GADD45beta/GADD45gamma and MEKK4 comprise a genetic pathway mediating STAT4-independent IFNgamma production in T cells

GADD45A: With or without you

The growth arrest and DNA damage inducible (GADD)45 family includes three small and ubiquitously distributed proteins (GADD45A, GADD45B, and GADD45G) that regulate numerous cellular processes associated with stress signaling and injury response. Here, we provide a comprehensive review of the current literature investigating GADD45A, the first discovered member of the family. We first depict how its levels are regulated by a myriad of genotoxic and non-genotoxic stressors, and through the combined action of intricate transcriptional, posttranscriptional, and even, posttranslational mechanisms. GADD45A is a recognized tumor suppressor and, for this reason, we next summarize its role in cancer, as well as the different mechanisms by which it regulates cell cycle, DNA repair, and apoptosis. Beyond these most well-known actions, GADD45A may also influence catabolic and anabolic pathways in the liver, adipose tissue and skeletal muscle, among others. Not surprisingly, GADD45A may trigger AMP-activated protein kinase activity, a master regulator of metabolism, and is known to act as a transcriptional coregulator of numerous nuclear receptors. GADD45A has also been reported to display a cytoprotective role by regulating inflammation, fibrosis and oxidative stress in several organs and tissues, and is regarded an important contributor for the development of heart failure. Overall data point to that GADD45A may play an important role in metabolic, neurodegenerative and cardiovascular diseases, and also autoimmune-related disorders. Thus, the potential mechanisms by which dysregulation of GADD45A activity may contribute to the progression of these diseases are also reviewed below.

The dairy-derived peptide Miltin exerts anti-obesity effects by increasing adipocyte thermogenesis

Growing research has highlighted that the consumption of dairy products improves the metabolic health in obese individuals by functioning as regulatory modulators. However, the molecular basis of this effect remains largely unknown. Herein, we report a dairy-derived peptide, which we named Miltin, that activates the thermogenesis of brown adipocytes and increases white adipocyte browning. Previously, Miltin was merely identified for its antioxidant capacity, although it is commonly present in different dairy products. In this study, we revealed the effect of Miltin in modulating adipose thermogenesis and further explored its potential in treating obesity through in vivo and in vitro strategies. The administration of Miltin in mice fed with a high-fat diet resulted in enhanced thermogenesis, improved glucose homeostasis, and reduced body mass and lipid accumulation, indicating the anti-obesity effect of Miltin. Genomic analysis revealed that Miltin modulates thermogenesis by inducing the activation of the MAPK signaling pathway by preferentially interacting with GADD45γ to promote its stability. Together, our findings indicate that Miltin's role in initiating the thermogenesis of adipocytes makes it a potential anti-obesity therapy for future development.

A systems and computational biology perspective on advancing CAR therapy

In the recent decades, chimeric antigen receptor (CAR) therapy signaled a new revolutionary approach to cancer treatment. This method seeks to engineer immune cells expressing an artificially designed receptor, which would endue those cells with the ability to recognize and eliminate tumor cells. While some CAR therapies received FDA approval and others are subject to clinical trials, many aspects of their workings remain elusive. Techniques of systems and computational biology have been frequently employed to explain the operating principles of CAR therapy and suggest further design improvements. In this review, we sought to provide a comprehensive account of those efforts. Specifically, we discuss various computational models of CAR therapy ranging in scale from organismal to molecular. Then, we describe the molecular and functional properties of costimulatory domains frequently incorporated in CAR structure. Finally, we describe the signaling cascades by which those costimulatory domains elicit cellular response against the target. We hope that this comprehensive summary of computational and experimental studies will further motivate the use of systems approaches in advancing CAR therapy.

Distinctive transcriptomic and epigenomic signatures of bone marrow-derived myeloid cells and microglia in CNS autoimmunity

In the context of autoimmunity, myeloid cells of the central nervous system (CNS) constitute an ontogenically heterogeneous population that includes yolk sac-derived microglia and infiltrating bone marrow-derived cells (BMC). We previously identified a myeloid cell subset in the brain and spinal cord that expresses the surface markers CD88 and CD317 and is associated with the onset and persistence of clinical disease in the murine model of the human CNS autoimmune disorder, experimental autoimmune encephalomyelitis (EAE). We employed an experimental platform utilizing single-cell transcriptomic and epigenomic profiling of bone marrow-chimeric mice to categorically distinguish BMC from microglia during CNS autoimmunity. Analysis of gene expression and chromosomal accessibility identified CD88+CD317+ myeloid cells in the CNS of EAE mice as originating from BMC and microglia. Interestingly, each cell lineage exhibited overlapping and unique gene expression patterns and transcription factor motifs that allowed their segregation. Our observations will facilitate determining pathogenic contributions of BMC and microglia in CNS autoimmune disease. Ultimately, this agnostic characterization of myeloid cells will be required for devising disease stage-specific and tissue-specific interventions for CNS inflammatory and neurodegenerative disorders.

Inflammatory-miR-301a circuitry drives mTOR and Stat3-dependent PSC activation in chronic pancreatitis and PanIN

Activated pancreatic stellate cells (PSCs) are the main cells involved in chronic pancreatitis and pancreatic intraepithelial neoplasia lesion (PanIN). Fine-tuning the precise molecular targets in PSC activation might help the development of PSC-specific therapeutic strategies to tackle progression of pancreatic cancer-related fibrosis. miR-301a is a pro-inflammatory microRNA known to be activated by multiple inflammatory factors in the tumor stroma. Here, we show that miR-301a is highly expressed in activated PSCs in mice, sustained tissue fibrosis in caerulein-induced chronic pancreatitis, and accelerated PanIN formation. Genetic ablation of miR-301a reduced pancreatic fibrosis in mouse models with chronic pancreatitis and PanIN. Cell proliferation and activation of PSCs was inhibited by downregulation of miR-301a via two of its targets, Tsc1 and Gadd45g. Moreover, aberrant PSC expression of miR-301a and Gadd45g restricted the interplay between PSCs and pancreatic cancer cells in tumorigenesis. Our findings suggest that miR-301a activates two major cell proliferation pathways, Tsc1/mTOR and Gadd45g/Stat3, in vivo, to facilitate development of inflammatory-induced PanIN and maintenance of PSC activation and desmoplasia in pancreatic cancer.

Revealing the transcriptional heterogeneity of organ‐specific metastasis in human gastric cancer using single‐cell RNA Sequencing

Background

Deciphering intra‐ and inter‐tumoural heterogeneity is essential for understanding the biology of gastric cancer (GC) and its metastasis and identifying effective therapeutic targets. However, the characteristics of different organ‐tropism metastases of GC are largely unknown.

Methods

Ten fresh human tissue samples from six patients, including primary tumour and adjacent non‐tumoural samples and six metastases from different organs or tissues (liver, peritoneum, ovary, lymph node) were evaluated using single‐cell RNA sequencing. Validation experiments were performed using histological assays and bulk transcriptomic datasets.

