JAKs go nuclear: emerging role of nuclear JAK1 and JAK2 in gene expression and cell growth

JAK2 inhibitors improve RA combined with pulmonary fibrosis in rats by downregulating SMAD3 phosphorylation

BACKGROUND

JAK inhibitors are well known for the treatment of rheumatoid arthritis (RA), but whether they can be used to treat pulmonary fibrosis, a common extra-articular disease of RA, remains to be clarified.

METHODS

A jak2 inhibitor, CEP33779 (CEP), was administered to a rat model of RA-associated interstitial lung disease to observe the degree of improvement in both joint swelling and pulmonary fibrosis. HFL1 cells were stimulated with TGF-β1 to observe the expression of p-JAK2. Then, different concentrations of related gene inhibitors (JAK2, TGFβ-R1/2, and p-STAT3) or silencers (STAT3, JAK2) were administered to HFL1 cells, and the expression levels of related proteins were detected to explore the underlying mechanisms of action.

RESULTS

CEP not only reduced the degree of joint swelling and inflammation in rats but also improved lung function, inhibited the pro-inflammatory factors IL-1β and IL-6, reduced lung inflammation and collagen deposition, and alleviated lung fibrosis. CEP decreased the expression levels of TGFβ-R2, p-SMAD, p-STAT3, and ECM proteins in rat lung tissues. TGF-β1 induced HFL1 cells to highly express p-JAK2, with the most pronounced expression at 48 h. The levels of p-STAT3, p-SMAD3, and ECM-related proteins were significantly reduced after inhibition of either JAK2 or STAT3.

CONCLUSION

JAK2 inhibitors may be an important and novel immunotherapeutic drug that can improve RA symptoms while also delaying or blocking the development of associated pulmonary fibrotic disease. The mechanism may be related to the downregulation of p-STAT3 protein via inhibition of the JAK2/STAT signaling pathway, which affects the phosphorylation of SMAD3.

FERM domain-containing proteins are active components of the cell nucleus

The FERM domain is a conserved and widespread protein module that appeared in the common ancestor of amoebae, fungi, and animals, and is therefore now found in a wide variety of species. The primary function of the FERM domain is localizing to the plasma membrane through binding lipids and proteins of the membrane; thus, for a long time, FERM domain-containing proteins (FDCPs) were considered exclusively cytoskeletal. Although their role in the cytoplasm has been extensively studied, the recent discovery of the presence and importance of cytoskeletal proteins in the nucleus suggests that FDCPs might also play an important role in nuclear function. In this review, we collected data on their nuclear localization, transport, and possible functions, which are still scattered throughout the literature, with special regard to the role of the FERM domain in these processes. With this, we would like to draw attention to the exciting, new dimension of the role of FDCPs, their nuclear activity, which could be an interesting novel direction for future research.

Pirfenidone and nintedanib attenuate pulmonary fibrosis in mice by inhibiting the expression of JAK2

Background

Pirfenidone and nintedanib were approved by the Food and Drug Administration (FDA) for the treatment of idiopathic pulmonary fibrosis (IPF). These two drugs can slow the progression of the disease, but the specific mechanisms are not fully understood. In the current study, bleomycin (BLM) induced pulmonary fibrosis in mice was accompanied by high p-JAK2 expression in lung tissue, mainly in the nucleus. The expression of p-JAK2 significantly decreased after intragastric administration of pirfenidone and nintedanib. p-JAK2 is reportedly expressed mainly in the cytoplasm and exerts its effect by activating downstream p-STAT3 in the nucleus.

Methods

In vivo experiments, pulmonary fibrosis was induced in mice with BLM and then treated with pirfenidone and nintedanib. The levels of transforming growth factor-β (TGF-β1), SP-A, SP-D and KL-6 in serum were measured by enzyme-linked immunosorbent assay (ELISA). Pathological staining was performed to assess lung fibrosis in mice, Western blot was performed to detect the expression levels of relevant proteins, and immunofluorescence was performed to observe the fluorescence expression of p-JAK2. In cellular experiments, MLE12 was stimulated with TGF-β1 and intervened with TGF-β1 receptor inhibitor and si-JAK2, pirfenidone and nintedanib, respectively, and the related protein expression levels were detected by Western blot.

Results

In both in vivo and in vitro experiments, pirfenidone and nintedanib were found to attenuate the expression of lung fibrosis markers by inhibiting the expression of JAK2, which may reduce the entry of p-JAK2 into the nucleus by downregulating JAK2 phosphorylation through inhibition of the TGF-β receptor. In contrast, inhibition of JAK2 expression greatly reduced the expression of TGF-β receptor and α-smooth muscles actin (a myofibroblast activation marker).

Conclusions

In both in vivo and in vitro experiments, the present study demonstrated that TGF-β1 promotes JAK2 phosphorylation through a non-classical pathway, and conversely, inhibition of JAK2 expression affects the TGF-β1 signalling pathway. Therefore, we speculate that TGF-β1 and JAK2 signaling pathways interact with each other and participate in fibrosis.

Immunolocalization and Expression of JAK1 and JAK3 in the Skin of Dust Mite-Sensitive Beagle Dogs before and after Allergen Exposure

Janus kinase (JAK) pathways have emerged as targets of treatment, yet localization and expression of JAK1 and JAK3 in canine atopic skin have not been studied. This study aimed to compare the localization and expression of JAK1 and JAK3 in the skin of atopic dogs before and after allergen exposure. Skin biopsies taken from atopic beagles sensitized to house dust mites (HDM) before (D0) and after four weeks (D28) of allergen exposure were stained. Staining was subjectively scored by examiners unaware of the source of the slides. Image J was used for the semiquantitative assessment of staining intensity. JAK1 and JAK3 staining was epidermal and dermal. JAK1 staining was cytoplasmic, primarily found in basal keratinocytes and dermal cells, while JAK 3 was nuclear (all epidermal levels and on dermal inflammatory cells). Epidermal thickness was significantly higher on D28 than on D0 (p < 0.0001). For JAK1, epidermal staining divided by epithelial thickness was significantly lower on D28 (p = 0.0002) compared to D0. For JAK3 staining, intensity in the dermis was significantly higher on D28 (p = 0.0405) compared to D0. We conclude that decreased expression of JAK1 in the epidermis and increased expression of JAK3 in the dermis of atopic dogs occur after allergen exposure.

Crosstalk between the JAK2 and TGF-β1 signaling pathways in scleroderma-related interstitial lung disease targeted by baricitinib

BACKGROUND AND OBJECTIVE

Systemic sclerosis (SSc) is an immune-mediated rheumatic disease characterized by fibrosis and vascular lesions. Interstitial lung disease is an early complication of SSc and the main cause of death from SSc. Although baricitinib shows good efficacy in a variety of connective tissue diseases, its role in systemic sclerosis-related interstitial lung disease (SSc-ILD) is unclear. The objective of our study was to explore the effect and mechanism of baricitinib in SSc-ILD.

METHODS

We explored crosstalk between the JAK2 and TGF-β1 pathways. In vivo experiments, SSc-ILD mice model were constructed by subcutaneous injection of PBS or bleomycin (7.5 mg/kg) and intragastric administration of 0.5% CMC-Na or baricitinib (5 mg/kg) once every two days. We used ELISA, qRT‒PCR, western blot and immunofluorescence staining to evaluate the degree of fibrosis. In vitro experiments, we used TGF-β1 and baricitinib to stimulate human fetal lung fibroblasts (HFLs) and assessed protein expression by western blot.

RESULTS

The vivo experiments showed that baricitinib notably alleviated skin and lung fibrosis, decreased the concentration of pro-inflammatory factors and increased those of the anti-inflammatory factors. Baricitinib affected the expression of TGF-β1 and TβRI/II inhibitiing JAK2. In the vitro experiments, following the culture of HFLs with baricitinib or a STAT3 inhibitor for 48 h, the expression levels of TβRI/II decreased. Conversely, with successful inhibition of TGF-β receptors in HFLs, JAK2 protein expression decreased.

