Controlling nuclear JAKs and STATs for specific gene activation by IFNγ

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.

Prolonged STAT1 activation in neurons drives a pathological transcriptional response

Neurons require physiological IFN-γ signaling to maintain central nervous system (CNS) homeostasis, however, pathological IFN-γ signaling can cause CNS pathologies. The downstream signaling mechanisms that cause these drastically different outcomes in neurons has not been well studied. We hypothesized that different levels of IFN-γ signaling in neurons results in differential activation of its downstream transcription factor, signal transducer and activator of transduction 1 (STAT1), causing varying outcomes. Using primary cortical neurons, we showed that physiological IFN-γ elicited brief and transient STAT1 activation, whereas pathological IFN-γ induced prolonged STAT1 activation, which primed the pathway to be more responsive to a subsequent IFN-γ challenge. This is an IFN-γ specific response, as other IFNs and cytokines did not elicit such STAT1 activation nor priming in neurons. Additionally, we did not see the same effect in microglia or astrocytes, suggesting this non-canonical IFN-γ/STAT1 signaling is unique to neurons. Prolonged STAT1 activation was facilitated by continuous janus kinase (JAK) activity, even in the absence of IFN-γ. Finally, although IFN-γ initially induced a canonical IFN-γ transcriptional response in neurons, pathological levels of IFN-γ caused long-term changes in synaptic pathway transcripts. Overall, these findings suggest that IFN-γ signaling occurs via non-canonical mechanisms in neurons, and differential STAT1 activation may explain how neurons have both homeostatic and pathological responses to IFN-γ signaling.

Unique aspects of IFN-γ/STAT1 signaling in neurons

The IFN-γ/STAT1 immune signaling pathway impacts many homeostatic and pathological aspects of neurons, beyond its canonical role in controlling intracellular pathogens. Well known for its potent pro-inflammatory and anti-viral functions in the periphery, the IFN-γ/STAT1 pathway is rapidly activated then deactivated to prevent excessive inflammation; however, neurons utilize unique IFN-γ/STAT1 activation patterns, which may contribute to the non-canonical neuron-specific downstream effects. Though it is now well-established that the immune system interacts and supports the CNS in health and disease, many aspects regarding IFN-γ production in the CNS and how neurons respond to IFN-γ are unclear. Additionally, it is not well understood how the diversity of the IFN-γ/STAT1 pathway is regulated in neurons to control homeostatic functions, support immune surveillance, and prevent pathologies. In this review, we discuss the neuron-specific mechanisms and kinetics of IFN-γ/STAT1 activation, the potential sources and entry sites of IFN-γ in the CNS, and the diverse set of homeostatic and pathological effects IFN-γ/STAT1 signaling in neurons has on CNS health and disease. We will also highlight the different contexts and conditions under which IFN-γ-induced STAT1 activation has been studied in neurons, and how various factors might contribute to the vast array of downstream effects observed.

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.

Noncanonical IFN Signaling, Steroids, and STATs: A Probable Role of V-ATPase

A small group of only seven transcription factors known as STATs (signal transducer and activator of transcription) are considered to be canonical determinants of specific gene activation for a plethora of ligand/receptor systems. The activation of STATs involves a family of four tyrosine kinases called JAK kinases. JAK1 and JAK2 activate STAT1 in the cytoplasm at the heterodimeric gamma interferon (IFNγ) receptor, while JAK1 and TYK2 activate STAT1 and STAT2 at the type I IFN heterodimeric receptor. The same STATs and JAKs are also involved in signaling by functionally different cytokines, growth factors, and hormones. Related to this, IFNγ-activated STAT1 binds to the IFNγ-activated sequence (GAS) element, but so do other STATs that are not involved in IFNγ signaling. Activated JAKs such as JAK2 and TYK2 are also involved in the epigenetics of nucleosome unwrapping for exposure of DNA to transcription. Furthermore, activated JAKs and STATs appear to function coordinately for specific gene activation. These complex events have not been addressed in canonical STAT signaling. Additionally, the function of noncoding enhancer RNAs, including their role in enhancer/promoter interaction is not addressed in the canonical STAT signaling model. In this perspective, we show that JAK/STAT signaling, involving membrane receptors, is essentially a variation of cytoplasmic nuclear receptor signaling. Focusing on IFN signaling, we showed that ligand, IFN receptor, the JAKs, and the STATs all undergo endocytosis and ATP-dependent nuclear translocation to promoters of genes specifically activated by IFNs. We argue here that the vacuolar ATPase (V-ATPase) proton pump probably plays a key role in endosomal membrane crossing by IFNs for receptor cytoplasmic binding. Signaling of nuclear receptors such as those of estrogen and dihydrotestosterone provides templates for making sense of the specificity of gene activation by closely related cytokines, which has implications for lymphocyte phenotypes.