Results

Malignant epithelial subclusters associated with invasion features, intraperitoneal metastasis propensity, epithelial–mesenchymal transition‐induced tumour stem cell phenotypes, or dormancy‐like characteristics were discovered. High expression of the first three subcluster‐associated genes displayed worse overall survival than those with low expression in a GC cohort containing 407 samples. Immune and stromal cells exhibited cellular heterogeneity and created a pro‐tumoural and immunosuppressive microenvironment. Furthermore, a 20‐gene signature of lymph node‐derived exhausted CD8⁺ T cells was acquired to forecast lymph node metastasis and validated in GC cohorts. Additionally, although anti‐NKG2A (KLRC1) antibody have not been used to treat GC patients even in clinical trials, we uncovered not only malignant tumour cells but one endothelial subcluster, mucosal‐associated invariant T cells, T cell‐like B cells, plasmacytoid dendritic cells, macrophages, monocytes, and neutrophils may contribute to HLA‐E‐KLRC1/KLRC2 interaction with cytotoxic/exhausted CD8⁺ T cells and/or natural killer (NK) cells, suggesting novel clinical therapeutic opportunities in GC. Additionally, our findings suggested that PD‐1 expression in CD8⁺ T cells might predict clinical responses to PD‐1 blockade therapy in GC.

Conclusions

This study provided insights into heterogeneous microenvironment of GC primary tumours and organ‐specific metastases and provide support for precise diagnosis and treatment.

LncRNA-MAP3K4 regulates vascular inflammation through the p38 MAPK signaling pathway and cis-modulation of MAP3K4

Chronic vascular inflammation plays a key role in the pathogenesis of atherosclerosis. Long non-coding RNAs (lncRNAs) have emerged as essential inflammation regulators. We identify a novel lncRNA termed lncRNA-MAP3K4 that is enriched in the vessel wall and regulates vascular inflammation. In the aortic intima, lncRNA-MAP3K4 expression was reduced by 50% during the progression of atherosclerosis (chronic inflammation) and 70% during endotoxemia (acute inflammation). lncRNA-MAP3K4 knockdown reduced the expression of key inflammatory factors (eg, ICAM-1, E-selectin, MCP-1) in endothelial cells or vascular smooth muscle cells and decreased monocytes adhesion to endothelium, as well as reducing TNF-α, IL-1β, COX2 expression in macrophages. Mechanistically, lncRNA-MAP3K4 regulates inflammation through the p38 MAPK signaling pathway. lncRNA-MAP3K4 shares a bidirectional promoter with MAP3K4, an upstream regulator of the MAPK signaling pathway, and regulates its transcription in cis. lncRNA-MAP3K4 and MAP3K4 show coordinated expression in response to inflammation in vivo and in vitro. Similar to lncRNA-MAP3K4, MAP3K4 knockdown reduced the expression of inflammatory factors in several different vascular cells. Furthermore, lncRNA-MAP3K4 and MAP3K4 knockdown showed cooperativity in reducing inflammation in endothelial cells. Collectively, these findings unveil the role of a novel lncRNA in vascular inflammation by cis-regulating MAP3K4 via a p38 MAPK pathway.

XPA deficiency affects the ubiquitin-proteasome system function

Xeroderma pigmentosum complementation group A (XPA), is defective in xeroderma pigmentosum patients, causing pre-disposition to skin cancer and neurological abnormalities, which is not well understood. Here, we analyzed the XPA-deficient cells transcriptional profile under oxidative stress. The imbalance in of ubiquitin-proteasome system (UPS) gene expression was observed in XPA-deficient cells and the involvement of nuclear factor erythroid 2-related factor-2 (NFE2L2) was indicated. Co-immunoprecipitation assays showed the interaction between XPA, apurinic-apyrimidinic endonuclease 1 (APE1) and NFE2L2 proteins. Decreased NFE2L2 protein expression and proteasome activity was also observed in XPA-deficient cells. The data suggest the involvement of the growth arrest and DNA-damage-inducible beta (GADD45β) in NFE2L2 functions. Similar results were obtained in xpa-1 (RNAi) Caenorhabditis elegans suggesting the conservation of XPA and NFE2L2 interactions. In conclusion, stress response activation occurs in XPA-deficient cells under oxidative stress; however, these cells fail to activate the UPS cytoprotective response, which may contribute to XPA patient's phenotypes.

Stress-responsive MTK1 SAPKKK serves as a redox sensor that mediates delayed and sustained activation of SAPKs by oxidative stress

Cells respond to oxidative stress by inducing intracellular signaling, including stress-activated p38 and JNK MAPK (SAPK) pathways, but the underlying mechanisms remain unclear. Here, we report that the MAP three kinase 1 (MTK1) SAPK kinase kinase (SAPKKK) functions as an oxidative-stress sensor that perceives the cellular redox state and transduces it into SAPK signaling. Following oxidative stress, MTK1 is rapidly oxidized and gradually reduced at evolutionarily conserved cysteine residues. These coupled oxidation-reduction modifications of MTK1 elicit its catalytic activity. Gene knockout experiments showed that oxidative stress-induced SAPK signaling is mediated by coordinated activation of the two SAPKKKs, MTK1 and apoptosis signal-regulating kinase 1 (ASK1), which have different time and dose-response characteristics. The MTK1-mediated redox sensing system is crucial for delayed and sustained SAPK activity and dictates cell fate decisions including cell death and interleukin-6 production. Our results delineate a molecular mechanism by which cells generate optimal biological responses under fluctuating redox environments.

DMSO impairs the transcriptional program for maternal-to-embryonic transition by altering histone acetylation

Dimethyl sulfoxide (DMSO) is widely used in basic and clinical research, yet its toxicity and biocompatibility properties remain elusive. Here, we report that exposure of mouse zygotes to 2% DMSO perturbed the transcriptional program, critical for maternal-to-embryonic transition and provoked developmental arrest at the 2- or 4-cell stage. Mechanistically, DMSO decreased total protein acetylation in the 2-cell embryos but increased histone H3 and H4 acetylations, as well as p53, H3K9, and H3K27 acetylations. The epigenetic changes led to an altered expression pattern of 16.26% of total valid genes in DMSO-exposed embryos. Among the affected genes, expression of maternal and minor zygotic gene activation (ZGA) genes was enhanced, whereas the ubiquitin-proteasome system, major ZGA transcripts, embryonic gene activation, the cell cycle, and ribosomal biogenesis genes were suppressed. Therefore, we conclude that DMSO causes developmental arrest by disrupting maternal-to-embryonic transition; hence, caution should be exerted when using it as a solvent.

Preclinical toxicology and safety pharmacology of the first-in-class GADD45β/MKK7 inhibitor and clinical candidate, DTP3

Aberrant NF-κB activity drives oncogenesis and cell survival in multiple myeloma (MM) and many other cancers. However, despite an aggressive effort by the pharmaceutical industry over the past 30 years, no specific IκBα kinase (IKK)β/NF-κB inhibitor has been clinically approved, due to the multiple dose-limiting toxicities of conventional NF-κB-targeting drugs. To overcome this barrier to therapeutic NF-κB inhibition, we developed the first-in-class growth arrest and DNA-damage-inducible (GADD45)β/mitogen-activated protein kinase kinase (MKK)7 inhibitor, DTP3, which targets an essential, cancer-selective cell-survival module downstream of the NF-κB pathway. As a result, DTP3 specifically kills MM cells, ex vivo and in vivo, ablating MM xenografts in mice, with no apparent adverse effects, nor evident toxicity to healthy cells. Here, we report the results from the preclinical regulatory pharmacodynamic (PD), safety pharmacology, pharmacokinetic (PK), and toxicology programmes of DTP3, leading to the approval for clinical trials in oncology. These results demonstrate that DTP3 combines on-target-selective pharmacology, therapeutic anticancer efficacy, favourable drug-like properties, long plasma half-life and good bioavailability, with no target-organs of toxicity and no adverse effects preclusive of its clinical development in oncology, upon daily repeat-dose administration in both rodent and non-rodent species. Our study underscores the clinical potential of DTP3 as a conceptually novel candidate therapeutic selectively blocking NF-κB survival signalling in MM and potentially other NF-κB-driven cancers.