CONCLUSIONS

Baricitinib attenuated bleomycin-induced skin and lung fibrosis in SSc-ILD mice model by targeting JAK2 and regulating of the crosstalk between the JAK2 and TGF-β1 signaling pathways.

Jmjd1c demethylates STAT3 to restrain plasma cell differentiation and rheumatoid arthritis

Appropriate regulation of B cell differentiation into plasma cells is essential for humoral immunity while preventing antibody-mediated autoimmunity; however, the underlying mechanisms, especially those with pathological consequences, remain unclear. Here, we found that the expression of Jmjd1c, a member of JmjC domain histone demethylase, in B cells but not in other immune cells, protected mice from rheumatoid arthritis (RA). In humans with RA, JMJD1C expression levels in B cells were negatively associated with plasma cell frequency and disease severity. Mechanistically, Jmjd1c demethylated STAT3, rather than histone substrate, to restrain plasma cell differentiation. STAT3 Lys140 hypermethylation caused by Jmjd1c deletion inhibited the interaction with phosphatase Ptpn6 and resulted in abnormally sustained STAT3 phosphorylation and activity, which in turn promoted plasma cell generation. Germinal center B cells devoid of Jmjd1c also acquired strikingly increased propensity to differentiate into plasma cells. STAT3 Lys140Arg point mutation completely abrogated the effect caused by Jmjd1c loss. Mice with Jmjd1c overexpression in B cells exhibited opposite phenotypes to Jmjd1c-deficient mice. Overall, our study revealed Jmjd1c as a critical regulator of plasma cell differentiation and RA and also highlighted the importance of demethylation modification for STAT3 in B cells.

Canonical and noncanonical regulatory roles for JAK2 in the pathogenesis of rheumatoid arthritis-associated interstitial lung disease and idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) and rheumatoid arthritis-associated interstitial lung disease (RA-ILD) are two fibrotic interstitial lung diseases that share the usual interstitial pneumonia (UIP) injury pattern. Here, we report that RNA sequencing of lung biopsies from patients with RA-ILD and IPF revealed shared and distinct disease-causing pathways. Analysis of transcriptomic data identified a JAK2 related JAK/STAT signaling pathway gene signature that distinguishes RA-UIP from idiopathic UIP. This was further confirmed by immunohistostaining, which identified JAK2 phosphorylation with two distinct forms of activation: a cytoplasmic form of JAK2 activation in most IPF cases (13/20) and a nuclear form of p-JAK2 in RA-UIP (5/5) and a minority of IPF (6/20) cases. Further immunohistostaining identified STAT5A&B as the downstream transcriptional activator for JAK2-mediated canonical signal transduction and phosphorylation of Tyr41 on histone H3 (H3Y41ph) as the downstream epigenetic regulation site for JAK2-mediated noncanonical signal transduction. Gene Set Enrichment Analysis (GSEA) of the RNA-Seq data further supported this shared pathogenic mechanism for the two diseases with the enrichment of STAT5A&B target gene sets as well as the JAK2 regulated H3Y41ph target gene set. This regulatory role of JAK2 in the pathogenesis of pulmonary fibrosis was further demonstrated by the attenuation of bleomycin-induced murine pulmonary fibrosis using a JAK2-selective pharmacological inhibitor CEP33779. In vitro studies with normal and IPF derived lung fibroblasts revealed a central role for JAK2 as an essential intermediary molecule in TGF-β-mediated myofibroblast trans-differentiation, proliferation, and extracellular matrix protein production. These observations support a crucial role for JAK2 as an intermediary molecule in fibrotic lung disease development.

Tyrphostin AG1024 Suppresses Coronaviral Replication by Downregulating JAK1 via an IR/IGF-1R Independent Proteolysis Mediated by Ndfip1/2_NEDD4-like E3 Ligase Itch

JAK1 depletion or downregulation was previously reported to account for coronavirus inhibition. Here, we found that AG1024, an IR (insulin receptor) and IGF-1R (insulin-like growth factor 1 receptor) inhibitor, diminishes JAK1 protein levels and exerts anti-coronaviral activities with EC50 values of 5.2 ± 0.3 μM against transmissible gastroenteritis coronavirus (TGEV) and 4.3 ± 0.3 μM against human flu coronavirus OC43. However, although the IR and IGF-1R signaling pathways are activated by insulin or IGF-1 in swine testis cells, they are not triggered upon TGEV infection. AG1024, therefore, inhibits coronaviral replication and downregulates JAK1 protein levels independently of IR and IGF-1R. Moreover, JAK1 proteolysis caused by AG1024 was found through activation of upstream Ndfip1/2 and its effector NEDD4-like E3 ligase Itch. In addition, ouabain, which was reported to mediate JAK1 proteolysis causing anti-coronaviral activity by activation of Ndfip1/2 and NEDD4 E3 ligase, additively inhibited anti-coronaviral activity and JAK1 diminishment in combination with AG1024. This study provides novel insights into the pharmacological effects of AG1024 and Itch E3 ligase mediated JAK1 proteolysis and identified Ndfip1/2 as a cognate effector for JAK1 proteolysis via the diversified E3 ligases NEDD4 and NEDD4-like Itch. These findings are expected to provide valued information for the future development of anti-viral agents.

Expression of RUNX1-JAK2 in Human Induced Pluripotent Stem Cell-Derived Hematopoietic Cells Activates the JAK-STAT and MYC Pathways

A heterogeneous genetic subtype of B-cell precursor acute lymphoblastic leukemia is driven by constitutive kinase-activation, including patients with JAK2 fusions. In our study, we model the impact of a novel JAK2 fusion protein on hematopoietic development in human induced pluripotent stem cells (hiPSCs). We insert the RUNX1-JAK2 fusion into one endogenous RUNX1 allele through employing in trans paired nicking genome editing. Tagging of the fusion with a degron facilitates protein depletion using the heterobifunctional compound dTAG-13. Throughout in vitro hematopoietic differentiation, the expression of RUNX1-JAK2 is driven by endogenous RUNX1 regulatory elements at physiological levels. Functional analysis reveals that RUNX1-JAK2 knock-in cell lines yield fewer hematopoietic progenitors, due to RUNX1 haploinsufficiency. Nevertheless, these progenitors further differentiate toward myeloid lineages to a similar extent as wild-type cells. The expression of the RUNX1-JAK2 fusion protein only elicits subtle effects on myeloid differentiation, and is unable to transform early hematopoietic progenitors. However, phosphoprotein and transcriptome analyses reveal that RUNX1-JAK2 constitutively activates JAK-STAT signaling in differentiating hiPSCs and at the same time upregulates MYC targets—confirming the interaction between these pathways. This proof-of-principle study indicates that conditional expression of oncogenic fusion proteins in combination with hematopoietic differentiation of hiPSCs may be applicable to leukemia-relevant disease modeling.

Signal transducer and activator of transcription (STAT) 1 and STAT3 are expressed in the human ovary and have Janus kinase 1-independent functions in the COV434 human granulosa cell line

Ovarian granulosa cells are fundamental for oocyte maintenance and maturation. Recent studies have demonstrated the importance of members of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathway in the granulosa cell population of mouse and horse ovaries, with perturbation of JAK1 signalling in the mouse shown to impair oocyte maintenance and accelerate primordial follicle activation. The presence and role of the JAK/STAT pathway in human granulosa cells has yet to be elucidated. In this study, expression of JAK1, STAT1 and STAT3 was detected in oocytes and granulosa cells of human ovarian sections from fetal (40 weeks gestation) and premenopausal ovaries (34-41 years of age; n=3). To determine the effects of JAK1 signalling in granulosa cells, the human granulosa-like cell line COV434 was used, with JAK1 inhibition using ruxolitinib. Chemical inhibition of JAK1 in COV434 cells with 100nM ruxolitinib for 72h resulted in significant increases in STAT3 mRNA (P=0.034) and p-Y701-STAT1 protein (P=0.0117), demonstrating a role for JAK1 in modulating STAT in granulosa cells. This study implicates a conserved role for JAK/STAT signalling in human ovary development, warranting further investigation of this pathway in human granulosa cell function.

