p300/CBP is required for transcriptional induction by interleukin-4 and interacts with Stat6

Type II Interleukin-4 Receptor Activation in Basal Breast Cancer Cells Promotes Tumor Progression via Metabolic and Epigenetic Modulation

Interleukin-4 (IL4) is a Th2 cytokine that can signal through two different receptors, one of which-the type II receptor-is overexpressed by various cancer cells. Previously, we have shown that type II IL4 receptor signaling increases proliferation and metastasis in mouse models of breast cancer, as well as increasing glucose and glutamine metabolism. Here, we expand on those findings to determine mechanistically how IL4 signaling links glucose metabolism and histone acetylation to drive proliferation in the context of triple-negative breast cancer (TNBC). We used a combination of cellular, biochemical, and genomics approaches to interrogate TNBC cell lines, which represent a cancer type where high expression of the type II IL4 receptor is linked to reduced survival. Our results indicate that type II IL4 receptor activation leads to increased glucose uptake, Akt and ACLY activation, and histone acetylation in TNBC cell lines. Inhibition of glucose uptake through the deletion of Glut1 ablates IL4-induced proliferation. Additionally, pharmacological inhibition of histone acetyltransferase P300 attenuates IL4-mediated gene expression and proliferation in vitro. Our work elucidates a role for type II IL4 receptor signaling in promoting TNBC progression, and highlights type II IL4 signaling, as well as histone acetylation, as possible targets for therapy.

Mutations associated with progression in follicular lymphoma predict inferior outcomes at diagnosis: Alliance A151303

Follicular lymphoma (FL) is clinically heterogeneous, with select patients tolerating extended watch-and-wait, whereas others require prompt treatment, suffer progression of disease within 24 months of treatment (POD24), and/or experience aggressive histologic transformation (t-FL). Because our understanding of the relationship between genetic alterations in FL and patient outcomes remains limited, we conducted a clinicogenomic analysis of 370 patients with FL or t-FL (from Cancer and Leukemia Group B/Alliance trials 50402/50701/50803, or real-world cohorts from Washington University School of Medicine, Cleveland Clinic, or University of Miami). FL subsets by grade, stage, watch-and-wait, or POD24 status did not differ by mutation burden, whereas mutation burden was significantly higher in relapsed/refractory (rel/ref) FL and t-FL than in newly diagnosed (dx) FL. Nonetheless, mutation burden in dx FL was not associated with frontline progression-free survival (PFS). CREBBP was the only gene more commonly mutated in FL than in t-FL yet mutated CREBBP was associated with shorter frontline PFS in FL. Mutations in 20 genes were more common in rel/ref FL or t-FL than in dx FL, including 6 significantly mutated genes (SMGs): STAT6, TP53, IGLL5, B2M, SOCS1, and MYD88. We defined a mutations associated with progression (MAP) signature as ≥2 mutations in these 7 genes (6 rel/ref FL or t-FL SMGs plus CREBBP). Patients with dx FL possessing a MAP signature had shorter frontline PFS, revealing a 7-gene set offering insight into FL progression risk potentially more generalizable than the m7-Follicular Lymphoma International Prognostic Index (m7-FLIPI), which had modest prognostic value in our cohort. Future studies are warranted to validate the poor prognosis associated with a MAP signature in dx FL, potentially facilitating novel trials specifically in this high-risk subset of patients.

Distinct Responses to IL4 in Macrophages Mediated by JNK

IL(Interleukin)-4 is the main macrophage M2-type activator and induces an anti-inflammatory phenotype called alternative activation. The IL-4 signaling pathway involves the activation of STAT (Signal Transducer and Activator of Transcription)-6 and members of the MAPK (Mitogen-activated protein kinase) family. In primary-bone-marrow-derived macrophages, we observed a strong activation of JNK (Jun N-terminal kinase)-1 at early time points of IL-4 stimulation. Using selective inhibitors and a knockout model, we explored the contribution of JNK-1 activation to macrophages' response to IL-4. Our findings indicate that JNK-1 regulates the IL-4-mediated expression of genes typically involved in alternative activation, such as Arginase 1 or Mannose receptor, but not others, such as SOCS (suppressor of cytokine signaling) 1 or p21^Waf-1 (cyclin dependent kinase inhibitor 1A). Interestingly, we have observed that after macrophages are stimulated with IL-4, JNK-1 has the capacity to phosphorylate STAT-6 on serine but not on tyrosine. Chromatin immunoprecipitation assays revealed that functional JNK-1 is required for the recruitment of co-activators such as CBP (CREB-binding protein)/p300 on the promoter of Arginase 1 but not on p21^Waf-1. Taken together, these data demonstrate the critical role of STAT-6 serine phosphorylation by JNK-1 in distinct macrophage responses to IL-4.

Multilayered allosteric modulation of coupled folding and binding by phosphorylation, peptidyl-prolyl cis/trans isomerization, and diversity of interaction partners

Intrinsically disordered proteins (IDPs) play key roles in cellular regulation, including signal transduction, transcription, and cell-cycle control. Accordingly, IDPs can commonly interact with numerous different target proteins, and their interaction networks are expected to be highly regulated. However, many of the underlying regulatory mechanisms have remained unclear. Here, we examine the representative case of the nuclear coactivator binding domain (NCBD) of the large multidomain protein CBP, a hub in transcriptional regulation, and the interaction with several of its binding partners. Single-molecule Förster resonance energy transfer measurements show that phosphorylation of NCBD reduces its binding affinity, with effects that vary depending on the binding partner and the site and number of modifications. The complexity of the interaction is further increased by the dependence of the affinities on peptidyl-prolyl cis/trans isomerization in NCBD. Overall, our results reveal the potential for allosteric regulation on at least three levels: the different affinities of NCBD for its different binding partners, the differential modulation of these affinities by phosphorylation, and the effect of peptidyl-prolyl cis/trans isomerization on binding.

How phosphorylation impacts intrinsically disordered proteins and their function

Phosphorylation is the most common post-translational modification (PTM) in eukaryotes, occurring particularly frequently in intrinsically disordered proteins (IDPs). These proteins are highly flexible and dynamic by nature. Thus, it is intriguing that the addition of a single phosphoryl group to a disordered chain can impact its function so dramatically. Furthermore, as many IDPs carry multiple phosphorylation sites, the number of possible states increases, enabling larger complexities and novel mechanisms. Although a chemically simple and well-understood process, the impact of phosphorylation on the conformational ensemble and molecular function of IDPs, not to mention biological output, is highly complex and diverse. Since the discovery of the first phosphorylation site in proteins 75 years ago, we have come to a much better understanding of how this PTM works, but with the diversity of IDPs and their capacity for carrying multiple phosphoryl groups, the complexity grows. In this Essay, we highlight some of the basic effects of IDP phosphorylation, allowing it to serve as starting point when embarking on studies into this topic. We further describe how recent complex cases of multisite phosphorylation of IDPs have been instrumental in widening our view on the effect of protein phosphorylation. Finally, we put forward perspectives on the phosphorylation of IDPs, both in relation to disease and in context of other PTMs; areas where deep insight remains to be uncovered.

