Two novel protein-tyrosine kinases, each with a second phosphotransferase-related catalytic domain, define a new class of protein kinase

Pathogenesis of allergic diseases and implications for therapeutic interventions

Allergic diseases such as allergic rhinitis (AR), allergic asthma (AAS), atopic dermatitis (AD), food allergy (FA), and eczema are systemic diseases caused by an impaired immune system. Accompanied by high recurrence rates, the steadily rising incidence rates of these diseases are attracting increasing attention. The pathogenesis of allergic diseases is complex and involves many factors, including maternal-fetal environment, living environment, genetics, epigenetics, and the body's immune status. The pathogenesis of allergic diseases exhibits a marked heterogeneity, with phenotype and endotype defining visible features and associated molecular mechanisms, respectively. With the rapid development of immunology, molecular biology, and biotechnology, many new biological drugs have been designed for the treatment of allergic diseases, including anti-immunoglobulin E (IgE), anti-interleukin (IL)-5, and anti-thymic stromal lymphopoietin (TSLP)/IL-4, to control symptoms. For doctors and scientists, it is becoming more and more important to understand the influencing factors, pathogenesis, and treatment progress of allergic diseases. This review aimed to assess the epidemiology, pathogenesis, and therapeutic interventions of allergic diseases, including AR, AAS, AD, and FA. We hope to help doctors and scientists understand allergic diseases systematically.

The JAK-STAT Signaling Pathway in Epilepsy

Epilepsy is defined as spontaneous recurrent seizures in the brain. There is increasing evidence that inflammatory mediators and immune cells are involved in epileptic seizures. As more research is done on inflammatory factors and immune cells in epilepsy, new targets for the treatment of epilepsy will be revealed. The Janus kinase-signal transducer and transcriptional activator (JAKSTAT) signaling pathway is strongly associated with many immune and inflammatory diseases, At present, more and more studies have found that the JAK-STAT pathway is involved in the development and development of epilepsy, indicating the JAK-STAT pathway's potential promise as a target in epilepsy treatment. In this review, we discuss the composition, activation, and regulation of the JAK-STAT pathway and the relationship between the JAK-STAT pathway and epilepsy. In addition, we summarize the common clinical inhibitors of JAK and STAT that we would expect to be used in epilepsy treatment in the future.

The JAK/STAT signaling pathway: from bench to clinic

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway was discovered more than a quarter-century ago. As a fulcrum of many vital cellular processes, the JAK/STAT pathway constitutes a rapid membrane-to-nucleus signaling module and induces the expression of various critical mediators of cancer and inflammation. Growing evidence suggests that dysregulation of the JAK/STAT pathway is associated with various cancers and autoimmune diseases. In this review, we discuss the current knowledge about the composition, activation, and regulation of the JAK/STAT pathway. Moreover, we highlight the role of the JAK/STAT pathway and its inhibitors in various diseases.

Induced Mitochondrial Alteration and DNA Damage via IFNGR-JAK2-STAT1-PARP1 Pathway Facilitates Viral Hepatitis Associated Hepatocellular Carcinoma Aggressiveness and Stemness

Simple Summary

Hepatitis virus is a major risk factor for liver cancer. We analyzed possible synergism between momelotinib and sorafenib in hepatitis virus-associated liver cancer. The combined effect of momelotinib and sorafenib both at in vitro and in vivo synergistically sup-presses the proliferation of vHCC cells and effectively reduces the tumor burden. Our results showed that momelotinib effectively suppressed the expression of the IFNGR-JAK-STAT-PARP1 pathway, which results in the downregulation of cancer stem cell genes and enhances the antitumor efficacy of sorafenib by initiating the expression of apoptosis-related genes and inhibiting the DNA repair gene in vHCC cells, thus maximizing its therapeutic potential for patients with HCC.

Abstract

Background: Hepatitis virus is a major risk factor for liver cancer. The mitochondrial dysfunction IFN gamma-related pathways are activated after virus infection. Jak family-related protein is involved in the downstream of IFN gamma-related pathways. However, the effect of the IFNGR-JAK-STAT pathway acting as functional regulators of their related protein expression on virus infection and hepatocellular carcinoma (HCC) remains unclear. Interestingly, the role of the DNA repair gene (PARP1) in therapy resistant cancers also has not been studied and explored well. In this study, we hypothesized that momelotinib could suppress the progression of HCC by targeting Jak family related and PARP1 DNA repair protein. Based on this observation, we link the relevant targets of the JAK family and the potential applications of targeted therapy inhibitors. Methods: We analyzed possible synergism between momelotinib and sorafenib in hepatitis virus-associated liver cancer. Immunostaining, colony formation assay, cell invasion, migration, and tumorsphere-formation assay were used for drug cytotoxicity, cell viability, and possible molecular mechanism. Result: We first demonstrated that the expression of Jak1 and 2 is significantly upregulated in vHCC than in nvHCC/normal liver tissues. In addition, the gene expression of IFN gamma-related pathways is activated after virus infection. Additionally, we found that momelotinib significantly inhibited the growth of HCC cells and reduces the expression of Jak2, which showed the importance of momelotinib in targeting Jak2 and reducing tumorigenesis in HCC. Meanwhile, momelotinib effectively inhibited the IFNGR-JAK-STAT pathway and reduced the migratory/invasive ability of vHCC cells through down-regulating EMT biomarkers (E-cadherin and vimentin), transcription factor (Slug), and significantly inhibits the DNA damage repair enzyme PARP1. It also induced cell apoptosis of vHCC cells. Furthermore, the combined effect of momelotinib and sorafenib both at in vitro and in vivo synergistically suppresses the proliferation of vHCC cells and effectively reduces the tumor burden. Conclusions: Our results showed that momelotinib effectively suppressed the expression of the IFNGR-JAK-STAT-PARP1 pathway, which results in the downregulation of cancer stem cell genes and enhances the antitumor efficacy of sorafenib by initiating the expression of apoptosis-related genes and inhibiting the DNA repair gene in vHCC cells, thus maximizing its therapeutic potential for patients with HCC.

