiology is needed. Emerging evidence indicates that S-palmitoylation, a reversible post-translational modification that involves the linkage of the saturated fatty acid palmitate to protein cysteine residues, directs many aspects of macrophage physiology in health and disease. By controlling protein activity, stability, trafficking, and protein–protein interactions, studies identified a key role of S-palmitoylation in endocytosis, inflammatory signaling, chemotaxis, and lysosomal function. Here, we provide an in-depth overview of the impact of S-palmitoylation on these cellular processes in macrophages in health and disease. Findings discussed in this review highlight the therapeutic potential of modulators of S-palmitoylation in immunopathologies, ranging from infectious and chronic inflammatory disorders to metabolic conditions.

Protein cysteine palmitoylation in immunity and inflammation

Protein cysteine palmitoylation, or S-palmitoylation, has been known for about 40 years, and thousands of proteins in humans are known to be modified. Because of the large number of proteins modified, the importance and physiological functions of S-palmitoylation are enormous. However, most of the known physiological functions of S-palmitoylation can be broadly classified into two categories, neurological or immunological. This review provides a summary on the function of S-palmitoylation from the immunological perspective. Several important immune signaling pathways are discussed, including STING, NOD1/2, JAK-STAT in cytokine signaling, T-cell receptor signaling, chemotactic GPCR signaling, apoptosis, phagocytosis, and endothelial and epithelial integrity. This review is not meant to be comprehensive, but rather focuses on specific examples to highlight the versatility of palmitoylation in regulating immune signaling, as well as the potential and challenges of targeting palmitoylation to treat immune diseases.

Function of Protein S-Palmitoylation in Immunity and Immune-Related Diseases

Protein S-palmitoylation is a covalent and reversible lipid modification that specifically targets cysteine residues within many eukaryotic proteins. In mammalian cells, the ubiquitous palmitoyltransferases (PATs) and serine hydrolases, including acyl protein thioesterases (APTs), catalyze the addition and removal of palmitate, respectively. The attachment of palmitoyl groups alters the membrane affinity of the substrate protein changing its subcellular localization, stability, and protein-protein interactions. Forty years of research has led to the understanding of the role of protein palmitoylation in significantly regulating protein function in a variety of biological processes. Recent global profiling of immune cells has identified a large body of S-palmitoylated immunity-associated proteins. Localization of many immune molecules to the cellular membrane is required for the proper activation of innate and adaptive immune signaling. Emerging evidence has unveiled the crucial roles that palmitoylation plays to immune function, especially in partitioning immune signaling proteins to the membrane as well as to lipid rafts. More importantly, aberrant PAT activity and fluctuations in palmitoylation levels are strongly correlated with human immunologic diseases, such as sensory incompetence or over-response to pathogens. Therefore, targeting palmitoylation is a novel therapeutic approach for treating human immunologic diseases. In this review, we discuss the role that palmitoylation plays in both immunity and immunologic diseases as well as the significant potential of targeting palmitoylation in disease treatment.

Protein S-palmitoylation in immunity

S-palmitoylation is a reversible posttranslational lipid modification of proteins. It controls protein activity, stability, trafficking and protein–protein interactions. Recent global profiling of immune cells and targeted analysis have identified many S-palmitoylated immunity-associated proteins. Here, we review S-palmitoylated immune receptors and effectors, and their dynamic regulation at cellular membranes to generate specific and balanced immune responses. We also highlight how this understanding can drive therapeutic advances to pharmacologically modulate immune responses.

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.

Role of Host-Mediated Post-Translational Modifications (PTMs) in RNA Virus Pathogenesis

Being opportunistic intracellular pathogens, viruses are dependent on the host for their replication. They hijack host cellular machinery for their replication and survival by targeting crucial cellular physiological pathways, including transcription, translation, immune pathways, and apoptosis. Immediately after translation, the host and viral proteins undergo a process called post-translational modification (PTM). PTMs of proteins involves the attachment of small proteins, carbohydrates/lipids, or chemical groups to the proteins and are crucial for the proteins’ functioning. During viral infection, host proteins utilize PTMs to control the virus replication, using strategies like activating immune response pathways, inhibiting viral protein synthesis, and ultimately eliminating the virus from the host. PTM of viral proteins increases solubility, enhances antigenicity and virulence properties. However, RNA viruses are devoid of enzymes capable of introducing PTMs to their proteins. Hence, they utilize the host PTM machinery to promote their survival. Proteins from viruses belonging to the family: Togaviridae, Flaviviridae, Retroviridae, and Coronaviridae such as chikungunya, dengue, zika, HIV, and coronavirus are a few that are well-known to be modified. This review discusses various host and virus-mediated PTMs that play a role in the outcome during the infection.