Nrf2-mediated anti-inflammatory polarization of macrophages as therapeutic targets for osteoarthritis

Macrophages are the most abundant immune cells within the synovial joints, and also the main innate immune effector cells triggering the initial inflammatory responses in the pathological process of osteoarthritis (OA). The transition of synovial macrophages between pro-inflammatory and anti-inflammatory phenotypes can play a key role in building the intra-articular microenvironment. The pro-inflammatory cascade induced by TNF-α, IL-1β, and IL-6 is closely related to M1 macrophages, resulting in the production of pro-chondrolytic mediators. However, IL-10, IL1RA, CCL-18, IGF, and TGF are closely related to M2 macrophages, leading to the protection of cartilage and the promoted regeneration. The inhibition of NF-κB signaling pathway is central in OA treatment via controlling inflammatory responses in macrophages, while the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway appears not to attract widespread attention in the field. Nrf2 is a transcription factor encoding a large number of antioxidant enzymes. The activation of Nrf2 can have antioxidant and anti-inflammatory effects, which can also have complex crosstalk with NF-κB signaling pathway. The activation of Nrf2 can inhibit the M1 polarization and promote the M2 polarization through potential signaling transductions including TGF-β/SMAD, TLR/NF-κB, and JAK/STAT signaling pathways, with the regulation or cooperation of Notch, NLRP3, PI3K/Akt, and MAPK signaling. And the expression of heme oxygenase-1 (HO-1) and the negative regulation of Nrf2 for NF-κB can be the main mechanisms for promotion. Furthermore, the candidates of OA treatment by activating Nrf2 to promote M2 phenotype macrophages in OA are also reviewed in this work, such as itaconate and fumarate derivatives, curcumin, quercetin, melatonin, mesenchymal stem cells, and low-intensity pulsed ultrasound.

Epithelial STAT6 O-GlcNAcylation drives a concerted anti-helminth alarmin response dependent on tuft cell hyperplasia and Gasdermin C

The epithelium is an integral component of mucosal barrier and host immunity. Following helminth infection, the intestinal epithelial cells secrete "alarmin" cytokines, such as interleukin-25 (IL-25) and IL-33, to initiate the type 2 immune responses for helminth expulsion and tolerance. However, it is unknown how helminth infection and the resulting cytokine milieu drive epithelial remodeling and orchestrate alarmin secretion. Here, we report that epithelial O-linked N-Acetylglucosamine (O-GlcNAc) protein modification was induced upon helminth infections. By modifying and activating the transcription factor STAT6, O-GlcNAc transferase promoted the transcription of lineage-defining Pou2f3 in tuft cell differentiation and IL-25 production. Meanwhile, STAT6 O-GlcNAcylation activated the expression of Gsdmc family genes. The membrane pore formed by GSDMC facilitated the unconventional secretion of IL-33. GSDMC-mediated IL-33 secretion was indispensable for effective anti-helminth immunity and contributed to induced intestinal inflammation. Protein O-GlcNAcylation can be harnessed for future treatment of type 2 inflammation-associated human diseases.

Structural and mutational analysis of member-specific STAT functions

BACKGROUND

The STAT family of transcription factors control gene expression in response to signals from various stimulus. They display functions in diseases ranging from autoimmunity and chronic inflammatory disease to cancer and infectious disease.

SCOPE OF REVIEW

This work uses an approach informed by structural data to explore how domain-specific structural variations, post-translational modifications, and the cancer genome mutational landscape dictate STAT member-specific activities.

MAJOR CONCLUSIONS

We illustrated the structure-function relationship of STAT proteins and highlighted their effect on member-specific activity. We correlated disease-linked STAT mutations to the structure and cancer genome mutational landscape and proposed rational drug targeting approaches of oncogenic STAT pathway addiction.

GENERAL SIGNIFICANCE

Hyper-activated STATs and their variants are associated with multiple diseases and are considered high value oncology targets. A full understanding of the molecular basis of member-specific STAT-mediated signaling and the strategies to selectively target them requires examination of the difference in their structures and sequences.

Molecular Mechanisms of Eosinophilic Esophagitis

Food hypersensitivity is a group of diseases arising from a specific immune response that reproduces on exposure to a given food. The current understanding of molecular mechanisms and immunopathology of non-IgE-mediated/mixed food hypersensitivity, e.g., eosinophilic esophagitis, contains many gaps in knowledge. This review aims to provide a modern classification and identify the primary diseases of non-IgE-mediated/mixed food hypersensitivity reactions, delineate the distinctive molecular features, and discuss recent findings in the immunopathology of eosinophilic esophagitis that may become a basis to develop valid biomarkers and novel therapies for this disease. Eosinophilic esophagitis is a recently recognized allergic-mediated disease with eosinophil-predominant esophagus inflammation. Its pathogenesis is a complicated network of interactions and signaling between epithelial, mesenchymal, and immune cells on molecular and intercellular levels. Alterations produced by overactivation of some cytokine signaling pathways, e.g., IL-13 or thymic stromal lymphopoietin (TSLP), were evolved and observed in this review from the viewpoints of molecular, genetic, epigenetic, and transcriptomic changes. Despite substantial experimental data, the reliable and representative mechanism of eosinophilic esophagitis pathogenesis has yet to show itself. So, the place of esophagitis between mixed and non-IgE-mediated allergic disorders and between eosinophilic gastrointestinal disorders currently seems vague and unclear.

Metabolic Reprogramming Induces Germinal Center B Cell Differentiation through Bcl6 Locus Remodeling

The germinal center (GC) reaction is essential for long-lived humoral immunity. However, molecular requirements for the induction of Bcl6, the master regulator for GC B cell differentiation, remain unclear. Through screening for cytokines and other stimuli that regulate Bcl6 expression, we identify IL-4 as the strongest inducer. IL-4 signaling alters the metabolomic profile in activated B cells and induces accumulation of the TCA cycle intermediate α-ketoglutarate (αKG), which is required for activation of the Bcl6 gene locus. Mechanistically, after IL-4 treatment, STAT6 bound to the known enhancers in the Bcl6 locus recruits UTX, a demethylase for the repressive histone mark H3K27me3 that requires αKG as a cofactor. In turn, the H3K27me3 demethylation activates the enhancers and transcription of the Bcl6 gene. We propose that IL-4-mediated metabolic reprogramming in B cells is pivotal for epigenomic activation of Bcl6 expression to promote GC B cell differentiation.

Maternal high-fat diet activates hepatic interleukin-4 in rat male offspring accompanied by increased eosinophil infiltration

Interleukin-4 (IL-4) is activated as an immune response during infection or tissue injury. Epigenetic programming of maternal high-fat (HF) diet has long-term effects in the offspring. In the present study, we investigated the epigenetic regulation of IL-4 in a maternal HF diet model in the liver of adult offspring. Timed-pregnant Sprague-Dawley rats were fed either control (C) or HF diet throughout gestation and lactation. Offspring were placed on a control diet after weaning, generating C/C and HF/C groups. The liver was collected at 12 wk of age, followed by histological and molecular analysis to investigate the maternal programming effects on IL-4 by HF diet. Maternal HF diet significantly induced mRNA expression and protein level of IL-4 and promoted hypomethylation of Il4 compared with the control group. Methylation-selective PCR (MSP) confirmed that maternal HF diet increased RNA polymerase II, acetylation of histone H4, and dimethylation of histone 3 lysine 4 at the +6 kb region of Il4. Moreover, the rat eosinophil marker Siglec-F was increased and colocalized with IL-4 in the liver. In conclusion, our study indicated that IL-4 was increased in liver cells in response to maternal HF diet. This coincides with DNA hypomethylation in combination with chromatin remodeling at the +6 kb region of the 3' downstream region as well as an induced immune cell infiltration, especially eosinophil infiltration, in the liver of offspring.NEW & NOTEWORTHY The present study identifies that maternal high-fat-diet-induced IL-4 upregulation is associated with DNA hypomethylation at the +6 kb region of the 3' downstream region of the gene. Furthermore, our results confirm that the induced Il4 expression in the liver of male offspring corresponds to the induced immune cell, especially eosinophil, infiltration.