Runx3 Mediates Resistance to Intracellular Bacterial Infection by Promoting IL12 Signaling in Group 1 ILC and NCR+ILC3

Innate lymphoid cells (ILCs) are the most recently identified family of the innate immune system and are hypothesized to modulate immune functions prior to the generation of adaptive immune responses. Subsets of ILCs reside in the mucosa and regulate immune responses to external pathogens; however, their role and the mechanism by which they protect against intracellular bacterial infection is not completely understood. In this report, using S. typhimurium and L. monocytogenes, we found that the levels of group 1 ILCs and NCR⁺ ILC3s were increased upon infection and that these increases were associated with Runt-related transcription factor 3 (Runx3) expression. Runx3 ^fl/fl PLZF-cre mice were much more sensitive to infection with the intracellular bacterial pathogens S. typhimurium and L. monocytogenes partially due to abnormal Group 1 ILC and NCR⁺ILC3 function. We also found that Runx3 directly binds to the Il12Rβ2 promoter and intron 8 to accelerate the expression of Il12Rβ2 and modulates IFNγ secretion triggered by the IL12/ STAT4 axis. Therefore, we demonstrate that Runx3 influences group 1 ILC- and NCR+ILC3-mediated immune protection against intracellular bacterial infections of both the gut and liver.

Molecular cloning, characterization and functional analysis of a putative mitogen-activated protein kinase kinase kinase 4 (MEKK4) from blood clam Tegillarca granosa

The mitogen-activated protein kinase (MAPK) cascades stand for one of the most important signaling mechanisms in response to environmental stimuli. In the present study, we cloned and identified for the first time the full-length cDNA of MAPK kinase kinase 4 (TgMEKK4) from Blood clam Tegillarca granosa using rapid amplification of cDNA ends method. The full-length cDNA of TgMEKK4 was of 1605 bp in length, encoding a polypeptide of 364 amino acids with a predicted molecular mass of 41.22 kDa and theoretical isoelectric point of 6.29. The conserved MEKK4-domain was identified in TgMEKK4 by SMART program analysis. Homology analysis of the deduced amino acid sequence of TgMEKK4 with other known sequences revealed that TgMEKK4 shared 58%-80% identity to MEKK4s from other species. TgMEKK4 mRNA transcripts could be detected in all tissues examined with the highest expression level in the gill by qRT-PCR. The mRNA expression of TgMEKK4 was up-regulated significantly in hemocytes after Vibrio parahaemolyticus, Vibrio alginolyticus and Lipopolysaccharide (LPS) challenges. Overexpression of TgMEKK4 in HEK 293T cells resulted in the activation of JNK and ERK, but not p38. Consistently, In vivo study indicated that LPS stimulation enhanced JNK, ERK and p38 phosphorylation in blood clams. These results suggest that TgMEKK4 is a powerful factor in the regulation of genes that may be involved in innate immune response of blood clam.

p38α regulates cytokine-induced IFNγ secretion via the Mnk1/eIF4E pathway in Th1 cells

The p38 mitogen-activated protein kinase (MAPK) pathway is involved in the regulation of immune and inflammatory processes. We used p38α-conditional, p38β-deficient and p38α/β double-null mouse models to address the role of these two p38 MAPK in CD4⁺ T cells, and found that p38α deficiency causes these cells to hyperproliferate. Our studies indicate that both p38α and p38β are dispensable for T helper cell type 1 (Th1) differentiation but, by controlling interferon (IFN)γ and tumor necrosis factor (TNF)α production, are critical for normal Th1 effector function. We found that both p38α and p38β modulate T-cell receptor-induced IFNγ and TNFα production, whereas only p38α regulates cytokine-induced IFNγ production. The lack of p38α and p38β did not affect transcription and mRNA stability of Ifng. However, the absence of p38α in Th1 cells resulted in a decreased MNK1 phosphorylation after cytokine activation, and MNK1 inhibition blocked IFNγ production. Our results indicate that p38α regulates IFNγ secretion through the activation of the MNK1/eIF4E pathway of translation initiation and identify specific functions for p38α and p38β in T-cell proliferation.

Cell Signaling and Stress Responses

Stress-signaling pathways are evolutionarily conserved and play an important role in the maintenance of homeostasis. These pathways are also critical for adaptation to new cellular environments. The endoplasmic reticulum (ER) unfolded protein response (UPR) is activated by biosynthetic stress and leads to a compensatory increase in ER function. The JNK and p38 MAPK signaling pathways control adaptive responses to intracellular and extracellular stresses, including environmental changes such as UV light, heat, and hyperosmotic conditions, and exposure to inflammatory cytokines. Metabolic stress caused by a high-fat diet represents an example of a stimulus that coordinately activates both the UPR and JNK/p38 signaling pathways. Chronic activation of these stress-response pathways ultimately causes metabolic changes associated with obesity and altered insulin sensitivity. Stress-signaling pathways, therefore, represent potential targets for therapeutic intervention in the metabolic stress response and other disease processes.

Gadd45a Protein Promotes Skeletal Muscle Atrophy by Forming a Complex with the Protein Kinase MEKK4

Skeletal muscle atrophy is a serious and highly prevalent condition that remains poorly understood at the molecular level. Previous work found that skeletal muscle atrophy involves an increase in skeletal muscle Gadd45a expression, which is necessary and sufficient for skeletal muscle fiber atrophy. However, the direct mechanism by which Gadd45a promotes skeletal muscle atrophy was unknown. To address this question, we biochemically isolated skeletal muscle proteins that associate with Gadd45a as it induces atrophy in mouse skeletal muscle fibers in vivo. We found that Gadd45a interacts with multiple proteins in skeletal muscle fibers, including, most prominently, MEKK4, a mitogen-activated protein kinase kinase kinase that was not previously known to play a role in skeletal muscle atrophy. Furthermore, we found that, by forming a complex with MEKK4 in skeletal muscle fibers, Gadd45a increases MEKK4 protein kinase activity, which is both sufficient to induce skeletal muscle fiber atrophy and required for Gadd45a-mediated skeletal muscle fiber atrophy. Together, these results identify a direct biochemical mechanism by which Gadd45a induces skeletal muscle atrophy and provide new insight into the way that skeletal muscle atrophy occurs at the molecular level.

