Brain Endothelial- and Epithelial-Specific Interferon Receptor Chain 1 Drives Virus-Induced Sickness Behavior and Cognitive Impairment.

Sickness behavior and cognitive dysfunction occur frequently by unknown mechanisms in virus-infected individuals with malignancies treated with type I interferons (IFNs) and in patients with autoimmune disorders. We found that during sickness behavior, single-stranded RNA viruses, double-stranded RNA ligands, and IFNs shared pathways involving engagement of melanoma differentiation-associated protein 5 (MDA5), retinoic acid-inducible gene 1 (RIG-I), and mitochondrial antiviral signaling protein (MAVS), and subsequently induced IFN responses specifically in brain endothelia and epithelia of mice. Behavioral alterations were specifically dependent on brain endothelial and epithelial IFN receptor chain 1 (IFNAR). Using gene profiling, we identified that the endothelia-derived chemokine ligand CXCL10 mediated behavioral changes through impairment of synaptic plasticity. These results identified brain endothelial and epithelial cells as natural gatekeepers for virus-induced sickness behavior, demonstrated tissue specific IFNAR engagement, and established the CXCL10-CXCR3 axis as target for the treatment of behavioral changes during virus infection and type I IFN therapy.

Discovery of structural diverse reversible BTK inhibitors utilized to develop a novel in vivo CD69 and CD86 PK/PD mouse model.

For the past two decades, BTK a tyrosine kinase and member of the Tec family has been a drug target of significant interest due to its potential to selectively treat various B cell-mediated diseases such as CLL, MCL, RA, and MS. Owning to the challenges encountered in identifying drug candidates exhibiting the potency block B cell activation via BTK inhibition, the pharmaceutical industry has relied on the use of covalent/irreversible inhibitors to address this unmet medical need. Herein, we describe a medicinal chemistry campaign to identify structurally diverse reversible BTK inhibitors originating from HITS identified using a fragment base screen. The leads were optimized to improve the potency and in vivo ADME properties resulting in a structurally distinct chemical series used to develop and validate a novel in vivo CD69 and CD86 PD assay in rodents.

Immune thrombocytopenia in alemtuzumab-treated MS patients: Incidence, detection, and management.

BACKGROUND: Alemtuzumab is a highly effective therapy for relapsing-remitting multiple sclerosis (RRMS), and immune thrombocytopenia (ITP) has been identified as a risk. OBJECTIVE: To examine ITP incidence, treatment, and outcomes during the clinical development of alemtuzumab for RRMS and discuss postmarketing experience outside clinical trials. METHODS: CAMMS223 and Comparison of Alemtuzumab and Rebif® Efficacy in Multiple Sclerosis (CARE-MS) I and II investigated two annual courses of alemtuzumab 12 mg (or 24 mg in CAMMS223/CARE-MS II) versus subcutaneous interferon beta-1a three times per week. Patients completing core studies could enroll in an extension. Monthly monitoring for ITP continued until 48 months after the last alemtuzumab infusion. RESULTS: Of 1485 alemtuzumab-treated MS patients in the clinical development program, 33 (2.2%) developed ITP (alemtuzumab 12 mg, 24 [2.0%]; alemtuzumab 24 mg, 9 [3.3%]) over median 6.1 years of follow-up after the first infusion; most had a sustained response to first-line ITP therapy with corticosteroids, platelets, and/or intravenous immunoglobulin. All cases occurred within 48 months of the last alemtuzumab infusion. Postmarketing surveillance data suggest that the ITP incidence is not higher in clinical practice than in clinical trials. CONCLUSION: Alemtuzumab-associated ITP occurs in approximately 2% of patients and is responsive to therapy. Careful monitoring is key for detection and favorable outcomes.

Incidence, management, and outcomes of autoimmune nephropathies following alemtuzumab treatment in patients with multiple sclerosis.