Protein Palmitoylation in Leukocyte Signaling and Function

Palmitoylation is a post-translational modification (PTM) based on thioester-linkage between palmitic acid and the cysteine residue of a protein. This covalent attachment of palmitate is reversibly and dynamically regulated by two opposing sets of enzymes: palmitoyl acyltransferases containing a zinc finger aspartate-histidine-histidine-cysteine motif (PAT-DHHCs) and thioesterases. The reversible nature of palmitoylation enables fine-tuned regulation of protein conformation, stability, and ability to interact with other proteins. More importantly, the proper function of many surface receptors and signaling proteins requires palmitoylation-meditated partitioning into lipid rafts. A growing number of leukocyte proteins have been reported to undergo palmitoylation, including cytokine/chemokine receptors, adhesion molecules, pattern recognition receptors, scavenger receptors, T cell co-receptors, transmembrane adaptor proteins, and signaling effectors including the Src family of protein kinases. This review provides the latest findings of palmitoylated proteins in leukocytes and focuses on the functional impact of palmitoylation in leukocyte function related to adhesion, transmigration, chemotaxis, phagocytosis, pathogen recognition, signaling activation, cytotoxicity, and cytokine production.

The emerging roles of ZDHHCs-mediated protein palmitoylation in the antiviral innate immune responses

Post-translational modifications (PTMs) play a pivotal role in expanding functional protein diversity. During viral infection, pathogen-associated molecular patterns derived from viruses are recognized by pattern recognition receptors present in the membrane surface and the cytoplasm of infected cells, which subsequently induces the antiviral innate immunity to protect the host from the invading viruses. Fatty acylation modification is identified as a post-translation lipid modification process. Mounting evidence is presented that lipid modification functions as a novel regulatory mechanism of antiviral innate immunity. In mammalian cells, DHHC (Asp-His-His-Cys) domain is indispensable for most of the palmitoylation modification, which belongs to fatty acylation. ZDHHC family proteins are composed of 23 members in human cells. In this review, we will summarize the recent findings of the regulatory mechanism of the palmitoylation in the process of host antiviral innate immunity against viruses.

Protein Palmitoylation and Its Role in Bacterial and Viral Infections

S-palmitoylation is a reversible, enzymatic posttranslational modification of proteins in which palmitoyl chain is attached to a cysteine residue via a thioester linkage. S-palmitoylation determines the functioning of proteins by affecting their association with membranes, compartmentalization in membrane domains, trafficking, and stability. In this review, we focus on S-palmitoylation of proteins, which are crucial for the interactions of pathogenic bacteria and viruses with the host. We discuss the role of palmitoylated proteins in the invasion of host cells by bacteria and viruses, and those involved in the host responses to the infection. We highlight recent data on protein S-palmitoylation in pathogens and their hosts obtained owing to the development of methods based on click chemistry and acyl-biotin exchange allowing proteomic analysis of protein lipidation. The role of the palmitoyl moiety present in bacterial lipopolysaccharide and lipoproteins, contributing to infectivity and affecting recognition of bacteria by innate immune receptors, is also discussed.

Protein Lipidation: Occurrence, Mechanisms, Biological Functions, and Enabling Technologies

Protein lipidation, including cysteine prenylation, N-terminal glycine myristoylation, cysteine palmitoylation, and serine and lysine fatty acylation, occurs in many proteins in eukaryotic cells and regulates numerous biological pathways, such as membrane trafficking, protein secretion, signal transduction, and apoptosis. We provide a comprehensive review of protein lipidation, including descriptions of proteins known to be modified and the functions of the modifications, the enzymes that control them, and the tools and technologies developed to study them. We also highlight key questions about protein lipidation that remain to be answered, the challenges associated with answering such questions, and possible solutions to overcome these challenges.

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.