Activation of the STAT3 Signaling Pathway by the RNA-Dependent RNA Polymerase Protein of Arenavirus

Arenaviruses cause chronic and asymptomatic infections in their natural host, rodents, and several arenaviruses cause severe hemorrhagic fever that has a high mortality in infected humans, seriously threatening public health. There are currently no FDA-licensed drugs available against arenaviruses; therefore, it is important to develop novel antiviral strategies to combat them, which would be facilitated by a detailed understanding of the interactions between the viruses and their hosts. To this end, we performed a transcriptomic analysis on cells infected with arenavirus lymphocytic choriomeningitis virus (LCMV), a neglected human pathogen with clinical significance, and found that the signal transducer and activator of transcription 3 (STAT3) signaling pathway was activated. A further investigation indicated that STAT3 could be activated by the RNA-dependent RNA polymerase L protein (Lp) of LCMV. Our functional analysis found that STAT3 cannot affect LCMV multiplication in A549 cells. We also found that STAT3 was activated by the Lp of Mopeia virus and Junin virus, suggesting that this activation may be conserved across certain arenaviruses. Our study explored the interactions between arenaviruses and STAT3, which may help us to better understand the molecular and cell biology of arenaviruses.

JAK-STAT in Early Hematopoiesis and Leukemia

Hematopoietic stem cells (HSCs) produce all the terminally differentiated blood cells and are controlled by extracellular signals from the microenvironment, the bone marrow (BM) niche, as well as intrinsic cell signals. Intrinsic signals include the tightly controlled action of signaling pathways, as the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Activation of JAK-STAT leads to phosphorylation of members of the STAT family to regulate proliferation, survival, and self-renewal of HSCs. Mutations in components of the JAK-STAT pathway are linked with defects in HSCs and hematologic malignancies. Accumulating mutations in HSCs and aging contribute to leukemia transformation. Here an overview of hematopoiesis, and the role of the JAK-STAT pathway in HSCs and in the promotion of leukemic transformation is presented. Therapeutic targeting of JAK-STAT and clinical implications of the existing research findings are also discussed.

Viral infections in humans and mice with genetic deficiencies of the type I IFN response pathway

Type I IFNs are so-named because they interfere with viral infection in vertebrate cells. The study of cellular responses to type I IFNs led to the discovery of the JAK-STAT signaling pathway, which also governs the response to other cytokine families. We review here the outcome of viral infections in mice and humans with engineered and inborn deficiencies, respectively, of (i) IFNAR1 or IFNAR2, selectively disrupting responses to type I IFNs, (ii) STAT1, STAT2, and IRF9, also impairing cellular responses to type II (for STAT1) and/or III (for STAT1, STAT2, IRF9) IFNs, and (iii) JAK1 and TYK2, also impairing cellular responses to cytokines other than IFNs. A picture is emerging of greater redundancy of human type I IFNs for protective immunity to viruses in natural conditions than was initially anticipated. Mouse type I IFNs are essential for protection against a broad range of viruses in experimental conditions. These findings suggest that various type I IFN-independent mechanisms of human cell-intrinsic immunity to viruses have yet to be discovered.

Translating JAKs to Jakinibs

The discovery of JAKs and STATs and their roles in cytokine and IFN action represented a significant basic advance and a new paradigm in cell signaling. This was quickly followed by discoveries pointing to their essential functions, including identification of JAK3 mutations as a cause of SCID. This and other findings predicted the use of therapeutically targeting JAKs as a new strategy for treating immune and inflammatory diseases. This now is a reality with seven approved jakinibs being used to treat multiple forms of arthritis, inflammatory bowel disease and myeloproliferative neoplasms, and numerous ongoing clinical trials in other settings. This story provides interesting insights into the process of translating basic discoveries and also reveals the need to return to basic work to fill gaps that now become apparent.

JAK/STAT and VEGF/PAK1 signaling as emerging targets for topical treatment of psoriasis: a pilot study

Psoriasis is reportedly modulated by the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) or vascular endothelial growth factor/p21-activated kinase 1 (VEGF/PAK1) pathways. However, no research has evaluated the expression of JAK/STAT and VEGF/PAK1 signaling pathway molecules in human psoriasis skin tissue concurrently. We investigated the expression of autocrine STAT1, STAT3, VEGF, suppressor of cytokine signaling-1 (SOCS1), SOCS3, and PAK1 in psoriatic tissues. Skin biopsies were retrospectively collected from 55 patients with psoriasis from the tissue biobank. Skin biopsies from 40 healthy volunteers undergoing plastic surgery were used as controls. Immunohistochemical staining revealed that STAT1, STAT3, SOCS1, SOCS3, VEGF, and PAK1 were present at significantly higher levels in the psoriasis samples compared to the control group. Similarly, the mRNA expression of these signaling molecules was also significantly upregulated in psoriatic skin. Additionally, some of the molecules in these two signaling pathways exhibited significant positive correlations. In summary, we present pilot evidence that JAK/STAT and VEGF/PAK1 signaling molecules are expressed in psoriasis, which may provide topical treatment targets for this disease.

Targeting Janus Kinases and Signal Transducer and Activator of Transcription 3 to Treat Inflammation, Fibrosis, and Cancer: Rationale, Progress, and Caution