BACKGROUND: Autoimmune disorders including nephropathies have been reported more frequently in alemtuzumab-treated multiple sclerosis (MS) patients than in the general population. OBJECTIVE: Describe instances of autoimmune nephropathy in alemtuzumab-treated MS patients. METHODS: Cases were identified from safety monitoring within the alemtuzumab relapsing-remitting multiple sclerosis (RRMS) clinical development program (CDP) or post-marketing, or following off-label use. RESULTS: As of 16 June 2017, 16 autoimmune nephropathies have occurred following alemtuzumab treatment for MS. The incidence of autoimmune nephropathies was 0.34% within the CDP (5/1485 patients). The five CDP cases (one of anti-glomerular basement membrane (anti-GBM) disease, two of membranous glomerulonephropathy, and two of serum anti-GBM antibody without typical anti-GBM disease) were identified early, responded to conventional therapy (where needed), and had favorable outcomes. Three of 11 cases outside the CDP occurred following off-label alemtuzumab use prior to approval for RRMS and were all anti-GBM disease. Diagnosis was delayed in one of these three cases and another did not receive appropriate treatment; all three cases resulted in end-stage renal failure. All anti-GBM disease cases with documented urinalysis demonstrated prior microscopic hematuria. CONCLUSION: Close monitoring of alemtuzumab-treated MS patients facilitates diagnosis and treatment early in the nephropathy course when preservation of renal function is more likely.

IFN-ß Selectively Inhibits IL-2 Production through CREM-Mediated Chromatin Remodeling.

IFN-ß is widely used in the treatment of multiple sclerosis, yet the mechanism facilitating its efficacy remains unclear. IL-2 production by activated T cells, including those mediating autoimmunity, and subsequent autocrine stimulation is vital for T cell expansion and function. In this study, we demonstrate that in mouse and human T cells, IFN-ß specifically inhibits the production of IL-2 upon TCR engagement without affecting other cytokines or activation markers. Rather than disrupting TCR signaling, IFN-ß alters histone modifications in the IL-2 promoter to retain the locus in an inaccessible configuration. This in turn is mediated through the upregulation of the transcriptional suppressor CREM by IFN-ß and consequent recruitment of histone deacetylases to the IL-2 promoter. In accordance, ablation of CREM expression or inhibition of histone deacetylases activity eliminates the suppressive effects of IFN-ß on IL-2 production. Collectively, these findings provide a molecular basis by which IFN-ß limits T cell responses.

Concomitant TLR/RLH signaling of radioresistant and radiosensitive cells is essential for protection against vesicular stomatitis virus infection.

Several studies indicated that TLR as well as retinoic acid-inducible gene I-like helicase (RLH) signaling contribute to vesicular stomatitis virus (VSV)-mediated triggering of type I IFN (IFN-I) responses. Nevertheless, TLR-deficient MyD88(-/-)Trif(-/-) mice and RLH-deficient caspase activation and recruitment domain adaptor inducing IFN-ß (Cardif)(-/-) mice showed only marginally enhanced susceptibility to lethal VSV i.v. infection. Therefore, we addressed whether concomitant TLR and RLH signaling, or some other additional mechanism, played a role. To this end, we generated MyD88(-/-)Trif(-/-)Cardif(-/-) (MyTrCa(-/-)) mice that succumbed to low-dose i.v. VSV infection with similar kinetics as IFN-I receptor-deficient mice. Three independent approaches (i.e., analysis of IFN-α/ß serum levels, experiments with IFN-ß reporter mice, and investigation of local IFN-stimulated gene induction) revealed that MyTrCa(-/-) mice did not mount IFN-I responses following VSV infection. Of note, treatment with rIFN-α protected the animals, qualifying MyTrCa(-/-) mice as a model to study the contribution of different immune cell subsets to the production of antiviral IFN-I. Upon adoptive transfer of wild-type plasmacytoid dendritic cells and subsequent VSV infection, MyTrCa(-/-) mice displayed significantly reduced viral loads in peripheral organs and showed prolonged survival. On the contrary, adoptive transfer of wild-type myeloid dendritic cells did not have such effects. Analysis of bone marrow chimeric mice revealed that TLR and RLH signaling of radioresistant and radiosensitive cells was required for efficient protection. Thus, upon VSV infection, plasmacytoid dendritic cell-derived IFN-I primarily protects peripheral organs, whereas concomitant TLR and RLH signaling of radioresistant stroma cells as well as of radiosensitive immune cells is needed to effectively protect against lethal disease.

