Complementation by the protein tyrosine kinase JAK2 of a mutant cell line defective in the interferon-gamma signal transduction pathway

Exercise-derived peptide protects against pathological cardiac remodeling

Background

Exercise training protects the heart against pathological cardiac remodeling and confers cardioprotection from heart failure. However, the underlying mechanism is still elusive.

Methods

An integrative analysis of multi-omics data of the skeletal muscle in response to exercise is performed to search for potential exerkine. Then, CCDC80tide is examined in humans after acute exercise. The role of CCDC80tide is assessed in a mouse model of hypertensive cardiac remodeling and in hypertension-mediated cell injury models. The transcriptomic analysis and immunoprecipitation assay are conducted to explore the mechanism.

Findings

The coiled-coil domain-containing protein 80 (CCDC80) is found strongly positively associated with exercise. Interestingly, exercise stimuli induce the secretion of C-terminal CCDC80 (referred as CCDC80tide hereafter) via EVs-encapsulated CCDC80tide into the circulation. Importantly, cardiac-specific expression of CCDC80tide protects against angiotensin II (Ang II)-induced cardiac hypertrophy and fibrosis in mice. In in vitro studies, the expression of CCDC80tide reduces Ang II-induced cardiomyocyte hypertrophy, cardiac microvascular endothelial cell (CMEC) inflammation, and mitigated vascular smooth muscle cell (VSMC) proliferation and collagen formation. To understand the cardioprotective effect of CCDC80tide, a transcriptomic analysis reveals a dramatic inhibition of the STAT3 (Signal transducer and activator of transcription 3) signaling pathway in CCDC80tide overexpressing cells. Mechanistically, CCDC80tide selectively interacts with the kinase-active form of JAK2 (Janus kinase 2) and consequently inhibits its kinase activity to phosphorylate and activate STAT3.

Interpretation

The results provide new insights into exercise-afforded cardioprotection in pathological cardiac remodeling and highlight the therapeutic potential of CCDC80tide in heart failure treatment.

Funding

This work was supported by the National Natural Science Foundation of China [Grant/Award Numbers: 81770428, 81830010, 82130012, 81900438, 82100447); Shanghai Science and Technology Committee [Grant/Award Numbers: 21S11903000, 19JC1415702]; Emerging and Advanced Technology Programs of Hospital Development Center of Shanghai [Grant/Award Number: SHDC12018129]; China Postdoctoral Science Foundation [2021M692108]; and China National Postdoctoral Program for Innovative Talents [BX20200211].

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

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

Importance of Type I and III Interferons at Respiratory and Intestinal Barrier Surfaces

Interferons (IFNs) constitute the first line of defense against microbial infections particularly against viruses. They provide antiviral properties to cells by inducing the expression of hundreds of genes known as interferon-stimulated genes (ISGs). The two most important IFNs that can be produced by virtually all cells in the body during intrinsic innate immune response belong to two distinct families: the type I and type III IFNs. The type I IFN receptor is ubiquitously expressed whereas the type III IFN receptor's expression is limited to epithelial cells and a subset of immune cells. While originally considered to be redundant, type III IFNs have now been shown to play a unique role in protecting mucosal surfaces against pathogen challenges. The mucosal specific functions of type III IFN do not solely rely on the restricted epithelial expression of its receptor but also on the distinct means by which type III IFN mediates its anti-pathogen functions compared to the type I IFN. In this review we first provide a general overview on IFNs and present the similarities and differences in the signal transduction pathways leading to the expression of either type I or type III IFNs. By highlighting the current state-of-knowledge of the two archetypical mucosal surfaces (e.g. the respiratory and intestinal epitheliums), we present the differences in the signaling cascades used by type I and type III IFNs to uniquely induce the expression of ISGs. We then discuss in detail the role of each IFN in controlling pathogen infections in intestinal and respiratory epithelial cells. Finally, we provide our perspective on novel concepts in the field of IFN (stochasticity, response heterogeneity, cellular polarization/differentiation and tissue microenvironment) that we believe have implications in driving the differences between type I and III IFNs and could explain the preferences for type III IFNs at mucosal surfaces.

Molecular Structure and Function of Janus Kinases: Implications for the Development of Inhibitors

Cytokines can trigger multiple signalling pathways, including Janus tyrosine kinases [JAK] and signal transducers and activators of transcription [STATS] pathways. JAKs are cytoplasmic proteins that, following the binding of cytokines to their receptors, transduce the signal by phosphorylating STAT proteins which enter the nuclei and rapidly target gene promoters to regulate gene transcription. Due to the critical involvement of JAK proteins in mediating innate and adaptive immune responses, these family of kinases have become desirable pharmacological targets in inflammatory diseases, including ulcerative colitis and Crohn's disease. In this review we provide an overview of the main cytokines that signal through the JAK/STAT pathway and the available in vivo evidence on mutant or deleted JAK proteins, and discuss the implications of pharmacologically targeting this kinase family in the context of inflammatory diseases.

Defective Influenza A Virus RNA Products Mediate MAVS-Dependent Upregulation of Human Leukocyte Antigen Class I Proteins

Human leukocyte antigens (HLAs) are cell surface proteins that regulate innate and adaptive immune responses to viral infection by engaging with receptors on immune cells. Many viruses have evolved ways to evade host immune responses by modulating HLA expression and/or processing. Here, we provide evidence that aberrant RNA products of influenza virus genome replication can trigger retinoic acid-inducible gene I (RIG-I)/mitochondrial antiviral signaling (MAVS)-dependent remodeling of the cell surface, increasing surface presentation of HLA proteins known to inhibit the activation of an immune cell known as a natural killer (NK) cell. While this HLA upregulation would seem to be advantageous to the virus, it is kept in check by the viral nonstructural 1 (NS1) protein, which limits RIG-I activation and interferon production by the infected cell.

Influenza A virus (IAV) increases the presentation of class I human leukocyte antigen (HLA) proteins that limit antiviral responses mediated by natural killer (NK) cells, but molecular mechanisms for these processes have not yet been fully elucidated. We observed that infection with A/Fort Monmouth/1/1947(H1N1) IAV significantly increased the presentation of HLA-B, -C, and -E on lung epithelial cells. Virus entry was not sufficient to induce HLA upregulation because UV-inactivated virus had no effect. Aberrant internally deleted viral RNAs (vRNAs) known as mini viral RNAs (mvRNAs) and defective interfering RNAs (DI RNAs) expressed from an IAV minireplicon were sufficient for inducing HLA upregulation. These defective RNAs bind to retinoic acid-inducible gene I (RIG-I) and initiate mitochondrial antiviral signaling (MAVS) protein-dependent antiviral interferon (IFN) responses. Indeed, MAVS was required for HLA upregulation in response to IAV infection or ectopic mvRNA/DI RNA expression. The effect was partially due to paracrine signaling, as we observed that IAV infection or mvRNA/DI RNA-expression stimulated production of IFN-β and IFN-λ1 and conditioned media from these cells elicited a modest increase in HLA surface levels in naive epithelial cells. HLA upregulation in response to aberrant viral RNAs could be prevented by the Janus kinase (JAK) inhibitor ruxolitinib. While HLA upregulation would seem to be advantageous to the virus, it is kept in check by the viral nonstructural 1 (NS1) protein; we determined that NS1 limits cell-intrinsic and paracrine mechanisms of HLA upregulation. Taken together, our findings indicate that aberrant IAV RNAs stimulate HLA presentation, which may aid viral evasion of innate immunity.