Association of IFNGR1 and IFNG genetic polymorphisms with the risk for pulmonary tuberculosis in the Chinese Tibetan population

Interferon-gamma (IFNG) and its receptor (IFNGR1) are principal genes that associated with tuberculosis. In the current study we aimed to explore the genetic association of polymorphisms of IFNG and IFNGR1 with the risk of pulmonary tuberculosis (PTB) in the Chinese Tibetan population. We selected 467 PTB patients and 503 healthy controls to genotype 9 single nucleotide polymorphisms (SNPs). The unconditional logistic regression analysis was applied for assessing the associations, and the risk of PTB were evaluated by calculating the odds ratio (OR) and 95% confidence interval (CI). The results showed that mutants of rs9376268, rs1327475 and rs1327474 in IFNGR1 played a protective role in the PTB risk under genotype, dominant and additive model (P<0.05). On the contrary, minor allele “A” of rs2069705 in IFNG significantly increased the risk of PTB under genotype, dominant and additive model (P<0.05). However, after Bonferroni's multiple adjustment was applied to our data, which level of significant was set at P<0.0011 (0.05/45). Only variant of rs9376268 was significantly associated decrease the PTB susceptibility under additive model (OR=0.73, 95%CI=0.61-0.88, P<0.001). Furthermore, in the haplotype analysis, we found that the haplotypes “C-G-G-A-C”, “C-G-A-G-T” and “T-A-G-G-T” of rs9376267-rs9376268-rs1327475-rs7749390-rs1327474 block were extremely decreased the PTB risk (P<0.01), however, the haplotypes “C-G-G-A-T”, “T-G-G-G-T” and “C-G-G-G-T” of the block were extremely increased the PTB risk (P<0.01). These results suggested that variants of IFNGR1 may have a close relation with the PTB risk in Chinese Tibetan population.

Noncanonical IFN Signaling: Mechanistic Linkage of Genetic and Epigenetic Events

The canonical model of cytokine signaling via the JAK/STAT pathway dominates our view of signal transduction but provides no insight into the significance of the simultaneous presence of activated JAKs and STATs in the nucleus of cells treated with cytokines. Such a mechanistic shortcoming challenges the usefulness of the model in its present form. Focusing on the interferon (IFN) cytokines, we have developed a noncanonical model of IFN signaling that naturally connects activated JAKs and STATs at or near response elements of genes that are activated by the IFNs. Specifically, cells treated with IFNγ showed association of activated STAT1α and JAK2 at the GAS element of genes activated by IFNγ. For IFNα treated cells, the association involved activated STAT1α and TYK2 JAK kinase at the ISRE promoter. The power of the noncanonical model is that it provides mechanistic insight into specific gene activation at the level of the associated epigenetics, akin to that of steroid/steroid receptor signaling.

IL-3 Maintains Activation of the p90S6K/RPS6 Pathway and Increases Translation in Human Eosinophils

IL-5 is a major therapeutic target to reduce eosinophilia. However, all of the eosinophil-activating cytokines, such as IL-5, IL-3, and GM-CSF, are typically present in atopic diseases, including allergic asthma. As a result of the functional redundancy of these three cytokines on eosinophils and the loss of IL-5R on airway eosinophils, it is important to take IL-3 and GM-CSF into account to efficiently reduce tissue eosinophil functions. Moreover, these three cytokines signal through a common β-chain receptor but yet differentially affect protein production in eosinophils. Notably, the increased ability of IL-3 to induce the production of proteins, such as semaphorin-7A, without affecting mRNA levels suggests a unique influence of IL-3 on translation. The purpose of this study was to identify the mechanisms by which IL-3 distinctively affects eosinophil function compared with IL-5 and GM-CSF, with a focus on protein translation. Peripheral blood eosinophils were used to study intracellular signaling and protein translation in cells activated with IL-3, GM-CSF, or IL-5. We establish that, unlike GM-CSF or IL-5, IL-3 triggers prolonged signaling through activation of ribosomal protein S6 (RPS6) and the upstream kinase 90-kDa ribosomal S6 kinase (p90S6K). Blockade of p90S6K activation inhibited phosphorylation of RPS6 and IL-3-enhanced semaphorin-7A translation. Furthermore, in an allergen-challenged environment, in vivo phosphorylation of RPS6 and p90S6K was enhanced in human airway compared with circulating eosinophils. Our findings provide new insights into the mechanisms underlying differential activation of eosinophils by IL-3, GM-CSF, and IL-5. These observations identify IL-3 and its downstream intracellular signals as novel targets that should be considered to modulate eosinophil functions.