Host STAT2/type I interferon axis controls tumor growth.

The role of STAT2 in mediating the antigrowth effects of type I interferon (IFN) is well-documented in vitro. Yet evidence of IFN-activated STAT2 as having tumor suppressor function in vivo and participation in antitumor immunity is lacking. Here we show in a syngeneic tumor transplantation model that STAT2 reduces tumor growth. Stat2(-/-) mice formed larger tumors compared to wild type (WT) mice. IFN-ß treatment of Stat2(-/-) mice did not cause tumor regression. Gene expression analysis revealed a small subset of immunomodulatory genes to be downregulated in tumors established in Stat2(-/-) mice. Additionally, we found tumor antigen cross-presentation by Stat2(-/-) dendritic cells to T cells to be impaired. Adoptive transfer of tumor antigen specific CD8(+) T cells primed by Stat2(-/-) dendritic cells into tumor-bearing Stat2(-/-) mice did not induce tumor regression with IFN-ß intervention. We observed that an increase in the number of CD4(+) and CD8(+) T cells in the draining lymph nodes of IFN-ß-treated tumor-bearing WT mice was absent in IFN-ß treated Stat2(-/-) mice. Thus our study provides evidence for further evaluation of STAT2 function in cancer patients receiving type I IFN based immunotherapy.

HCV infection selectively impairs type I but not type III IFN signaling.

A stable and persistent Hepatitis C virus (HCV) replication cell culture model was developed to examine clearance of viral replication during long-term treatment using interferon-α (IFN-α), IFN-λ, and ribavirin (RBV). Persistently HCV-infected cell culture exhibited an impaired antiviral response to IFN-α+RBV combination treatment, whereas IFN-λ treatment produced a strong and sustained antiviral response that cleared HCV replication. HCV replication in persistently infected cells induced chronic endoplasmic reticulum (ER) stress and an autophagy response that selectively down-regulated the functional IFN-α receptor-1 chain of type I, but not type II (IFN-γ) or type III (IFN-λ) IFN receptors. Down-regulation of IFN-α receptor-1 resulted in defective JAK-STAT signaling, impaired STAT phosphorylation, and impaired nuclear translocation of STAT. Furthermore, HCV replication impaired RBV uptake, because of reduced expression of the nucleoside transporters ENT1 and CNT1. Silencing ER stress and the autophagy response using chemical inhibitors or siRNA additively inhibited HCV replication and induced viral clearance by the IFN-α+RBV combination treatment. These results indicate that HCV induces ER stress and that the autophagy response selectively impairs type I (but not type III) IFN signaling, which explains why IFN-λ (but not IFN-α) produced a sustained antiviral response against HCV. The results also indicate that inhibition of ER stress and of the autophagy response overcomes IFN-α+RBV resistance mechanisms associated with HCV infection.

IRF7-dependent IFN-ß production in response to RANKL promotes medullary thymic epithelial cell development.

The contributions of IFN regulatory factor (IRF) 3/7 and the type I IFNs IFN-α/ß to the innate host defense have been extensively investigated; however, their role in thymic development is less clear. In this study, we show that mice lacking the type I IFN receptor IFN-α/ß receptor (IFNAR) or the downstream transcription factor STAT1 harbor a significant reduction in self-Ag-presenting, autoimmune regulator (AIRE)(+) medullary thymic epithelial cells (mTECs). Constitutive IFNAR signaling occurs in the thymic medulla in the absence of infection or inflammation. Receptor activator for NF-κB (RANK) ligand stimulation results in IFN-ß upregulation, which in turn inhibits RANK signaling and facilitates AIRE expression in mTECs. Finally, we find that IRF7 is required for thymic IFN-ß induction, maintenance of thymic architecture, and mTEC differentiation. We conclude that spatially and temporally coordinated cross talks between the RANK ligand/RANK and IRF7/IFN-ß/IFNAR/STAT1 pathways are essential for differentiation of AIRE(+) mTECs.