αα-Hub domains and intrinsically disordered proteins: A decisive combo

Hub proteins are central nodes in protein-protein interaction networks with critical importance to all living organisms. Recently, a new group of folded hub domains, the αα-hubs, was defined based on a shared αα-hairpin supersecondary structural foundation. The members PAH, RST, TAFH, NCBD, and HHD are found in large proteins such as Sin3, RCD1, TAF4, CBP, and harmonin, which organize disordered transcriptional regulators and membrane scaffolds in interactomes of importance to human diseases and plant quality. In this review, studies of structures, functions, and complexes across the αα-hubs are described and compared to provide a unified description of the group. This analysis expands the associated molecular concepts of "one domain-one binding site", motif-based ligand binding, and coupled folding and binding of intrinsically disordered ligands to additional concepts of importance to signal fidelity. These include context, motif reversibility, multivalency, complex heterogeneity, synergistic αα-hub:ligand folding, accessory binding sites, and supramodules. We propose that these multifaceted protein-protein interaction properties are made possible by the characteristics of the αα-hub fold, including supersite properties, dynamics, variable topologies, accessory helices, and malleability and abetted by adaptability of the disordered ligands. Critically, these features provide additional filters for specificity. With the presentations of new concepts, this review opens for new research questions addressing properties across the group, which are driven from concepts discovered in studies of the individual members. Combined, the members of the αα-hubs are ideal models for deconvoluting signal fidelity maintained by folded hubs and their interactions with intrinsically disordered ligands.

Visualization and Sequencing of Accessible Chromatin Reveals Cell Cycle and Post-HDAC inhibitor Treatment Dynamics

Chromatin accessibility is a predictor of gene expression, cell division, and cell type specificity. NicE-viewSeq (Nicking Enzyme-assisted viewing and Sequencing) allows accessible chromatin visualization and sequencing with overall lower mitochondrial DNA and duplicated sequences interference relative to ATAC-see. Using NicE-viewSeq, we interrogated the accessibility of chromatin in a cell cycle (G1, S, and G2/M)-specific manner using mammalian cells. Despite DNA replication and subsequent condensation of chromatin to chromosomes, chromatin accessibility remained generally preserved with minimal subtle alterations. Genome-wide alteration of chromatin accessibility within TSS and enhancer elements gradually decreased as cells progressed from G1 to G2M, with distinct differential accessibility near consensus transcription factors sites. Inhibition of histone deacetylases promoted accessible chromatin within gene bodies, correlating with apoptotic gene expression. In addition, reduced chromatin accessibility for the MYC oncogene pathway correlated with downregulation of pertinent genes. Surprisingly, repetitive RNA loci expression remained unaltered following histone acetylation-mediated increased accessibility. Therefore, we suggest that subtle changes in chromatin accessibility are a prerequisite during the cell cycle and histone deacetylase inhibitor-mediated therapeutics.

Mapping the interactions of adenoviral E1A proteins with the p160 nuclear receptor coactivator binding domain of CBP

Many viruses deregulate the cell and force transcription of viral genes by competing with cellular proteins for binding to the transcriptional co-activators CREB-binding protein (CBP) and p300. Through its interactions with CBP/p300 and the retinoblastoma protein, the adenovirus (AdV) early region 1A (E1A) oncoprotein hijacks the cell cycle and, in rodents, transforms the cell; the mechanistic and structural basis for these effects remain unclear. In this study we compare the affinity of protein constructs from the E1A proteins from two adenovirus serotypes, non-oncogenic AdV5 and highly oncogenic AdV12, for binding to the nuclear receptor coactivator binding domain (NCBD) of CBP. NMR spectra show that the E1A constructs from both serotypes are intrinsically disordered in the free state and that each contains three homologous binding sites for the NCBD, one in the N-terminal region and two within conserved region 1 (CR1) of E1A. The binding sites in CR1 correspond to the motifs that bind the retinoblastoma protein and the TAZ2 domain of CBP/p300. The E1A and NCBD peptides fold synergistically upon complex formation. Binding affinities determined from NMR titrations show that, although the overall affinities for AdV5 and AdV12 E1A are comparable, there are significant differences between the two E1A serotypes in the relative strength with which their constituent interaction motifs bind to the NCBD. The individual E1A interaction motifs were unable to compete effectively with p53 for binding to the NCBD and both the N-terminal region and CR1 region of E1A are required for efficient competition with p53.

Histone acetyltransferases: challenges in targeting bi-substrate enzymes

Histone acetyltransferases (HATs) are epigenetic enzymes that install acetyl groups onto lysine residues of cellular proteins such as histones, transcription factors, nuclear receptors, and enzymes. HATs have been shown to play a role in diseases ranging from cancer and inflammatory diseases to neurological disorders, both through acetylations of histone proteins and non-histone proteins. Several HAT inhibitors, like bi-substrate inhibitors, natural product derivatives, small molecules, and protein–protein interaction inhibitors, have been developed. Despite their potential, a large gap remains between the biological activity of inhibitors in in vitro studies and their potential use as therapeutic agents. To bridge this gap, new potent HAT inhibitors with improved properties need to be developed. However, several challenges have been encountered in the investigation of HATs and HAT inhibitors that hinder the development of new HAT inhibitors. HATs have been shown to function in complexes consisting of many proteins. These complexes play a role in the activity and target specificity of HATs, which limits the translation of in vitro to in vivo experiments. The current HAT inhibitors suffer from undesired properties like anti-oxidant activity, reactivity, instability, low potency, or lack of selectivity between HAT subtypes and other enzymes. A characteristic feature of HATs is that they are bi-substrate enzymes that catalyze reactions between two substrates: the cofactor acetyl coenzyme A (Ac-CoA) and a lysine-containing substrate. This has important—but frequently overlooked—consequences for the determination of the inhibitory potency of small molecule HAT inhibitors and the reproducibility of enzyme inhibition experiments. We envision that a careful characterization of molecular aspects of HATs and HAT inhibitors, such as the HAT catalytic mechanism and the enzyme kinetics of small molecule HAT inhibitors, will greatly improve the development of potent and selective HAT inhibitors and provide validated starting points for further development towards therapeutic agents.

Interleukin-4 Downregulation of Involucrin Expression in Human Epidermal Keratinocytes Involves Stat6 Sequestration of the Coactivator CREB-Binding Protein

Skin barrier defects play an important role in atopic dermatitis (AD). Involucrin, an important barrier protein suppressed in human AD, is downregulated by interleukin-4 (IL-4). However, the molecular mechanism for IL-4 downregulation of involucrin has not been delineated, and especially how Stat6, a transcriptional activator, represses involucrin expression is unknown. Since Stats usually recruit p300/CBP in the general transcription machinery of their target genes and involucrin expression also involves p300/CBP, we hypothesize that Stat6 activated by IL-4 may sequestrate p300/CBP from the involucrin transcription complex, thus suppressing involucrin expression in keratinocytes. Using IL-4 transgenic mice, an AD mouse model, we find that involucrin expression is similarly downregulated as in human AD. In HaCat cells, the Jak inhibitor and dominant negative studies indicate that the Jaks-Stat6 pathway is involved in IL-4 downregulation of involucrin. Next, we transfected HaCat cells with an involucrin promoter-luciferase construct and then treated them with IL-4. IL-4 greatly suppresses the promoter activity, which is totally abolished by cotransfecting the CREB-binding protein (CBP) expression vector, indicating that IL-4 cannot downregulate involucrin in the presence of excess CBP. Finally, chromatin immunoprecipitation assay demonstrates that IL-4 decreases CBP binding to the involucrin transcription complex. For the first time, we defined a molecular mechanism for IL-4 downregulation of involucrin in keratinocytes, which may play an important role in the pathogenesis of AD.

Histone acetyltransferease p300 modulates TIM4 expression in dendritic cells

TIM4 (T cell immunoglobulin mucin domain molecule-4) plays a critical role in the initiation of skewed T helper (Th) 2 polarization. The factors regulating TIM4 expression are unclear. This study tests a hypothesis that p300 and STAT6 (signal transducer and activator transcription-6) regulates TIM4 expression in dendritic cells (DC). In this study, a food allergy mouse model was developed with ovalbumin (a specific antigen) and cholera toxin (CT; an adjuvant). The chromatin immunoprecipitation assay was performed to evaluate the chromatin changes at TIM4 and STAT6 promoters. The TIM4 expression was evaluated by real time RT-PCR and Western blotting. The results showed that high levels of p300 and TIM4 were detected in the intestinal DCs of mice with intestinal allergy. p300 is involved in the CT-induced TIM4 expression in DCs. p300 interacts with the chromatin at the TIM4 promoter locus in DCs isolated from allergic mice. CT increases p300 expression to regulate STAT6 levels in DCs. STAT6 mediates the CT-induced TIM4 expression in DCs. In conclusion, p300 and STAT6 mediate the microbial product CT-induced TIM4 expression in DCs.