SIP1 is a downstream effector of GADD45G in senescence induction and growth inhibition of liver tumor cells

Cellular senescence evasion caused by the inactivation of tumor suppressive programs is implicated in tumor initiation and therapeutic resistance. Our previous study has shown that the downregulation of growth arrest and DNA damage 45G (GADD45G) contributes to senescence bypass in hepatocellular carcinoma (HCC). Here, we report that the Smad-interacting protein-1 (SIP1) is transcriptionally activated and functions critically in the GADD45G-induced tumor cell senescence. Knockdown of SIP1 significantly abrogates the suppressive effects of GADD45G on the growth of xenografted liver tumor in vivo. The essential role of SIP1 in GADD45G activities is further validated in the model of the proteasome inhibitor MG132-induced cell senescence. We further show that JNK but not p38 MAPK activation is involved in the GADD45G-mediated SIP1 upregulation, and that JNK inhibition counteracts the GADD45G-induced cellular senescence. More importantly, we show that GADD45G and SIP1 expression are coincidently downregulated in primary human HCC tissues. Together, our results establish that the dowregulation of GADD45G-SIP1 axis may contribute to cellular senescence evasion and HCC development.

Comparative analysis of developmentally regulated expressions of Gadd45a, Gadd45b, and Gadd45g in the mouse and marmoset cerebral cortex

The cerebral cortex is an indispensable region that is involved in higher cognitive function in the mammalian brain, and is particularly evolved in the primate brain. It has been demonstrated that cortical areas are formed by both innate and activity-dependent mechanisms. However, it remains unknown what molecular changes induce cortical expansion and complexity during primate evolution. Active DNA methylation/demethylation is one of the epigenetic mechanisms that can modify gene expression via the methylation/demethylation of promoter regions. Three growth arrest and DNA damage-inducible small nuclear proteins, Gadd45 alpha, beta, and gamma, have been identified as regulators of methylation status. To understand the involvement of epigenetic factors in primate cortical evolution, we started by analyzing expression of these demethylation genes in the developing common marmoset (Callithrix jacchus) and mouse (Mus musculus) brain. In the marmoset brain, we found that cortical expression levels of Gadd45 alpha and gamma were reduced during development, whereas there was high expression of Gadd45 beta in some areas of the adult brain, including the prefrontal, temporal, posterior parietal and insula cortices, which are particularly expanded in greater primates and humans. Compared to the marmoset brain, there were no clear regional differences and constant or reduced Gadd45 expression was seen between juvenile and adult mouse brain. Double staining with a neuronal marker revealed that most Gadd45-expressing cells were NeuN-positive neurons. Thus, these results suggest the possibility that differential Gadd45 expression affects neurons, contributing cortical evolution and diversity.

Molecular Characterization, Polymorphism, and Association of Porcine GADD45G Gene

Growth arrest and DNA-damage-inducible gamma (GADD45G) is a reproduction related gene. In this study, the full-length cDNA sequence of porcine GADD45G gene was cloned through rapid amplification of cDNA ends (RACE) method. The porcine GADD45G gene encodes a protein of 159 amino acids that shares high homology with the GADD45G of nine species: chimpanzee (97%), sumatran orangutan (97%), white-tufted-ear marmoset (97%), northern white-cheeked gibbon (97%), cattle (97%), human (97%), rhesus monkey (97%), rat (96%), and mouse (95%). This novel porcine gene was assigned to GeneID: 100152997. Phylogenetic analysis revealed that the porcine GADD45G gene has a closer genetic relationship with the GADD45G gene of cattle. Computer-assisted analysis indicated that porcine GADD45G gene is structured in four exons and three introns. PCR-Rsa I-RFLP was established to detect an A/G mutation on the position of 294-bp of coding sequence and eight pig breeds display obvious genotype and allele frequency differences at this mutation locus. Association of this SNP with litter size traits was assessed in Large White (n = 100) and Landrace (n = 100) pig populations, and result demonstrated that this polymorphic locus was significantly associated with the litter size of all parities in Large White and Landrace sows (P < 0.01). Therefore, porcine GADD45G gene could be a useful candidate gene in selection for increasing the litter size. These data serve as a foundation for further insight into this novel porcine gene.

Cancer-selective targeting of the NF-κB survival pathway with GADD45β/MKK7 inhibitors

Constitutive NF-κB signaling promotes survival in multiple myeloma (MM) and other cancers; however, current NF-κB-targeting strategies lack cancer cell specificity. Here, we identify the interaction between the NF-κB-regulated antiapoptotic factor GADD45β and the JNK kinase MKK7 as a therapeutic target in MM. Using a drug-discovery strategy, we developed DTP3, a D-tripeptide, which disrupts the GADD45β/MKK7 complex, kills MM cells effectively, and, importantly, lacks toxicity to normal cells. DTP3 has similar anticancer potency to the clinical standard, bortezomib, but more than 100-fold higher cancer cell specificity in vitro. Notably, DTP3 ablates myeloma xenografts in mice with no apparent side effects at the effective doses. Hence, cancer-selective targeting of the NF-κB pathway is possible and, at least for myeloma patients, promises a profound benefit.

GADD45 proteins: roles in cellular senescence and tumor development

The growth arrest and DNA damage 45 (GADD45) family genes regulate DNA repair, cell cycle, cell survival, apoptosis, senescence, and DNA demethylation in the cells under various stress stimuli, such as oxidative stress, UV radiation, and oncogenic stress. Recent studies have provided important insights regarding how different oncogenic stresses activate GADD45 signaling pathway and lead to disparate influences on tumor initiation. In this review, we discuss the deregulation and cellular function of GADD45 proteins in the context of cancer development. We also highlight recent advances in exploring the tumor suppressive function of GADD45 proteins-triggered cellular senescence.

Transgenic expression of Map3k4 rescues T-associated sex reversal (Tas) in mice

Disorders of sex development in the human population range in severity from mild genital defects to gonadal sex reversal. XY female development has been associated with heterozygous mutations in several genes, including SOX9, WT1 and MAP3K1. In contrast, XY sex reversal in mice usually requires complete absence of testis-determining gene products. One exception to this involves T-associated sex reversal (Tas), a phenomenon characterized by the formation of ovotestes or ovaries in XY mice hemizygous for the hairpin-tail (T(hp)) or T-Orleans (T(Orl)) deletions on proximal mouse chromosome 17. We recently reported that mice heterozygous for a null allele of Map3k4, which resides in the T(hp) deletion, exhibit XY ovotestis development and occasional gonadal sex reversal on the sensitized C57BL/6J-Y(AKR) (B6-Y(AKR)) genetic background, reminiscent of the Tas phenotype. However, these experiments did not exclude the possibility that loss of other loci in the T(hp) deletion, or other effects of the deletion itself, might contribute to Tas. Here, we show that disruption to Sry expression underlies XY gonadal defects in B6-Y(AKR) embryos harbouring the T(hp) deletion and that a functional Map3k4 bacterial artificial chromosome rescues these abnormalities by re-establishing a normal Sry expression profile. These data demonstrate that Map3k4 haploinsufficiency is the cause of T-associated sex reversal and that levels of this signalling molecule are a major determinant of the expression profile of Sry.

Transcriptional profiling reveals molecular signatures associated with HIV permissiveness in Th1Th17 cells and identifies peroxisome proliferator-activated receptor gamma as an intrinsic negative regulator of viral replication

BACKGROUND

We previously demonstrated that primary Th1Th17 cells are highly permissive to HIV-1, whereas Th1 cells are relatively resistant. Molecular mechanisms underlying these differences remain unknown.