Regulatory effects of mTORC2 complexes in type I IFN signaling and in the generation of IFN responses.

IFNs transduce signals by binding to cell surface receptors and activating cellular pathways and regulatory networks that control transcription of IFN-stimulated genes (ISGs) and mRNA translation, leading to generation of protein products that mediate biological responses. Previous studies have shown that type I IFN receptor-engaged pathways downstream of AKT and mammalian target of rapamycin complex (mTORC) 1 play important roles in mRNA translation of ISGs and the generation of IFN responses, but the roles of mTORC2 complexes in IFN signaling are unknown. We provide evidence that mTORC2 complexes control IFN-induced phosphorylation of AKT on serine 473 and their function is ultimately required for IFN-dependent gene transcription via interferon-stimulated response elements. We also demonstrate that such complexes exhibit regulatory effects on other IFN-dependent mammalian target of rapamycin-mediated signaling events, likely via engagement of the AKT/mTORC1 axis, including IFN-induced phosphorylation of S6 kinase and its effector rpS6, as well as phosphorylation of the translational repressor 4E-binding protein 1. We also show that induction of ISG protein expression and the generation of antiviral responses are defective in Rictor and mLST8-KO cells. Together, our data provide evidence for unique functions of mTORC2 complexes in the induction of type I IFN responses and suggest a critical role for mTORC2-mediated signals in IFN signaling.

Protein tyrosine phosphatase 1B is a key regulator of IFNAR1 endocytosis and a target for antiviral therapies.

Type 1 interferons (IFN1) elicit antiviral defenses by activating the cognate receptor composed of IFN-α/ß receptor chain 1 (IFNAR1) and IFNAR2. Down-regulation of this receptor occurs through IFN1-stimulated IFNAR1 ubiquitination, which exposes a Y466-based linear endocytic motif within IFNAR1 to recruitment of the adaptin protein-2 complex (AP2) and ensuing receptor endocytosis. Paradoxically, IFN1-induced Janus kinase-mediated phosphorylation of Y466 is expected to decrease its affinity for AP2 and to inhibit the endocytic rate. To explain how IFN1 promotes Y466 phosphorylation yet stimulates IFNAR1 internalization, we proposed that the activity of a protein tyrosine phosphatase (PTP) is required to enable both events by dephosphorylating Y466. An RNAi-based screen identified PTP1B as a specific regulator of IFNAR1 endocytosis stimulated by IFN1, but not by ligand-independent inducers of IFNAR1 ubiquitination. PTP1B is a promising target for treatment of obesity and diabetes; numerous research programs are aimed at identification and characterization of clinically relevant inhibitors of PTP1B. PTP1B is capable of binding and dephosphorylating IFNAR1. Genetic or pharmacologic modulation of PTP1B activity regulated IFN1 signaling in a manner dependent on the integrity of Y466 within IFNAR1 in human cells. These effects were less evident in mouse cells whose IFNAR1 lacks an analogous motif. PTP1B inhibitors robustly augmented the antiviral effects of IFN1 against vesicular stomatitis and hepatitis C viruses in human cells and proved beneficial in feline stomatitis patients. The clinical significance of these findings in the context of using PTP1B inhibitors to increase the therapeutic efficacy of IFN against viral infections is discussed.

Essential role for the Mnk pathway in the inhibitory effects of type I interferons on myeloproliferative neoplasm (MPN) precursors.