STAT5 in Cancer and Immunity

Signal transducers and activators of transcription 5 (STAT5a and STAT5b) are highly homologous proteins that are encoded by 2 separate genes and are activated by Janus-activated kinases (JAK) downstream of cytokine receptors. STAT5 proteins are activated by a wide variety of hematopoietic and nonhematopoietic cytokines and growth factors, all of which use the JAK-STAT signalling pathway as their main mode of signal transduction. STAT5 proteins critically regulate vital cellular functions such as proliferation, differentiation, and survival. The physiological importance of STAT5 proteins is underscored by the plethora of primary human tumors that have aberrant constitutive activation of these proteins, which significantly contributes to tumor cell survival and malignant progression of disease. STAT5 plays an important role in the maintenance of normal immune function and homeostasis, both of which are regulated by specific members of IL-2 family of cytokines, which share a common gamma chain (γ(c)) in their receptor complex. STAT5 critically mediates the biological actions of members of the γ(c) family of cytokines in the immune system. Essentially, STAT5 plays a critical role in the function and development of Tregs, and consistently activated STAT5 is associated with a suppression in antitumor immunity and an increase in proliferation, invasion, and survival of tumor cells. Thus, therapeutic targeting of STAT5 is promising in cancer.

Monoacylglycerol lipase promotes Fcγ receptor-mediated phagocytosis in microglia but does not regulate LPS-induced upregulation of inflammatory cytokines

Monoacylglycerol lipase (MAGL) is important for neuroinflammation. However, the regulatory mechanisms underlying its expression and function remain unknown. Lipopolysaccharide (LPS) treatment post-translationally upregulated MAGL expression, whereas it downregulated MAGL transcription through a Stat6-mediated mechanism in microglia. Neither MAGL knockdown nor JZL-184, a selective MAGL inhibitor, suppressed LPS-induced upregulation of inflammatory cytokines in microglia. Moreover, exogenous expression of MAGL in BV-2 microglial cell line, which lacks endogenous MAGL, did not promote the induction of inflammatory cytokines by LPS treatment. Interestingly, MAGL knockdown reduced Fcγ receptor-mediated phagocytosis in primary microglia, and introduction of MAGL into the BV-2 cells increased Fcγ receptor-mediated phagocytosis. Collectively, these results suggest that MAGL regulates phagocytosis, but not LPS-mediated cytokine induction in microglia.

Reciprocal occupancy of BCL6 and STAT5 on Growth Hormone target genes: contrasting transcriptional outcomes and promoter-specific roles of p300 and HDAC3

Expression of the Growth Hormone (GH)-stimulated gene Socs2 (Suppressor of Cytokine Signaling 2) is mediated by the transcription activator STAT5 (Signal Transducer and Activator of Transcription 5) and the transcription repressor BCL6 (B-Cell Lymphoma 6). ChIP-Sequencing identified Cish (Cytokine-Inducible SH2-containing protein) and Bcl6 as having similar patterns of reciprocal occupancy by BCL6 and STAT5 in response to GH, though GH stimulates Cish and inhibits Bcl6 expression. The co-activator p300 occupied Socs2, Cish and Bcl6 promoters, and enhanced STAT5-mediated activation of Socs2 and Cish. In contrast, on Bcl6, p300 functioned as a repressor and inhibited in conjunction with STAT5 or BCL6. The co-repressor HDAC3 (Histone deacetylase 3) inhibited the Socs2, Cish and Bcl6 promoters in the presence of STAT5. Thus transcriptional outcomes on GH-regulated genes occupied by BCL6 and STAT5 are determined in a promoter-specific fashion by co-regulatory proteins which mediate the distinction between activating and repressive transcription factors.

Two histone/protein acetyltransferases, CBP and p300, are indispensable for Foxp3+ T-regulatory cell development and function

T-regulatory (Treg) cells are important to immune homeostasis, and Treg cell deficiency or dysfunction leads to autoimmune disease. A histone/protein acetyltransferase (HAT), p300, was recently found to be important for Treg function and stability, but further insights into the mechanisms by which p300 or other HATs affect Treg biology are needed. Here we show that CBP, a p300 paralog, is also important in controlling Treg function and stability. Thus, while mice with Treg-specific deletion of CBP or p300 developed minimal autoimmune disease, the combined deletion of CBP and p300 led to fatal autoimmunity by 3 to 4 weeks of age. The effects of CBP and p300 deletion on Treg development are dose dependent and involve multiple mechanisms. CBP and p300 cooperate with several key Treg transcription factors that act on the Foxp3 promoter to promote Foxp3 production. CBP and p300 also act on the Foxp3 conserved noncoding sequence 2 (CNS2) region to maintain Treg stability in inflammatory environments by regulating pCREB function and GATA3 expression, respectively. Lastly, CBP and p300 regulate the epigenetic status and function of Foxp3. Our findings provide insights into how HATs orchestrate multiple aspects of Treg development and function and identify overlapping but also discrete activities for p300 and CBP in control of Treg cells.

Signal transducer and activator of transcription 6 directly regulates human ORMDL3 expression

Orosomucoid-like 3 (ORMDL3) has been associated with asthma and a series of autoimmune disorders, and is involved in endoplasmic reticulum-mediated inflammatory responses. However, its clinical significance and the molecular mechanism underlying its expression are still largely unclear. To elucidate the mechanisms of human ORMDL3 transcriptional regulation, we cloned a 1.5 kb genomic DNA fragment containing the putative promoter region and evaluated its transcriptional activity in a luciferase reporter system by deletion analysis. We identified a 68 bp region that functions as a minimal promoter. Bioinformatics analysis predicted that the -64 to -56 bp region contained a signal transducer and activator of transcription 6 (STAT6) binding site. Electrophoretic mobility shift assay and chromatin immunoprecipitation demonstrated that STAT6 bound to its binding site within the ORMDL3 promoter. STAT6 over-expression or knockdown trans-activated or trans-inhibited, respectively, the ORMDL3 promoter containing the STAT6-binding motif. Treatment with interleukins 4 or 13 increased ORMDL3 promoter activity as well as endogenous ORMDL3 expression. Immunoprecipitation and ChIP/Re-ChIP assays revealed that STAT6 and p300 exist in the same protein complex that binds to the ORMDL3 promoter. Our study confirmed that STAT6 plays important roles in regulating the expression of human ORMDL3 by directly binding to the promoter region, which may shed light on a possible role in various human diseases.

Deacetylation of C/EBPβ is required for IL-4-induced arginase-1 expression in murine macrophages

The amount of arginine available at inflammatory loci is a limiting factor for the growth of several cells of the immune system. IL-4-induced activation of macrophages produced arginase-1, which converts arginine into ornithine, a precursor of polyamines and proline. Trichostatin A (TSA), a pan-inhibitor of histone deacetylases (HDACs), inhibited IL-4-induced arginase-1 expression. TSA showed promoter-specific effects on the IL-4-responsive genes. While TSA inhibited the expression of arginase-1, fizz1, and mrc1, other genes, such as ym,1 mgl1, and mgl2, were not affected. The inhibition of arginase-1 occurred at the transcriptional level with the inhibition of polymerase II binding to the promoter. IL-4 induced STAT6 phosphorylation and binding to DNA. These activities were not affected by TSA treatment. However, TSA inhibited C/EBPβ DNA binding. This inhibitor induced acetylation on lysine residues 215-216, which are critical for DNA binding. Finally, using macrophages from STAT6 KO mice we showed that STAT6 is required for the DNA binding of C/EBPβ. These results demonstrate that the acetylation/deacetylation balance strongly influences the expression of arginase-1, a gene of alternative activation of macrophages. These findings also provide a molecular mechanism to explain the control of gene expression through deacetylase activity.