IMPORTANCE Human leukocyte antigens (HLAs) are cell surface proteins that regulate innate and adaptive immune responses to viral infection by engaging with receptors on immune cells. Many viruses have evolved ways to evade host immune responses by modulating HLA expression and/or processing. Here, we provide evidence that aberrant RNA products of influenza virus genome replication can trigger retinoic acid-inducible gene I (RIG-I)/mitochondrial antiviral signaling (MAVS)-dependent remodeling of the cell surface, increasing surface presentation of HLA proteins known to inhibit the activation of an immune cell known as a natural killer (NK) cell. While this HLA upregulation would seem to be advantageous to the virus, it is kept in check by the viral nonstructural 1 (NS1) protein, which limits RIG-I activation and interferon production by the infected cell.

Loss of ZIP facilitates JAK2-STAT3 activation in tamoxifen-resistant breast cancer

Tamoxifen is beneficial in treating estrogen receptor–positive breast cancer, but resistance to this treatment eventually ensues. A method to identify mechanisms of tamoxifen resistance identified the histone deacetylase ZIP, leading to the finding that increased expression of the tyrosine kinase JAK2 is one important factor. As a result of this discovery, it may be possible to use an inhibitor of JAK2 to block the aberrant activation of STAT3 caused by ZIP deficiency to help overcome or prevent tamoxifen resistance.

Tamoxifen, a widely used modulator of the estrogen receptor (ER), targets ER-positive breast cancer preferentially. We used a powerful validation-based insertion mutagenesis method to find that expression of a dominant-negative, truncated form of the histone deacetylase ZIP led to resistance to tamoxifen. Consistently, increased expression of full-length ZIP gives the opposite phenotype, inhibiting the expression of genes whose products mediate resistance. An important example is JAK2. By binding to two specific sequences in the promoter, ZIP suppresses JAK2 expression. Increased expression and activation of JAK2 when ZIP is inhibited lead to increased STAT3 phosphorylation and increased resistance to tamoxifen, both in cell culture experiments and in a mouse xenograft model. Furthermore, data from human tumors are consistent with the conclusion that decreased expression of ZIP leads to resistance to tamoxifen in ER-positive breast cancer.

Tumor Interferon Signaling Is Regulated by a lncRNA INCR1 Transcribed from the PD-L1 Locus

Tumor interferon (IFN) signaling promotes PD-L1 expression to suppress T cell-mediated immunosurveillance. We identify the IFN-stimulated non-coding RNA 1 (INCR1) as a long noncoding RNA (lncRNA) transcribed from the PD-L1 locus and show that INCR1 controls IFNγ signaling in multiple tumor types. Silencing INCR1 decreases the expression of PD-L1, JAK2, and several other IFNγ-stimulated genes. INCR1 knockdown sensitizes tumor cells to cytotoxic T cell-mediated killing, improving CAR T cell therapy. We discover that PD-L1 and JAK2 transcripts are negatively regulated by binding to HNRNPH1, a nuclear ribonucleoprotein. The primary transcript of INCR1 binds HNRNPH1 to block its inhibitory effects on the neighboring genes PD-L1 and JAK2, enabling their expression. These findings introduce a mechanism of tumor IFNγ signaling regulation mediated by the lncRNA INCR1 and suggest a therapeutic target for cancer immunotherapy.

Zika virus non-structural protein NS4A restricts eye growth in Drosophila through regulation of JAK/STAT signaling

To gain a comprehensive view of the changes in host gene expression underlying Zika virus (ZIKV) pathogenesis, we performed whole-genome RNA sequencing (RNA-seq) of ZIKV-infected Drosophila adult flies. RNA-seq analysis revealed that ZIKV infection alters several and diverse biological processes, including stress, locomotion, lipid metabolism, imaginal disc morphogenesis and regulation of JAK/STAT signaling. To explore the interaction between ZIKV infection and JAK/STAT signaling regulation, we generated genetic constructs overexpressing ZIKV-specific non-structural proteins NS2A, NS2B, NS4A and NS4B. We found that ectopic expression of non-structural proteins in the developing Drosophila eye significantly restricts growth of the larval and adult eye and correlates with considerable repression of the in vivo JAK/STAT reporter, 10XStat92E-GFP At the cellular level, eye growth defects are associated with reduced rate of proliferation without affecting the overall rate of apoptosis. In addition, ZIKV NS4A genetically interacts with the JAK/STAT signaling components; co-expression of NS4A along with the dominant-negative form of domeless or StatRNAi results in aggravated reduction in eye size, while co-expression of NS4A in HopTuml (also known as hopTum ) mutant background partially rescues the hop-induced eye overgrowth phenotype. The function of ZIKV NS4A in regulating growth is maintained in the wing, where ZIKV NS4A overexpression in the pouch domain results in reduced growth linked with diminished expression of Notch targets, Wingless (Wg) and Cut, and the Notch reporter, NRE-GFP Thus, our study provides evidence that ZIKV infection in Drosophila results in restricted growth of the developing eye and wing, wherein eye phenotype is induced through regulation of JAK/STAT signaling, whereas restricted wing growth is induced through regulation of Notch signaling. The interaction of ZIKV non-structural proteins with the conserved host signaling pathways further advance our understanding of ZIKV-induced pathogenesis.This article has an associated First Person interview with the first author of the paper.

Inflammatory cytokines: from discoveries to therapies in IBD

Introduction: Although the etiology of inflammatory bowel diseases (IBD) remains unknown, accumulating evidence suggests that the intestinal tissue damage in these disorders is due to a dynamic interplay between immune cells and non-immune cells, which is mediated by cytokines produced within the inflammatory microenvironment. Areas covered: We review the available data about the role of inflammatory cytokines in IBD pathophysiology and provide an overview of the therapeutic options to block the function of such molecules. Expert opinion: Genome studies, in vitro experiments with patients' samples and animal models of colitis, have largely advanced our understanding of how cytokines modulate the ongoing mucosal inflammation in IBD. However, not all the cytokines produced within the damaged gut seem to play a major role in the amplification and perpetuation of the IBD-associated inflammatory cascade. Indeed, while some of the anti-cytokine compounds are effective in some subgroups of IBD patients, others have no benefit. In this complex scenario, a major unmet need is the identification of biomarkers that can predict response to therapy and facilitate a personalized therapeutic approach, which maximizes the benefits and limits the adverse events.

HDAC is indispensable for IFN-γ-induced B7-H1 expression in gastric cancer

Background

B7 homolog 1 (B7-H1) overexpression on tumor cells is an important mechanism of immune evasion in gastric cancer (GC). Elucidation of the regulation of B7-H1 expression is urgently required to guide B7-H1-targeted cancer therapy. Interferon gamma (IFN-γ) is thought to be the main driving force behind B7-H1 expression, and epigenetic factors including histone acetylation are recently linked to the process. Here, we investigated the potential role of histone deacetylase (HDAC) in IFN-γ-induced B7-H1 expression in GC. The effect of Vorinostat (SAHA), a small molecular inhibitor of HDAC, on tumor growth and B7-H1 expression in a mouse GC model was also evaluated.

Results

RNA-seq data from The Cancer Genome Atlas revealed that expression of B7-H1, HDAC1–3, 6–8, and 10 and SIRT1, 3, 5, and 6 was higher, and expression of HDAC5 and SIRT4 was lower in GC compared to that in normal gastric tissues; that HDAC3 and HDAC1 expression level significantly correlated with B7-H1 in GC with a respective r value of 0.42 (p < 0.001) and 0.21 (p < 0.001). HDAC inhibitor (Trichostatin A, SAHA, and sodium butyrate) pretreatment suppressed IFN-γ-induced B7-H1 expression on HGC-27 cells. HDAC1 and HDAC3 gene knockdown had the same effect. SAHA pretreatment or HDAC knockdown resulted in impaired IFN-γ signaling, demonstrated by the reduction of JAK2, p-JAK1, p-JAK2, and p-STAT1 expression and inefficient STAT1 nuclear translocation. Furthermore, SAHA pretreatment compromised IFN-γ-induced upregulation of histone H3 lysine 9 acetylation level in B7-H1 gene promoter. In the grafted mouse GC model, SAHA treatment suppressed tumor growth, inhibited B7-H1 expression, and elevated the percentage of tumor-infiltrating CD8+ T cells.