The mechanisms of generation of the antineoplastic effects of interferons (IFNs) in malignant hematopoietic cells remain to be precisely defined. We examined the activation of type I IFN-dependent signaling pathways in malignant cells transformed by Jak2V617F, a critical pathogenic mutation in myeloproliferative neoplasms (MPNs). Our studies demonstrate that during engagement of the type I IFN receptor (IFNAR), there is activation of Jak-Stat pathways and also engagement of Mnk kinases. Activation of Mnk kinases is regulated by the Mek/Erk pathway and is required for the generation of IFN-induced growth inhibitory responses, but Mnk kinase activation does not modulate IFN-regulated Jak-Stat signals. We demonstrate that for type I IFNs to exert suppressive effects in malignant hematopoietic progenitors from patients with polycythemia vera, induction of Mnk kinase activity is required, as evidenced by studies involving pharmacological inhibition of Mnk or siRNA-mediated Mnk knockdown. Altogether, these findings provide evidence for key and essential roles of the Mnk kinase pathway in the generation of the antineoplastic effects of type I IFNs in Jak2V617F-dependent MPNs.

Interferon ß induces clearance of mutant ataxin 7 and improves locomotion in SCA7 knock-in mice.

We showed previously, in a cell model of spinocerebellar ataxia 7, that interferon beta induces the expression of PML protein and the formation of PML protein nuclear bodies that degrade mutant ataxin 7, suggesting that the cytokine, used to treat multiple sclerosis, might have therapeutic value in spinocerebellar ataxia 7. We now show that interferon beta also induces PML-dependent clearance of ataxin 7 in a preclinical model, SCA7(266Q/5Q) knock-in mice, and improves motor function. Interestingly, the presence of mutant ataxin 7 in the mice induces itself the expression of endogenous interferon beta and its receptor. Immunohistological studies in brains from two patients with spinocerebellar ataxia 7 confirmed that these modifications are also caused by the disease in humans. Interferon beta, administered intraperitoneally three times a week in the knock-in mice, was internalized with its receptor in Purkinje and other cells and translocated to the nucleus. The treatment induced PML protein expression and the formation of PML protein nuclear bodies and decreased mutant ataxin 7 in neuronal intranuclear inclusions, the hallmark of the disease. No reactive gliosis or other signs of toxicity were observed in the brain or internal organs. The performance of the SCA7(266Q/5Q) knock-in mice was significantly improved on two behavioural tests sensitive to cerebellar function: the Locotronic® Test of locomotor function and the Beam Walking Test of balance, motor coordination and fine movements, which are affected in patients with spinocerebellar ataxia 7. In addition to motor dysfunction, SCA7(266Q/5Q) mice present abnormalities in the retina as in patients: ataxin 7-positive neuronal intranuclear inclusions that were reduced by interferon beta treatment. Finally, since neuronal death does not occur in the cerebellum of SCA7(266Q/5Q) mice, we showed in primary cell cultures expressing mutant ataxin 7 that interferon beta treatment improves Purkinje cell survival.

Sprouty proteins are negative regulators of interferon (IFN) signaling and IFN-inducible biological responses.

Interferons (IFNs) have important antiviral and antineoplastic properties, but the precise mechanisms required for generation of these responses remain to be defined. We provide evidence that during engagement of the Type I IFN receptor (IFNR), there is up-regulation of expression of Sprouty (Spry) proteins 1, 2, and 4. Our studies demonstrate that IFN-inducible up-regulation of Spry proteins is Mnk kinase-dependent and results in suppressive effects on the IFN-activated p38 MAP kinase (MAPK), the function of which is required for transcription of interferon-stimulated genes (ISGs). Our data establish that ISG15 mRNA expression and IFN-dependent antiviral responses are enhanced in Spry1,2,4 triple knock-out mouse embryonic fibroblasts, consistent with negative feedback regulatory roles for Spry proteins in IFN-mediated signaling. In other studies, we found that siRNA-mediated knockdown of Spry1, Spry2, or Spry4 promotes IFN-inducible antileukemic effects in vitro and results in enhanced suppressive effects on malignant hematopoietic progenitors from patients with polycythemia vera. Altogether, our findings demonstrate that Spry proteins are potent regulators of Type I IFN signaling and negatively control induction of Type I IFN-mediated biological responses.