Before it was molecularly cloned in 1994, acute-phase response factor or signal transducer and activator of transcription (STAT)3 was the focus of intense research into understanding the mammalian response to injury, particularly the acute-phase response. Although known to be essential for liver production of acute-phase reactant proteins, many of which augment innate immune responses, molecular cloning of acute-phase response factor or STAT3 and the research this enabled helped establish the central function of Janus kinase (JAK) family members in cytokine signaling and identified a multitude of cytokines and peptide hormones, beyond interleukin-6 and its family members, that activate JAKs and STAT3, as well as numerous new programs that their activation drives. Many, like the acute-phase response, are adaptive, whereas several are maladaptive and lead to chronic inflammation and adverse consequences, such as cachexia, fibrosis, organ dysfunction, and cancer. Molecular cloning of STAT3 also enabled the identification of other noncanonical roles for STAT3 in normal physiology, including its contribution to the function of the electron transport chain and oxidative phosphorylation, its basal and stress-related adaptive functions in mitochondria, its function as a scaffold in inflammation-enhanced platelet activation, and its contributions to endothelial permeability and calcium efflux from endoplasmic reticulum. In this review, we will summarize the molecular and cellular biology of JAK/STAT3 signaling and its functions under basal and stress conditions, which are adaptive, and then review maladaptive JAK/STAT3 signaling in animals and humans that lead to disease, as well as recent attempts to modulate them to treat these diseases. In addition, we will discuss how consideration of the noncanonical and stress-related functions of STAT3 cannot be ignored in efforts to target the canonical functions of STAT3, if the goal is to develop drugs that are not only effective but safe. SIGNIFICANCE STATEMENT: Key biological functions of Janus kinase (JAK)/signal transducer and activator of transcription (STAT)3 signaling can be delineated into two broad categories: those essential for normal cell and organ development and those activated in response to stress that are adaptive. Persistent or dysregulated JAK/STAT3 signaling, however, is maladaptive and contributes to many diseases, including diseases characterized by chronic inflammation and fibrosis, and cancer. A comprehensive understanding of JAK/STAT3 signaling in normal development, and in adaptive and maladaptive responses to stress, is essential for the continued development of safe and effective therapies that target this signaling pathway.

JAK/STAT3 Pathway in Human Intestinal Epithelial Cells During Trefoil Factor 3(TFF3) Mediated Cell Migration

Objective:

Trefoil factor family is expressed in several tissues of the body and provides gastric and intestinal protection and healing. This research aims to indicate the mechanism involved in its function.

Methods:

The intestinal epithelial cells were pretreated with JAK inhibitor AG490 or the concentration of 60ug/ml human recombinant trefoil factor, while the levels of phospho-STAT3, E-cadherin and N-cadherin were detected by Western Blotting. The levels of Matrix Metalloproteinases, Ecadherin and N-cadherin were evaluated by quantitative real time PCR. The cell migration was assessed by the transwell assay and the scratch assay. The immunofluorescence method was performed to detect the reduction of molecular E-cadherin.

Results:

hTFF3 activates the JAK/STAT3 pathway in HT-29 cells. The effect of JAK/STAT3 pathway mechanism on cell migration promoted by hTFF3. TFF3 promoting cell migration is associated with increased gene transcription of MMPs. hTFF3 alters E-cadherin expression. hTFF3 activates the expression of N-cadherin and down-regulates E-cadherin expression in HT-29 Cells.

Conclusion:

We have shown that TFF3 activated the JAK/STAT3 pathway. TFF3 increased the level of Matrix Metalloproteinases and N-cadherin, decreased that of E-cadherin, while AG490 had the opposite effect. TFF3 accelerated cell migration and the AG490 relieved the migrating rate to control the levels. TFF3 activated JAK/STAT3 pathway which was associated with intestinal epithelial cell migration.

Genetic Susceptibility of the Host in Virus-Induced Diabetes

Enteroviruses, especially Coxsackie B viruses, are among the candidate environmental factors causative of type 1 diabetes. Host genetic factors have an impact on the development of virus-induced diabetes (VID). Host background, in terms of whether the host is prone to autoimmunity, should also be considered when analyzing the role of target genes in VID. In this review, we describe the genetic susceptibility of the host based on studies in humans and VID animal models. Understanding the host genetic factors should contribute not only to revealing the mechanisms of VID development, but also in taking measures to prevent VID.

Genome-wide and structural analyses of pseudokinases encoded in the genome of Arabidopsis thaliana provide functional insights

Protein Kinase-Like Non-Kinases (PKLNKs), commonly known as "pseudokinases", are homologous to eukaryotic Ser/Thr/Tyr protein kinases (PKs) but lack the crucial aspartate residue in the catalytic loop, indispensable for phosphotransferase activity. Therefore, they are predicted to be "catalytically inactive" enzyme homologs. Analysis of protein-kinase like sequences from Arabidopsis thaliana led to the identification of more than 120 pseudokinases lacking catalytic aspartate, majority of which are closely related to the plant-specific receptor-like kinase family. These pseudokinases engage in different biological processes, enabled by their diverse domain architectures and specific subcellular localizations. Structural comparison of pseudokinases with active and inactive conformations of canonical PKs, belonging to both plant and animal origin, revealed unique structural differences. The currently available crystal structures of pseudokinases show that the loop topologically equivalent to activation segment of PKs adopts a distinct-folded conformation, packing against the pseudoenzyme core, in contrast to the extended and inhibitory geometries observed for active and inactive states, respectively, of catalytic PKs. Salt-bridge between ATP-binding Lys and DFG-Asp as well as hydrophobic interactions between the conserved nonpolar residue C-terminal to the equivalent DFG motif and nonpolar residues in C-helix mediate such a conformation in pseudokinases. This results in enhanced solvent accessibility of the pseudocatalytic loop in pseudokinases that can possibly serve as an interacting surface while associating with other proteins. Specifically, our analysis identified several residues that may be involved in pseudokinase regulation and hints at the repurposing of pseudocatalytic residues to achieve mechanistic control over noncatalytic functions of pseudoenzymes.

Structural Understanding of Interleukin 6 Family Cytokine Signaling and Targeted Therapies: Focus on Interleukin 11

Cytokines are small signaling proteins that have central roles in inflammation and cell survival. In the half-century since the discovery of the first cytokines, the interferons, over fifty cytokines have been identified. Amongst these is interleukin (IL)-6, the first and prototypical member of the IL-6 family of cytokines, nearly all of which utilize the common signaling receptor, gp130. In the last decade, there have been numerous advances in our understanding of the structural mechanisms of IL-6 family signaling, particularly for IL-6 itself. However, our understanding of the detailed structural mechanisms underlying signaling by most IL-6 family members remains limited. With the emergence of new roles for IL-6 family cytokines in disease and, in particular, roles of IL-11 in cardiovascular disease, lung disease, and cancer, there is an emerging need to develop therapeutics that can progress to clinical use. Here we outline our current knowledge of the structural mechanism of signaling by the IL-6 family of cytokines. We discuss how this knowledge allows us to understand the mechanism of action of currently available inhibitors targeting IL-6 family cytokine signaling, and most importantly how it allows for improved opportunities to pharmacologically disrupt cytokine signaling. We focus specifically on the need to develop and understand inhibitors that disrupt IL-11 signaling.