Conclusion

HDAC is indispensable for IFN-γ-induced B7-H1 in GC. The study suggests the possibility of targeting B7-H1 using small molecular HDAC inhibitors for cancer treatment.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0589-6) contains supplementary material, which is available to authorized users.

Interferons type II and their receptors R1 and R2 in fish species: Evolution, structure, and function

Interferon gamma (IFN-γ) is one of the key players in the immune system of vertebrates. The evolution and properties of IFN-γ and its receptors in fish species are of special interest as they point to the origin of innate immunity in vertebrates. We studied the phylogeny, biophysical and structural properties of IFN-γ and its receptors. Our phylogeny analysis suggests the existence of two groups of IFN-γ related proteins, one specific for Acanthomorpha, the other for Cypriniformes, Characiformes and Siluriformes. The analysis further shows an ancient duplication of the gene for IFN-γ receptor 1 (IFN- γR1) and the parallel existence of the duplicated genes in all current teleost fish species. In contrast, only one gene can be found for receptor 2, IFN- γR2. The specificity of the interaction between IFN- γ and both types of IFN- γR1 was determined by microscale thermophoresis measurements of the equilibrium dissociation constants for the proteins from three fish species. The measured preference of IFN- γ for one of the two forms of receptor 1agrees with the bioinformatic analysis of the coevolution between IFN- γ and receptor 1. To elucidate structural relationships between IFN-γ of fish and other vertebrate species, we determined the crystal structure of IFN-γ from olive flounder (Paralichthys olivaceus, PoliIFN-γ) at crystallographic resolution of 2.3 Å and the low-resolution structures of Takifugu rubripes, Oreochromis niloticus, and Larimichthys crocea IFN-γ by small angle X-ray diffraction. The overall PoliIFN-γ fold is the same as the fold of the other known IFN- γ structures but there are some significant structural differences, namely the additional C-terminal helix G and a different angle between helices C and D in PoliIFN-γ.

Primary Resistance to PD-1 Blockade Mediated by JAK1/2 Mutations

Loss-of-function mutations in JAK1/2 can lead to acquired resistance to anti-programmed death protein 1 (PD-1) therapy. We reasoned that they may also be involved in primary resistance to anti-PD-1 therapy. JAK1/2-inactivating mutations were noted in tumor biopsies of 1 of 23 patients with melanoma and in 1 of 16 patients with mismatch repair-deficient colon cancer treated with PD-1 blockade. Both cases had a high mutational load but did not respond to anti-PD-1 therapy. Two out of 48 human melanoma cell lines had JAK1/2 mutations, which led to a lack of PD-L1 expression upon interferon gamma exposure mediated by an inability to signal through the interferon gamma receptor pathway. JAK1/2 loss-of-function alterations in The Cancer Genome Atlas confer adverse outcomes in patients. We propose that JAK1/2 loss-of-function mutations are a genetic mechanism of lack of reactive PD-L1 expression and response to interferon gamma, leading to primary resistance to PD-1 blockade therapy.

SIGNIFICANCE

A key functional result from somatic JAK1/2 mutations in a cancer cell is the inability to respond to interferon gamma by expressing PD-L1 and many other interferon-stimulated genes. These mutations result in a genetic mechanism for the absence of reactive PD-L1 expression, and patients harboring such tumors would be unlikely to respond to PD-1 blockade therapy. Cancer Discov; 7(2); 188-201. ©2016 AACR.See related commentary by Marabelle et al., p. 128This article is highlighted in the In This Issue feature, p. 115.

Primary Resistance to PD-1 Blockade Mediated by JAK1/2 Mutations

Loss-of-function mutations in JAK1/2 can lead to acquired resistance to anti-programmed death protein 1 (PD-1) therapy. We reasoned that they may also be involved in primary resistance to anti-PD-1 therapy. JAK1/2-inactivating mutations were noted in tumor biopsies of 1 of 23 patients with melanoma and in 1 of 16 patients with mismatch repair-deficient colon cancer treated with PD-1 blockade. Both cases had a high mutational load but did not respond to anti-PD-1 therapy. Two out of 48 human melanoma cell lines had JAK1/2 mutations, which led to a lack of PD-L1 expression upon interferon gamma exposure mediated by an inability to signal through the interferon gamma receptor pathway. JAK1/2 loss-of-function alterations in The Cancer Genome Atlas confer adverse outcomes in patients. We propose that JAK1/2 loss-of-function mutations are a genetic mechanism of lack of reactive PD-L1 expression and response to interferon gamma, leading to primary resistance to PD-1 blockade therapy.

SIGNIFICANCE

A key functional result from somatic JAK1/2 mutations in a cancer cell is the inability to respond to interferon gamma by expressing PD-L1 and many other interferon-stimulated genes. These mutations result in a genetic mechanism for the absence of reactive PD-L1 expression, and patients harboring such tumors would be unlikely to respond to PD-1 blockade therapy. Cancer Discov; 7(2); 188-201. ©2016 AACR.See related commentary by Marabelle et al., p. 128This article is highlighted in the In This Issue feature, p. 115.

Mutations Associated with Acquired Resistance to PD-1 Blockade in Melanoma

BACKGROUND

Approximately 75% of objective responses to anti-programmed death 1 (PD-1) therapy in patients with melanoma are durable, lasting for years, but delayed relapses have been noted long after initial objective tumor regression despite continuous therapy. Mechanisms of immune escape in this context are unknown.

METHODS

We analyzed biopsy samples from paired baseline and relapsing lesions in four patients with metastatic melanoma who had had an initial objective tumor regression in response to anti-PD-1 therapy (pembrolizumab) followed by disease progression months to years later.

RESULTS

Whole-exome sequencing detected clonal selection and outgrowth of the acquired resistant tumors and, in two of the four patients, revealed resistance-associated loss-of-function mutations in the genes encoding interferon-receptor-associated Janus kinase 1 (JAK1) or Janus kinase 2 (JAK2), concurrent with deletion of the wild-type allele. A truncating mutation in the gene encoding the antigen-presenting protein beta-2-microglobulin (B2M) was identified in a third patient. JAK1 and JAK2 truncating mutations resulted in a lack of response to interferon gamma, including insensitivity to its antiproliferative effects on cancer cells. The B2M truncating mutation led to loss of surface expression of major histocompatibility complex class I.

CONCLUSIONS

In this study, acquired resistance to PD-1 blockade immunotherapy in patients with melanoma was associated with defects in the pathways involved in interferon-receptor signaling and in antigen presentation. (Funded by the National Institutes of Health and others.).

Growth hormone signaling pathways

Over 20years ago, our laboratory showed that growth hormone (GH) signals through the GH receptor-associated tyrosine kinase JAK2. We showed that GH binding to its membrane-bound receptor enhances binding of JAK2 to the GHR, activates JAK2, and stimulates tyrosyl phosphorylation of both JAK2 and GHR. The activated JAK2/GHR complex recruits a variety of signaling proteins, thereby initiating multiple signaling pathways and cellular responses. These proteins and pathways include: 1) Stat transcription factors implicated in the expression of multiple genes, including the gene encoding insulin-like growth factor 1; 2) Shc adapter proteins that lead to activation of the grb2-SOS-Ras-Raf-MEK-ERK1,2 pathway; 3) insulin receptor substrate proteins implicated in the phosphatidylinositol-3-kinase and Akt pathway; 4) signal regulatory protein α, a transmembrane scaffold protein that recruits proteins including the tyrosine phosphatase SHP2; and 5) SH2B1, a scaffold protein that can activate JAK2 and enhance GH regulation of the actin cytoskeleton. Our recent work has focused on the function of SH2B1. We have shown that SH2B1β is recruited to and phosphorylated by JAK2 in response to GH. SH2B1 localizes to the plasma membrane, cytoplasm and focal adhesions; it also cycles through the nucleus. SH2B1 regulates the actin cytoskeleton and promotes GH-dependent motility of RAW264.7 macrophages. Mutations in SH2B1 have been found in humans exhibiting severe early-onset childhood obesity and insulin resistance. These mutations impair SH2B1 enhancement of GH-induced macrophage motility. As SH2B1 is expressed ubiquitously and is also recruited to a variety of receptor tyrosine kinases, our results raise the possibility that effects of SH2B1 on the actin cytoskeleton in various cell types, including neurons, may play a role in regulating body weight.