Pathogen recognition receptor signaling accelerates phosphorylation-dependent degradation of IFNAR1.

An ability to sense pathogens by a number of specialized cell types including the dendritic cells plays a central role in host's defenses. Activation of these cells through the stimulation of the pathogen-recognition receptors induces the production of a number of cytokines including Type I interferons (IFNs) that mediate the diverse mechanisms of innate immunity. Type I IFNs interact with the Type I IFN receptor, composed of IFNAR1 and IFNAR2 chains, to mount the host defense responses. However, at the same time, Type I IFNs elicit potent anti-proliferative and pro-apoptotic effects that could be detrimental for IFN-producing cells. Here, we report that the activation of p38 kinase in response to pathogen-recognition receptors stimulation results in a series of phosphorylation events within the IFNAR1 chain of the Type I IFN receptor. This phosphorylation promotes IFNAR1 ubiquitination and accelerates the proteolytic turnover of this receptor leading to an attenuation of Type I IFN signaling and the protection of activated dendritic cells from the cytotoxic effects of autocrine or paracrine Type I IFN. In this paper we discuss a potential role of this mechanism in regulating the processes of innate immunity.

Vascular endothelial growth factor-induced elimination of the type 1 interferon receptor is required for efficient angiogenesis.

Angiogenesis is stimulated by vascular endothelial growth factor (VEGF) and antagonized by type 1 interferons, including IFN-α/ß. On engaging their respective receptors (VEGFR2 and IFNAR), both stimuli activate protein kinase D2 (PKD2) and type 1 IFNs require PKD2 activation and recruitment to IFNAR1 to promote the phosphorylation-dependent ubiquitination, down-regulation, and degradation of the cognate receptor chain, IFNAR1. Data reveal that PKD2 activity is dispensable for VEGF-stimulated down-regulation of VEGFR2. Remarkably, VEGF treatment promotes the recruitment of PKD2 to IFNAR1 as well as ensuing phosphorylation, ubiquitination, and degradation of IFNAR1. In cells exposed to VEGF, phosphorylation-dependent degradation of IFNAR1 leads to an inhibition of type 1 IFN signaling and is required for efficient VEGF-stimulated angiogenesis. Importance of this mechanism for proangiogenic or antiangiogenic responses in cells exposed to counteracting stimuli and the potential medical significance of this regulation are discussed.

Bcr-abl signals to desensitize chronic myeloid leukemia cells to IFNα via accelerating the degradation of its receptor.

Constitutive activity of Bcr-abl fusion protein kinase causes chronic myeloid leukemia (CML). Inhibitors of Bcr-abl such as imatinib mesylate have replaced the cytokine IFNα as the primary treatment for the management of patients with this malignancy. We found that pretreatment of CML cells with imatinib mesylate augments the antigrowth effects of IFNα. Furthermore, introduction of Bcr-abl into non-CML cells inhibits the cellular responses to IFNα. This inhibition is mediated via a mechanism that involves activation of protein kinase D2. The latter promotes an accelerated phosphorylation-dependent degradation of the interferon-α/ß receptor 1 chain of the type I interferon receptor, leading to attenuation of IFNα signaling. We discuss the relationship between Bcr-abl activity and IFNα signaling as a molecular basis of the combination of inhibitors of Bcr-abl and IFNα for CML treatment.

Endocrine and multiple sclerosis outcomes in patients with autoimmune thyroid events in the alemtuzumab CARE-MS studies.