Discovery and evaluation of Atopaxar hydrobromide, a novel JAK1 and JAK2 inhibitor, selectively induces apoptosis of cancer cells with constitutively activated STAT3

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway plays a vital role in immunity, cell division, cell death and tumor formation. Disrupted JAK-STAT signaling may lead to various diseases, especially cancer and immune disorders. Because of its importance, this signaling pathway has received significant attention from the pharmaceutical and biotechnology industries as a therapeutic target for drug design. However, few JAK or STATs inhibitors have been developed for cancer treatment. We used an in vitro STAT3 luciferase reporter assay to find novel inhibitors that could effectively block the JAK-STAT pathway. In our study, we screened 16,081 drug-like chemicals and found that atopaxar hydrobromide (AHB) is a specific inhibitor of JAK-STAT3 signaling. Our results suggest that AHB not only blocks constitutively activated and cytokine-induced STAT3 phosphorylation but also inhibits JAK1 and JAK2 phosphorylation. Moreover, AHB induces G1 phase cell cycle arrest, which stops cancer cell growth and induces apoptosis. AHB also inhibited tumor cell growth in vivo. In conclusion, AHB is a potential inhibitor that could be developed as a JAK-STAT pathway drug.

Chemical proteomics reveals target selectivity of clinical Jak inhibitors in human primary cells

Kinobeads are a set of promiscuous kinase inhibitors immobilized on sepharose beads for the comprehensive enrichment of endogenously expressed protein kinases from cell lines and tissues. These beads enable chemoproteomics profiling of kinase inhibitors of interest in dose-dependent competition studies in combination with quantitative mass spectrometry. We present improved bead matrices that capture more than 350 protein kinases and 15 lipid kinases from human cell lysates, respectively. A multiplexing strategy is suggested that enables determination of apparent dissociation constants in a single mass spectrometry experiment. Miniaturization of the procedure enabled determining the target selectivity of the clinical BCR-ABL inhibitor dasatinib in peripheral blood mononuclear cell (PBMC) lysates from individual donors. Profiling of a set of Jak kinase inhibitors revealed kinase off-targets from nearly all kinase families underpinning the need to profile kinase inhibitors against the kinome. Potently bound off-targets of clinical inhibitors suggest polypharmacology, e.g. through MRCK alpha and beta, which bind to decernotinib with nanomolar affinity.

The molecular details of cytokine signaling via the JAK/STAT pathway

More than 50 cytokines signal via the JAK/STAT pathway to orchestrate hematopoiesis, induce inflammation and control the immune response. Cytokines are secreted glycoproteins that act as intercellular messengers, inducing proliferation, differentiation, growth, or apoptosis of their target cells. They act by binding to specific receptors on the surface of target cells and switching on a phosphotyrosine-based intracellular signaling cascade initiated by kinases then propagated and effected by SH2 domain-containing transcription factors. As cytokine signaling is proliferative and often inflammatory, it is tightly regulated in terms of both amplitude and duration. Here we review molecular details of the cytokine-induced signaling cascade and describe the architectures of the proteins involved, including the receptors, kinases, and transcription factors that initiate and propagate signaling and the regulatory proteins that control it.

MTMR2 promotes invasion and metastasis of gastric cancer via inactivating IFNγ/STAT1 signaling

Background

The aberrant expression of myotubularin-related protein 2 (MTMR2) has been found in some cancers, but little is known about the roles and clinical relevance. The present study aimed to investigate the roles and clinical relevance of MTMR2 as well as the underlying mechanisms in gastric cancer (GC).

Methods

MTMR2 expression was examined in 295 GC samples by using immunohistochemistry (IHC). The correlation between MTMR2 expression and clinicopathological features and outcomes of the patients was analyzed. The roles of MTMR2 in regulating the invasive and metastatic capabilities of GC cells were observed using gain-and loss-of-function assays both in vitro and in vivo. The pathways involved in MTMR2-regulating invasion and metastasis were selected and identified by using mRNA expression profiling. Functions and underlying mechanisms of MTMR2-mediated invasion and metastasis were further investigated in a series of in vitro studies.

Results

MTMR2 was highly expressed in human GC tissues compared to adjacent normal tissues and its expression levels were significantly correlated with depth of invasion, lymph node metastasis, and TNM stage. Patients with MTMR2^high had significantly shorter lifespan than those with MTMR2^low. Cox regression analysis showed that MTMR2 was an independent prognostic indicator for GC patients. Knockdown of MTMR2 significantly reduced migratory and invasive capabilities in vitro and metastases in vivo in GC cells, while overexpressing MTMR2 achieved the opposite results. MTMR2 knockdown and overexpression markedly inhibited and promoted the epithelial-mesenchymal transition (EMT), respectively. MTMR2 mediated EMT through the IFNγ/STAT1/IRF1 pathway to promote GC invasion and metastasis. Phosphorylation of STAT1 and IRF1 was increased by MTMR2 knockdown and decreased by MTMR2 overexpression accompanying with ZEB1 down-regulation and up-regulation, respectively. Silencing IRF1 upregulated ZEB1, which induced EMT and consequently enhanced invasion and metastasis in GC cells.

Conclusions

Our findings suggest that MTMR2 is an important promoter in GC invasion and metastasis by inactivating IFNγ/STAT1 signaling and may act as a new prognostic indicator and a potential therapeutic target for GC.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1186-z) contains supplementary material, which is available to authorized users.