RESULTS

Exposure to replication competent and single-round VSV-G pseudotyped HIV strains provide evidence that superior HIV replication in Th1Th17 vs. Th1 cells was regulated by mechanisms located at entry and post-entry levels. Genome-wide transcriptional profiling identified transcripts upregulated (n = 264) and downregulated (n = 235) in Th1Th17 vs. Th1 cells (p-value < 0.05; fold change cut-off 1.3). Gene Set Enrichment Analysis revealed pathways enriched in Th1Th17 (nuclear receptors, trafficking, p38/MAPK, NF-κB, p53/Ras, IL-23) vs. Th1 cells (proteasome, interferon α/β). Differentially expressed genes were classified into biological categories using Gene Ontology. Th1Th17 cells expressed typical Th17 markers (IL-17A/F, IL-22, CCL20, RORC, IL-26, IL-23R, CCR6) and transcripts functionally linked to regulating cell trafficking (CEACAM1, MCAM), activation (CD28, CD40LG, TNFSF13B, TNFSF25, PTPN13, MAP3K4, LTB, CTSH), transcription (PPARγ, RUNX1, ATF5, ARNTL), apoptosis (FASLG), and HIV infection (CXCR6, FURIN). Differential expression of CXCR6, PPARγ, ARNTL, PTPN13, MAP3K4, CTSH, SERPINB6, PTK2, and ISG20 was validated by RT-PCR, flow cytometry and/or confocal microscopy. The nuclear receptor PPARγ was preferentially expressed by Th1Th17 cells. PPARγ RNA interference significantly increased HIV replication at levels post-entry and prior HIV-DNA integration. Finally, the activation of PPARγ pathway via the agonist Rosiglitazone induced the nuclear translocation of PPARγ and a robust inhibition of viral replication.

CONCLUSIONS

Thus, transcriptional profiling in Th1Th17 vs. Th1 cells demonstrated that HIV permissiveness is associated with a superior state of cellular activation and limited antiviral properties and identified PPARγ as an intrinsic negative regulator of viral replication. Therefore, triggering PPARγ pathway via non-toxic agonists may contribute to limiting covert HIV replication and disease progression during antiretroviral treatment.

Suppression of collagen-induced arthritis in growth arrest and DNA damage-inducible protein 45β-deficient mice

OBJECTIVE

Growth arrest and DNA damage-inducible protein 45β (GADD45β) is involved in stress responses, cell cycle regulation, and oncogenesis. Previous studies demonstrated that GADD45β deficiency exacerbates K/BxN serum-induced arthritis and experimental allergic encephalomyelitis (EAE) in mice, indicating that GADD45β plays a suppressive role in innate and adaptive immune responses. To further understand how GADD45β regulates autoimmunity, we evaluated collagen-induced arthritis in GADD45β-/- mice.

METHODS

Wild-type (WT) and GADD45β-/- DBA/1 mice were immunized with bovine type II collagen (CII). Serum anticollagen antibody levels were quantified by enzyme-linked immunosorbent assay. Expression of cytokines and matrix metalloproteinases in the joint and spleen was determined by quantitative polymerase chain reaction. The in vitro T cell cytokine response to CII was measured by multiplex analysis. CD4+CD25+ Treg cells and Th17 cells were quantified using flow cytometry.

RESULTS

GADD45β-/- mice showed significantly lower arthritis severity and joint destruction compared with WT mice. MMP-3 and MMP-13 expression was also markedly reduced in GADD45β-/- mice. However, serum anti-CII antibody levels were similar in both groups. FoxP3 and interleukin-10 (IL-10) expression was increased 2-3-fold in splenocytes from arthritic GADD45β-/- mice compared with those from WT mice. Flow cytometric analysis showed greater numbers of CD4+CD25+ Treg cells in the spleen of GADD45β-/- mice than in the spleen of WT mice. In vitro studies showed that interferon-γ and IL-17 production by T cells was significantly decreased in GADD45β-/- mice.

CONCLUSION

Unlike passive K/BxN arthritis and EAE, GADD45β deficiency in CIA was associated with lower arthritis severity, elevated IL-10 expression, decreased IL-17 production, and increased numbers of Treg cells. The data suggest that GADD45β plays a complex role in regulating adaptive immunity and, depending on the model, either enhances or suppresses inflammation.

Gadd45 proteins in immunity

The vertebrate immune system protects the host against invading pathogens such as viruses, bacteria and parasites. It consists of an innate branch and an adaptive branch that provide immediate and long-lasting protection, respectively. As the immune system is composed of different cell types and distributed throughout the whole body, immune cells need to communicate with each other. Intercellular communication in the immune system is mediated by cytokines, which bind to specific receptors on the cell surface and activate intracellular signalling networks. Growth arrest and DNA damage-inducible 45 (Gadd45) proteins are important components of these intracellular signalling networks. They are induced by a number of cytokines and by bacterial lipopolysaccharide. Within the innate immune system, Gadd45 proteins are crucial for the differentiation of myeloid cells as well as for the function of granulocytes and macrophages. Moreover, Gadd45β regulates autophagy, a catabolic pathway that also degrades intracellular pathogens. Regarding adaptive immunity, Gadd45 proteins are especially well characterized in T cells. For instance, Gadd45β and Gadd45γ regulate cytokine expression and Th1 differentiation, while Gadd45α inhibits p38 kinase activation downstream of the T cell receptor. Due to their many functions in the immune system, deficiency in Gadd45 proteins causes autoimmune diseases and less efficient tumour immunosurveillance.

p38 mitogen-activated protein kinase (p38 MAPK)-mediated autoimmunity: lessons to learn from ANCA vasculitis and pemphigus vulgaris

Evidence is beginning to accumulate that p38 mitogen activated protein kinase (p38 MAPK) signaling pathway plays an important role in the regulation of cellular and humoral autoimmune responses. The exact mechanisms and the degree by which the p38 MAPK pathway participates in the immune-mediated induction of diseases have started to emerge. This review discusses the recent advances in the molecular dissection of the p38 MAPK pathway and the findings generated by reports investigating its role in the pathogenesis of autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and autoimmune hepatitis. Application of newly-developed protocols based on sensitive flow cytometric detection has proven to be a useful tool in the investigation of the phosphorylation of p38 MAPK within different peripheral blood mononuclear cell populations and may help us to better understand the enigmatic role of this signaling cascade in the induction of autoimmunity as well as its role in immunosuppressive-induced remission. Special attention is paid to reported data proposing a specific role for autoantibody-induced activation of p38 MAPK-mediated immunopathology in the pathogenesis of autoimmune blistering diseases and anti-neutrophilic antibody-mediated vasculitides.

GADD45G functions in male sex determination by promoting p38 signaling and Sry expression

Male sex determination in mammals is induced by Sry, a gene whose regulation is poorly understood. Here we show that mice mutant for the stress-response gene Gadd45g display complete male-to-female sex reversal. Gadd45g and Sry have a strikingly similar expression pattern in the genital ridge, and they are coexpressed in gonadal somatic cells. In Gadd45g mutants, Sry expression is delayed and reduced, and yet Sry seemed to remain poised for expression, because its promoter is demethylated on schedule and is occupied by active histone marks. Instead, p38 MAPK signaling is impaired in Gadd45g mutants. Moreover, the transcription factor GATA4, which is required for Sry expression, binds to the Sry promoter in vivo in a MAPK-dependent manner. The results suggest that a signaling cascade, involving GADD45G → p38 MAPK → GATA4 → SRY, regulates male sex determination.