Cigarette smoke-induced MMP2 and MMP9 secretion from aortic vascular smooth cells is mediated via the Jak/Stat pathway

It is hypothesized that cigarette smoke may increase MMP2 and MMP9 secretion through Jak/Stat pathway in the aorta, thereby facilitating abdominal aortic aneurysm (AAA) formation/progression in smokers. We observed through zymograms that treatment of male rat aortic vascular smooth muscle cells (RASMC) with an aqueous extract of cigarette smoke (CSE) for 24 hours resulted in a significant increase in pro-MMP9 (P = .005) and a modest increase in pro-MMP2 (P = .055) production. Western blot with protein extracts from CSE-treated RASMC showed up-regulation of pStat3, pJak2, and T-Jak2 and unchanged levels of T-Stat3. Transfection of RASMC with small interfering RNAs for Jak2, Stat3, or both Jak2 and Stat3 significantly reduced pro-MMP9 (P < .005) and pro-MMP2 (P < .05) in medium of CSE-treated RASMC compared with control small interfering RNA-transfected cells. Immunoprecipitation with total Jak2 antibody showed increased pStat3 and T-Stat3 in the cytoplasm and nucleus of CSE-treated RASMC. Immunofluorescence revealed increased presence of pJak2, T-Jak2, pStat3, and T-Stat3 in the cytoplasm and nucleus of the CSE-treated cells. Treatment of control human tissues with CSE resulted in pro-MMP9 secretion and up-regulation of the Jak/Stat proteins. In addition, AAA tissues showed more pJak2 and pStat3 than control human tissues. Therefore, inhibiting the Jak/Stat pathway could be a potential therapeutic approach in the treatment of AAA.

Type I interferon mimetics bypass vaccinia virus decoy receptor virulence factor for protection of mice against lethal infection

The canonical model of interferon (IFN) signaling focuses solely on the activation of STAT transcription factors which, according to the model, are initiated by the singular event of cross-linkage of the receptor extracellular domain by the IFN. The IFN has no further function beyond this. The model thus provides no approach to circumventing poxviruses decoy receptors that compete with the IFN receptors for IFNs. This simple event has allowed smallpox virus to decimate human populations throughout the ages. We have developed a noncanonical model of IFN signaling that has resulted in the development of small peptide mimetics to both types I and II IFNs. In this report, we focus on a type I IFN mimetic at positions 152 to 189, IFN-α1(152-189), which corresponds to the C terminus of human IFN-α1. This mimetic functions intracellularly and is thus not recognized by the B18R vaccinia virus decoy receptor. Mimetic synthesized with an attached palmitate (lipo-) for cell penetration protects mice from a lethal dose of vaccinia virus, while the parent IFN-α1 is ineffective. Unlike IFN-α1, the mimetic does not bind to the B18R decoy receptor. It further differs from the parent IFN in that it lacks the toxicity of weight loss and bone marrow suppression in mice while at the same time possessing a strong adjuvant effect on the immune system. The mimetic is thus an innate and adaptive immune regulator that is evidence of the dynamic nature of the noncanonical model of IFN signaling, in stark contrast to the canonical or classical model of signaling.