The Role of JAK/STAT Molecular Pathway in Vascular Remodeling Associated with Pulmonary Hypertension

Pulmonary hypertension is defined as a group of diseases characterized by a progressive increase in pulmonary vascular resistance (PVR), which leads to right ventricular failure and premature death. There are multiple clinical manifestations that can be grouped into five different types. Pulmonary artery remodeling is a common feature in pulmonary hypertension (PH) characterized by endothelial dysfunction and smooth muscle pulmonary artery cell proliferation. The current treatments for PH are limited to vasodilatory agents that do not stop the progression of the disease. Therefore, there is a need for new agents that inhibit pulmonary artery remodeling targeting the main genetic, molecular, and cellular processes involved in PH. Chronic inflammation contributes to pulmonary artery remodeling and PH, among other vascular disorders, and many inflammatory mediators signal through the JAK/STAT pathway. Recent evidence indicates that the JAK/STAT pathway is overactivated in the pulmonary arteries of patients with PH of different types. In addition, different profibrotic cytokines such as IL-6, IL-13, and IL-11 and growth factors such as PDGF, VEGF, and TGFβ1 are activators of the JAK/STAT pathway and inducers of pulmonary remodeling, thus participating in the development of PH. The understanding of the participation and modulation of the JAK/STAT pathway in PH could be an attractive strategy for developing future treatments. There have been no studies to date focused on the JAK/STAT pathway and PH. In this review, we focus on the analysis of the expression and distribution of different JAK/STAT isoforms in the pulmonary arteries of patients with different types of PH. Furthermore, molecular canonical and noncanonical JAK/STAT pathway transactivation will be discussed in the context of vascular remodeling and PH. The consequences of JAK/STAT activation for endothelial cells and pulmonary artery smooth muscle cells’ proliferation, migration, senescence, and transformation into mesenchymal/myofibroblast cells will be described and discussed, together with different promising drugs targeting the JAK/STAT pathway in vitro and in vivo.

Loss of sarcomeric proteins via upregulation of JAK/STAT signaling underlies interferon-γ-induced contractile deficit in engineered human myocardium

The level of circulating interferon-γ (IFNγ) is elevated in various clinical conditions including autoimmune and inflammatory diseases, sepsis, acute coronary syndrome, and viral infections. As these conditions are associated with high risk of myocardial dysfunction, we investigated the effects of IFNγ on 3D fibrin-based engineered human cardiac tissues ("cardiobundles"). Cardiobundles were fabricated from human pluripotent stem cell-derived cardiomyocytes, exposed to 0-20 ng/ml of IFNγ on culture days 7-14, and assessed for changes in tissue structure, viability, contractile force and calcium transient generation, action potential propagation, cytokine secretion, and expression of select genes and proteins. We found that application of IFNγ induced a dose-dependent reduction in contractile force generation, deterioration of sarcomeric organization, and cardiomyocyte disarray, without significantly altering cell viability, action potential propagation, or calcium transient amplitude. At molecular level, the IFNγ-induced structural and functional deficits could be attributed to altered balance of pro- and anti-inflammatory cytokines, upregulation of JAK/STAT signaling pathway (JAK1, JAK2, and STAT1), and reduced expression of myosin heavy chain, myosin light chain-2v, and sarcomeric α-actinin. Application of clinically used JAK/STAT inhibitors, tofacitinib and baricitinib, fully prevented IFNγ-induced cardiomyopathy, confirming the critical roles of this signaling pathway in inflammatory cardiac disease. Taken together, our in vitro studies in engineered myocardial tissues reveal direct adverse effects of pro-inflammatory cytokine IFNγ on human cardiomyocytes and establish the foundation for a potential use of cardiobundle platform in modeling of inflammatory myocardial disease and therapy. STATEMENT OF SIGNIFICANCE: Various inflammatory and autoimmune diseases including rheumatoid arthritis, sepsis, lupus erythematosus, Chagas disease, and others, as well as viral infections including H1N1 influenza and COVID-19 show increased systemic levels of a pro-inflammatory cytokine interferon-γ (IFNγ) and are associated with high risk of heart disease. Here we explored for the first time if chronically elevated levels of IFNγ can negatively affect structure and function of engineered human heart tissues in vitro. Our studies revealed IFNγ-induced deterioration of myofibrillar organization and contractile force production in human cardiomyocytes, attributed to decreased expression of multiple sarcomeric proteins and upregulation of JAK/STAT signaling pathway. FDA-approved JAK inhibitors fully blocked the adverse effects of IFNγ, suggesting a potentially effective strategy against human inflammatory cardiomyopathy.

SENP1-mediated deSUMOylation of JAK2 regulates its kinase activity and platinum drug resistance

The JAK2/STAT pathway is hyperactivated in many cancers, and such hyperactivation is associated with a poor clinical prognosis and drug resistance. The mechanism regulating JAK2 activity is complex. Although translocation of JAK2 between nucleus and cytoplasm is an important regulatory mechanism, how JAK2 translocation is regulated and what is the physiological function of this translocation remain largely unknown. Here, we found that protease SENP1 directly interacts with and deSUMOylates JAK2, and the deSUMOylation of JAK2 leads to its accumulation at cytoplasm, where JAK2 is activated. Significantly, this novel SENP1/JAK2 axis is activated in platinum-resistant ovarian cancer in a manner dependent on a transcription factor RUNX2 and activated RUNX2/SENP1/JAK2 is critical for platinum-resistance in ovarian cancer. To explore the application of anti-SENP1/JAK2 for treatment of platinum-resistant ovarian cancer, we found SENP1 deficiency or treatment by SENP1 inhibitor Momordin Ic significantly overcomes platinum-resistance of ovarian cancer. Thus, this study not only identifies a novel mechanism regulating JAK2 activity, but also provides with a potential approach to treat platinum-resistant ovarian cancer by targeting SENP1/JAK2 pathway.

An activity-dependent determinant of synapse elimination in the mammalian brain

To establish functional neural circuits in the brain, synaptic connections are refined by neural activity during development, where active connections are maintained and inactive ones are eliminated. However, the molecular signals that regulate synapse refinement remain to be elucidated. When we inactivate a subset of neurons in the mouse cingulate cortex, their callosal connections are eliminated through activity-dependent competition. Using this system, we identify JAK2 tyrosine kinase as a key regulator of inactive synapse elimination. We show that JAK2 is necessary and sufficient for elimination of inactive connections; JAK2 is activated at inactive synapses in response to signals from other active synapses; STAT1, a substrate of JAK2, mediates inactive synapse elimination; JAK2 signaling is critical for physiological refinement of synapses during normal development; and JAK2 regulates synapse refinement in multiple brain regions. We propose that JAK2 is an activity-dependent switch that serves as a determinant of inactive synapse elimination.

Mucosal Epithelial Jak Kinases in Health and Diseases

Janus kinases (Jaks) are a family of nonreceptor tyrosine kinase that include four different members, viz., Jak1, Jak2, Jak3, and Tyk2. Jaks play critical roles in immune cells functions; however, recent studies suggest they also play essential roles in nonimmune cell physiology. This review highlights the significance of epithelial Jaks in understanding the molecular basis of some of the diseases through regulation of epithelial-mesenchymal transition, cell survival, cell growth, development, and differentiation. Growth factors and cytokines produced by the cells of hematopoietic origin use Jak kinases for signal transduction in both immune and nonimmune cells. Among Jaks, Jak3 is widely expressed in both immune cells and in intestinal epithelial cells (IECs) of both humans and mice. Mutations that abrogate Jak3 functions cause an autosomal severe combined immunodeficiency disease (SCID) while activating Jak3 mutations lead to the development of hematologic and epithelial cancers. A selective Jak3 inhibitor CP-690550 (Xeljanz) approved by the FDA for certain chronic inflammatory conditions demonstrates immunosuppressive activity in rheumatoid arthritis, psoriasis, and organ transplant rejection. Here, we also focus on the consequences of Jak3-directed drugs on adverse effects in light of recent discoveries in mucosal epithelial functions of Jak3 with some information on other Jaks. Lastly, we brief on structural implications of Jak3 domains beyond the immune cells. As information about the roles of Jak3 in gastrointestinal functions and associated diseases are only just emerging, in the review, we summarize its implications in gastrointestinal wound repair, inflammatory bowel disease, obesity-associated metabolic syndrome, and epithelial cancers. Lastly, we shed lights on identifying potential novel targets in developing therapeutic interventions of diseases associated with dysfunctional IEC.