Gadd45γ and Map3k4 interactions regulate mouse testis determination via p38 MAPK-mediated control of Sry expression

Loss of the kinase MAP3K4 causes mouse embryonic gonadal sex reversal due to reduced expression of the testis-determining gene, Sry. However, because of widespread expression of MAP3K4, the cellular basis of this misregulation was unclear. Here, we show that mice lacking Gadd45γ also exhibit XY gonadal sex reversal caused by disruption to Sry expression. Gadd45γ is expressed in a dynamic fashion in somatic cells of the developing gonads from 10.5 days postcoitum (dpc) to 12.5 dpc. Gadd45γ and Map3k4 genetically interact during sex determination, and transgenic overexpression of Map3k4 rescues gonadal defects in Gadd45γ-deficient embryos. Sex reversal in both mutants is associated with reduced phosphorylation of p38 MAPK and GATA4. In addition, embryos lacking both p38α and p38β also exhibit XY gonadal sex reversal. Taken together, our data suggest a requirement for GADD45γ in promoting MAP3K4-mediated activation of p38 MAPK signaling in embryonic gonadal somatic cells for testis determination in the mouse.

Obesity is mediated by differential aryl hydrocarbon receptor signaling in mice fed a Western diet

BACKGROUND

Obesity is a growing worldwide problem with genetic and environmental causes, and it is an underlying basis for many diseases. Studies have shown that the toxicant-activated aryl hydrocarbon receptor (AHR) may disrupt fat metabolism and contribute to obesity. The AHR is a nuclear receptor/transcription factor that is best known for responding to environmental toxicant exposures to induce a battery of xenobiotic-metabolizing genes.

OBJECTIVES

The intent of the work reported here was to test more directly the role of the AHR in obesity and fat metabolism in lieu of exogenous toxicants.

METHODS

We used two congenic mouse models that differ at the Ahr gene and encode AHRs with a 10-fold difference in signaling activity. The two mouse strains were fed either a low-fat (regular) diet or a high-fat (Western) diet.

RESULTS

The Western diet differentially affected body size, body fat:body mass ratios, liver size and liver metabolism, and liver mRNA and miRNA profiles. The regular diet had no significant differential effects.

CONCLUSIONS

The results suggest that the AHR plays a large and broad role in obesity and associated complications, and importantly, may provide a simple and effective therapeutic strategy to combat obesity, heart disease, and other obesity-associated illnesses.

Mammalian MAPK signal transduction pathways activated by stress and inflammation: a 10-year update

The mammalian stress-activated families of mitogen-activated protein kinases (MAPKs) were first elucidated in 1994, and by 2001, substantial progress had been made in identifying the architecture of the pathways upstream of these kinases as well as in cataloguing candidate substrates. This information remains largely sound. Nevertheless, an informed understanding of the physiological and pathophysiological roles of these kinases remained to be accomplished. In the past decade, there has been an explosion of new work using RNAi in cells, as well as transgenic, knockout and conditional knockout technology in mice that has provided valuable insight into the functions of stress-activated MAPK pathways. These findings have important implications in our understanding of organ development, innate and acquired immunity, and diseases such as atherosclerosis, tumorigenesis, and type 2 diabetes. These new developments bring us within striking distance of the development and validation of novel treatment strategies. Herein we first summarize the molecular components of the mammalian stress-regulated MAPK pathways and their regulation as described thus far. We then review some of the in vivo functions of these pathways.

GADD45γ regulates TNF-α and IL-6 synthesis in THP-1 cells

OBJECTIVE AND DESIGN

This study investigated the link between growth arrest and DNA damage 45γ (GADD45γ) expression and tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) synthesis.

METHODS

We stimulated THP-1 monocyte cells using lipopolysaccharide (LPS). We knocked-down and over-expressed GADD45γ using lentiviral vectors harboring GADD45γ short hairpin RNA and GADD45γ open reading frame, respectively. To inhibit activation of c-Jun-terminal kinase (JNK), we used a specific inhibitor, SP600125.

RESULTS

LPS stimulation of THP-1 cells resulted in increased expression of GADD45γ mRNA which reached its peak 2 h after stimulation and gradually diminished thereafter. TNF-α and IL-6 were up-regulated at both the mRNA and protein levels in activated THP-1 cells. Knock-down of GADD45γ reduced TNF-α protein production by up to 75 % and IL-6 protein by up to 60 %. In contrast, over-expression of GADD45γ increased TNF-α production by six-fold and IL-6 protein by 80-fold. There was a discrepancy between TNF-α mRNA and its protein level, whereas IL-6 mRNA and its protein level were correlated. Knock-down of GADD45γ decreased the JNK activity, suggesting that JNK may play the role of a downstream mediator for the pro-inflammatory effects of GADD45γ.

CONCLUSIONS

We show evidence that GADD45γ may regulate TNF-α and IL-6 expression in activated THP-1 monocyte cells.

Hepatocyte proliferation/growth arrest balance in the liver of mice during E. multilocularis infection: a coordinated 3-stage course

Background

Alveolar echinococcosis (AE) is characterized by the tumor-like growth of Echinococcus (E.) multilocularis. Very little is known on the influence of helminth parasites which develop in the liver on the proliferation/growth arrest metabolic pathways in the hepatocytes of the infected liver over the various stages of infection.

Methodology/Principal Findings

Using Western blot analysis, qPCR and immunohistochemistry, we measured the levels of MAPKs activation, Cyclins, PCNA, Gadd45β, Gadd45γ, p53 and p21 expression in the murine AE model, from day 2 to 360 post-infection. Within the early (day 2–60) and middle (day60–180) stages, CyclinB1 and CyclinD1 gene expression increased up to day30 and then returned to control level after day60; Gadd45β, CyclinA and PCNA increased all over the period; ERK1/2 was permanently activated. Meanwhile, p53, p21 and Gadd45γ gene expression, and caspase 3 activation, gradually increased in a time-dependent manner. In the late stage (day180–360), p53, p21 and Gadd45γ gene expression were significantly higher in infected mice; JNK and caspase 3 were activated. TUNEL analysis showed apoptosis of hepatocytes. No significant change in CyclinE, p53 mRNA and p-p38 expression were observed at any time.

Conclusions

Our data support the concept of a sequential activation of metabolic pathways which 1) would first favor parasitic, liver and immune cell proliferation and survival, and thus promote metacestode fertility and tolerance by the host, and 2) would then favor liver damage/apoptosis, impairment in protein synthesis and xenobiotic metabolism, as well as promote immune deficiency, and thus contribute to the dissemination of the protoscoleces after metacestode fertility has been acquired. These findings give a rational explanation to the clinical observations of hepatomegaly and of unexpected survival of AE patients after major hepatic resections, and of chronic liver injury, necrosis and of hepatic failure at an advanced stage and in experimental animals.