Control of Tyrosine Kinase Signalling by Small Adaptors in Colorectal Cancer

Tyrosine kinases (TKs) phosphorylate proteins on tyrosine residues as an intracellular signalling mechanism to coordinate intestinal epithelial cell communication and fate decision. Deregulation of their activity is ultimately connected with carcinogenesis. In colorectal cancer (CRC), it is still unclear how aberrant TK activities contribute to tumour formation because TK-encoding genes are not frequently mutated in this cancer. In vertebrates, several TKs are under the control of small adaptor proteins with potential important physiopathological roles. For instance, they can exert tumour suppressor functions in human cancer by targeting several components of the oncogenic TK signalling cascades. Here, we review how the Src-like adaptor protein (SLAP) and the suppressor of cytokine signalling (SOCS) adaptor proteins regulate the SRC and the Janus kinase (JAK) oncogenic pathways, respectively, and how their loss of function in the intestinal epithelium may influence tumour formation. We also discuss the potential therapeutic value of these adaptors in CRC.

Oncogenic Signaling Induced by HCV Infection

The liver is frequently exposed to toxins, metabolites, and oxidative stress, which can challenge organ function and genomic stability. Liver regeneration is therefore a highly regulated process involving several sequential signaling events. It is thus not surprising that individual oncogenic mutations in hepatocytes do not necessarily lead to cancer and that the genetic profiles of hepatocellular carcinomas (HCCs) are highly heterogeneous. Long-term infection with hepatitis C virus (HCV) creates an oncogenic environment by a combination of viral protein expression, persistent liver inflammation, oxidative stress, and chronically deregulated signaling events that cumulate as a tipping point for genetic stability. Although novel direct-acting antivirals (DAA)-based treatments efficiently eradicate HCV, the associated HCC risk cannot be fully eliminated by viral cure in patients with advanced liver disease. This suggests that HCV may persistently deregulate signaling pathways beyond viral cure and thereby continue to perturb cancer-relevant gene function. In this review, we summarize the current knowledge about oncogenic signaling pathways derailed by chronic HCV infection. This will not only help to understand the mechanisms of hepatocarcinogenesis but will also highlight potential chemopreventive strategies to help patients with a high-risk profile of developing HCC.

Targeting JAK-STAT signal transduction in IBD

An unmet medical need exists for novel targeted therapies for inflammatory bowel disease (IBD) as many patients experience inadequate responses to antibody-based biologics. An oral drug formulation with reduced production costs and redundancy for healthcare staff to administer therapy ideally should result in diminished healthcare expenses and improved patient compliance. A new drug class of small molecules, the Janus kinase (JAK) inhibitors (jakinibs), fulfills these criteria and has recently shown efficacy in IBD. Here we provide an overview of the mode of action of jakinibs and provide a comprehensive overview of existing clinical studies. Convincing clinical data show that a complex cytokine-driven inflammation can efficiently be modulated by therapeutic inhibition of the JAK proteins.

Protein⁻Protein Interactions with Connexin 43: Regulation and Function

Connexins are integral membrane building blocks that form gap junctions, enabling direct cytoplasmic exchange of ions and low-molecular-mass metabolites between adjacent cells. In the heart, gap junctions mediate the propagation of cardiac action potentials and the maintenance of a regular beating rhythm. A number of connexin interacting proteins have been described and are known gap junction regulators either through direct effects (e.g., kinases) or the formation of larger multifunctional complexes (e.g., cytoskeleton scaffold proteins). Most connexin partners can be categorized as either proteins promoting coupling by stimulating forward trafficking and channel opening or inhibiting coupling by inducing channel closure, internalization, and degradation. While some interactions have only been implied through co-localization using immunohistochemistry, others have been confirmed by biophysical methods that allow detection of a direct interaction. Our understanding of these interactions is, by far, most well developed for connexin 43 (Cx43) and the scope of this review is to summarize our current knowledge of their functional and regulatory roles. The significance of these interactions is further exemplified by demonstrating their importance at the intercalated disc, a major hub for Cx43 regulation and Cx43 mediated effects.

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.

Viral manipulation of STAT3: Evade, exploit, and injure

Signal transducer and activator of transcription 3 (STAT3) is a key regulator of numerous physiological functions, including the immune response. As pathogens elicit an acute phase response with concerted activation of STAT3, they are confronted with two evolutionary options: either curtail it or employ it. This has important consequences for the host, since abnormal STAT3 function is associated with cancer development and other diseases. This review provides a comprehensive outline of how human viruses cope with STAT3-mediated inflammation and how this affects the host. Finally, we discuss STAT3 as a potential target for antiviral therapy.

Purification of SOCS (Suppressor of Cytokine Signaling) SH2 Domains for Structural and Functional Studies

Src Homology 2 (SH2) domains are protein domains which have a high binding affinity for specific amino acid sequences containing a phosphorylated tyrosine residue. The Suppressors of Cytokine Signaling (SOCS) proteins use an SH2 domain to bind to components of certain cytokine signaling pathways to downregulate the signaling cascade. The recombinantly produced SH2 domains of various SOCS proteins have been used to undertake structural and functional studies elucidating the method of how such targeting occurs. Here, we describe the protocol for the recombinant production and purification of SOCS SH2 domains, with an emphasis on SOCS3.

Endometrial Carcinoma: Specific Targeted Pathways

Endometrial cancer (EC) is the most common gynecologic malignancy in the western world with more than 280,000 cases per year worldwide. Prognosis for EC at early stages, when primary surgical resection is the most common initial treatment, is excellent. Five-year survival rate is around 70 %.Several molecular alterations have been described in the different types of EC. They occur in genes involved in important signaling pathways. In this chapter, we will review the most relevant altered pathways in EC, including PI3K/AKT/mTOR, RAS-RAF-MEK-ERK, Tyrosine kinase, WNT/β-Catenin, cell cycle, and TGF-β signaling pathways. At the end of the chapter, the most significant clinical trials will be briefly discussed.This information is important to identify specific targets for therapy.