Thromboembolic Adverse Drug Reactions in Janus Kinase (JAK) Inhibitors: Does the Inhibitor Specificity Play a Role?

Recent advances in immunology enabled the characterization of several signal transmitting pathways responsible for proper cytokine and chemokine signaling. Among them, Janus kinases (JAKs) are essential components of receptor activation systems. The discovery of JAK kinases enabled the synthesis of JAK kinase inhibitors (JAKi or Jakinibs), which have proven to be efficacious in the treatment of hematologic malignancies and several rheumatological disorders and continue to be investigated in many clinical indications. Blocking multiple cytokines belonging to several cytokine families with a single small molecule may, however, create a potential risk for the patients. Recently, a higher risk of thromboembolic complications, namely, deep vein thrombosis and pulmonary embolism, has been recognized as the main concern during treatment with Jakinibs. At present, it is not entirely clear whether this increased risk is related to direct cytokine blockade, the presence of concomitant diseases in treated patients or other unknown circumstances that work together to increase the risk of this side effect. In this review, we discuss data on the risk of thromboembolic side effects, with special emphasis on the mechanism that may be responsible for this increased risk. Many indirect data indicate that higher thromboembolic risk may be related to the specificity of JAK inhibitor action, such that preferentially blocking one signaling pathway upsets the balance between pro and anti-thrombotic activities.

Clinical Aspects of Janus Kinase (JAK) Inhibitors in the Cardiovascular System in Patients with Rheumatoid Arthritis

Janus kinase (JAK) inhibitors, a novel class of targeted synthetic disease-modifying antirheumatic drugs (DMARDs), have shown their safety and efficacy in rheumatoid arthritis (RA) and are being intensively tested in other autoimmune and inflammatory disorders. Targeting several cytokines with a single small compound leads to blocking the physiological response of hundreds of genes, thereby providing the background to stabilize the immune response. Unfortunately, blocking many cytokines with a single drug may also bring some negative consequences. In this review, we focused on the activity of JAK inhibitors in the cardiovascular system of patients with RA. Special emphasis was put on the modification of heart performance, progression of atherosclerosis, lipid profile disturbance, and risk of thromboembolic complications. We also discussed potential pathophysiological mechanisms that may be responsible for such JAK inhibitor-associated side effects.

Natural cardenolides suppress coronaviral replication by downregulating JAK1 via a Na+/K+-ATPase independent proteolysis

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Natural cardenolides suppress coronaviral activity via downregulating JAK1.

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Natural cardenolides downregulate JAK1 in a Na⁺/K⁺-ATPase independent manner.

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Ouabain (cardenolides) activates Ndfip1/2 and NEDD4 to mediate JAK1 proteolysis.

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Ndfip1/2 and NEDD4 mediated JAK1 proteolysis attenuates coronaviral activity.

An unprecedented biological function of natural cardenolides independent of their membrane target Na⁺/K⁺-ATPase is disclosed. Previously, we reported that cardenolides impart anti-transmissible gastroenteritis coronavirus (anti-TGEV) activity through the targeting of Na⁺/K⁺-ATPase and its associated PI3K_PDK1_RSK2 signaling. Swine testis cells with Na⁺/K⁺-ATPase α1 knocked down exhibited decreased susceptibility to TGEV infectivity and attenuated PI3K_PDK1_RSK2 signaling. Herein, we further explored a Na⁺/K⁺-ATPase-independent signaling axis induced by natural cardenolides that also afforded significant anti-coronaviral activity for porcine TGEV and human HCoV-OC43. Using pharmacological inhibition and gene silencing techniques, we found that this anti-TGEV or anti-HCoV-OC43 activity was caused by JAK1 proteolysis and mediated through upstream activation of Ndfip1/2 and its effector NEDD4. This study provides novel insights into the pharmacological effects of natural cardenolides, and is expected to inform their future development as antiviral agents.

Two common disease-associated TYK2 variants impact exon splicing and TYK2 dosage

TYK2 belongs to the JAK protein tyrosine kinase family and mediates signaling of numerous antiviral and immunoregulatory cytokines (type I and type III IFNs, IL-10, IL-12, IL-22, IL-23) in immune and non-immune cells. After many years of genetic association studies, TYK2 is recognized as a susceptibility gene for some inflammatory and autoimmune diseases (AID). Seven TYK2 variants have been associated with AIDs in Europeans, and establishing their causality remains challenging. Previous work showed that a protective variant (P1104A) is hypomorphic and also a risk allele for mycobacterial infection. Here, we have studied two AID-associated common TYK2 variants: rs12720270 located in intron 7 and rs2304256, a non-synonymous variant in exon 8 that causes a valine to phenylalanine substitution (c.1084 G > T, Val362Phe). We found that this amino acid substitution does not alter TYK2 expression, catalytic activity or ability to relay signaling in EBV-B cell lines or in reconstituted TYK2-null cells. Based on in silico predictions that these variants may impact splicing of exon 8, we: i) analyzed TYK2 transcripts in genotyped EBV-B cells and in CRISPR/Cas9-edited cells, ii) measured splicing using minigene assays, and iii) performed eQTL (expression quantitative trait locus) analysis of TYK2 transcripts in primary monocytes and whole blood cells. Our results reveal that the two variants promote the inclusion of exon 8, which, we demonstrate, is essential for TYK2 binding to cognate receptors. In addition and in line with GTEx (Genetic Tissue Expression) data, our eQTL results show that rs2304256 mildly enhances TYK2 expression in whole blood. In all, these findings suggest that these TYK2 variants are not neutral but instead have a potential impact in AID.

TYK2 in Tumor Immunosurveillance

We review the history of the tyrosine kinase 2 (TYK2) as the founding member of the Janus kinase (JAK) family and outline its structure-function relation. Gene-targeted mice and hereditary defects of TYK2 in men have established the biological and pathological functions of TYK2 in innate and adaptive immune responses to infection and cancer and in (auto-)inflammation. We describe the architecture of the main cytokine receptor families associated with TYK2, which activate signal transducers and activators of transcription (STATs). We summarize the cytokine receptor activities with well characterized dependency on TYK2, the types of cells that respond to cytokines and TYK2 signaling-induced cytokine production. TYK2 may drive beneficial or detrimental activities, which we explain based on the concepts of tumor immunoediting and the cancer-immunity cycle in the tumor microenvironment. Finally, we summarize current knowledge of TYK2 functions in mouse models of tumor surveillance. The biology and biochemistry of JAKs, TYK2-dependent cytokines and cytokine signaling in tumor surveillance are well covered in recent reviews and the oncogenic properties of TYK2 are reviewed in the recent Special Issue ‘Targeting STAT3 and STAT5 in Cancer’ of Cancers.

JAK-STAT Signaling: A Double-Edged Sword of Immune Regulation and Cancer Progression

Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling mediates almost all immune regulatory processes, including those that are involved in tumor cell recognition and tumor-driven immune escape. Antitumor immune responses are largely driven by STAT1 and STAT2 induction of type I and II interferons (IFNs) and the downstream programs IFNs potentiate. Conversely, STAT3 has been widely linked to cancer cell survival, immunosuppression, and sustained inflammation in the tumor microenvironment. The discovery of JAK-STAT cross-regulatory mechanisms, post-translational control, and non-canonical signal transduction has added a new level of complexity to JAK-STAT governance over tumor initiation and progression. Endeavors to better understand the vast effects of JAK-STAT signaling on antitumor immunity have unearthed a wide range of targets, including oncogenes, miRNAs, and other co-regulatory factors, which direct specific phenotypical outcomes subsequent to JAK-STAT stimulation. Yet, the rapidly expanding field of therapeutic developments aimed to resolve JAK-STAT aberrations commonly reported in a multitude of cancers has been marred by off-target effects. Here, we discuss JAK-STAT biology in the context of immunity and cancer, the consequences of pathway perturbations and current therapeutic interventions, to provide insight and consideration for future targeting innovations.