Background: Alemtuzumab is an effective therapy for relapsing multiple sclerosis. Autoimmune thyroid events are a common adverse event. Objective: Describe endocrine and multiple sclerosis outcomes over 6 years for alemtuzumab-treated relapsing multiple sclerosis patients in the phase 3 CARE-MS I, II, and extension studies who experienced adverse thyroid events. Methods: Endocrine and multiple sclerosis outcomes were evaluated over 6 years. Thyroid event cases, excluding those pre-existing or occurring after Year 6, were adjudicated retrospectively by expert endocrinologists independently of the sponsor and investigators. Results: Thyroid events were reported for 378/811 (46.6%) alemtuzumab-treated patients. Following adjudication, endocrinologists reached consensus on 286 cases (75.7%). Of these, 39.5% were adjudicated to Graves' disease, 2.5% Hashimoto's disease switching to hyperthyroidism, 15.4% Hashimoto's disease, 4.9% Graves' disease switching to hypothyroidism, 10.1% transient thyroiditis, and 27.6% with uncertain diagnosis; inclusion of anti-thyroid antibody status reduced the number of uncertain diagnoses. Multiple sclerosis outcomes of those with and without thyroid events were similar. Conclusion: Adjudicated thyroid events occurring over 6 years for alemtuzumab-treated relapsing multiple sclerosis patients were primarily autoimmune. Thyroid events were considered manageable and did not affect disease course. Thyroid autoimmunity is a common but manageable adverse event in alemtuzumab-treated relapsing multiple sclerosis patients.ClinicalTrials.gov Registration Numbers: CARE-MS I (NCT00530348); CARE-MS II (NCT00548405); CARE-MS Extension (NCT00930553).

Tyrosine phosphorylation of protein kinase D2 mediates ligand-inducible elimination of the Type 1 interferon receptor.

Type 1 interferons (including IFNα/ß) activate their cell surface receptor to induce the intracellular signal transduction pathways that play an important role in host defenses against infectious agents and tumors. The extent of cellular responses to IFNα is limited by several important mechanisms including the ligand-stimulated and specific serine phosphorylation-dependent degradation of the IFNAR1 chain of Type 1 IFN receptor. Previous studies revealed that acceleration of IFNAR1 degradation upon IFN stimulation requires activities of tyrosine kinase TYK2 and serine/threonine protein kinase D2 (PKD2), whose recruitment to IFNAR1 is also induced by the ligand. Here we report that activation of PKD2 by IFNα (but not its recruitment to the receptor) depends on TYK2 catalytic activity. PKD2 undergoes IFNα-inducible tyrosine phosphorylation on specific phospho-acceptor site (Tyr-438) within the plekstrin homology domain. Activated TYK2 is capable of facilitating this phosphorylation in vitro. Tyrosine phosphorylation of PKD2 is required for IFNα-stimulated activation of this kinase as well as for efficient serine phosphorylation and degradation of IFNAR1 and ensuing restriction of the extent of cellular responses to IFNα.

Role of p38 protein kinase in the ligand-independent ubiquitination and down-regulation of the IFNAR1 chain of type I interferon receptor.

Phosphorylation-dependent ubiquitination and degradation of the IFNAR1 chain of type I interferon (IFN) receptor is a robust and specific mechanism that limits the magnitude and duration of IFNα/ß signaling. Besides the ligand-inducible IFNAR1 degradation, the existence of an "inside-out" signaling that accelerates IFNAR1 turnover in the cells undergoing the endoplasmic reticulum (ER) stress and activated unfolded protein responses has been recently described. The latter pathway does not require either presence of ligands (IFNα/ß) or catalytic activity of Janus kinases (JAK). Instead, this pathway relies on activation of the PKR-like ER kinase (PERK) and ensuing specific priming phosphorylation of IFNAR1. Here, we describe studies that identify the stress activated p38 protein kinase as an important regulator of IFNAR1 that acts downstream of PERK. Results of the experiments using pharmacologic p38 kinase inhibitors, RNA interference approach, and cells from p38α knock-out mice suggest that p38 kinase activity is required for priming phosphorylation of IFNAR1 in cells undergoing unfolded protein response. We further demonstrate an important role of p38 kinase in the ligand-independent stimulation of IFNAR1 ubiquitination and degradation and ensuing attenuation of IFNα/ß signaling and anti-viral defenses. We discuss the distinct importance of p38 kinase in regulating the overall responses to type I IFN in cells that have been already exposed to IFNα/ß versus those cells that are yet to encounter these cytokines.