Short peptide type I interferon mimetics: therapeutics for experimental allergic encephalomyelitis, melanoma, and viral infections

The classical canonical model of interferon (IFN) signaling focuses solely on the activation of STAT transcription factors, which limits the model in terms of specific gene activation, associated epigenetic events, and IFN mimetic development. Accordingly, we have developed a noncanonical model of IFN signaling and report the development of short type I IFN peptide mimetic peptides based on the model. The mimetics, human IFNα1(152-189), human IFNβ(150-187), and ovine IFNτ(156-195) are derived from the C-terminus of the parent IFNs and function intracellularly based on the noncanonical model. Vaccinia virus produces a decoy IFN receptor (B18R) that inhibits type I IFN, but the IFN mimetics bypass B18R for effective antiviral activity. By contrast, both parent IFNs and mimetics inhibited vesicular stomatitis virus. The mimetics also possessed anti-tumor activity against murine melanoma B16 tumor cells in culture and in mice, including synergizing with suppressor of cytokine signaling 1 antagonist. Finally, the mimetics were potent therapeutics against experimental allergic encephalomyelitis, a mouse model of multiple sclerosis. The mimetics lack toxic side effects of the parent IFNs and, thus, are a potent therapeutic replacement of IFNs as therapeutics.

Upregulation of the large conductance voltage- and Ca2+-activated K+ channels by Janus kinase 2

The iberiotoxin-sensitive large conductance voltage- and Ca(2+)-activated potassium (BK) channels (maxi-K(+)-channels) hyperpolarize the cell membrane thus supporting Ca(2+) entry through Ca(2+)-release activated Ca(2+) channels. Janus kinase-2 (JAK2) has been identified as novel regulator of ion transport. To explore whether JAK2 participates in the regulation of BK channels, cRNA encoding Ca(2+)-insensitive BK channels (BK(M513I+Δ899-903)) was injected into Xenopus oocytes with or without cRNA encoding wild-type JAK2, gain-of-function (V617F)JAK2, or inactive (K882E)JAK2. K(+) conductance was determined by dual electrode voltage clamp and BK-channel protein abundance by confocal microscopy. In A204 alveolar rhabdomyosarcoma cells, iberiotoxin-sensitive K(+) current was determined utilizing whole cell patch clamp. A204 cells were further transfected with JAK2 and BK-channel transcript, and protein abundance was quantified by RT-PCR and Western blotting, respectively. As a result, the K(+) current in BK(M513I+Δ899-903)-expressing oocytes was significantly increased following coexpression of JAK2 or (V617F)JAK2 but not (K882E)JAK2. Coexpression of the BK channel with (V617F)JAK2 but not (K882E)JAK2 enhanced BK-channel protein abundance in the oocyte cell membrane. Exposure of BK-channel and (V617F)JAK2-expressing oocytes to the JAK2 inhibitor AG490 (40 μM) significantly decreased K(+) current. Inhibition of channel insertion by brefeldin A (5 μM) decreased the K(+) current to a similar extent in oocytes expressing the BK channel alone and in oocytes expressing the BK channel and (V617F)JAK2. The iberiotoxin (50 nM)-sensitive K(+) current in rhabdomyosarcoma cells was significantly decreased by AG490 pretreatment (40 μM, 12 h). Moreover, overexpression of JAK2 in A204 cells significantly enhanced BK channel mRNA and protein abundance. In conclusion, JAK2 upregulates BK channels by increasing channel protein abundance in the cell membrane.

Down-regulation of the epithelial Na⁺ channel ENaC by Janus kinase 2

Janus kinase-2 (JAK2), a signaling molecule mediating effects of various hormones including leptin and growth hormone, has previously been shown to modify the activity of several channels and carriers. Leptin is known to inhibit and growth hormone to stimulate epithelial Na(+) transport, effects at least partially involving regulation of the epithelial Na(+) channel ENaC. However, no published evidence is available regarding an influence of JAK2 on the activity of the epithelial Na(+) channel ENaC. In order to test whether JAK2 participates in the regulation of ENaC, cRNA encoding ENaC was injected into Xenopus oocytes with or without additional injection of cRNA encoding wild type JAK2, gain-of-function (V617F)JAK2 or inactive (K882E)JAK2. Moreover, ENaC was expressed with or without the ENaC regulating ubiquitin ligase Nedd4-2 with or without JAK2, (V617F)JAK2 or (K882E)JAK2. ENaC was determined from amiloride (50 μM)-sensitive current (I(amil)) in dual electrode voltage clamp. Moreover, I(amil) was determined in colonic tissue utilizing Ussing chambers. As a result, the I(amil) in ENaC-expressing oocytes was significantly decreased following coexpression of JAK2 or (V617F)JAK2, but not by coexpression of (K882E)JAK2. Coexpression of JAK2 and Nedd4-2 decreased I(amil) in ENaC-expressing oocytes to a larger extent than coexpression of Nedd4-2 alone. Exposure of ENaC- and JAK2-expressing oocytes to JAK2 inhibitor AG490 (40 μM) significantly increased I(amil). In colonic epithelium, I(amil) was significantly enhanced by AG490 pretreatment (40 μM, 1 h). In conclusion, JAK2 is a powerful inhibitor of ENaC.