Evidence for a non-canonical JAK/STAT signaling pathway in the synthesis of the brain's major ion channels and neurotransmitter receptors

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is a major signaling molecule that the brain uses to control a vast network of intracellular cascades fundamental to properties of learning and memory, and cognition. While much is known about BDNF signaling in the healthy nervous system where it controls the mitogen activated protein kinase (MAPK) and cyclic-AMP pathways, less is known about its role in multiple brain disorders where it contributes to the dysregulated neuroplasticity seen in epilepsy and traumatic brain injury (TBI). We previously found that neurons respond to prolonged BDNF exposure (both in vivo (in models of epilepsy and TBI) and in vitro (in BDNF treated primary neuronal cultures)) by activating the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signaling pathway. This pathway is best known for its association with inflammatory cytokines in non-neuronal cells.

RESULTS

Here, using deep RNA-sequencing of neurons exposed to BDNF in the presence and absence of well characterized JAK/STAT inhibitors, and without non-neuronal cells, we determine the BDNF transcriptome that is specifically regulated by agents that inhibit JAK/STAT signaling. Surprisingly, the BDNF-induced JAK/STAT transcriptome contains ion channels and neurotransmitter receptors coming from all the major classes expressed in the brain, along with key modulators of synaptic plasticity, neurogenesis, and axonal remodeling. Analysis of this dataset has revealed a unique non-canonical mechanism of JAK/STATs in neurons as differential gene expression mediated by STAT3 is not solely dependent upon phosphorylation at residue 705 and may involve a BDNF-induced interaction of STAT3 with Heterochromatin Protein 1 alpha (HP1α).

CONCLUSIONS

These findings suggest that the neuronal BDNF-induced JAK/STAT pathway involves more than STAT3 phosphorylation at 705, providing the first evidence for a non-canonical mechanism that may involve HP1α. Our analysis reveals that JAK/STAT signaling regulates many of the genes associated with epilepsy syndromes where BDNF levels are markedly elevated. Uncovering the mechanism of this novel form of BDNF signaling in the brain may provide a new direction for epilepsy therapeutics and open a window into the complex mechanisms of STAT3 transcriptional regulation in neurological disease.

IL-6/JAK1 pathway drives PD-L1 Y112 phosphorylation to promote cancer immune evasion

Glycosylation of immune receptors and ligands, such as T cell receptor and coinhibitory molecules, regulates immune signaling activation and immune surveillance. However, how oncogenic signaling initiates glycosylation of coinhibitory molecules to induce immunosuppression remains unclear. Here we show that IL-6-activated JAK1 phosphorylates programmed death-ligand 1 (PD-L1) Tyr112, which recruits the endoplasmic reticulum-associated N-glycosyltransferase STT3A to catalyze PD-L1 glycosylation and maintain PD-L1 stability. Targeting of IL-6 by IL-6 antibody induced synergistic T cell killing effects when combined with anti-T cell immunoglobulin mucin-3 (anti-Tim-3) therapy in animal models. A positive correlation between IL-6 and PD-L1 expression was also observed in hepatocellular carcinoma patient tumor tissues. These results identify a mechanism regulating PD-L1 glycosylation initiation and suggest the combination of anti-IL-6 and anti-Tim-3 as an effective marker-guided therapeutic strategy.

Immunohistochemical study of janus kinase 1/signal transducer and activator of transcription 3 in psoriasis vulgaris

Background: Human JAKs are responsible for generating docking sites for human SSTAT phosphorylation. The role of JAKs in psoriasis pathogenesis has not been clearly explained. Aim: To investigate the role of JAK1 in psoriasis pathogenesis and to assess if this role is mediated through STAT3 or not, through evaluation of their immunohistochemical expression in the skin of psoriatic patients. Methods: This case-control study was carried out on 26 patients presenting with psoriasis vulgaris versus 26 age- and sex-matched apparently healthy volunteers. Psoriasis Area and Severity Index (PASI) scores were used to evaluate psoriasis severity. From all controls and cases (lesional and perilesional), skin biopsies were taken for histopathological and immunohistochemical JAK1 and STAT3 evaluation. Results: There was significant stepwise upregulation of JAK1 from controls to perilesional to lesional psoriatic skin of the patient group in both epidermis and dermis (P≤0.001 for both). Dermal JAK1 H-score was significantly associated with psoriasis severity (P=0.01). STAT3 was significantly overexpressed in lesional psoriatic skin over nonlesional skin (P<0.001). There were significant positive correlations between lesional H-scores for STAT3 and Psoriasis Area and Severity Index scores in epidermis (r=0.63, P<0.001), and in dermis (r=0.47, P=0.04). There was a significant positive correlation between JAK1 and STAT3 expression in epidermal lesional psoriatic skin (r=0.44, P=0.03). Conclusion: JAK1 has a proinflammatory effect in psoriasis pathogenesis, which could be mediated through increasing STAT3 expression in psoriasis. JAK1 and STAT3 tissue expression could be markers of psoriasis severity. JAK1 may be used as a target for immunotherapy in psoriasis-management programs.

KDM3A histone demethylase functions as an essential factor for activation of JAK2-STAT3 signaling pathway

Janus tyrosine kinase 2 (JAK2)-signal transducer and activator of transcription 3 (STAT3) signaling pathway is essential for modulating cellular development, differentiation, and homeostasis. Thus, dysregulation of JAK2-STAT3 signaling pathway is frequently associated with human malignancies. Here, we provide evidence that lysine-specific demethylase 3A (KDM3A) functions as an essential epigenetic enzyme for the activation of JAK2-STAT3 signaling pathway. KDM3A is tyrosine-phosphorylated by JAK2 in the nucleus and functions as a STAT3-dependent transcriptional coactivator. JAK2-KDM3A signaling cascade induced by IL-6 leads to alteration of histone H3K9 methylation as a predominant epigenetic event, thereby providing the functional and mechanistic link between activation of JAK2-STAT3 signaling pathway and its epigenetic control. Together, our findings demonstrate that inhibition of KDM3A phosphorylation could be a potent therapeutic strategy to control oncogenic effect of JAK2-STAT3 signaling pathway.

Are Janus Kinase Inhibitors Superior over Classic Biologic Agents in RA Patients?

The Janus Kinases (JAKs) are a family of intracellular tyrosine kinases that provide transmission signals from cytokine, interferons, and many hormones receptors to the nucleus resulting in synthesis of many biologically active compounds and changing cell metabolism and function. That was theoretical background to synthetize the JAK inhibitors (Jakinibs). In recent years a substantial battery of evidence has been collected indicating the potential role of Jakinibs to interact with the specific elements of the immune system, therefore changing the inflammatory response. JAK kinase blockade offers a unique opportunity to block most of the key cytokines enabling the deep interaction into immune system functioning. Following discovery first Jakinibs were intensively studied in various forms of autoimmune diseases, including rheumatoid arthritis, and finally two Jakinibs tofacitinib and Baricitinib have been approved for the treatment of rheumatoid arthritis. Some clinical data indicated that under special circumstances Jakinibs may be even superior to biologics in the treatment of RA; however this suggestion should be verified in large clinical and observational studies.