Global functional profiling of human ubiquitome identifies E3 ubiquitin ligase DCST1 as a novel negative regulator of Type-I interferon signaling

Type I interferon (IFN-I) mediated innate immune response controls virus infections by inducing the expression of interferon stimulated genes (ISGs). Although ubiquitination plays key roles in immune signaling regulation, a human genome-wide understanding of the role of E3 ubiquitin ligases in interferon mediated ISG induction is lacking. Here, we report a genome-wide profiling of the effect of ectopic expression of 521 E3 ubiquitin ligases and substrate recognition subunits encoded in the human genome (which constitutes 84.4% of all ubiquitination related genes encoded in the human genome, hereafter termed Human Ubiquitome) on IFNβ mediated induction of interferon stimulated DNA response element (ISRE) driven reporter activity. We identified 96 and 42 genes of the human ubiquitome as novel negative and positive regulators of interferon signaling respectively. Furthermore, we characterized DCST1 as a novel E3 ubiquitin ligase negatively regulating interferon response. Ectopic expression and gene silencing of DCST1 respectively attenuated and increased ISRE reporter activity. DCST1 regulated Type I interferon signaling by interacting with and promoting ubiquitination-mediated degradation of STAT2, an essential component of antiviral gene induction. In summary, this study provided a systems level view on the role of human ubiquitination associated genes in Type I interferon response.

Glycosylation-Dependent IFN-γR Partitioning in Lipid and Actin Nanodomains Is Critical for JAK Activation

Understanding how membrane nanoscale organization controls transmembrane receptors signaling activity remains a challenge. We studied interferon-γ receptor (IFN-γR) signaling in fibroblasts from homozygous patients with a T168N mutation in IFNGR2. By adding a neo-N-glycan on IFN-γR2 subunit, this mutation blocks IFN-γ activity by unknown mechanisms. We show that the lateral diffusion of IFN-γR2 is confined by sphingolipid/cholesterol nanodomains. In contrast, the IFN-γR2 T168N mutant diffusion is confined by distinct actin nanodomains where conformational changes required for Janus-activated tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) activation by IFN-γ could not occur. Removing IFN-γR2 T168N-bound galectins restored lateral diffusion in lipid nanodomains and JAK/STAT signaling in patient cells, whereas adding galectins impaired these processes in control cells. These experiments prove the critical role of dynamic receptor interactions with actin and lipid nanodomains and reveal a new function for receptor glycosylation and galectins. Our study establishes the physiological relevance of membrane nanodomains in the control of transmembrane receptor signaling in vivo. VIDEO ABSTRACT.

Amplified RLR signaling activation through an interferon-stimulated gene-endoplasmic reticulum stress-mitochondrial calcium uniporter protein loop

Type I interferon (IFN-I) is critical for a host against viral and bacterial infections via induction of hundreds of interferon-stimulated genes (ISGs), but the mechanism underlying the regulation of IFN-I remains largely unknown. In this study, we first demonstrate that ISG expression is required for optimal IFN-β levels, an effect that is further enhanced by endoplasmic reticulum (ER) stress. Furthermore, we identify mitochondrial calcium uniporter protein (MCU) as a mitochondrial antiviral signaling protein (MAVS)-interacting protein that is important for ER stress induction and amplified MAVS signaling activation. In addition, by performing an ectopic expression assay to screen a library of 117 human ISGs for effects on IFN-β levels, we found that tumor necrosis factor receptor 1 (TNFR1) significantly increases IFN-β levels independent of ER stress. Altogether, our findings suggest that MCU and TNFR1 are involved in the regulation of RIG-I-like receptors (RLR) signaling.

Hemagglutinin of Influenza A Virus Antagonizes Type I Interferon (IFN) Responses by Inducing Degradation of Type I IFN Receptor 1

Influenza A virus (IAV) employs diverse strategies to circumvent type I interferon (IFN) responses, particularly by inhibiting the synthesis of type I IFNs. However, it is poorly understood if and how IAV regulates the type I IFN receptor (IFNAR)-mediated signaling mode. In this study, we demonstrate that IAV induces the degradation of IFNAR subunit 1 (IFNAR1) to attenuate the type I IFN-induced antiviral signaling pathway. Following infection, the level of IFNAR1 protein, but not mRNA, decreased. Indeed, IFNAR1 was phosphorylated and ubiquitinated by IAV infection, which resulted in IFNAR1 elimination. The transiently overexpressed IFNAR1 displayed antiviral activity by inhibiting virus replication. Importantly, the hemagglutinin (HA) protein of IAV was proved to trigger the ubiquitination of IFNAR1, diminishing the levels of IFNAR1. Further, influenza A viral HA1 subunit, but not HA2 subunit, downregulated IFNAR1. However, viral HA-mediated degradation of IFNAR1 was not caused by the endoplasmic reticulum (ER) stress response. IAV HA robustly reduced cellular sensitivity to type I IFNs, suppressing the activation of STAT1/STAT2 and induction of IFN-stimulated antiviral proteins. Taken together, our findings suggest that IAV HA causes IFNAR1 degradation, which in turn helps the virus escape the powerful innate immune system. Thus, the research elucidated an influenza viral mechanism for eluding the IFNAR signaling pathway, which could provide new insights into the interplay between influenza virus and host innate immunity.