TEC and MAPK Kinase Signalling Pathways in T helper (TH) cell Development, TH2 Differentiation and Allergic Asthma

Significant advances in our understanding of the signalling events during T cell development and differentiation have been made in the past few decades. It is clear that ligation of the T cell receptor (TCR) triggers a series of proximal signalling cascades regulated by an array of protein kinases. These orchestrated and highly regulated series of events, with differential requirements of particular kinases, highlight the disparities between αβ+CD4+ T cells. Throughout this review we summarise both new and old studies, highlighting the role of Tec and MAPK in T cell development and differentiation with particular focus on T helper 2 (TH2) cells. Finally, as the allergy epidemic continues, we feature the role played by TH2 cells in the development of allergy and provide a brief update on promising kinase inhibitors that have been tested in vitro, in pre-clinical disease models in vivo and into clinical studies.

Gadd45a and Gadd45g regulate neural development and exit from pluripotency in Xenopus

Gadd45 genes encode a small family of multifunctional stress response proteins, mediating cell proliferation, apoptosis, DNA repair and DNA demethylation. Their role during embryonic development is incompletely understood. Here we identified Xenopus Gadd45b, compared Gadd45a, Gadd45b and Gadd45g expression during Xenopus embryogenesis, and characterized their gain and loss of function phenotypes. Gadd45a and Gadd45g act redundantly and double Morpholino knock down leads to pleiotropic phenotypes, including shortened axes, head defects and misgastrulation. In contrast, Gadd45b, which is expressed at very low levels, shows little effect upon knock down or overexpression. Gadd45ag double Morphants show reduced neural cell proliferation and downregulation of pan-neural and neural crest markers. In contrast, Gadd45ag Morphants display increased expression of multipotency marker genes including Xenopus oct4 homologs as well as gastrula markers, while mesodermal markers are downregulated. The results indicate that Gadd45ag are required for early embryonic cells to exit pluripotency and enter differentiation.

Differential gene expression between wild-type and Gulo-deficient mice supplied with vitamin C

The aim of this study was to test the hypothesis that hepatic vitamin C (VC) levels in VC deficient mice rescued with high doses of VC supplements still do not reach the optimal levels present in wild-type mice. For this, we used a mouse scurvy model (sfx) in which the L-gulonolactone oxidase gene (Gulo) is deleted. Six age- (6 weeks old) and gender- (female) matched wild-type (WT) and sfx mice (rescued by administering 500 mg of VC/L) were used as the control (WT) and treatment (MT) groups (n = 3 for each group), respectively. Total hepatic RNA was used in triplicate microarray assays for each group. EDGE software was used to identify differentially expressed genes and transcriptomic analysis was used to assess the potential genetic regulation of Gulo gene expression. Hepatic VC concentrations in MT mice were significantly lower than in WT mice, even though there were no morphological differences between the two groups. In MT mice, 269 differentially expressed transcripts were detected (≥ twice the difference between MT and WT mice), including 107 up-regulated and 162 down-regulated genes. These differentially expressed genes included stress-related and exclusively/predominantly hepatocyte genes. Transcriptomic analysis identified a major locus on chromosome 18 that regulates Gulo expression. Since three relevant oxidative genes are located within the critical region of this locus we suspect that they are involved in the down-regulation of oxidative activity in sfx mice.

MEKK3 regulates IFN-gamma production in T cells through the Rac1/2-dependent MAPK cascades

MEKK3 is a conserved Ser/Thr protein kinase belonging to the MAPK kinase kinase (MAP3K) family. MEKK3 is constitutively expressed in T cells, but its function in T cell immunity has not been fully elucidated. Using Mekk3 T cell conditional knockout (T-cKO) mice, we show that MEKK3 is required for T cell immunity in vivo. Mekk3 T-cKO mice had reduced T cell response to bacterial infection and were defective in clearing bacterial infections. The Ag-induced cytokine production, especially IFN-γ production, was impaired in Mekk3-deficient CD4 T cells. The TCR-induced ERK1/2, JNK, and p38 MAPKs activation was also defective in Mekk3-deficient CD4 T cells. In vitro, MEKK3 is not required for Th1 and Th2 cell differentiation. Notably, under a nonpolarizing condition (Th0), Mekk3 deficiency led to a significant reduction of IFN-γ production in CD4 T cells. Furthermore, the IL-12/IL-18-driven IFN-γ production and MAPK activation in Mekk3-deficient T cells was not affected suggesting that MEKK3 may selectively mediate the TCR-induced MAPK signals for IFN-γ production. Finally, we found that MEKK3 activation by TCR stimulation requires Rac1/2. Taken together, our study reveals a specific role of MEKK3 in mediating the TCR signals for IFN-γ production.

Gadd45a is an RNA binding protein and is localized in nuclear speckles

Background

The Gadd45 proteins play important roles in growth control, maintenance of genomic stability, DNA repair, and apoptosis. Recently, Gadd45 proteins have also been implicated in epigenetic gene regulation by promoting active DNA demethylation. Gadd45 proteins have sequence homology with the L7Ae/L30e/S12e RNA binding superfamily of ribosomal proteins, which raises the question if they may interact directly with nucleic acids.

Principal Findings

Here we show that Gadd45a binds RNA but not single- or double stranded DNA or methylated DNA in vitro. Sucrose density gradient centrifugation experiments demonstrate that Gadd45a is present in high molecular weight particles, which are RNase sensitive. Gadd45a displays RNase-sensitive colocalization in nuclear speckles with the RNA helicase p68 and the RNA binding protein SC35. A K45A point mutation defective in RNA binding was still active in DNA demethylation. This suggests that RNA binding is not absolutely essential for demethylation of an artificial substrate. A point mutation at G39 impared RNA binding, nuclear speckle localization and DNA demethylation, emphasizing its relevance for Gadd45a function.

Significance

The results implicate RNA in Gadd45a function and suggest that Gadd45a is associated with a ribonucleoprotein particle.

Gadd45b and Gadd45g are important for anti-tumor immune responses

An effective Th1 type cell-mediated immune response against cancer cells is critical in limiting cancer progression. Gadd45b, a signaling molecule highly up-regulated during Th1 type responses, is studied for its role in limiting tumor growth. Mouse B16 melanoma cells implanted into Gadd45b(-/-) mice grew faster than those in WT or Gadd45b(+/-) littermate controls. The defect of Gadd45b(-/-) mice in tumor immunosurveillance was attributed to the reduced expression of IFN-gamma, granzyme B, and CCR5 in Gadd45b(-/-) CD8(+) T cells at the tumor site. Activation of p38 MAP kinase, but not ERK or JNK, by either TCR-stimuli or IL-12 and IL-18 is diminished in Gadd45b(-/-) CD8(+) T cells, resulting in reduced production of IFN-gamma. In addition, mRNA of T-bet and Eomes were reduced in Gadd45b(-/-) CD8(+) T cells, supporting a critical role of Gadd45b in shaping the Th1 fate. More importantly, the tumor vaccination, which is effective in WT mice, failed in Gadd45b/Gadd45g doubly deficient mice. Collectively, these data demonstrate that members of the Gadd45 gene family are important for anti-tumor immune responses.