Transcriptional regulation by STAT6

Signal transducer and activator of transcription (STAT) proteins are critical mediators of cytokine signaling. Among the seven STAT proteins, STAT6 is activated by IL-4 and IL-13 and plays a predominant role in the immune system. However, there is increasing evidence that STAT6 may function in other tissues and organ systems. IL-4, IL-13, and STAT6 promote humoral immunity, clearance of helminthic parasites as well as the pathogenesis of allergic disorders like asthma, food allergies, and atopic dermatitis. In this review, we will describe our current understanding of the biological functions of STAT6 and summarize recent advances in understanding the molecular mechanisms by which STAT6 regulates transcription.

Histone acetyltransferase p300 acetylates Pax5 and strongly enhances Pax5-mediated transcriptional activity

Pax5/B cell lineage specific activator protein (BSAP) is a B lineage-specific regulator that controls the B lineage-specific gene expression program and immunoglobulin gene V(H) to DJ(H) recombination. Despite extensive studies on its multiple functions, little is known about how the activity of Pax5 is regulated. Here, we show that co-expression of histone acetyltransferase E1A binding protein p300 dramatically enhances Pax5-mediated transcriptional activation. The p300-mediated enhancement is dependent on its intrinsic histone acetyltransferase activity. Moreover, p300 interacts with the C terminus of Pax5 and acetylates multiple lysine residues within the paired box DNA binding domain of Pax5. Mutations of lysine residues 67 and 87/89 to alanine within Pax5 abolish p300-mediated enhancement of Pax5-induced Luc-CD19 reporter expression in HEK293 cells and prevent Pax5 to activate endogenous Cd19 and Blnk expression in Pax5(-/-) murine pro B cells. These results uncover a novel level of regulation of Pax5 function by p300-mediated acetylation.

Epigenetic regulation of the IL-13-induced human eotaxin-3 gene by CREB-binding protein-mediated histone 3 acetylation

The etiology of a variety of chronic inflammatory disorders has been attributed to the interaction of genetic and environmental factors. Herein, we identified a link between epigenetic regulation and IL-13-driven eotaxin-3 in the pathogenesis of chronic allergic inflammation. We first demonstrated that the cAMP-responsive element (CRE) site in the eotaxin-3 promoter affects IL-13-induced eotaxin-3 promoter activity. Furthermore, the CRE-binding protein-binding protein (CBP), a histone acetyltransferase, induced base-line and IL-13-induced eotaxin-3 promoter activity. Additionally, IL-13 treatment promoted global histone 3 acetylation as well as the formation of a complex containing CBP and STAT6 and the subsequent acetylation of histone 3 at the eotaxin-3 promoter. CBP gene silencing decreased IL-13-induced transcription of eotaxin-3. Conversely, inhibition of histone deacetylation increased IL-13-induced eotaxin-3 production. Clinical studies demonstrated markedly increased global acetylation of histone 3 in the inflamed tissue of patients with allergic inflammation. Collectively, these results identify an epigenetic mechanism involving CBP and chromatin remodeling in regulating IL-13-induced chemokine transcription.

Investigation of the interaction between CREB-binding protein and STAT4/STAT6

Coactivator CBP (CREB-binding protein) has been implicated in the regulation of transcription for all signal transducer and activator of transcription factors (STATs); however, the mechanism remains unclear. Using yeast two-hybrid screening and immunoprecipitation techniques, we investigated the direct interaction of CBP with STAT4 and STAT6. The full-length CBP and five fragments of CBP (residues 1-436, 529-1200, 1-697, 967-1574 and 1678-2175) were constructed using pGBKT7 vectors, while STAT4, STAT6 and N-terminal deleted STAT4 were constructed using pGADT7 vectors. It was found that STAT4, but not STAT6, interacted directly with the 1678-2175 fragment of CBP containing the ZZ, TAZ2 and SID domain. The N-terminal of STAT4 plays an important role in this interaction since N-terminal deleted STAT4 failed to bind to any CBP fragment. The results were confirmed by immunoprecipitation using HA-tagged STAT4 or STAT6 and c-Myc tagged CBP. This work will contribute to our understanding of the mechanisms of Th cytokine imbalance.

PARP-14 functions as a transcriptional switch for Stat6-dependent gene activation

A subset of poly ADP-ribose polymerases (PARP) that also contain macro domains regulate transcription. One such macro PARP, PARP-14 alters interleukin 4 (IL-4) and Stat6-dependent transcription. Stat6, activated by IL-4 plays an important role in T helper cell immunity and B cell responses. Here we define the mechanism by which PARP-14 regulates Stat6-activated transcription. Under non-stimulating conditions, PARP-14 recruits HDAC 2 and 3 to IL-4 responsive promoters. In the presence of IL-4, PARP-14 promotes efficient binding of Stat6 to its target genes. Moreover, HDAC 2 and 3 are released from the promoter with an IL-4 signal, this is aided by the ADP-ribosylation of the HDACs by PARP-14. The HDACs and PARP-14 get replaced by coactivators containing HAT activity. Based on these observations we put forth a mechanism in which PARP-14 functions as a transcriptional switch for Stat6-dependent gene induction. Thus, in the absence of a signal PARP-14 acts as a transcriptional repressor by recruiting HDACs. In contrast, in the presence of IL-4 the catalytic activity of PARP-14 facilitates Stat6 binding to the promoter, and release of HDACs so as to activate transcription.

Mast cell homeostasis and the JAK-STAT pathway

The Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway mediates important responses in immune cells. Activation of any of the four JAK family members leads to phosphorylation of one or more of seven STAT family members. Phosphorylation of STAT family members leads to their dimerization and translocation into the nucleus, in which they bind specific DNA sequences to activate gene transcription. Regulation of JAKs and STATs therefore has a significant effect on signal transduction and subsequent cellular responses. Mast cells are important mediators of allergic disease and asthma. These cells have the ability to cause profound inflammation and vasodilation upon the release of preformed mediators, as well as subsequent synthesis of new inflammatory mediators. The regulation of mast cells is therefore of intense interest for the treatment of allergic disease. An important regulator of mast cells, STAT5, is activated downstream of the receptors for immunoglobulin E, interleukin-3 and stem cell factor. STAT5 contributes to mast cell homeostasis, by mediating proliferation, survival, and mediator release. Regulators of the JAK-STAT pathway, such as the suppressors of cytokine signaling (SOCS) and protein inhibitor of activated STAT (PIAS) proteins, are required to fine tune the immune response and maintain homeostasis. A better understanding of the role and regulation of JAKs and STATs in mast cells is vital for the development of new therapeutics.

Effects of allergic airway disease on mouse adenovirus type 1 respiratory infection

Virus infection may contribute to asthma pathogenesis. In turn, a Th2-polarized pulmonary environment may increase host susceptibility to infection. We used a cockroach antigen (CRA) model of allergic airway disease to test the hypothesis that Th2 cytokine overproduction increases susceptibility to mouse adenovirus type 1 (MAV-1). CRA sensitization led to upregulated lung expression of IL-4 and IL-13, lung cellular inflammation, and exaggerated airway mucus production. Following intranasal MAV-1 infection, lung cellular inflammation was more pronounced in CRA-sensitized mice than in unsensitized mice at 7 days post-infection but not at a later time point. CRA sensitization did not significantly suppress lung IFN-gamma expression, and lung IFN-gamma expression was upregulated in both CRA-sensitized mice and unsensitized mice over the course of MAV-1 infection. Despite CRA-induced differences in pulmonary inflammation, MAV-1 viral loads in lung and spleen and MAV-1 gene expression in the lung did not differ between CRA-sensitized and unsensitized mice. Our data therefore suggest that MAV-1 pathogenesis is not affected directly or indirectly by the Th2 polarization associated with allergic airway disease.