Tofacitinib for the treatment of ulcerative colitis

INTRODUCTION

Management of patients with active ulcerative colitis (UC), one of the most frequent inflammatory bowel diseases in human beings, is mainly based on the use of mesalamine and corticosteroids. Since in the long-term, these two drugs may be ineffective in nearly one third of the patients, immunosuppressants and/or biologics are needed to control disease activity.

AREAS COVERED

The marked activation of JAK/STAT molecules in inflamed mucosa of UC patients and the demonstration that UC-associated mucosal injury is driven by soluble factors that signal through JAK/STAT pathways led to investigation of JAK inhibitors for the treatment of active UC. Tofacitinib, an oral inhibitor of the cytokine-driven JAK-STAT signalling cascade, has recently been proposed for the treatment of moderate-to-severe UC. Phase 2 study showed the efficacy of tofacitinib to induce clinical and endoscopic improvement/remission and the safety profile of the drug. Herein the authors review this compound.

EXPERT OPINION

The results obtained from clinical trials with tofacitinib suggest that this drug could be a new treatment option for patients with moderate to severe UC. However, further experimentation is needed to assess the efficacy of this drug in selected subgroups of patients as well as to maintain remission and to determine the long-term safety profile of the drug.

Tyrosine kinase 2 - Surveillant of tumours and bona fide oncogene

Tyrosine kinase 2 (TYK2) is a member of the Janus kinase (JAK) family, which transduces cytokine and growth factor signalling. Analysis of TYK2 loss-of-function revealed its important role in immunity to infection, (auto-) immunity and (auto-) inflammation. TYK2-deficient patients unravelled high similarity between mice and men with respect to cellular signalling functions and basic immunology. Genome-wide association studies link TYK2 to several autoimmune and inflammatory diseases as well as carcinogenesis. Due to its cytokine signalling functions TYK2 was found to be essential in tumour surveillance. Lately TYK2 activating mutants and fusion proteins were detected in patients diagnosed with leukaemic diseases suggesting that TYK2 is a potent oncogene. Here we review the cell intrinsic and extrinsic functions of TYK2 in the characteristics preventing and enabling carcinogenesis. In addition we describe an unexpected function of kinase-inactive TYK2 in tumour rejection.

Combining HDAC inhibitors with oncolytic virotherapy for cancer therapy

Histone deacetylase (HDAC) enzymes play a critical role in the epigenetic regulation of cellular functions and signaling pathways in many cancers. HDAC inhibitors (HDACi) have been validated for single use or in combination with other drugs in oncologic therapeutics. An even more novel combination therapy with HDACi is to use them with an oncolytic virus. HDACi may lead to an amplification of tumor-specific lytic effects by facilitating increased cycles of viral replication, but there may also be direct anticancer effects of the drug by itself. Here, we review the molecular mechanisms of anti-cancer effects of the combination of oncolytic viruses with HDACi.

CXCL10/CXCR3 signaling mediates inhibitory action by interferon-gamma on CRF-stimulated adrenocorticotropic hormone (ACTH) release

Secretion of hormones by the anterior pituitary gland can be stimulated or inhibited by paracrine factors that are produced during inflammatory reactions. The inflammation cytokine interferon-gamma (IFN-γ) is known to inhibit corticotropin-releasing factor (CRF)-stimulated adrenocorticotropin (ACTH) release but its signaling mechanism is not yet known. Using rat anterior pituitary, we previously demonstrated that the CXC chemokine ligand 10 (CXCL10), known as interferon-γ (IFN-γ) inducible protein 10 kDa, is expressed in dendritic cell-like S100β protein-positive (DC-like S100β-positive) cells and that its receptor CXCR3 is expressed in ACTH-producing cells. DC-like S100β-positive cells are a subpopulation of folliculo-stellate cells in the anterior pituitary. In the present study, we examine whether CXCL10/CXCR3 signaling between DC-like S100β-positive cells and ACTH-producing cells mediates inhibition of CRF-activated ACTH-release by IFN-γ, using a CXCR3 antagonist in the primary pituitary cell culture. We found that IFN-γ up-regulated Cxcl10 expression via JAK/STAT signaling and proopiomelanocortin (Pomc) expression, while we reconfirmed that IFN-γ inhibits CRF-stimulated ACTH-release. Next, we used a CXCR3 agonist in primary culture to analyze whether CXCL10 induces Pomc-expression and ACTH-release using a CXCR3 agonist in the primary culture. The CXCR3 agonist significantly stimulated Pomc-expression and inhibited CRF-induced ACTH-release, while ACTH-release in the absence of CRF did not change. Thus, the present study leads us to an assumption that CXCL10/CXCR3 signaling mediates inhibition of the CRF-stimulated ACTH-release by IFN-γ. Our findings bring us to an assumption that CXCL10 from DC-like S100β-positive cells acts as a local modulator of ACTH-release during inflammation.

The two interfaces of the STAT1 N-terminus exhibit opposite functions in IFNγ-regulated gene expression

Defective cooperative DNA binding of STAT1 (signal transducer and activator of transcription 1) transcription factor has impact on interferon-γ(IFNγ)-regulated transcriptional responses. In this study, we generated N-terminal gain-of-function mutants of this protein which exhibited hyperactive cooperativity and assessed their functional consequences on gene expression. Our data show that four negatively charged, surface-exposed amino acid residues in the N-terminal domain dimer are engaged in the disassembly of tyrosine-phosphorylated tetrameric complexes on DNA and prevent the occurrence of higher-order STAT1 oligomers on low-affinity DNA binding sites. Owing to their improved tetramer stability, the N-terminal mutants showed relaxed sequence requirements for the binding to DNA as compared to the wild-type protein. Similarly to a STAT1 mutant with impaired tetramerization, the N-terminal gain-of-function mutants showed elevated tyrosine-phosphorylation levels and prolonged nuclear accumulation upon stimulation of cells with IFNγ. However, in contrast to the global impairment of IFNγ signalling in tetramerization-deficient mutants, the transcriptional consequences of the N-terminal gain-of-function mutants are rather distinct and affect gene expression locally in a promoter-specific manner. Thus, we conclude that the STAT1 N-domain acts as a double-edged sword: while one interface is crucial for the formation of tetrameric complexes on IFNγ-regulated promoters, the opposite interface harbours an inhibitory mechanism that limits the accumulation of higher-order oligomers simply by disrupting cooperative DNA binding.

DNA binding reduces the dissociation rate of STAT1 dimers and impairs the interdimeric exchange of protomers

BACKGROUND

A shift between two dimer conformations has been proposed for the transcription factor STAT1 (signal transducer and activator of transcription 1) which links DNA binding of the parallel dimer to tyrosine dephosphorylation of the antiparallel dimer as two consecutive and important steps in interferon- γ (IFNγ)-mediated signalling. However, neither the kinetics nor the molecular mechanisms involved in this conformational transition have been determined so far.