IMPORTANCE

Influenza A virus (IAV) infection causes significant morbidity and mortality worldwide and remains a major health concern. When triggered by influenza viral infection, host cells produce type I interferon (IFN) to block viral replication. Although IAV was shown to have diverse strategies to evade this powerful, IFN-mediated antiviral response, it is not well-defined if IAV manipulates the IFN receptor-mediated signaling pathway. Here, we uncovered that influenza viral hemagglutinin (HA) protein causes the degradation of type I IFN receptor subunit 1 (IFNAR1). HA promoted phosphorylation and polyubiquitination of IFNAR1, which facilitated the degradation of this receptor. The HA-mediated elimination of IFNAR1 notably decreased the cells' sensitivities to type I IFNs, as demonstrated by the diminished expression of IFN-induced antiviral genes. This discovery could help us understand how IAV regulates the host innate immune response to create an environment optimized for viral survival in host cells.

Analytical use of multi-protein Fluorescence Resonance Energy Transfer to demonstrate membrane-facilitated interactions within cytokine receptor complexes

Experiments measuring Fluorescence Resonance Energy Transfer (FRET) between cytokine receptor chains and their associated proteins led to hypotheses describing their organization in intact cells. These interactions occur within a larger protein complex or within a given nano-environment. To illustrate this complexity empirically, we developed a protocol to analyze FRET among more than two fluorescent proteins (multi-FRET). In multi-FRET, we model FRET among more than two fluorophores as the sum of all possible pairwise interactions within the complex. We validated our assumption by demonstrating that FRET among pairs within a fluorescent triplet resembled FRET between each pair measured in the absence of the third fluorophore. FRET between two receptor chains increases with increasing FRET between the ligand-binding chain (e.g., IFN-γR1, IL-10R1 and IFN-λR1) and an acylated fluorescent protein that preferentially resides within subsections of the plasma membrane. The interaction of IL-10R2 with IFN-λR1 or IL-10R1 results in decreased FRET between IL-10R2 and the acylated fluorescent protein. Finally, we analyzed FRET among four fluorescent proteins to demonstrate that as FRET between IFN-γR1 and IFN-γR2 or between IFN-αR1 and IFN-αR2c increases, FRET among other pairs of proteins changes within each complex.

Differential effects of type I and II interferons on myeloid cells and resistance to intracellular bacterial infections

The type I and II interferons (IFNs) play important roles in regulating immune responses during viral and bacterial infections and in the context of autoimmune and neoplastic diseases. These two IFN types bind to distinct cell surface receptors that are expressed by nearly all cells to trigger signal transduction events and elicit diverse cellular responses. In some cases, type I and II IFNs trigger similar cellular responses, while in other cases, the IFNs have unique or antagonistic effects on host cells. Negative regulators of IFN signaling also modulate cellular responses to the IFNs and play important roles in maintaining immunological homeostasis. In this review, we provide an overview of how IFNs stimulate cellular responses. We discuss the disparate effects of type I and II IFNs on host resistance to certain intracellular bacterial infections and provide an overview of models that have been proposed to account for these disparate effects. Mechanisms of antagonistic cross talk between type I and II IFNs are also introduced.

Palmitoylation, pathogens and their host

S-Palmitoylation, the only reversible post-translational lipid modification, confers unique biochemical and functional properties to proteins. Although it has long been known that viral proteins are palmitoylated, recent studies reveal that this modification plays a critical role for pathogens of all kinds and at multiple steps of their life cycle. The present review examines the involvement of S-palmitoylation in infection by viruses, bacteria and parasites and illustrates how pathogens have evolved to manipulate the host palmitoylation machinery.

Emerging roles for protein S-palmitoylation in immunity from chemical proteomics

The activation of innate and adaptive immune signaling pathways and effector functions often occur at cellular membranes and are regulated by complex mechanisms. Here we review the growing number of proteins which are known to be regulated by S-palmitoylation in immune cells emerging from recent advances in chemical proteomics. These chemical proteomic studies have highlighted the roles of this dynamic lipid modification in regulating the specificity and strength of immune responses in different lymphocyte populations.