STAT3 regulation of glioblastoma pathogenesis

Malignant gliomas are the most common primary brain tumors. Despite efforts to find effective treatments, these tumors remain incurable. The failure of malignant gliomas to respond to conventional cancer therapies may reflect the unique biology of these tumors, underscoring the need for new approaches in their investigation. Recently, progress has been made in characterization of the molecular pathogenesis of glioblastoma using a developmental neurobiological perspective, by exploring the role of signaling pathways that control the differentiation of neural stem cells along the glial lineage. The transcription factor STAT3, which has an established function in neural stem cell and astrocyte development, has been found to play dual tumor suppressive and oncogenic roles in glial malignancy depending on the mutational profile of the tumor. These findings establish a novel developmental paradigm in the study of glioblastoma pathogenesis and provide the rationale for patient-tailored therapy in the treatment of this devastating disease.

Structural basis for recruitment of CBP/p300 coactivators by STAT1 and STAT2 transactivation domains

CBP/p300 transcriptional coactivators mediate gene expression by integrating cellular signals through interactions with multiple transcription factors. To elucidate the molecular and structural basis for CBP-dependent gene expression, we determined structures of the CBP TAZ1 and TAZ2 domains in complex with the transactivation domains (TADs) of signal transducer and activator of transcription 2 (STAT2) and STAT1, respectively. Despite the topological similarity of the TAZ1 and TAZ2 domains, subtle differences in helix packing and surface grooves constitute major determinants of target selectivity. Our results suggest that TAZ1 preferentially binds long TADs capable of contacting multiple surface grooves simultaneously, whereas smaller TADs that are restricted to a single contiguous binding surface form complexes with TAZ2. Complex formation for both STAT TADs involves coupled folding and binding, driven by intermolecular hydrophobic and electrostatic interactions. Phosphorylation of S727, required for maximal transcriptional activity of STAT1, does not enhance binding to any of the CBP domains. Because the different STAT TADs recognize different regions of CBP/p300, there is a potential for multivalent binding by STAT heterodimers that could enhance the recruitment of the coactivators to promoters.

STAT5 activity in pancreatic β-cells

Signal transducer and activator of transcription (STAT)5A and -5B are latent transcription factors activated by cytokines and hormones of the cytokine family. In pancreatic insulin-secreting β-cells, STAT5A and -5B are activated primarily by prolactin and growth hormone stimulation and are important mediators of the potent stimulation of proliferation and insulin production caused by these hormones. STAT5A and -5B are both expressed in β-cells and control the expression of a number of mRNAs implicated in cell replication control, insulin biosynthesis and secretion. In addition to STAT5A and -5B being transcriptional activators, they may also repress gene transcription. By these means, STAT5 proteins increase the levels of anti-apoptotic transcripts in β-cells and repress expression of pro-apoptotic genes. This review focuses on the anti-apoptotic role of STAT5 signaling, providing a mechanism for β-cell resistance to pro-apoptotic cytokines, Type 1 diabetes mellitus and obesity-associated β-cell stress. It is clear from studies of STAT5 signaling in pancreatic β-cells that STAT5 is important for postnatal β-cell compensatory growth (as in pregnancy or obesity) and in the defense against β-cell stress factors.

Proteomic analysis to identify biomarker proteins in pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is the fifth most common cause of death from cancer in Korea. PDAC is difficult to diagnose at an early stage and even more difficult to cure. Thus, there is an urgent need to identify molecular targets for early diagnosis and effective treatment. The objectives of this study were to identify differentially expressed biomarker proteins of PDAC using proteomic analysis, to validate the identified biomarker proteins associated with carcinogenesis using western blot analysis and to evaluate clinical factors influencing expression of candidate biomarker proteins.

METHODS

In the present study, we carried out proteomic analysis in 10 pairs of PDAC specimens with matching adjacent normal tissues to clarify the different patterns of protein expression. The proteins were separated by high-resolution 2-D polyacrylamide gel electrophoresis (2D PAGE) and the differentially expressed proteins were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Differential expression of candidate biomarker proteins associated with carcinogenesis was further validated using western blot analysis. Standard statistical analysis was carried out in an attempt to establish a correlation between clinical variables and expression of candidate biomarker proteins.

RESULTS

Analysis of PDAC and the adjacent normal tissues showed reproducibly similar proteomic patterns for each group. Approximately 700 spots each were seen by silver-stained gels from both PDAC and normal tissues. Differentially expressed protein spots were gel digested and identified by MALDI-TOF MS. Twenty-five proteins were identified, of which five proteins (galectin-1, enolase-2, alpha-1-antitrypsin, N-myc interactor, peroxiredoxin-4) were previously reported as being differentially expressed either at the mRNA level or protein level in human cancer. The five proteins were selected for candidate biomarker proteins related to carcinogenesis. These proteins were further validated by western blot analysis. Among the candidate biomarker proteins, galectin-1 expression was highly correlated to histology (P = 0.019), T stage (P = 0.047), N stage (P = 0.033) and American Joint Committee on Cancer stage (P = 0.011).

CONCLUSION

Differentially expressed 25 proteins in PDAC were identified using proteomic analysis and five proteins related to carcinogenesis were validated by western blot analysis. Galectin-1 expression was highly correlated to tumour histology and stage.

P160/SRC/NCoA coactivators form complexes via specific interaction of their PAS-B domain with the CID/AD1 domain

Transcriptional activation involves the ordered recruitment of coactivators via direct interactions between distinct binding domains and recognition motifs. The p160/SRC/NCoA coactivator family comprises three members (NCoA-1, -2 and -3), which are organized in multiprotein coactivator complexes. We had identified the PAS-B domain of NCoA-1 as an LXXLL motif binding domain. Here we show that NCoA family members are able to interact with other full-length NCoA proteins via their PAS-B domain and they specifically interact with the CBP-interaction domain (CID/AD1) of NCoA-1. Peptide competition, binding experiments and mutagenesis of LXXLL motifs point at distinct binding motif specificities of the NCoA PAS-B domains. NMR studies of different NCoA-1-PAS-B/LXXLL peptide complexes revealed similar although not identical binding sites for the CID/AD1 and STAT6 transactivation domain LXXLL motifs. In mechanistic studies, we found that overexpression of the PAS-B domain is able to disturb the binding of NCoA-1 to CBP in cells and that a CID/AD1 peptide competes with STAT6 for NCoA-1 in vitro. Moreover, the expression of an endogenous androgen receptor target gene is affected by the overexpression of the NCoA-1 or NCoA-3 PAS-B domains. Our study discloses a new, complementary mechanism for the current model of coactivator recruitment to target gene promoters.

Characterization of a family of novel cysteine- serine-rich nuclear proteins (CSRNP)

Gene array analysis has been widely used to identify genes induced during T cell activation. Our studies identified an immediate early gene that is strongly induced in response to IL-2 in mouse T cells which we named cysteine- serine-rich nuclear protein-1 (CSRNP-1). The human ortholog was previously identified as an AXIN1 induced gene (AXUD1). The protein does not contain sequence defined domains or motifs annotated in public databases, however the gene is a member of a family of three mammalian genes that share conserved regions, including cysteine- and serine-rich regions and a basic domain, they encode nuclear proteins, possess transcriptional activation domain and bind the sequence AGAGTG. Consequently we propose the nomenclature of CSRNP-1, -2 and -3 for the family. To elucidate the physiological functions of CSRNP-1, -2 and -3, we generated mice deficient for each of these genes by homologous recombination in embryonic stem cells. Although the CSRNP proteins have the hallmark of transcription factors and CSRNP-1 expression is highly induced by IL-2, deletion of the individual genes had no obvious consequences on normal mouse development, hematopoiesis or T cell functions. However, combined deficiencies cause partial neonatal lethality suggesting that the genes have redundant functions.