The secret life of kinases: insights into non-catalytic signalling functions from pseudokinases

Over the past decade, our understanding of the mechanisms by which pseudokinases, which comprise ∼10% of the human and mouse kinomes, mediate signal transduction has advanced rapidly with increasing structural, biochemical, cellular and genetic studies. Pseudokinases are the catalytically defective counterparts of conventional, active protein kinases and have been attributed functions as protein interaction domains acting variously as allosteric modulators of conventional protein kinases and other enzymes, as regulators of protein trafficking or localisation, as hubs to nucleate assembly of signalling complexes, and as transmembrane effectors of such functions. Here, by categorising mammalian pseudokinases based on their known functions, we illustrate the mechanistic diversity among these proteins, which can be viewed as a window into understanding the non-catalytic functions that can be exerted by conventional protein kinases.

The Future of Janus Kinase Inhibitors in Inflammatory Bowel Disease

Inflammatory bowel diseases, such as ulcerative colitis and Crohn's disease, are disabling conditions characterised by chronic, relapsing inflammation of the gastrointestinal tract. Current treatments are not universally effective or, in the case of therapeutic antibodies, are hampered by immune responses. Janus kinase inhibitors are orally delivered small molecules that target cytokine signalling by preventing phosphorylation of Janus kinases associated with the cytokine receptor. Subsequently, phosphorylation of signal transducers and activators of transcription that relay Janus kinase signalling and transcription of cytokines in the nucleus will be diminished. Key cytokines in the pathogenesis of inflammatory bowel diseases are targeted by Janus kinase inhibitors. Several Janus kinase inhibitors are in development for the treatment of inflammatory bowel diseases. Tofacitinib, inhibiting signalling via all Janus kinase family members, was effective in phase 2 and 3 trials in moderate-severe ulcerative colitis. GSK2586184, a Janus kinase 1 selective inhibitor, induced clinical and endoscopic response in ulcerative colitis; however, the study was discontinued at an early stage due to liver toxicity observed in systemic lupus patients receiving the drug. Filgotinib, a Janus kinase 1 selective inhibitor investigated in treatment of Crohn's disease, was superior to placebo. As adverse events associated with the broad immunological effect of these agents have been reported, the future application of these drugs is potentially limited. We will discuss the treatment efficacy of Janus kinase inhibition in inflammatory bowel diseases, how current Janus kinase inhibitors available target immune responses relevant in inflammatory bowel disease, and whether more specific kinase inhibition could be effective.

The use of kinase inhibitors in solid organ transplantation

INTRODUCTION

Despite the efficacy of current immunosuppression regimes used in solid organ transplantation, graft dysfunction, graft lost and antibody-mediated rejection continue to be problematic. As a result, clear attraction in exploiting key potential targets controlled by kinase phosphorylation has led to a number of studies exploring the use of these drugs in transplantation. Aim In this review, we consider the role of tyrosine kinase as a target in transplantation and summarize the relevant studies on kinase inhibitors that have been reported to date.

METHODS

Narrative review of literature from inception to December 2016, using OVID interface searching EMBASE and MEDLINE databases. All studies related to kinase based immunosuppression were examined for clinical relevance with no exclusion criteria. Key ideas were extracted and referenced.

CONCLUSION

The higher incidence of infections when using kinase inhibitors is an important consideration, however the number and range inhibitors and their clinical indications are likely to expand, but their exact role in transplantation is yet to be determined.

Molecular modeling study of CP-690550 derivatives as JAK3 kinase inhibitors through combined 3D-QSAR, molecular docking, and dynamics simulation techniques

To develop more potent JAK3 kinase inhibitors, a series of CP-690550 derivatives were investigated using combined molecular modeling techniques, such as 3D-QSAR, molecular docking and molecular dynamics (MD). The leave-one-out correlation (q²) and non-cross-validated correlation coefficient (r²) of the best CoMFA model are 0.715 and 0.992, respectively. The q² and r² values of the best CoMSIA model are 0.739 and 0.995, respectively. The steric, electrostatic, and hydrophobic fields played important roles in determining the inhibitory activity of CP-690550 derivatives. Some new JAK3 kinase inhibitors were designed. Some of them have better inhibitory activity than the most potent Tofacitinib (CP-690550). Molecular docking was used to identify some key amino acid residues at the active site of JAK3 protein. 10ns MD simulations were successfully performed to confirm the detailed binding mode and validate the rationality of docking results. The calculation of the binding free energies by MMPBSA method gives a good correlation with the predicted biological activity. To our knowledge, this is the first report on MD simulations and free energy calculations for this series of compounds. The combination results of this study will be valuable for the development of potent and novel JAK3 kinase inhibitors.

The Janus Kinase (JAK) FERM and SH2 Domains: Bringing Specificity to JAK-Receptor Interactions

The Janus kinases (JAKs) are non-receptor tyrosine kinases essential for signaling in response to cytokines and interferons and thereby control many essential functions in growth, development, and immune regulation. JAKs are unique among tyrosine kinases for their constitutive yet non-covalent association with class I and II cytokine receptors, which upon cytokine binding bring together two JAKs to create an active signaling complex. JAK association with cytokine receptors is facilitated by N-terminal FERM and SH2 domains, both of which are classical mediators of peptide interactions. Together, the JAK FERM and SH2 domains mediate a bipartite interaction with two distinct receptor peptide motifs, the proline-rich "Box1" and hydrophobic "Box2," which are present in the intracellular domain of cytokine receptors. While the general sidechain chemistry of Box1 and Box2 peptides is conserved between receptors, they share very weak primary sequence homology, making it impossible to posit why certain JAKs preferentially interact with and signal through specific subsets of cytokine receptors. Here, we review the structure and function of the JAK FERM and SH2 domains in light of several recent studies that reveal their atomic structure and elucidate interaction mechanisms with both the Box1 and Box2 receptor motifs. These crystal structures demonstrate how evolution has repurposed the JAK FERM and SH2 domains into a receptor-binding module that facilitates interactions with multiple receptors possessing diverse primary sequences.