JAK2 mediates lung fibrosis, pulmonary vascular remodelling and hypertension in idiopathic pulmonary fibrosis: an experimental study

BACKGROUND

Pulmonary hypertension (PH) is a common disorder in patients with idiopathic pulmonary fibrosis (IPF) and portends a poor prognosis. Recent studies using vasodilators approved for PH have failed in improving IPF mainly due to ventilation (V)/perfusion (Q) mismatching and oxygen desaturation. Janus kinase type 2 (JAK2) is a non-receptor tyrosine kinase activated by a broad spectrum of profibrotic and vasoactive mediators, but its role in PH associated to PH is unknown.

OBJECTIVE

The study of JAK2 as potential target to treat PH in IPF.

METHODS AND RESULTS

JAK2 expression was increased in pulmonary arteries (PAs) from IPF (n=10; 1.93-fold; P=0.0011) and IPF+PH (n=9; 2.65-fold; P<0.0001) compared with PA from control subjects (n=10). PA remodelling was evaluated in human pulmonary artery endothelial cells (HPAECs) and human pulmonary artery smooth muscle cells (HPASMCs) from patients with IPF in vitro treated with the JAK2 inhibitor JSI-124 or siRNA-JAK2 and stimulated with transforming growth factor beta. Both JSI-124 and siRNA-JAK2 inhibited the HPAEC to mesenchymal transition and the HPASMCs to myofibroblast transition and proliferation. JAK2 inhibition induced small PA relaxation in precision-cut lung slice experiments. PA relaxation was dependent of the large conductance calcium-activated potassium channel (BK_Ca). JAK2 inhibition activated BK_Ca channels and reduced intracellular Ca²⁺. JSI-124 1 mg/kg/day, reduced bleomycin-induced lung fibrosis, PA remodelling, right ventricular hypertrophy, PA hypertension and V/Q mismatching in rats. The animal studies followed the ARRIVE guidelines.

CONCLUSIONS

JAK2 participates in PA remodelling and tension and may be an attractive target to treat IPF associated to PH.

The JAK2 pathway is activated in idiopathic pulmonary fibrosis

Background

Idiopathic pulmonary fibrosis (IPF) is the most rapidly progressive and fatal fibrotic disorder, with no curative therapies. The signal transducer and activator of transcription 3 (STAT3) protein is activated in lung fibroblasts and alveolar type II cells (ATII), thereby contributing to lung fibrosis in IPF. Although activation of Janus kinase 2 (JAK2) has been implicated in proliferative disorders, its role in IPF is unknown. The aim of this study was to analyze JAK2 activation in IPF, and to determine whether JAK2/STAT3 inhibition is a potential therapeutic strategy for this disease.

Methods and results

JAK2/p-JAK2 and STAT3/pSTAT3 expression was evaluated using quantitative real time-PCR, western blotting, and immunohistochemistry. Compared to human healthy lung tissue (n = 10) both proteins were upregulated in the lung tissue of IPF patients (n = 12). Stimulating primary ATII and lung fibroblasts with transforming growth factor beta 1 or interleukin (IL)-6/IL-13 activated JAK2 and STAT3, inducing epithelial to mesenchymal and fibroblast to myofibroblast transitions. Dual p-JAK2/p-STAT3 inhibition with JSI-124 or silencing of JAK2 and STAT3 genes suppressed ATII and the fibroblast to myofibroblast transition, with greater effects than the sum of those obtained using JAK2 or STAT3 inhibitors individually. Dual rather than single inhibition was also more effective for inhibiting fibroblast migration, preventing increases in fibroblast senescence and Bcl-2 expression, and ameliorating impaired autophagy. In rats administered JSI-124, a dual inhibitor of p-JAK2/p-STAT3, at a dose of 1 mg/kg/day, bleomycin-induced lung fibrosis was reduced and collagen deposition in the lung was inhibited, as were JAK2 and STAT3 activation and several markers of fibrosis, autophagy, senescence, and anti-apoptosis.

Conclusions

JAK2 and STAT3 are activated in IPF, and their dual inhibition may be an attractive strategy for treating this disease.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0728-9) contains supplementary material, which is available to authorized users.

JAK3 as an Emerging Target for Topical Treatment of Inflammatory Skin Diseases

The recent interest and elucidation of the JAK/STAT signaling pathway created new targets for the treatment of inflammatory skin diseases (ISDs). JAK inhibitors in oral and topical formulations have shown beneficial results in psoriasis and alopecia areata. Patients suffering from other ISDs might also benefit from JAK inhibition. Given the development of specific JAK inhibitors, the expression patterns of JAKs in different ISDs needs to be clarified. We aimed to analyze the expression of JAK/STAT family members in a set of prevalent ISDs: psoriasis, lichen planus (LP), cutaneous lupus erythematosus (CLE), atopic dermatitis (AD), pyoderma gangrenosum (PG) and alopecia areata (AA) versus healthy controls for (p)JAK1, (p)JAK2, (p)JAK3, (p)TYK2, pSTAT1, pSTAT2 and pSTAT3. The epidermis carried in all ISDs, except for CLE, a strong JAK3 signature. The dermal infiltrate showed a more diverse expression pattern. JAK1, JAK2 and JAK3 were significantly overexpressed in PG and AD suggesting the need for pan-JAK inhibitors. In contrast, psoriasis and LP showed only JAK1 and JAK3 upregulation, while AA and CLE were characterized by a single dermal JAK signal (pJAK3 and pJAK1, respectively). This indicates that the latter diseases may benefit from more targeted JAK inhibitors. Our in vitro keratinocyte psoriasis model displayed reversal of the psoriatic JAK profile following tofacitinib treatment. This direct interaction with keratinocytes may decrease the need for deep skin penetration of topical JAK inhibitors in order to exert its effects on dermal immune cells. In conclusion, these results point to the important contribution of the JAK/STAT pathway in several ISDs. Considering the epidermal JAK3 expression levels, great interest should go to the investigation of topical JAK3 inhibitors as therapeutic option of ISDs.

Leptin augments recruitment of IRF-1 and CREB to thrombospondin-1 gene promoter in vascular smooth muscle cells in vitro

We previously reported that high pathophysiological concentrations of leptin, the adipocyte-secreted peptide, upregulate the expression of a potent proatherogenic matricellular protein, thrombospondin-1 (TSP-1), in vascular smooth muscle cells. Moreover, this regulation was found to occur at the level of transcription; however, the underlying molecular mechanisms remain unknown. The goal of the present study was to investigate the specific transcriptional mechanisms that mediate upregulation of TSP-1 expression by leptin. Primary human aortic smooth muscle cell cultures were transiently transfected with different TSP-1 gene (THBS1) promoter-linked luciferase reporter constructs, and luciferase activity in response to leptin (100 ng/ml) was assessed. We identified a long THBS1 promoter (-1270/+750) fragment with specific leptin response elements that are required for increased TSP-1 transcription by leptin. Promoter analyses, protein/DNA array and gel shift assays demonstrated activation and association of transcription factors, interferon regulatory factor-1 (IRF-1) and cAMP response element-binding protein (CREB), to the distal fragment of the THBS1 promoter in response to leptin. Supershift, chromatin immunoprecipitation, and coimmunoprecipitation assays revealed formation of a single complex between IRF-1 and CREB in response to leptin; importantly, recruitment of this complex to the THBS1 promoter mediated leptin-induced TSP-1 transcription. Finally, binding sequence decoy oligomer and site-directed mutagenesis revealed that regulatory elements for both IRF-1 (-1019 to -1016) and CREB (-1198 to -1195), specific to the distal THBS1 promoter, were required for leptin-induced TSP-1 transcription. Taken together, these findings demonstrate that leptin promotes a cooperative association between IRF-1 and CREB on the THBS1 promoter driving TSP-1 transcription in vascular smooth muscle cells.