RESULTS

Our results demonstrated that the dissociation of dimers into monomers and their subsequent re-association into newly formed tyrosine-phosphorylated dimers is a relatively slow process as compared to the fast release from high-affinity DNA-binding sites, termed GAS (gamma-activated sequence). In addition, we noted an inhibitory effect of GAS binding on the exchange rate of protomers, indicating that DNA binding substantially impedes the recombination of dimeric STAT1. Furthermore, we found that reciprocal aminoterminal interactions between two STAT1 molecules are not required for the interchange of protomers, as an oligomerization-deficient point mutant displayed similar interdimeric exchange kinetics as the wild-type molecule.

CONCLUSIONS

Our results demonstrate that DNA binding impairs the oscillation rate between STAT1 conformers. Furthermore, these data suggest that the rapid release from high-affinity GAS sites is not a rate-limiting step in IFNγ-mediated signal transduction. Further investigations are needed to decipher the physiological significance of the observed dissociation/re-association process of STAT1 dimers.

Induction of a unique isoform of the NCOA7 oxidation resistance gene by interferon β-1b

We demonstrate that interferon (IFN)-β-1b induces an alternative-start transcript containing the C-terminal TLDc domain of nuclear receptor coactivator protein 7 (NCOA7), a member of the OXR family of oxidation resistance proteins. IFN-β-1b induces NCOA7-AS (alternative start) expression in peripheral blood mononuclear cells (PBMCs) obtained from healthy individuals and multiple sclerosis patients and human fetal brain cells, astrocytoma, neuroblastoma, and fibrosarcoma cells. NCOA7-AS is a previously undocumented IFN-β-inducible gene that contains only the last 5 exons of full-length NCOA7 plus a unique first exon (exon 10a) that is not found in longer forms of NCOA7. This exon encodes a domain closely related to an important class of bacterial aldo-keto oxido-reductase proteins that play a critical role in regulating redox activity. We demonstrate that NCOA7-AS is induced by IFN and LPS, but not by oxidative stress and exhibits, independently, oxidation resistance activity. We further demonstrate that induction of NCOA7-AS by IFN is dependent on IFN-receptor activation, the Janus kinase-signal transducers and activators of transcription (JAK-STAT) signaling pathway, and a canonical IFN-stimulated response element regulatory sequence upstream of exon 10a. We describe a new role for IFN-βs involving a mechanism of action that leads to an increase in resistance to inflammation-mediated oxidative stress.

JAK2 tyrosine kinase phosphorylates and is negatively regulated by centrosomal protein Ninein

JAK2 is a cytoplasmic tyrosine kinase critical for cytokine signaling. In this study, we have identified a novel centrosome-associated complex containing ninein and JAK2. We have found that active JAK2 localizes around the mother centrioles, where it partly colocalizes with ninein, a protein involved in microtubule (MT) nucleation and anchoring. We demonstrated that JAK2 is an important regulator of centrosome function. Depletion of JAK2 or use of JAK2-null cells causes defects in MT anchoring and increased numbers of cells with mitotic defects; however, MT nucleation is unaffected. We showed that JAK2 directly phosphorylates the N terminus of ninein while the C terminus of ninein inhibits JAK2 kinase activity in vitro. Overexpressed wild-type (WT) or C-terminal (amino acids 1179 to 1931) ninein inhibits JAK2. This ninein-dependent inhibition of JAK2 significantly decreases prolactin- and interferon gamma (IFN-γ)-induced tyrosyl phosphorylation of STAT1 and STAT5. Downregulation of ninein enhances JAK2 activation. These results indicate that JAK2 is a novel member of centrosome-associated complex and that this localization regulates both centrosomal function and JAK2 kinase activity, thus controlling cytokine-activated molecular pathways.

Suppression of Smad-1 mRNA expression level by Smad-2 likely control dichotomy of NF-κB and Smads mediated activation

The aim of this study was to find out how NF-κB and Smad-mediated signaling influenced the expression of astrogliogenic versus neurogenic markers of brain development in U4C cells which were either enriched (Tg Jak-1) or deprived in Jak-1 molecule (Jak-1 KO). Genetically modified U4C cells were transfected with NF-kB reporter plasmid in order to follow its activation when cells were cotransfected with different combinations of Smads constructs. In wild type cells no significant activation of NF-κB was observed while genetically modified cells exhibited somewhat different pattern of NF-κB activation depending on the Smad constructs combination used. The absence of NF-κB activation in Jak-1 transgenic cells transfected with Smad-1 plus Smad-3 was accompanied by the appearance of apoptotic cells as revealed by DAPI staining. Smad-1 expression was undetectable in Jak-1 transgenic cells and was downregulated in wild type cells upon transfection with Smad-2. The absence of p65 nuclear translocation in Smad-2 transfected cells and the presence of Smad-4 in nucleus of the same cells indicates dichotomy in NF-κB and Smads mediated signaling pathways. The significance of this study is that helps to elucidate the point of collaboration among three different signaling pathways - Jak-1 mediated cytokine signaling, NF-κB and Smads mediated pathways.

The molecular regulation of Janus kinase (JAK) activation

The JAK (Janus kinase) family members serve essential roles as the intracellular signalling effectors of cytokine receptors. This family, comprising JAK1, JAK2, JAK3 and TYK2 (tyrosine kinase 2), was first described more than 20 years ago, but the complexities underlying their activation, regulation and pleiotropic signalling functions are still being explored. Here, we review the current knowledge of their physiological functions and the causative role of activating and inactivating JAK mutations in human diseases, including haemopoietic malignancies, immunodeficiency and inflammatory diseases. At the molecular level, recent studies have greatly advanced our knowledge of the structures and organization of the component FERM (4.1/ezrin/radixin/moesin)-SH2 (Src homology 2), pseudokinase and kinase domains within the JAKs, the mechanism of JAK activation and, in particular, the role of the pseudokinase domain as a suppressor of the adjacent tyrosine kinase domain's catalytic activity. We also review recent advances in our understanding of the mechanisms of negative regulation exerted by the SH2 domain-containing proteins, SOCS (suppressors of cytokine signalling) proteins and LNK. These recent studies highlight the diversity of regulatory mechanisms utilized by the JAK family to maintain signalling fidelity, and suggest alternative therapeutic strategies to complement existing ATP-competitive kinase inhibitors.

Diverse intracellular pathogens activate type III interferon expression from peroxisomes

Type I interferon responses are considered the primary means by which viral infections are controlled in mammals. Despite this view, several pathogens activate antiviral responses in the absence of type I interferons. The mechanisms controlling type I interferon-independent responses are undefined. We found that RIG-I like receptors (RLRs) induce type III interferon expression in a variety of human cell types, and identified factors that differentially regulate expression of type I and type III interferons. We identified peroxisomes as a primary site of initiation of type III interferon expression, and revealed that the process of intestinal epithelial cell differentiation upregulates peroxisome biogenesis and promotes robust type III interferon responses in human cells. These findings highlight the importance of different intracellular organelles in specific innate immune responses.

Mechanism of activation of protein kinase JAK2 by the growth hormone receptor

Signaling from JAK (Janus kinase) protein kinases to STAT (signal transducers and activators of transcription) transcription factors is key to many aspects of biology and medicine, yet the mechanism by which cytokine receptors initiate signaling is enigmatic. We present a complete mechanistic model for activation of receptor-bound JAK2, based on an archetypal cytokine receptor, the growth hormone receptor. For this, we used fluorescence resonance energy transfer to monitor positioning of the JAK2 binding motif in the receptor dimer, substitution of the receptor extracellular domains with Jun zippers to control the position of its transmembrane (TM) helices, atomistic modeling of TM helix movements, and docking of the crystal structures of the JAK2 kinase and its inhibitory pseudokinase domain with an opposing kinase-pseudokinase domain pair. Activation of the receptor dimer induced a separation of its JAK2 binding motifs, driven by a ligand-induced transition from a parallel TM helix pair to a left-handed crossover arrangement. This separation leads to removal of the pseudokinase domain from the kinase domain of the partner JAK2 and pairing of the two kinase domains, facilitating trans-activation. This model may well generalize to other class I cytokine receptors.