MHC class II transactivator represses human IL-4 gene transcription by interruption of promoter binding with CBP/p300, STAT6 and NFAT1 via histone hypoacetylation

In addition to its property of enhancing major histocompatibility complex (MHC) class II expression, the class II transactivator (CIITA) was recently demonstrated to be involved in T helper type 1/type 2 (Th1/Th2) differentiation by regulating interleukin-4 (IL-4) gene transcription. There was however, controversy regarding whether CIITA promotes or suppresses IL-4 expression in the experiments with transgenic mice. To clarify the discrepancy by using simpler experimental systems, human Jurkat T cells that express IL-4 but not interferon-gamma, even if stimulated with phorbol 12-myristate 13-acetate plus ionomycin, were used for CIITA transfection. Significant suppression of IL-4 gene expression was demonstrated. Simultaneously, histones H3 and H4 in the IL-4 promoter were hypoacetylated. The suppression could be totally reversed by the histone deacetylatase inhibitor trichostatin A. Furthermore, the IL-4 expression was determined in primarily established human Th1/Th2 cells to which CIITA small interference RNA (siRNA) had been introduced. A substantially increased level of IL-4 was recorded in the CIITA siRNA-transfected Th1 cells, which was in parallel with significantly enhanced acetylation in histone H3 of the IL-4 promoter. Chromatin immunoprecipitation analysis indicated that CIITA abrogated the binding of coactivator CBP/p300 and transcription factors STAT6/NFAT1 to IL-4 promoter in the CIITA-transfected cells. In conclusion, CIITA was active in the repression of transcription activation of human IL-4 gene in both the T-cell line and the primary human CD4 T cells by preventing transcription factors from binding to IL-4 promoter through histone hypoacetylation. Our data confirm a potential significant role of CIITA in controlling Th1/Th2 differentiation via modulation of IL-4 gene activation.

p300 protein acetyltransferase activity suppresses systemic lupus erythematosus-like autoimmune disease in mice

Conditional knock-in mice expressing a histone acetyltransferase-deficient version of the transcriptional coregulator p300 exclusively in B lymphocytes die prematurely with full penetrance. The mice develop an autoimmune disease similar to systemic lupus erythematosus in its pathological manifestations, such as splenomegaly, glomerulonephritis, vasculitis, deposition of immune complexes, and production of autoantibodies against dsDNA. Aged mice show a severe reduction of transitional and marginal zone B cells and generate aberrant mature B cells. These B cells show diminished proliferation in response to stimulation of the BCR, but respond normally to other stimuli. Yet, the mice mount a normal primary immune response against a T-dependent Ag. In contrast, the memory response is impaired. In addition, serum Ig levels, in particular IgG2b, are increased. We conclude that p300 acetyltransferase activity is essential for maintaining self-tolerance of B lymphocytes. These findings support the concept of treating lupus with inhibitors of protein deacetylases and point to B cells as a critical target of these drugs.

Unphosphorylated STAT6 contributes to constitutive cyclooxygenase-2 expression in human non-small cell lung cancer

Cyclooxygenase-2 (COX-2) is frequently overexpressed in human cancers and contributes to the malignant phenotype. Our data indicate unphosphorylated signal transducers and activators of transcription 6 (STAT6) may transcriptionally upregulate COX-2 expression and protect against apoptosis in NSCLC cells. In A427 and H2122, NSCLC cell lines that constitutively express COX-2, only unphosphorylated STAT6 was detectable by western blot, thus, all of the following STAT6-dependent effects are attributed to the unphosphorylated protein. In both cell lines, small-interfering RNA-mediated knockdown of STAT6 or stable expression of dominant-negative STAT6 decreased COX-2 expression. In contrast, transfection with a phosphorylation-deficient mutant STAT6 increased COX-2 levels. Immunofluorescent staining revealed the presence of STAT6 in H2122 nuclei, suggesting a direct role in gene regulation for the unphosphorylated protein. Consistent with this hypothesis, unphosphorylated STAT6 increased luciferase expression from a COX-2 promoter reporter construct. STAT6 co-immunoprecipitated with the transcriptional co-activator, p300, and chromatin immunoprecipitation assays demonstrated that these proteins bind a consensus STAT6 binding site located within the COX-2 promoter. STAT6 DNA-binding specificity was confirmed by electrophoretic mobility shift assay. As COX-2 over-expression has been clearly linked to apoptosis resistance and other hallmarks of malignancy, these findings suggest a novel role of unphosphorylated STAT6 in the pathogenesis of non-small cell lung cancer.

Structure, function, and regulation of STAT proteins

The Signal Transducer and Activator of Transcription (STAT) family of proteins was first discovered in the 1990's as key proteins in cytokine signaling. Since then, the field has greatly advanced in the past 15 years, providing significant insight into the structure, function, and regulation of STATs. STATs are latent cytoplasmic transcription factors consisting of seven mammalian members. They are Tyr phosphorylated upon activation, a post-translational modification critical for dimerization, nuclear import, DNA binding, and transcriptional activation. In recent years, unphosphorylated STATs have also been observed to dimerize and drive transcription, albeit by yet an obscure mechanism. In addition, the function of cytoplasmic STATs is beginning to emerge. Here, we describe the structure, function, and regulation of both unphosphorylated and phosphorylated STATs. STAT isoforms from alternative splicing or proteolytic processing, and post-translational modifications affecting STAT activities are also discussed.

Characterization of RNA helicase A as component of STAT6-dependent enhanceosome

Signal transducer and activator of transcription 6 (STAT6) is a regulator of transcription for interleukin-4 (IL-4)-induced genes. The ability of STAT6 to activate transcription depends on functional interaction with other transcription factors and coactivators. We have characterized the mechanism of STAT6-mediated transcriptional activation by identifying STAT6 transcription activation domain (TAD) interacting nuclear proteins. The first of the identified proteins was coactivator protein p100, which regulates IL-4-induced transcription by connecting STAT6 with other transcriptional regulators. Here, we describe RNA helicase A (RHA) as a novel component of STAT6 transcriptosome. In vitro and in vivo experiments indicated that RHA did not directly interact with STAT6, but p100 protein was found to mediate the assembly of the ternary complex of STAT6-p100-RHA. In chromatin immunoprecipitation studies RHA together with p100 enhanced the binding of STAT6 on the human Igɛ promoter after IL-4 stimulation. RHA enhanced the IL-4-induced transcription, and the participation of RHA in IL-4-regulated transcription was supported by RNAi experiments. Our results suggest that RHA has an important role in the assembly of STAT6 transcriptosome. As RHA is also known to interact with chromatin modifying proteins, the RHA containing protein complexes may facilitate the entry of transcriptional apparatus to the IL-4 responsive promoters.

Selective potentiation of Stat-dependent gene expression by collaborator of Stat6 (CoaSt6), a transcriptional cofactor

The molecular mechanisms by which transcription is selectively activated and precisely controlled by signal transducer and activator of transcription (Stat) factors represent a central issue in cytokine-mediated cellular responses. Stat6 mediates responses to IL-4 and antagonizes Stat1 activated by IFN-gamma. We have discovered that Stat6 binds to collaborator of Stat6 (CoaSt6), a protein that lacks conventional coactivator motifs but contains three iterations of a domain found in the variant histone macroH2A. Although macroH2A participates in transcriptional silencing, the macro domains of CoaSt6 increased IL-4-induced gene expression. Moreover, CoaSt6 amplified Stat6-mediated but not IFN-gamma-induced gene expression, providing evidence of a selective coregulator of Stat-mediated gene transcription.

Stats: multifaceted regulators of transcription

The high-affinity binding interactions between interferons (IFNs) and their cognate cell surface receptors lead to the activation of receptor-associated Janus protein tyrosine kinases (Jaks) and subsequent phosphorylation and activation of a group of transcription factors, the signal transducers and activators of transcription (Stats). Upon IFN-induced activation, these Stat proteins form homodimeric and heterodimeric complexes that translocate to the nucleus and bind specific elements within the promoters of IFN-stimulated genes (ISGs). In addition to the well-studied IFN-induced ISG factor 3 (ISGF3) and Stat1:1 complexes, IFNs induce the formation of a number of other Stat-containing complexes, including Stat3:3 and Stat5:5 homodimers, as well as Stat2:1 and Stat5:CrkL heterodimers, that also mediate gene transcription. Moreover, emerging evidence suggests that particular amino acid residues within the individual Stat proteins contribute to different aspects of Stat function. These residues modulate the transcriptional activation potential of Stat-containing complexes and thereby influence the expression of ISGs. Indeed, the Stat proteins function in a multifaceted manner to regulate the expression of proteins that mediate IFN responses.