Janus kinases and Src family kinases in the regulation of EGF-induced vimentin expression in MDA-MB-468 breast cancer cells

Epithelial-mesenchymal transition (EMT) is an important process associated with the metastasis of breast cancer cells. Members of the Janus kinases (JAKs) and Src family kinases (SFKs) are implicated in the regulation of an invasive phenotype in various cancer cell types. Using the pharmacological inhibitors JAK Inhibitor I (a pan-JAK inhibitor) and PP2 we investigated the role of the JAKs and SFKs, respectively, in the regulation of EMT markers in the MDA-MB-468 breast cancer cell line model of epidermal growth factor (EGF)-induced EMT. We identified selective inhibition of EGF induction of the mesenchymal marker vimentin by PP2 and JAK Inhibitor I. The effect of JAK Inhibitor I on vimentin protein induction occurred at a concentration lower than that required to significantly inhibit EGF-mediated signal transducer and activator of transcription 3 (STAT3)-phosphorylation, suggesting involvement of a STAT3-independent mechanism of EGF-induced vimentin regulation by JAKs. Despite our identification of a role for the JAK family in EGF-induced vimentin protein expression, siRNA-mediated silencing of each member of the JAK family was unable to phenocopy pharmacological inhibition, indicating potential redundancy among the JAK family members in this pathway. While SFKs and JAKs do not represent global regulators of the EMT phenotype, our findings have identified a role for members of these signaling pathways in the regulation of EGF-induced vimentin expression in the MDA-MB-468 breast cancer cell line.

Oral tofacitinib for the treatment of adults with moderate to severe chronic plaque psoriasis

New treatments for psoriasis have been developed based on increasing knowledge of the underlying pathogenesis of the disease. The development of very safe and highly effective biologics has revolutionized the treatment of moderate-to-severe psoriasis. Biologics are not perfect, however, as they are delivered parenterally, immunogenic, and costly. Small molecule agents, with molecular weights of less than 1 kDa, are being developed and hold the advantage of being administered orally. Tofacitinib is an oral Janus kinase inhibitor that has been developed to disrupt the aberrant JAK-STAT pathway that contributes to the pathogenesis of psoriasis. Phase II and Phase III clinical trial results for tofacitinib are encouraging, demonstrating substantial efficacy and satisfactory safety in the treatment of patients with moderate-to-severe chronic plaque psoriasis. An effective oral treatment without the organ toxicities of methotrexate and cyclosporine, tofacitinib is a promising alternative to biologics in the treatment of moderate-to-severe psoriasis.

Hexim1, a Novel Regulator of Leptin Function, Modulates Obesity and Glucose Disposal

Leptin triggers signaling events with significant transcriptional responses that are essential to metabolic processes affecting obesity and glucose disposal. We asked whether hexamethylene bis-acetamide inducible-1 (Hexim1), an inhibitor of RNA II polymerase-dependent transcription elongation, regulates leptin-Janus kinase 2 signaling axis in the hypothalamus. We subjected C57BL6 Hexim1 heterozygous (HT) mice to high-fat diet and when compared with wild type, HT mice were resistant to high-fat diet-induced weight gain and remain insulin sensitive. HT mice exhibited increased leptin-pY(705)Stat3 signaling in the hypothalamus, with normal adipocyte size, increased type I oxidative muscle fiber density, and enhanced glucose transporter 4 expression. We also observed that normal Hexim1 protein level is required to facilitate the expression of CCAAT/enhancer-binding proteins (C/EBPs) required for adipogenesis and inducible suppressor of cytokine signaling 3 (SOCS) expression. Further support on the role of Hexim1 regulating C/EBPs during adipocyte differentiation was shown when HT 3T3L1 fibroblasts failed to undergo adipogenesis. Hexim1 selectively modulates leptin-mediated signal transduction pathways in the hypothalamus, the expression of C/EBPs and peroxisome proliferator-activated receptor-γ (PPAR γ) in skeletal muscle and adipose tissue during the adaptation to metabolic stress. We postulate that Hexim1 might be a novel factor involved in maintaining whole-body energy balance.

Genetics of myeloproliferative neoplasms

In the last decade, genomic studies have identified multiple recurrent somatic mutations in myeloproliferative neoplasms (MPNs). Beginning with the discovery of the JAK2 V617F mutation, multiple additional mutations have been found that constitutively activate cell-signaling pathways, including MPL, CBL, and LNK. Furthermore, several classes of epigenetic modifiers have also been identified, in patients with MPN, revealing a requirement for mutations in other pathways to cooperate with JAK-STAT pathway mutations in MPN pathogenesis. Mutations in the de novo DNA methylation protein, DNMT3A, demethylation machinery, TET2 and related IDH1/2 production of oncometabolite 2-hydroxygluterate, and polycomb complex proteins EZH2 and ASXL1 have opened new pathophysiologic clues into these diseases. The prognostic relevance of these novel disease alleles remains an important area of investigation, and clinical trials are currently underway to determine if these findings represent tractable therapeutic targets, either alone, or in combination with JAK2 inhibition.

Expression of signal transducer and activator of transcription 3 and its phosphorylated form is significantly upregulated in patients with papillary thyroid cancer

The aim of the present study was to investigate the expression of signal transducer and activator of transcription 3 (STAT3) and phosphorylated STAT3 (pSTAT3) in tissues of papillary thyroid cancer (PTC) in comparison with the expression in adjacent normal tissues. The expression of STAT3, pSTAT3, fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor-C (VEGF-C) was examined in tissues of 42 cases of PTC and the adjacent normal tissues of 20 of the 42 PTC cases using immunohistochemistry and western blotting. The association between the expression levels and the clinicopathological features was analyzed. The expression of STAT3, pSTAT3, FGF2 and VEGF-C in the PTC tissues (76.2, 42.9, 81.0 and 73.8%, respectively) was significantly higher than that in the normal tissues (P<0.05). In the PTC tissues, the expression of STAT3 was linearly correlated with the levels of pSTAT3 and VEGF-C (P<0.05). In conclusion, STAT3 and pSTAT3 are significantly upregulated in PTC tissues, and may potentially be used as markers to screen for PTC with lymph node metastasis.

Tofacitinib for the treatment of moderate-to-severe psoriasis

Because of the increased knowledge about the underlying cytokine network in psoriasis, selective systemic agents for the treatment of moderate-to-severe psoriasis have been developed during the past decade. The marked upregulation of JAK/STAT pathways in psoriasis and the identification of multiple key mediators in psoriasis pathogenesis that signal through JAK/STAT pathways led to investigation of JAK proteins as potential therapeutic targets for psoriasis treatment. A novel JAK-STAT inhibitor, tofacitinib, has been tested in preclinical studies for the treatment of psoriasis. Considering the satisfactory safety profile and the encouraging efficacy observed in the Phase II and Phase III trials, tofacitinib may represent an important therapeutic to be included into the psoriasis paradigm.

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.

Redox regulation of Janus kinase: The elephant in the room

The redox regulation of Janus kinases (JAKs) is a complex subject. Due to other redox-sensitive kinases in the kinome, redox-sensitive phosphatases, and cellular antioxidant systems and reactive oxygen species (ROS) production systems, the net biological outcomes of oxidative stress on JAK-dependent signal transduction vary according to the specific biological system examined. This review begins with a discussion of the biochemical evidence for a cysteine-based redox switch in the catalytic domain of JAKs, proceeds to consider direct and indirect regulatory mechanisms involved in biological experiments, and ends with a discussion of the role(s) of redox regulation of JAKs in various diseases.