The carboxy terminal region of the human cytomegalovirus immediate early 1 (IE1) protein disrupts type II inteferon signaling

Interferons (IFNs) activate the first lines of defense against viruses, and promote innate and adaptive immune responses to viruses. We report that the immediate early 1 (IE1) protein of human cytomegalovirus (HCMV) disrupts signaling by IFNγ. The carboxyl-terminal region of IE1 is required for this function. We found no defect in the initial events in IFNγ signaling or in nuclear accumulation of signal transducer and activator of transcription 1 (STAT1) in IE1-expressing cells. Moreover, we did not observe an association between disruption of IFNγ signaling and nuclear domain 10 (ND10) disruption. However, there is reduced binding of STAT1 homodimers to target gamma activated sequence (GAS) elements in the presence of IE1. Co-immunoprecipitation studies failed to support a direct interaction between IE1 and STAT1, although these studies revealed that the C-terminal region of IE1 was required for interaction with STAT2. Together, these results indicate that IE1 disrupts IFNγ signaling by interfering with signaling events in the nucleus through a novel mechanism.

JAK2 expression is associated with tumor-infiltrating lymphocytes and improved breast cancer outcomes: implications for evaluating JAK2 inhibitors

Janus kinase-2 (JAK2) supports breast cancer growth, and clinical trials testing JAK2 inhibitors are under way. In addition to the tumor epithelium, JAK2 is also expressed in other tissues including immune cells; whether the JAK2 mRNA levels in breast tumors correlate with outcomes has not been evaluated. Using a case-control design, JAK2 mRNA was measured in 223 archived breast tumors and associations with distant recurrence were evaluated by logistic regression. The frequency of correct pairwise comparisons of patient rankings based on JAK2 levels versus survival outcomes, the concordance index (CI), was evaluated using data from 2,460 patients in three cohorts. In the case-control study, increased JAK2 was associated with a decreasing risk of recurrence (multivariate P = 0.003, n = 223). Similarly, JAK2 was associated with a protective CI (<0.5) in the public cohorts: NETHERLANDS CI = 0.376, n = 295; METABRIC CI = 0.462, n = 1,981; OSLOVAL CI = 0.452, n = 184. Furthermore, JAK2 was strongly correlated with the favorable prognosis LYM metagene signature for infiltrating T cells (r = 0.5; P < 2 × 10(-16); n = 1,981) and with severe lymphocyte infiltration (P = 0.00003, n = 156). Moreover, the JAK1/2 inhibitor ruxolitinib potently inhibited the anti-CD3-dependent production of IFN-γ, a marker of the differentiation of Th cells along the tumor-inhibitory Th1 pathway. The potential for JAK2 inhibitors to interfere with the antitumor capacities of T cells should be evaluated.

Chicken interferons, their receptors and interferon-stimulated genes

The prevalence of pathogenic viruses is a serious issue as they pose a constant threat to both the poultry industry and to human health. To prevent these viral infections an understanding of the host-virus response is critical, especially for the development of novel therapeutics. One approach in the control of viral infections would be to boost the immune response through administration of cytokines, such as interferons. However, the innate immune response in chickens is poorly characterised, particularly concerning the interferon pathway. This review will provide an overview of our current understanding of the interferon system of chickens, including their cognate receptors and known interferon-stimulated gene products.

Involvement of JAK/STAT signaling in the pathogenesis of inflammatory bowel disease

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway constitute the fulcrum in many vital cellular processes, including cell growth, differentiation, proliferation, and regulatory immune functions. Various cytokines, growth factors, and protein tyrosine kinases communicate through the JAK/STAT pathway and regulate the transcription of numerous genes. In addition to their critical roles in a plethora of key cellular activities, the JAK/STAT signaling pathways also have been implicated in the pathogenesis of several diseases, including inflammatory bowel disease (IBD), especially since a JAK inhibitor recently has been shown to be effective in the treatment of ulcerative colitis. The aim of this review is to highlight the recent findings on the regulatory mechanism of JAK/STAT signaling pathways and to reveal the evolving comprehension of their interface which might be of interest for clinicians involved in IBD therapy. Further, it is described how these signaling pathways have been exploited for the development of promising novel JAK inhibitors with anti-inflammatory effects verified in clinical trials.

Identification of steroid-sensitive gene-1/Ccdc80 as a JAK2-binding protein

The tyrosine kinase Janus kinase 2 (JAK2) is activated by many cytokine receptors, including receptors for GH, leptin, and erythropoietin. However, very few proteins have been identified as binding partners for JAK2. Using a yeast 2-hybrid screen, we identified steroid-sensitive gene-1 (SSG1)/coiled-coil domain-containing protein 80 (Ccdc80) as a JAK2-binding partner. We demonstrate that Ccdc80 preferentially binds activated, tyrosyl-phosphorylated JAK2 but not kinase-inactive JAK2 (K882E) in both yeast and mammalian systems. Ccdc80 is tyrosyl phosphorylated in the presence of JAK2. The binding of Ccdc80 to JAK2 occurs via 1 or more of the 3 DUDES/SRPX (DRO1-URB-DRS-Equarin-SRPUL/sushi repeat containing protein, x-linked) domain 5 domains of Ccdc80. Mutagenesis of the second DUDES domain suggests that the N-terminal third of the DUDES domain is sufficient for JAK2 binding. Ccdc80 does not alter the kinase activity of JAK2. However, Ccdc80 increases GH-dependent phosphorylation of Stat (signal transducer and activator of transcription) 5b on Tyr699 and substantially enhances both basal and GH-dependent phosphorylation/activation of Stat3 on Tyr705. Furthermore, Ccdc80 belongs to the group of proteins that function both in the intracellular compartment and are secreted. Secreted Ccdc80 associates with the extracellular matrix and is also found in the medium. A substantial portion of the Ccdc80 detected in the medium is cleaved. Finally, consistent with the DUDES domain serving as a JAK2-binding domain, we also demonstrate that another protein that contains a DUDES domain, SRPX2, binds preferentially to the activated tyrosyl-phosphorylated form of JAK2.

G-protein-coupled receptor kinase interacting protein-1 mediates intima formation by regulating vascular smooth muscle proliferation, apoptosis, and migration

OBJECTIVE

The G-protein-coupled receptor kinase interacting protein-1 (GIT1) is a scaffold protein that is important for phospholipase Cγ and extracellular signal-regulated kinase 1/2 signaling induced by angiotensin II and epidermal growth factor. Because GIT1 regulates signaling by several vascular smooth muscle cell (VSMC) growth factors, we hypothesized that intima formation would be inhibited by GIT1 depletion.

APPROACH AND RESULTS

Complete carotid ligation was performed on GIT1 wild-type and knockout (KO) mice. We compared changes between GIT1 wild-type and KO mice in carotid vascular remodeling, VSMC proliferation, and apoptosis in vivo and in vitro. Our data demonstrated that GIT1 deficiency significantly decreased intima formation after carotid ligation as a result of both reduced VSMC proliferation and enhanced apoptosis. To confirm the effects of GIT1 in vitro, we performed proliferation and apoptosis assays in VSMC. In mouse aortic smooth muscle cells (MASM), we found that the growth rate and [3H]-thymidine incorporation of the GIT1 KO MASM were significantly decreased compared with the wild-type MASM. Cyclin D1, which is a key cell cycle regulator, was significantly decreased in GIT1 KO cells. Serum deprivation of GIT1 KO MASM increased apoptosis 3-fold compared with wild-type MASM. Treatment of rat aortic smooth muscle cells with GIT1 small interfering RNA impaired cell migration. Both phospholipase Cγ and extracellular signal-regulated kinase 1/2 signaling were required for GIT1-dependent VSMC proliferation and migration, whereas only phospholipase Cγ was involved in GIT1-mediated VSMC apoptosis.