Generation of Janus kinase 1 (JAK1) conditional knockout mice

The biological functions of the Janus kinase 1 (JAK1) are suggested to be pleiotropic since this signal transducer is ubiquitously expressed and coupled to a variety of cytokine receptors. Consequently, mice that are deficient in this tyrosine kinase were reported to die shortly after birth. To facilitate studies that address the biological and molecular functions of JAK1 during postnatal development, we performed gene targeting in embryonic stem cells and generated a Cre/lox-based conditional knockout mouse model. Expression of Cre recombinase in the germline converted the Jak1 conditional knockout allele (Jak1^fl ) into a null allele (Jak1^- ) that when subsequently crossed into homozygosity led to a complete absence of the JAK1 protein in developing embryos. JAK1 deficient embryos were visibly smaller starting at E15.5. Newborn pups exhibited signs of apnea and died within hours after birth. The examination of fibroblasts from conditional knockout embryos and their littermate wildtype controls expressing JAK1 showed that lack of this Janus kinase resulted in an impaired tyrosine phosphorylation and activation of the downstream Signal Transducers and Activators of Transcription (STATs) 1, 3, and 6. JAK1 conditional knockout mice will be an invaluable tool to study cytokine signaling during normal development and disease progression in adult animals.

Crystal Structure of a Complex of the Intracellular Domain of Interferon λ Receptor 1 (IFNLR1) and the FERM/SH2 Domains of Human JAK1

The crystal structure of a construct consisting of the FERM and SH2-like domains of the human Janus kinase 1 (JAK1) bound to a fragment of the intracellular domain of the interferon-λ receptor 1 (IFNLR1) has been determined at the nominal resolution of 2.1Å. In this structure, the receptor peptide forms an 85-Å-long extended chain, in which both the previously identified box1 and box2 regions bind simultaneously to the FERM and SH2-like domains of JAK1. Both domains of JAK1 are generally well ordered, with regions not seen in the crystal structure limited to loops located away from the receptor-binding regions. The structure provides a much more complete and accurate picture of the interactions between JAK1 and IFNLR1 than those given in earlier reports, illuminating the molecular basis of the JAK-cytokine receptor association. A glutamate residue adjacent to the box2 region in IFNLR1 mimics the mode of binding of a phosphotyrosine in classical SH2 domains. It was shown here that a deletion of residues within the box1 region of the receptor abolishes stable interactions with JAK1, although it was previously shown that box2 alone is sufficient to stabilize a similar complex of the interferon-α receptor and TYK2.

Molecular mechanisms of OLIG2 transcription factor in brain cancer

Oligodendrocyte lineage transcription factor 2 (OLIG2) plays a pivotal role in glioma development. Here we conducted a comprehensive study of the critical gene regulatory networks involving OLIG2. These include the networks responsible for OLIG2 expression, its translocation to nucleus, cell cycle, epigenetic regulation, and Rho-pathway interactions. We described positive feedback loops including OLIG2: loops of epigenetic regulation and loops involving receptor tyrosine kinases. These loops may be responsible for the prolonged oncogenic activity of OLIG2. The proposed schemes for epigenetic regulation of the gene networks involving OLIG2 are confirmed by patient survival (Kaplan-Meier) curves based on the cancer genome atlas (TCGA) datasets. Finally, we elucidate the Coherent-Gene Modules (CGMs) networks-framework of OLIG2 involvement in cancer. We showed that genes interacting with OLIG2 formed eight CGMs having a set of intermodular connections. We showed also that among the genes involved in these modules the most connected hub is EGFR, then, on lower level, HSP90 and CALM1, followed by three lower levels including epigenetic genes KDM1A and NCOR1. The genes on the six upper levels of the hierarchy are involved in interconnections of all eight CGMs and organize functionally defined gene-signaling subnetworks having specific functions. For example, CGM1 is involved in epigenetic control. CGM2 is significantly related to cell proliferation and differentiation. CGM3 includes a number of interconnected helix-loop-helix transcription factors (bHLH) including OLIG2. Many of these TFs are partially controlled by OLIG2. The CGM4 is involved in PDGF-related: angiogenesis, tumor cell proliferation and differentiation. These analyses provide testable hypotheses and approaches to inhibit OLIG2 pathway and relevant feed-forward and feedback loops to be interrogated. This broad approach can be applied to other TFs.

JAK-STAT signaling in cancer: From cytokines to non-coding genome

In the past decades, studies of the Janus kinases (JAKs) and signal transducers and activators of transcription (STATs) signaling have uncovered highly conserved programs linking cytokine signaling to the regulation of essential cellular mechanisms such as proliferation, invasion, survival, inflammation and immunity. Inhibitors of the JAK/STAT pathway are used for treatment of autoimmune diseases, such as rheumatoid arthritis or psoriasis. Aberrant JAK/STAT signaling has been identified to contribute to cancer progression and metastatic development. Targeting of JAK/STAT pathway is currently one of the most promising therapeutic strategies in prostate cancer (PCa), hematopoietic malignancies and sarcomas. Notably, newly identified regulators of JAK/STAT signaling, the non-coding RNAs transcripts and their role as important targets and potential clinical biomarkers are highlighted in this review. In addition to the established role of the JAK/STAT signaling pathway in traditional cytokine signaling the non-coding RNAs add yet another layer of hidden regulation and function. Understanding the crosstalk of non-coding RNA with JAK/STAT signaling in cancer is of critical importance and may result in better patient stratification not only in terms of prognosis but also in the context of therapy.

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.

Enhancing specificity in the Janus kinases: a study on the thienopyridine JAK2 selective mechanism combined molecular dynamics simulation

The superposition of the binding affinities between 19 and four JAK kinases.

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.