The role of a non-canonical JAK-STAT pathway in IFN therapy of poxvirus infection and multiple sclerosis: An example of Occam's Broom?

Signaling by cytokines such as the interferons (IFNs) involves Janus kinases (JAKs) and signal transducer and activator of transcription (STAT) transcription factors. The beauty of the classical model of JAK-STAT signaling is its simplicity in that JAK-activated STATs in the nucleus are responsible for specific gene activation. The fact that many ligands, growth factors, and hormones use the same STAT transcription factors, but exert different functions at the level of the cell, tissue, and organ would suggest significant shortcomings in the classical model. Our studies have resulted in the development of a non-canonical, more complex model of IFN signaling that bears a striking resemblance to that of steroid hormone (SH)/steroid receptor (SR) signaling. Thus, both types I and II IFN signaling involves nuclear translocation of complexed ligand, receptor, activated JAKs, and activated STATs to the promoters of the genes that are specifically activated by the IFNs, where they are involved in specific gene activation and epigenetic remodeling. Receptor intracellular domains play an important role in binding the C-terminus of the IFNs, which is the basis for our development of IFN mimetics. The IFN mimetics are not recognized by poxvirus decoy receptors, since the decoy receptors compete for extracellular binding and not intracellular binding. Further, the type I IFN mimetics provide therapeutic protection against experimental allergic encephalomyelitis (EAE), a model of multiple sclerosis, without the side effects. Extracellular receptor binding by intact IFN is the primary reason for undesirable side effects of flu-like symptoms, bone-marrow suppression, and weight loss. The non-canonical model of IFN signaling thus provides insight into the specificity of such signaling and a mechanism for development of IFN mimetics. It is our contention that this model applies to other cytokines.

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.

Comprehensive genomic profiling in diabetic nephropathy reveals the predominance of proinflammatory pathways

Despite advances in the treatment of diabetic nephropathy (DN), currently available therapies have not prevented the epidemic of progressive chronic kidney disease (CKD). The morbidity of CKD, and the inexorable increase in the prevalence of end-stage renal disease, demands more effective approaches to prevent and treat progressive CKD. We undertook next-generation sequencing in a rat model of diabetic nephropathy to study in depth the pathogenic alterations involved in DN with progressive CKD. We employed the obese, diabetic ZS rat, a model that develops diabetic nephropathy, characterized by progressive CKD, inflammation, and fibrosis, the hallmarks of human disease. We then used RNA-seq to examine the combined effects of renal cells and infiltrating inflammatory cells acting as a pathophysiological unit. The comprehensive systems biology analysis of progressive CKD revealed multiple interactions of altered genes that were integrated into morbid networks. These pathological gene assemblies lead to renal inflammation and promote apoptosis and cell cycle arrest in progressive CKD. Moreover, in what is clearly a major therapeutic challenge, multiple and redundant pathways were found to be linked to renal fibrosis, a major cause of kidney loss. We conclude that systems biology applied to progressive CKD in DN can be used to develop novel therapeutic strategies directed to restore critical anomalies in affected gene networks.

Novel mechanism of cytokine-induced disruption of epithelial barriers: Janus kinase and protein kinase D-dependent downregulation of junction protein expression