CONCLUSIONS

GIT1 is a novel mediator of vascular remodeling by regulating VSMC proliferation, migration, and apoptosis through phospholipase Cγ and extracellular signal-regulated kinase 1/2 signaling pathways.

JAK-STAT signaling in stem cells

Adult stem cells are essential for the regeneration and repair of tissues in an organism. Signals from many different pathways converge to regulate stem cell maintenance and differentiation while preventing overproliferation. Although each population of adult stem cells is unique, common themes arise by comparing the regulation of various stem cell types in an organism or by comparing similar stem cell types across species. The JAK-STAT signaling pathway, identified nearly two decades ago, is now known to be involved in many biological processes including the regulation of stem cells. Studies in Drosophila first implicated JAK-STAT signaling in the control of stem cell maintenance in the male germline stem cell microenvironment, or niche; subsequently it has been shown play a role in other niches in both Drosophila and mammals. In this chapter, we will address the role of JAK-STAT signaling in stem cells in the germline, intestinal, hematopoietic and neuronal niches in Drosophila as well as the hematopoietic and neuronal niches in mammals. We will comment on how the study of JAK-STAT signaling in invertebrate systems has helped to advance our understanding of signaling in vertebrates. In addition to the role of JAK- STAT signaling in stem cell niche homeostasis, we will also discuss the diseases, including cancers, that can arise when this pathway is misregulated.

Ixodes scapularis JAK-STAT pathway regulates tick antimicrobial peptides, thereby controlling the agent of human granulocytic anaplasmosis

Ixodes scapularis transmits the agent of human granulocytic anaplasmosis, among other pathogens. The mechanisms used by the tick to control Anaplasma phagocytophilum are not known. We demonstrate that the I. scapularis Janus kinase (JAK)-signaling transducer activator of transcription (STAT) pathway plays a critical role in A. phagocytophilum infection of ticks. The A. phagocytophilum burden increases in salivary glands and hemolymph when the JAK-STAT pathway is suppressed by RNA interference. The JAK-STAT pathway exerts its anti-Anaplasma activity presumably through STAT-regulated effectors. A salivary gland gene family encoding 5.3-kDa antimicrobial peptides is highly induced upon A. phagocytophilum infection of tick salivary glands. Gene expression and electrophoretic mobility shift assays showed that the 5.3-kDa antimicrobial peptide-encoding genes are regulated by tick STAT. Silencing of these genes increased A. phagocytophilum infection of tick salivary glands and transmission to mammalian host. These data suggest that the JAK-STAT signaling pathway plays a key role in controlling A. phagocytophilum infection in ticks by regulating the expression of antimicrobial peptides.

Identification of 34 novel proinflammatory proteins in a genome-wide macrophage functional screen

Signal transduction pathways activated by Toll-like Receptors and the IL-1 family of cytokines are fundamental to mounting an innate immune response and thus to clearing pathogens and promoting wound healing. Whilst mechanistic understanding of the regulation of innate signalling pathways has advanced considerably in recent years, there are still a number of critical controllers to be discovered. In order to characterise novel regulators of macrophage inflammation, we have carried out an extensive, cDNA-based forward genetic screen and identified 34 novel activators, based on their ability to induce the expression of cxcl2. Many are physiologically expressed in macrophages, although the majority of genes uncovered in our screen have not previously been linked to innate immunity. We show that expression of particular activators has profound but distinct impacts on LPS-induced inflammatory gene expression, including switch-type, amplifier and sensitiser behaviours. Furthermore, the novel genes identified here interact with the canonical inflammatory signalling network via specific mechanisms, as demonstrated by the use of dominant negative forms of IL1/TLR signalling mediators.

The JAK-STAT pathway at twenty

We look back on the discoveries that the tyrosine kinases TYK2 and JAK1 and the transcription factors STAT1, STAT2, and IRF9 are required for the cellular response to type I interferons. This initial description of the JAK-STAT pathway led quickly to additional discoveries that type II interferons and many other cytokines signal through similar mechanisms. This well-understood pathway now serves as a paradigm showing how information from protein-protein contacts at the cell surface can be conveyed directly to genes in the nucleus. We also review recent work on the STAT proteins showing the importance of several different posttranslational modifications, including serine phosphorylation, acetylation, methylation, and sumoylation. These remarkably proficient proteins also provide noncanonical functions in transcriptional regulation and they also function in mitochondrial respiration and chromatin organization in ways that may not involve transcription at all.

Biology and significance of the JAK/STAT signalling pathways

Since its discovery two decades ago, the activation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway by numerous cytokines and growth factors has resulted in it becoming one of the most well-studied intracellular signalling networks. The field has progressed from the identification of the individual components to high-resolution crystal structures of both JAK and STAT, and an understanding of the complexities of the molecular activation and deactivation cycle which results in a diverse, yet highly specific and regulated pattern of transcriptional responses. While there is still more to learn, we now appreciate how disruption and deregulation of this pathway can result in clinical disease and look forward to adoption of the next generation of JAK inhibitors in routine clinical treatment.

Signal Transducers and Activators of Transcription (STAT) family members in helminth infections

Helminth parasites are a diverse group of multicellular organisms. Despite their heterogeneity, helminths share many common characteristics, such as the modulation of the immune system of their hosts towards a permissive state that favors their development. They induce strong Th2-like responses with high levels of IL-4, IL-5 and IL-13 cytokines, and decreased production of proinflammatory cytokines such as IFN-γ. IL-4, IFN-γ and other cytokines bind with their specific cytokine receptors to trigger an immediate signaling pathway in which different tyrosine kinases (e.g. Janus kinases) are involved. Furthermore, a seven-member family of transcription factors named Signal Transducers and Activators of Transcription (STAT) that initiate the transcriptional activation of different genes are also involved and regulate downstream the JAK/STAT signaling pathway. However, how helminths avoid and modulate immune responses remains unclear; moreover, information concerning STAT-mediated immune regulation during helminth infections is scarce. Here, we review the research on mice deficient in STAT molecules, highlighting the importance of the JAK/STAT signaling pathway in regulating susceptibility and/or resistance in these infections.

Benzoxathiol derivative BOT-4-one suppresses L540 lymphoma cell survival and proliferation via inhibition of JAK3/STAT3 signaling

Persistently activated JAK/STAT3 signaling pathway plays a pivotal role in various human cancers including major carcinomas and hematologic tumors, and is implicated in cancer cell survival and proliferation. Therefore, inhibition of JAK/STAT3 signaling may be a clinical application in cancer therapy. Here, we report that 2-cyclohexylimino-6-methyl-6,7-dihydro-5H-benzo [1,3]oxathiol-4-one (BOT-4-one), a small molecule inhibitor of JAK/STAT3 signaling, induces apoptosis through inhibition of STAT3 activation. BOT-4-one suppressed cytokine (upd)-induced tyrosine phosphorylation and transcriptional activity of STAT92E, the sole Drosophila STAT homolog. Consequently, BOT-4-one significantly inhibited STAT3 tyrosine phosphorylation and expression of STAT3 downstream target gene SOCS3 in various human cancer cell lines, and its effect was more potent in JAK3-activated Hodgkin's lymphoma cell line than in JAK2-activated breast cancer and prostate cancer cell lines. In addition, BOT-4-one-treated Hodgkin's lymphoma cells showed decreased cell survival and proliferation by inducing apoptosis through down-regulation of STAT3 downstream target anti-apoptotic gene expression. These results suggest that BOT-4-one is a novel small molecule inhibitor of JAK3/STAT3 signaling and may have therapeutic potential in the treatment of human cancers harboring aberrant JAK3/STAT3 signaling, specifically Hodgkin's lymphoma.