Genome-Wide Association and Trans-ethnic Meta-Analysis for Advanced Diabetic Kidney Disease: Family Investigation of Nephropathy and Diabetes (FIND)

Diabetic kidney disease (DKD) is the most common etiology of chronic kidney disease (CKD) in the industrialized world and accounts for much of the excess mortality in patients with diabetes mellitus. Approximately 45% of U.S. patients with incident end-stage kidney disease (ESKD) have DKD. Independent of glycemic control, DKD aggregates in families and has higher incidence rates in African, Mexican, and American Indian ancestral groups relative to European populations. The Family Investigation of Nephropathy and Diabetes (FIND) performed a genome-wide association study (GWAS) contrasting 6,197 unrelated individuals with advanced DKD with healthy and diabetic individuals lacking nephropathy of European American, African American, Mexican American, or American Indian ancestry. A large-scale replication and trans-ethnic meta-analysis included 7,539 additional European American, African American and American Indian DKD cases and non-nephropathy controls. Within ethnic group meta-analysis of discovery GWAS and replication set results identified genome-wide significant evidence for association between DKD and rs12523822 on chromosome 6q25.2 in American Indians (P = 5.74x10^-9). The strongest signal of association in the trans-ethnic meta-analysis was with a SNP in strong linkage disequilibrium with rs12523822 (rs955333; P = 1.31x10^-8), with directionally consistent results across ethnic groups. These 6q25.2 SNPs are located between the SCAF8 and CNKSR3 genes, a region with DKD relevant changes in gene expression and an eQTL with IPCEF1, a gene co-translated with CNKSR3. Several other SNPs demonstrated suggestive evidence of association with DKD, within and across populations. These data identify a novel DKD susceptibility locus with consistent directions of effect across diverse ancestral groups and provide insight into the genetic architecture of DKD.

Type 2 diabetes is the most common cause of severe kidney disease worldwide and diabetic kidney disease (DKD) associates with premature death. Individuals of non-European ancestry have the highest burden of type 2 DKD; hence understanding the causes of DKD remains critical to reducing health disparities. Family studies demonstrate that genes regulate the onset and progression of DKD; however, identifying these genes has proven to be challenging. The Family Investigation of Diabetes and Nephropathy consortium (FIND) recruited a large multi-ethnic collection of individuals with type 2 diabetes with and without kidney disease in order to detect genes associated with DKD. FIND discovered and replicated a DKD-associated genetic locus on human chromosome 6q25.2 (rs955333) between the SCAF8 and CNKSR genes. Findings were supported by significantly different expression of genes in this region from kidney tissue of subjects with, versus without DKD. The present findings identify a novel kidney disease susceptibility locus in individuals with type 2 diabetes which is consistent across subjects of differing ancestries. In addition, FIND results provide a rich catalogue of genetic variation in DKD patients for future research on the genetic architecture regulating this common and devastating disease.

A Janus Kinase in the JAK/STAT signaling pathway from Litopenaeus vannamei is involved in antiviral immune response

The JAK/STAT signaling pathways are conserved in evolution and mediate diversity immune responses to virus infection. In the present study, a Janus kinase (designated as LvJAK) gene was cloned and characterized from Litopenaeus vannamei. LvJAK contained the characteristic JAK homology domain (JH domain) from JH1 to JH7 and showed 19% identity (34% similarity) and 21% identity (35% similarity) to Drosophila Hopscotch protein and Human JAK2 protein, respectively. The mRNA of LvJAK was highly expressed in hepatopancreas of L. vannamei and its expression level was prominently upregulated after the stimulation of Poly (I:C) and white spot syndrome virus (WSSV) challenges. There were 10 putative STAT binding motifs in the promoter region of LvJAK, and it could be regulated by LvJAK self or (and) LvSTAT, suggesting that LvJAK is the JAK/STAT pathway target gene and could function as a positive regulator to form a positive feedback loop. In addition, the silencing of LvJAK caused higher mortality rate and virus load, suggesting that LvJAK could play an important role in defense against WSSV. This is the first report about the complete set of JAK/STAT proteins in shrimp and the results provide the evidence of the positive feedback loop mediated by JAK protein present in the JAK/STAT pathway in invertebrates.

Roles of STATs signaling in cardiovascular diseases

In cardiac and many other systems, chronic stress activates avfamily of structurally and functionally conserved receptors and their downstream signaling molecules that entail tyrosine, serine or threonine phosphorylation to transfer the messages to the genetic machinery. However, the activation of the Janus kinases (JAKs) and their downstream signal transducer and activator of transcription (STATs) proteins is both characteristic of and unique to cytokine and growth factor signaling which plays a central role in heart physiology. Dysregulation of JAK-STAT signaling is associated with various cardiovascular diseases. The molecular signaling and specificity of the JAK-STAT pathway are modulated at many levels by distinct regulatory proteins. Here, we review recent studies on the regulation of the STAT signaling pathway that will enhance our ability to design rational therapeutic strategies for stress-induced heart failure.

Mechanisms of chronic JAK-STAT3-SOCS3 signaling in obesity

Janus kinase (JAK)-signal transducers and activators of transcription (STAT) signaling pathways are critical for the maintenance of homeostatic and developmental processes; however, deregulation and chronic activation of JAK-STAT3 results in numerous diseases. Among others, obesity is currently being intensively studied. In obesity, chronic JAK-STAT3 is activated by the CNS by increased circulating leptin levels leading to the development of leptin resistance, whereas in the peripheral organs chronic IL-6-induced JAK-STAT3 impairs insulin action. We report the consequences of chronic JAK-STAT3 induced signaling as present under obese conditions in the main metabolic organs.

The spectrum of STAT functions in mammary gland development

The signal transducer and activator of transcription (STAT) family of transcription factors have a spectrum of functions in mammary gland development. In some cases these roles parallel those of STATs in other organ systems, while in other instances the function of individual STATs in the mammary gland is specific to this tissue. In the immune system, STAT6 is associated with differentiation of T helper cells, while in the mammary gland, it has a fundamental role in the commitment of luminal epithelial cells to the alveolar lineage. STAT5A is required for the production of luminal progenitor cells from mammary stem cells and is essential for the differentiation of milk producing alveolar cells during pregnancy. By contrast, the initiation of regression following weaning heralds a dramatic and specific activation of STAT3, reflecting its pivotal role in the regulation of cell death and tissue remodeling during mammary involution. Although it has been demonstrated that STAT1 is regulated during a mammary developmental cycle, it is not yet determined whether it has a specific, non-redundant function. Thus, the mammary gland constitutes an unusual example of an adult organ in which different STATs are sequentially activated to orchestrate the processes of functional differentiation, cell death and tissue remodeling.