Conditional knockout mice reveal distinct functions for the global transcriptional coactivators CBP and p300 in T-cell development

The global transcriptional coactivators CREB-binding protein (CBP) and the closely related p300 interact with over 312 proteins, making them among the most heavily connected hubs in the known mammalian protein-protein interactome. It is largely uncertain, however, if these interactions are important in specific cell lineages of adult animals, as homozygous null mutations in either CBP or p300 result in early embryonic lethality in mice. Here we describe a Cre/LoxP conditional p300 null allele (p300flox) that allows for the temporal and tissue-specific inactivation of p300. We used mice carrying p300flox and a CBP conditional knockout allele (CBPflox) in conjunction with an Lck-Cre transgene to delete CBP and p300 starting at the CD4- CD8- double-negative thymocyte stage of T-cell development. Loss of either p300 or CBP led to a decrease in CD4+ CD8+ double-positive thymocytes, but an increase in the percentage of CD8+ single-positive thymocytes seen in CBP mutant mice was not observed in p300 mutants. T cells completely lacking both CBP and p300 did not develop normally and were nonexistent or very rare in the periphery, however. T cells lacking CBP or p300 had reduced tumor necrosis factor alpha gene expression in response to phorbol ester and ionophore, while signal-responsive gene expression in CBP- or p300-deficient macrophages was largely intact. Thus, CBP and p300 each supply a surprising degree of redundant coactivation capacity in T cells and macrophages, although each gene has also unique properties in thymocyte development.

Global transcriptional coactivators CREB-binding protein and p300 are highly essential collectively but not individually in peripheral B cells

CREB-binding protein (CBP) and its para-log p300 are transcriptional coactivators that physically or functionally interact with over 320 mammalian and viral proteins, including 36 that are essential for B cells in mice. CBP and p300 are generally considered limiting for transcription, yet their roles in adult cell lineages are largely unknown since homozygous null mutations in either gene or compound heterozygosity cause early embryonic lethality in mice. We tested the hypotheses that CBP and p300 are limiting and that each has unique properties in B cells, by using mice with Cre/LoxP conditional knockout alleles for CBP (CBP(flox)) and p300 (p300(flox)), which carry CD19(Cre) that initiates floxed gene recombination at the pro-B-cell stage. CD19(Cre)-mediated loss of CBP or p300 led to surprisingly modest deficits in B-cell numbers, whereas inactivation of both genes was not tolerated by peripheral B cells. There was a moderate decrease in B-cell receptor (BCR)-responsive gene expression in CBP or p300 homozygous null B cells, suggesting that CBP and p300 are essential for this signaling pathway that is crucial for B-cell homeostasis. These results indicate that individually CBP and p300 are partially limiting beyond the pro-B-cell stage and that other coactivators in B cells cannot replace their combined loss.

Role of histone and transcription factor acetylation in diabetes pathogenesis

Globally, diabetes (and, in particular, type 2 diabetes) represents a major challenge to world health. Currently in the United States, the costs of treating diabetes and its associated complications exceed 100 billion US dollars annually, and this figure is expected to soar in the near future. Despite decades of intense research efforts, the genetic basis of the events involved in the pathogenesis of diabetes is still poorly understood. Diabetes is a complex multigenic syndrome primarily due to beta-cell dysfunction associated with a variable degree of insulin resistance. Recent advances have led to exciting new developments with regard to our understanding of the mechanisms that regulate insulin transcription. These include data that implicate chromatin as a critical regulator of this event. The 'Histone Code' is a widely accepted hypothesis, whereby sequential modifications to the histones in chromatin lead to regulated transcription of genes. One of the modifications used in the histone code is acetylation. This is probably the best characterized modification of histones, which is carried out under the control of histone acetyltransferases (HATs) and histone deacetylases (HDACs). These enzymes also regulate the activity of a number of transcription factors through acetylation. Increasing evidence links possible dysregulation of these mechanisms in the pathogenesis of diabetes, with important therapeutic implications.

Interleukin-4 downregulates TNFalpha-induced IL-8 production in keratinocytes

Interleukin (IL)-8 is a CXC chemokine induced by pro-inflammatory cytokines such as TNFalpha, IL-1beta and IL-6 in different cell types including keratinocytes. IL-4 regulation of TNFalpha-induced IL-8 expression is cell-type specific. In this study, we show that in the keratinocyte cell line HaCaT, IL-4 decreases TNFalpha-induced IL-8 mRNA expression. We then investigated the mechanism of IL-4 effect and showed that IL-4 downregulates TNFalpha-induced IL-8 promoter activity in luciferase reporter assays. Moreover, overexpression of either the endogenous JAK inhibitor SOCS-1 or a dominant negative form of the STAT6 transcription factor (STAT6DeltaC) interferes with the IL-4 inhibitory effect on IL-8 promoter. Finally we demonstrate, using a NF-kappaB-dependent promoter luciferase construct that IL-4 interferes, at least in part, with NF-kappaB transcriptional activity. Overall our results suggest that IL-4 regulates TNFalpha-induced IL-8 expression at a transcriptional level and this mechanism involves STAT6 and NF-kappaB transcription factors.

A critical control element for interleukin-4 memory expression in T helper lymphocytes

Naive T helper (Th) lymphocytes are induced to express the il4 (interleukin-4) gene by simultaneous signaling through the T cell receptor and the interleukin (IL)-4 receptor. Upon restimulation with antigen, such preactivated Th lymphocytes can reexpress the il4 gene independent of IL-4 receptor signaling. This memory for expression of the il4 gene depends on epigenetic modification of the il4 gene locus and an increased expression of GATA-3, the key transcription factor for Th2 differentiation. Here, we have identified a phylogenetically conserved sequence, the conserved intronic regulatory element, in the first intron of the il4 gene containing a tandem GATA-3 binding site. We show that GATA-3 binds to this sequence in a position- and orientation-dependent manner, in vitro and in vivo. DNA demethylation and histone acetylation of this region occurs early and selectively in differentiating, IL-4-secreting Th2 lymphocytes. Deletion of the conserved element by replacement of the first exon and part of the first intron of the il4 gene with gfp leads to a defect in the establishment of memory for expression of IL-4, in that reexpression of IL-4 still requires costimulation by exogenous IL-4. The conserved intronic regulatory element thus links the initial epigenetic modification of the il4 gene to GATA-3 and serves as a genetic control element for memory expression of IL-4.

Induction of arginase I transcription by IL-4 requires a composite DNA response element for STAT6 and C/EBPβ

Arginine metabolism in macrophages during infection and inflammation is complex, owing to differential regulation of inducible nitric oxide synthase (iNOS) and arginases by cytokines and other agents. Changes in levels of Th2 cytokines such as interleukin-4 (IL-4) can play important roles in these conditions via effects on arginine metabolism. IL-4 alters macrophage arginine metabolism by inducing arginase I expression and inhibiting nitric oxide production. To determine the molecular basis for induction of arginase I, the promoter of the murine arginase I gene was cloned and analyzed by transfection in RAW 264.7 macrophage cells. IL-4 induction required a composite response element containing STAT6 and C/EBP sites located 2.86 kb upstream of the transcription start site. Competition experiments showed that STAT6 and C/EBPbeta bind to the STAT6 and C/EBP sites non-cooperatively. Elucidation of the mechanisms involved in regulation of arginase I transcription may provide a basis for developing strategies to modulate arginase expression in Th2 cytokine-predominant diseases.