The ductal epithelium plays a key role in physiological secretion of pancreatic enzymes into the digestive system. Loss of barrier properties of the pancreatic duct may contribute to the development of pancreatitis and metastatic dissemination of pancreatic tumors. Proinflammatory cytokines are essential mediators of pancreatic inflammation and tumor progression; however, their effects on the integrity and barrier properties of the ductal epithelium have not been previously addressed. In the present study, we investigate mechanisms of cytokine-induced disassembly of tight junctions (TJs) and adherens junctions (AJs) in a model pancreatic epithelium. Exposure of HPAF-II human pancreatic epithelial cell monolayers to interferon (IFN)γ disrupted integrity and function of apical junctions as manifested by increased epithelial permeability and cytosolic translocation of AJ and TJ proteins. Tumor necrosis factor (TNF)α potentiated the effects of IFNγ on pancreatic epithelial junctions. The cytokine-induced increase in epithelial permeability and AJ/TJ disassembly was attenuated by pharmacological inhibition of Janus kinase (JAK) and protein kinase D (PKD). Loss of apical junctions in IFNγ/TNFα-treated HPAF-II cells was accompanied by JAK and PKD dependent decrease in expression of AJ (E-cadherin, p120 catenin) and TJ (occludin, ZO-1) proteins. Depletion of E-cadherin or p120 catenin recapitulated the effects of cytokines on HPAF-II cell permeability and junctions. Our data suggests that proinflammatory cytokines disrupt pancreatic epithelial barrier via expressional downregulation of key structural components of AJs and TJs. This mechanism is likely to be important for pancreatic inflammatory injury and tumorigenesis.

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.

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.

Stimulation of Na(+) coupled phosphate transporter NaPiIIa by janus kinase JAK2

BACKGROUND

Na(+) coupled phosphate transporter NaPiIIa is the main carrier accomplishing phosphate transport across the apical cell membrane of proximal renal tubules and thus renal tubular phosphate reabsorption. The carrier is regulated by a wide variety of hormones and cellular signaling molecules. Hormones stimulating renal tubular phosphate transport and thus leading to hyperphosphatemia include growth hormone. Signaling of growth hormone involves activation of janus-activated kinase-2 JAK2, which has previously been shown to participate in the regulation of several Na(+) coupled transporters. Experiments exploring the effect of JAK2 on phosphate transport have, however, never been reported. The present study thus addressed the effect of JAK2 on NaPiIIa.

METHODS

cRNA encoding NaPiIIa was injected into Xenopus oocytes with or without additional injection of cRNA encoding wild type JAK2, the gain of function mutant JAK2(V617F) or inactive JAK2(K882E). Phosphate-induced current (I(NaPi)) reflecting electrogenic phosphate transport was determined by two electrode voltage clamp. Moreover, NaPiIIa protein abundance in the cell membrane was determined by chemiluminescence.

RESULTS

No appreciable I(NaPi) was observed in water injected oocytes or in oocytes expressing JAK2 alone. In NaPiIIa expressing oocytes I(NaPi) was significantly increased by additional expression of JAK2 or JAK2(V617F), but not by coexpression of JAK2(K882E). In oocytes expressing both, NaPiIIa and JAK2, I(NaPi) was gradually decreased by JAK2 inhibitor AG490 (40 μM). Coexpression of NaPiIIa and JAK2 or JAK2(V617F), but not of JAK2(K882E) increased NaPiIIa protein abundance in the cell membrane. Disruption of carrier protein insertion with Brefeldin A (5 μM) was followed by a decline of I(NaPi) to a similar extent in Xenopus oocytes expressing NaPiIIa with JAK2 and in Xenopus oocytes expressing NaPiIIa alone, suggesting that JAK2 did not affect carrier stability in the cell membrane.

CONCLUSION

JAK2 contributes to the regulation of phosphate transporter NaPiIIa.

A novel internalization motif regulates human IFN-γ R1 endocytosis

This study tested the hypothesis that the IFN-γ R1 287-YVSLI-91 intracellular motif regulates its endocytosis. IFN-γ exerts its biological activities by interacting with a specific cell-surface RC composed of two IFN-γ R1 and two IFN-γ R2 chains. Following IFN-γ binding and along with the initiation of signal transduction, the ligand and IFN-γ R1 are internalized. Two major types of consensus-sorting signals are described in receptors, which are rapidly internalized from the plasma membrane to intracellular compartments: tyrosine-based and dileucine-based internalization motifs. Transfection of HEK 293 cells and IFN-γ R1-deficient fibroblasts with WT and site-directed, mutagenesis-generated mutant IFN-γ R1 expression vectors helped us to identify region IFN-γ R1 287-YVSLI-291 as the critical domain required for IFN-γ-induced IFN-γ R1 internalization and Y287 and LI290-291 as part of a common structure essential for receptor endocytosis and function. This new endocytosis motif, YxxLI, shares characteristics of tyrosine-based and dileucine-based internalization motifs and is highly conserved in IFN-γ Rs across species. The IFN-γ R1 270-LI-271 dileucine motif, previously thought to be involved in this receptor endocytosis, showed to be unnecessary for receptor endocytosis.