Mechanism of HCV's resistance to IFN-α in cell culture involves expression of functional IFN-α receptor 1

The mechanisms underlying the Hepatitis C virus (HCV) resistance to interferon alpha (IFN-α) are not fully understood. We used IFN-α resistant HCV replicon cell lines and an infectious HCV cell culture system to elucidate the mechanisms of IFN-α resistance in cell culture. The IFN-α resistance mechanism of the replicon cells were addressed by a complementation study that utilized the full-length plasmid clones of IFN-α receptor 1 (IFNAR1), IFN-α receptor 2 (IFNAR2), Jak1, Tyk2, Stat1, Stat2 and the ISRE- luciferase reporter plasmid. We demonstrated that the expression of the full-length IFNAR1 clone alone restored the defective Jak-Stat signaling as well as Stat1, Stat2 and Stat3 phosphorylation, nuclear translocation and antiviral response against HCV in all IFN-α resistant cell lines (R-15, R-17 and R-24) used in this study. Moreover RT-PCR, Southern blotting and DNA sequence analysis revealed that the cells from both R-15 and R-24 series of IFN-α resistant cells have 58 amino acid deletions in the extracellular sub domain 1 (SD1) of IFNAR1. In addition, cells from the R-17 series have 50 amino acids deletion in the sub domain 4 (SD4) of IFNAR1 protein leading to impaired activation of Tyk2 kinase. Using an infectious HCV cell culture model we show here that viral replication in the infected Huh-7 cells is relatively resistant to exogenous IFN-α. HCV infection itself induces defective Jak-Stat signaling and impairs Stat1 and Stat2 phosphorylation by down regulation of the cell surface expression of IFNAR1 through the endoplasmic reticulum (ER) stress mechanisms. The results of this study suggest that expression of cell surface IFNAR1 is critical for the response of HCV to exogenous IFN-α.

Inhibition of interferon-α-induced signaling by hyperosmolarity and hydrophobic bile acids

Apart from viral conditions, host factors such as elevated bile acid concentrations are determinants of successful interferon-α (IFN-α) treatment in patients with chronic hepatitis C or B. The present study demonstrates that hydrophobic bile acids inhibit Jak1- and Tyk2-phosphorylation, which lead to blockade of STAT1-mediated IFN-α-signaling in the sodium-taurocholate cotransporting peptide (NTCP)-transfected human hepatoma cell line HepG2, resulting in a decreased mRNA and protein expression of IFN-stimulated genes such as myxovirus resistance protein A (MxA) or dsRNA-activated protein kinase (PKR). In addition, hyperosmotic stress leads to an inhibition of IFN-α-induced Jak1- and Tyk2-phosphorylation, and STAT1/STAT2-phosphorylation and gene expression. This inhibitory effect of hydrophobic bile acids or hyperosmolarity is not due to caspase-mediated cleavage or lysosomal degradation of the cognate receptors or to the generation of oxidative stress, activation of p38- or Erk-mediated MAPK pathways or phosphatase activity. Preincubation with the organic osmolyte betaine blocked the inhibitory effect of bile acids or hyperosmolarity on MxA protein expression, but had no effect on transcript levels or activation of STAT1, suggesting that betaine mediates its effects on MxA expression at a translational or post-translational level. Our findings could provide a rationale for betaine use in cholestatic HBV/HCV patients undergoing interferon therapy.

Local cytokine response upon respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the leading cause of childhood hospitalization and respiratory distress and has been recognized for several decades as a major health and economic burden worldwide. This virus has developed several virulence mechanisms to impair the establishment of a protective immune response to re-infection. Accordingly, inefficient immunological memory is usually generated after exposure to this pathogen. Furthermore, it has been shown that RSV can actively promote the induction of an inadequate cellular immune response at the site of infection that causes exacerbated inflammation in the respiratory tract. Such an inflammatory response is both inefficient for clearing the virus and can be responsible for detrimental symptoms, such as asthma and wheezing. Recent data suggest that RSV possesses molecular mechanisms to induce the secretion of pro-inflammatory cytokines that modulate the immune response and impair viral clearance by reducing IFN-γ production. Here, we discuss recent research leading to the identification of RSV virulence factors that are responsible of promoting a pro-inflammatory environment at the airways and their implications on pathogenicity.