IFN signaling: how a non-canonical model led to the development of IFN mimetics

The classical model of cytokine signaling dominates our view of specific gene activation by cytokines such as the interferons (IFNs). The importance of the model extends beyond cytokines and applies to hormones such as growth hormone (GH) and insulin, and growth factors such as epidermal growth factor (EGF) and fibroblast growth factor (FGF). According to this model, ligand activates the cell via interaction with the extracellular domain of the receptor. This results in activation of receptor or receptor-associated tyrosine kinases, primarily of the Janus activated kinase (JAK) family, phosphorylation and dimerization of the signal transducer and activator of transcription (STAT) transcription factors, which dissociate from the receptor cytoplasmic domain and translocate to the nucleus. This view ascribes no further role to the ligand, JAK kinase, or receptor in either specific gene activation or the associated epigenetic events. The presence of dimeric STATs in the nucleus essentially explains it all. Our studies have resulted in the development of a non-canonical, more complex model of IFNγ signaling that is akin to that of steroid hormone (SH)/steroid receptor (SR) signaling. We have shown that ligand, receptor, activated JAKs, and STATs are associated with specific gene activation, where the receptor subunit IFNGR1 functions as a co-transcription factor and the JAKs are involved in associated epigenetic events. We found that the type I IFN system functions similarly. The fact that GH receptor, insulin receptor, EGF receptor, and FGF receptor undergo nuclear translocation upon ligand binding suggests that they may also function similarly. The SH/SR nature of type I and II IFN signaling provides insight into the specificity of signaling by members of cytokine families. The non-canonical model could also provide better understanding to more complex cytokine families such as those of IL-2 and IL-12, whose members often use the same JAKs and STATs, but also have different functions and properties.

Short communication: nuclear JAK3 and its involvement in CD4 activation in HIV-infected patients

The subcellular localization of JAK3 was examined by quantitative image analysis. For the first time, JAK3 was found to be located in the nuclei of primary CD4 lymphocytes. A comparable quantity of JAK3 was recovered in CD4 lymphocytes from healthy donors and HIV-infected patients. By contrast, far more phosphorylated JAK3 (pJAK3) was found in the nuclei of CD4 lymphocytes from HIV-infected patients than from healthy donors. The correlation detected between the quantity of pJAK3 in the nuclei of CD4 lymphocytes and the increase in HLA-DR at their surface suggests that pJAK3 may play a role in the deleterious immune activation characterizing HIV-infected patients.

Activation of the IL-6R/Jak/stat pathway is associated with a poor outcome in resected pancreatic ductal adenocarcinoma

BACKGROUND AND OBJECTIVE

Chronic localized pancreatic inflammation in the form of chronic pancreatitis is an established risk factor for human pancreatic ductal adenocarcinoma (PDAC) development. Constitutive activation of inflammation-related signal transducer and activator of transcription (Stat)3 signaling has been implicated in the development and progression a number of malignancies, including PDAC. Although, the Janus Kinase (Jak)/Stat pathway is a potential drug target, clinicopathological, molecular, and prognostic features of Stat3-activated PDAC remain uncertain. Our aim was to determine the clinicopathological impact of this inflammatory pathway in resectable PDAC.

METHODS

Using a tissue microarray-based cohort of PDAC from 86 patients undergoing pancreaticoduodenectomy with curative intent and complete clinicopathological data available, we evaluated expression of the interleukin-6 receptor (IL-6R)/Jak/Stat pathway by immunohistochemistry. IL-6R, Jak, phospho (p)-Jak, Stat3, pStat3(Tyr705), and pStat3(Ser727) were assessed in PDAC and pancreatic intraepithelial neoplasia. A Cox regression multivariate analysis model was used to determine factors influencing survival. Activation of the IL-6R/Jak/Stat3 pathway was compared with the systemic inflammatory response as measured by serum C-reactive protein levels.

RESULTS

High pJak was associated with reduced overall survival in multivariate analysis when compared with those with moderate or low expression (p = 0.036; hazard ratio (HR) = 1.68) as was pStat3(Tyr705) (p < 0.001; HR = 2.66) independent of lymph node status and tumor grade. Patients with a combination of pJakhigh/pStat3(Tyr705) high expression had an especially poor prognosis (median survival of 8.8 months; 95 % CI, 4.4-13.2). While the IL-6R/Jak/Stat pathway did not correlate with serum C-reactive protein levels, high pStat3 expression was associated with a reduction in the density of the local tumoral immune response.

CONCLUSION

Activation of the Jak/Stat3 pathway via phosphorylation was associated with adverse outcome following resection of PDAC with curative intent supporting potential roles for pJak and pStat3 as prognostic biomarkers markers and therapeutic targets.

25-hydroxyvitamin D3 ameliorates periodontitis by modulating the expression of inflammation-associated factors in diabetic mice

Periodontitis is a complication of diabetes mellitus, and the two diseases are highly associated with the dysfunction of inflammatory mediators. 25-hydroxyvitamin D(3) (25(OH)D(3)) plays a pivotal role in inflammatory modulation, but little is known about its effects on the progression of diabetic periodontitis and the underlying mechanism. In this paper, we showed that 25(OH)D(3) ameliorated experimental periodontitis in diabetic mice. The intraperitoneal administration of 25(OH)D(3) to streptozotocin-induced diabetic mice reduced fasting glucose and serum TNF-α levels, leading to decreased alveolar bone loss. Western blot analyses of gingival epithelia showed that vitamin D receptor (VDR) and protein tyrosine phosphatase N2 (PTPN2) were upregulated, while the expression of NF-κB and the phosphorylation of Janus family kinase 1 (JAK1) were attenuated upon 25(OH)D(3) treatment. These data may provide an explanation for the therapeutic benefits and anti-inflammatory effects of 25(OH)D(3). Our findings should have important implications for the clinical therapy of diabetic periodontitis.

Type I IFN receptor controls activated TYK2 in the nucleus: implications for EAE therapy

Recent studies have suggested that activated wild-type and mutant Janus kinase JAK2 play a role in the epigenetics of histone modification, where it phosphorylates histone H3 on tyrosine 41(H3pY41). We showed that type I IFN signaling involves activated TYK2 in the nucleus. ChIP-PCR demonstrated the presence of receptor subunits IFNAR1 and IFNAR2 along with TYK2, STAT1, and H3pY41 specifically at the promoter of the OAS1 gene in IFN treated cells. A complex of IFNAR1, TYK2, and STAT1α was also shown in the nucleus by immunoprecipitation. IFN treatment was required for TYK2 activation in the nucleus. The presence of IFNAR1, IFNAR2, and activated STAT1 and STAT2, as well as the type I IFN in the nucleus of treated cells was confirmed by the combination of Western blotting and confocal microscopy. Trimethylated histone H3 lysine 9 underwent demethylation and subsequent acetylation specifically in the region of the OAS1 promoter. Resultant N-terminal truncated IFN mimetics functioned intracellularly as antivirals as well as therapeutics against experimental allergic encephalomyelitis without the undesirable side effects that limit the therapeutic efficacy of IFNβ in treatment of multiple sclerosis. The findings indicate that IFN signaling is complex like that of steroid signaling.

Thymidine phosphorylase inhibits vascular smooth muscle cell proliferation via upregulation of STAT3

Dysregulated growth and motility of vascular smooth muscle cells (VSMC) play important role in obstructive vascular diseases. We previously reported that gene transfer of thymidine phosphorylase (TP) into rat VSMC inhibits cell proliferation and attenuates balloon injury induced neointimal hyperplasia; however, the mechanism remains unclear. The current study identified a signaling pathway that mediates effect of TP inhibited VSMC proliferation with a TP activity-dependent manner. Rat VSMC overexpressing human TP gene (C2) or control empty vector (PC) were used. Serum stimulation induced constitutive STAT3 phosphorylation at tyrosine705 in C2 cell but not in PC, which was independent of JAK2 signaling pathway. Inhibition of Src family kinases activity inhibited STAT3 phosphorylation in C2 cells. Lyn activity was higher in C2 cell than in PC. SiRNA based gene knockdown of Lyn significantly decreased serum induced STAT3 phosphorylation in C2 and dramatically increased proliferation of this cell, suggesting that Lyn plays a pivotal role in TP inhibited VSMC proliferation. Unphosphorylated STAT3 (U-STAT3) expression was significantly increased in C2 cells, which may be due to the increased STAT3 transcription. Gene transfection of mouse wild-type or Y705F mutant STAT3 into PC cell or mouse primary cultured VSMC significantly reduced proliferation of these cells, suggesting that overexpression of U-STAT3 inhibits VSMC proliferation. We conclude that Lyn mediates TP induced STAT3 activation, which subsequently contributes to upregulate expression of U-STAT3. The U-STAT3 plays a critical role in inhibiting VSMC proliferation.