Steroid-like signalling by interferons: making sense of specific gene activation by cytokines

Many cytokines, hormones and growth factors use the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) pathway for cell signalling and specific gene activation. In the classical model, ligand is said to interact solely with the receptor extracellular domain, which triggers JAK activation of STATs at the receptor cytoplasmic domain. Activated STATs are then said to carry out nuclear events of specific gene activation. Given the limited number of STATs (seven) and the activation of the same STATs by cytokines with different functions, the mechanism of the specificity of their signalling is not obvious. Focusing on IFNγ (interferon γ), we have shown that ligand, receptor and activated JAKs are involved in nuclear events that are associated with specific gene activation, where the receptor subunit IFNGR1 (IFNγ receptor 1) functions as a transcription/co-transcription factor and the JAKs are involved in key epigenetic events. RTKs (receptor tyrosine kinases) such as EGFR [EGF (epidermal growth factor) receptor] and FGFR [FGF (fibroblast growth factor) receptor] also undergo nuclear translocation in association with their respective ligands. EGFR and FGFR, like IFNGR1, have been shown to function as transcription/co-transcription factors. The RTKs also regulate other kinases that have epigenetic effects. Our IFNγ model, as well as the RTKs EGFR and FGFR, have similarities to that of steroid receptor signalling. These systems consist of ligand-receptor-co-activator complexes at the genes that they activate. The co-activators consist of transcription factors and kinases, of which the latter play an important role in the associated epigenetics. It is our view that signalling by cytokines such as IFNγ is but a variation of specific gene activation by steroid hormones.

New mimetic peptides of the kinase-inhibitory region (KIR) of SOCS1 through focused peptide libraries

SOCS (suppressor of cytokine signalling) proteins are negative-feedback regulators of the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) pathway. Their expression levels are low under physiological conditions, but they are up-regulated in response to cytokine stimulation in many immune and inflammatory processes. Overexpression of SOCS1 in keratinocyte clones abrogates the IFNγ (interferon γ)-induced expression of many pro-inflammatory genes and the release of related chemokines by blocking the JAK/STAT pathway. SOCS1 inhibits JAK2 kinase activity by binding the catalytic site of JAK2, with its KIR (kinase-inhibitory region) acting as a pseudo-substrate of the enzyme. In the present study, we screened a focused combinatorial peptide library of KIR to identify new peptides able to mimic its function with an improved affinity towards the JAK2 catalytic site. Using an alanine-scanning method, KIR residues that are crucial for the interaction with JAK2 were unveiled. In this way, the KIR sequence was restricted to a shorter segment and ‘non-essential’ residues were replaced by different amino acids following a simplified combinatorial approach. We selected a new unnatural sequence able to bind to JAK2 with Kd values in the nanomolar range. This peptide was tested in human keratinocyte cultures and reduced the phosphorylation of STAT1 and the expression levels of IRF-1 (interferon regulatory factor-1).

Controlling Nuclear Jaks and Stats for Specific Gene Activation by Ifn γ and Other Cytokines: A Possible Steroid-like Connection

The mechanism of specific gene activation by cytokines that use JAK/STAT signalling pathway is unknown. There are four different types of JAKs and seven different types of STATs. In the classical model of signaling, ligand interacts solely with the receptor extracellular domain, which triggers JAK activation at the receptor cytoplasmic domain. Activated STATs are then said to carry out nuclear events of specific gene activation, including associated epigenetic changes that cause heterochromatin destabilization. Ligand, receptor, and JAKs play no further role in the classical model. Given the limited number of STATs and the activation of the same STATs by cytokines with different functions, the mechanism of the specificity of their signalling is not obvious. Focusing on gamma interferon (IFNγ), we have shown that ligand, receptor, and activated JAKs are involved in nuclear events that are associated with specific gene activation. In this model, receptor subunit IFNGR1 functions as a transcription/cotranscription factor and the JAKs are involved in key epigenetic events that are required for specific gene activation. The model has implications for gene activation in cancer as well as stem cell differentiation.