Restoration of IFNγR subunit assembly, IFNγ signaling and parasite clearance in Leishmania donovani infected macrophages: role of membrane cholesterol

Despite the presence of significant levels of systemic Interferon gamma (IFNγ), the host protective cytokine, Kala-azar patients display high parasite load with downregulated IFNγ signaling in Leishmania donovani (LD) infected macrophages (LD-MØs); the cause of such aberrant phenomenon is unknown. Here we reveal for the first time the mechanistic basis of impaired IFNγ signaling in parasitized murine macrophages. Our study clearly shows that in LD-MØs IFNγ receptor (IFNγR) expression and their ligand-affinity remained unaltered. The intracellular parasites did not pose any generalized defect in LD-MØs as IL-10 mediated signal transducer and activator of transcription 3 (STAT3) phosphorylation remained unaltered with respect to normal. Previously, we showed that LD-MØs are more fluid than normal MØs due to quenching of membrane cholesterol. The decreased rigidity in LD-MØs was not due to parasite derived lipophosphoglycan (LPG) because purified LPG failed to alter fluidity in normal MØs. IFNγR subunit 1 (IFNγR1) and subunit 2 (IFNγR2) colocalize in raft upon IFNγ stimulation of normal MØs, but this was absent in LD-MØs. Oddly enough, such association of IFNγR1 and IFNγR2 could be restored upon liposomal delivery of cholesterol as evident from the fluorescence resonance energy transfer (FRET) experiment and co-immunoprecipitation studies. Furthermore, liposomal cholesterol treatment together with IFNγ allowed reassociation of signaling assembly (phospho-JAK1, JAK2 and STAT1) in LD-MØs, appropriate signaling, and subsequent parasite killing. This effect was cholesterol specific because cholesterol analogue 4-cholestene-3-one failed to restore the response. The presence of cholesterol binding motifs [(L/V)-X(1-5)-Y-X(1-5)-(R/K)] in the transmembrane domain of IFNγR1 was also noted. The interaction of peptides representing this motif of IFNγR1 was studied with cholesterol-liposome and analogue-liposome with difference of two orders of magnitude in respective affinity (K(D): 4.27×10(-9) M versus 2.69×10(-7) M). These observations reinforce the importance of cholesterol in the regulation of function of IFNγR1 proteins. This study clearly demonstrates that during its intracellular life-cycle LD perturbs IFNγR1 and IFNγR2 assembly and subsequent ligand driven signaling by quenching MØ membrane cholesterol.

Differential biological activity of disease-associated JAK2 mutants

The JAK2V617F mutation has been identified in most patients with myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia and primary myelofibrosis. Although JAK2V617F is the predominant allele associated with MPNs, other activating Janus kinase 2 (JAK2) alleles (such as K539L, T875N) also have been identified in distinct MPNs. The basis for the differences in the in vivo effects of different JAK2 alleles remains unclear. We have characterized three different classes of disease-associated JAK2 mutants (JAK2V617F, JAK2K539L and JAK2T875N) and found significant differences in biochemical, signaling and transforming properties among these different classes of JAK2 mutants.

Innate immunity in the respiratory epithelium

The airway epithelium represents the first point of contact for inhaled foreign organisms. The protective arsenal of the airway epithelium is provided in the form of physical barriers and a vast array of receptors and antimicrobial compounds that constitute the innate immune system. Many of the known innate immune receptors, including the Toll-like receptors and nucleotide oligomerization domain-like receptors, are expressed by the airway epithelium, which leads to the production of proinflammatory cytokines and chemokines that affect microorganisms directly and recruit immune cells, such as neutrophils and T cells, to the site of infection. The airway epithelium also produces a number of resident antimicrobial proteins, such as lysozyme, lactoferrin, and mucins, as well as a swathe of cationic proteins. Dysregulation of the airway epithelial innate immune system is associated with a number of medical conditions that can result in compromised immunity and chronic inflammation of the lung. This review focuses on the innate immune capabilities of the airway epithelium and its role in protecting the lung from infection as well as the outcomes when its function is compromised.

Differential transcriptional responses to interferon-alpha and interferon-gamma in primary human hepatocytes

Interferon (IFN) plays a central role in the innate and adaptive antiviral immune responses. While IFN-alpha is currently approved for treating chronic hepatitis B and hepatitis C, in limited studies, IFN-gamma has not been shown to be effective for chronic hepatitis B or C. To identify the potential mechanism underlying the differential antiviral effects of IFN-alpha and IFN-gamma, we used cDNA microarray to profile the global transcriptional response to IFN-alpha and IFN-gamma in primary human hepatocytes, the target cell population of hepatitis viruses. Our results reveal distinct patterns of gene expression induced by these 2 cytokines. Overall, IFN-alpha induces more genes than IFN-gamma at the transcriptional level. Distinct sets of genes were induced by IFN-alpha and IFN-gamma with limited overlaps. IFN-alpha induces gene transcription at an early time point (6 h) but not at a later time point (18 h), while the effects of IFN-gamma are more prominent at 18 h than at 6 h, suggesting a delayed transcriptional response to IFN-gamma in the hepatocytes. These findings indicate differential actions of IFN-alpha and IFN-gamma in the context of therapeutic intervention for chronic viral infections in the liver.

A determinant of Sindbis virus neurovirulence enables efficient disruption of Jak/STAT signaling

Previous studies with Venezuelan equine encephalitis virus and Sindbis virus (SINV) indicate that alphaviruses are capable of suppressing the cellular response to type I and type II interferons (IFNs) by disrupting Jak/STAT signaling; however, the relevance of this signaling inhibition toward pathogenesis has not been investigated. The relative abilities of neurovirulent and nonneurovirulent SINV strains to downregulate Jak/STAT signaling were compared to determine whether the ability to inhibit IFN signaling correlates with virulence potential. The adult mouse neurovirulent strain AR86 was found to rapidly and robustly inhibit tyrosine phosphorylation of STAT1 and STAT2 in response to IFN-γ and/or IFN-β. In contrast, the closely related SINV strains Girdwood and TR339, which do not cause detectable disease in adult mice, were relatively inefficient inhibitors of STAT1/2 activation. Decreased STAT activation in AR86-infected cells was associated with decreased activation of the IFN receptor-associated tyrosine kinases Tyk2, Jak1, and Jak2. To identify the viral factor(s) involved, we infected cells with several panels of AR86/Girdwood chimeric viruses. Surprisingly, we found that a single amino acid determinant, threonine at nsP1 position 538, which is required for AR86 virulence, was also required for efficient disruption of STAT1 activation, and this determinant fully restored STAT1 inhibition when it was introduced into the avirulent Girdwood background. These data indicate that a key virulence determinant plays a critical role in downregulating the response to type I and type II IFNs, which suggests that the ability of alphaviruses to inhibit Jak/STAT signaling relates to their in vivo virulence potential.

The mEPN scheme: an intuitive and flexible graphical system for rendering biological pathways

Background

There is general agreement amongst biologists about the need for good pathway diagrams and a need to formalize the way biological pathways are depicted. However, implementing and agreeing how best to do this is currently the subject of some debate.

Results

The modified Edinburgh Pathway Notation (mEPN) scheme is founded on a notation system originally devised a number of years ago and through use has now been refined extensively. This process has been primarily driven by the author's attempts to produce process diagrams for a diverse range of biological pathways, particularly with respect to immune signaling in mammals. Here we provide a specification of the mEPN notation, its symbols, rules for its use and a comparison to the proposed Systems Biology Graphical Notation (SBGN) scheme.

Conclusions

We hope this work will contribute to the on-going community effort to develop a standard for depicting pathways and will provide a coherent guide to those planning to construct pathway diagrams of their biological systems of interest.