Activation of MTK1/MEKK4 induces cardiomyocyte death and heart failure

MTK1 (MEKK4) is a mitogen-activated protein kinase kinase kinase that regulates the activity of its downstream mitogen-activated kinases, p38, and c-Jun N-terminal kinase (JNK). However, the physiological function of MTK1 in the heart remains to be determined. Here, we attempted to elucidate the function of MTK1 in the heart using in vitro and in vivo models. MTK1 was activated in the hearts of mice subjected to pressure overload-induced heart failure. Overexpression of a constitutively active mutant of MTK1 (MTK1DeltaN) induced apoptosis in isolated neonatal rat cardiomyocytes, whereas a kinase domain-deleted form of MTK1 attenuated H(2)O(2)-induced apoptosis. Specific inhibitors of p38 or JNK effectively protected cardiomyocytes from MTK1DeltaN-induced cell death. In mice, cardiac-specific overexpression of MTK1DeltaN resulted in early mortality compared with the lifespan of littermate controls. Echocardiographic analysis revealed increases in end-diastolic and end-systolic left ventricular internal dimensions and a decrease in fractional shortening in MTK1DeltaN transgenic mice. In addition, the mice showed characteristic phenotypes of heart failure such as an increase in lung weight. The number of TUNEL-positive myocytes and the level of cleaved caspase 3 protein were both increased in MTK1DeltaN transgenic mice. Thus, MTK1 plays an important role in the regulation of cell death and is also involved in the pathogenesis of heart failure.

Regulation of JNK and p38 MAPK in the immune system: signal integration, propagation and termination

Stress-activated MAP kinases (MAPKs), comprised of JNK and p38, play prominent roles in the innate and adaptive immune systems. Activation of MAPKs is mediated by a three-tiered kinase module comprised of MAPK kinase kinases (MAP3Ks), MAPK kinases (MAP2Ks) and MAPKs through sequential protein phosphorylation. Activated MAPKs, in turn, phosphorylate transcription factors and other targets to regulate gene transcription and immune responses. Recent studies have provided new insight into the upstream and downstream components of the MAPK pathway that facilitate the activation and propagation of MAPK signaling in immune responses. Moreover, MAPK activity is negatively regulated by MAPK phosphatases (MKPs), a group of dual-specificity phosphatases that dephosphorylate and inactivate the MAPKs. Here we discuss the recent advances in our understanding of these regulatory processes in MAPK signaling with a focus on their impacts on immune function.

Loss of mitogen-activated protein kinase kinase kinase 4 (MAP3K4) reveals a requirement for MAPK signalling in mouse sex determination

Sex determination in mammals is controlled by the presence or absence of the Y-linked gene SRY. In the developing male (XY) gonad, sex-determining region of the Y (SRY) protein acts to up-regulate expression of the related gene, SOX9, a transcriptional regulator that in turn initiates a downstream pathway of testis development, whilst also suppressing ovary development. Despite the requirement for a number of transcription factors and secreted signalling molecules in sex determination, intracellular signalling components functioning in this process have not been defined. Here we report a role for the phylogenetically ancient mitogen-activated protein kinase (MAPK) signalling pathway in mouse sex determination. Using a forward genetic screen, we identified the recessive boygirl (byg) mutation. On the C57BL/6J background, embryos homozygous for byg exhibit consistent XY gonadal sex reversal. The byg mutation is an A to T transversion causing a premature stop codon in the gene encoding MAP3K4 (also known as MEKK4), a mitogen-activated protein kinase kinase kinase. Analysis of XY byg/byg gonads at 11.5 d post coitum reveals a growth deficit and a failure to support mesonephric cell migration, both early cellular processes normally associated with testis development. Expression analysis of mutant XY gonads at the same stage also reveals a dramatic reduction in Sox9 and, crucially, Sry at the transcript and protein levels. Moreover, we describe experiments showing the presence of activated MKK4, a direct target of MAP3K4, and activated p38 in the coelomic region of the XY gonad at 11.5 d post coitum, establishing a link between MAPK signalling in proliferating gonadal somatic cells and regulation of Sry expression. Finally, we provide evidence that haploinsufficiency for Map3k4 accounts for T-associated sex reversal (Tas). These data demonstrate that MAP3K4-dependent signalling events are required for normal expression of Sry during testis development, and create a novel entry point into the molecular and cellular mechanisms underlying sex determination in mice and disorders of sexual development in humans.

CD4+ T-cell-mediated anti-tumor immunity can be uncoupled from autoimmunity via the STAT4/STAT6 signaling axis

Previous reports have suggested that autoimmune sequelae may be an unavoidable consequence of successful immunization against tumor-associated antigens, which are typically non-mutated self-antigens. Using a melanoma model, we demonstrated that CD4(+) T-cell-mediated anti-tumor immunity and autoimmunity could be separated by modulating the STAT4/STAT6 signaling axis. Our results have revealed an unexpected dichotomy in the effector phase following cancer vaccination where anti-tumor immunity is mediated via a STAT6 and IL-4-dependent pathway, whereas autoimmune pathology is mediated via STAT4 through a mechanism that relies partially on IFN-gamma. Our results offer a possibility to elicit specific anti-tumor responses without triggering unwanted tissue autoimmune diseases.

Regulation of the immune response by stress-activated protein kinases

Activation of immune cells to mediate an immune response is often triggered by potential 'danger' or 'stress' stimuli that the organism receives. Within the mitogen-activated protein kinases (MAPKs) family, the stress-activated protein kinase (SAPK) group was defined as group of kinases that activated by stimuli that cause cell stress. In the immune cells, SAPKs are activated by antigen receptors (B- or T-cell receptors), Toll-like receptors, cytokine receptors, and physical-chemical changes in the environment among other stimuli. The SAPKs are established to be important mediators of intracellular signaling during adaptive and innate immune responses. Here we summarize what is currently known about the role of two sub-groups of SAPKs - c-Jun NH(2)-terminal kinase and p38 MAPK-in the function of specific components of the immune system and the overall contribution to the immune response.

Regulation of NF-kappaB-dependent T cell activation and development by MEKK3

The serine/threonine kinase MEKK3, also known as mitogen-activated protein kinase kinase kinase 3, is a critical activator of the transcription factor NF-kappaB in innate immunity. However, the physiological function of MEKK3 in adaptive immunity is unclear. Here we report that following TCR signaling, MEKK3 positively regulated the kinase, IkappaB kinase, leading to NF-kappaB activation. T cells lacking MEKK3 were defective in TCR-induced and cytokine-induced responses. Furthermore, T cell-specific deletion of MEKK3 resulted in reduced numbers of thymocytes and peripheral T cells. Thus, our results provide genetic evidence that MEKK3 plays a crucial role in adaptive immunity.

Formation of stress granules inhibits apoptosis by suppressing stress-responsive MAPK pathways

When confronted with environmental stress, cells either activate defence mechanisms to survive, or initiate apoptosis, depending on the type of stress. Certain types of stress, such as hypoxia, heatshock and arsenite (type 1 stress), induce cells to assemble cytoplasmic stress granules (SGs), a major adaptive defence mechanism. SGs are multimolecular aggregates of stalled translation pre-initiation complexes that prevent the accumulation of mis-folded proteins. Type 2 stress, which includes X-rays and genotoxic drugs, induce apoptosis through the stress-activated p38 and JNK MAPK (SAPK) pathways. A functional relationship between the SG and SAPK responses is unknown. Here, we report that SG formation negatively regulates the SAPK apoptotic response, and that the signalling scaffold protein RACK1 functions as a mediator between the two responses. RACK1 binds to the stress-responsive MTK1 MAPKKK and facilitates its activation by type 2 stress; however, under conditions of type 1 stress, RACK1 is sequestered into SGs. Thus, type 1 conditions suppress activation of the MTK1-SAPK pathway and apoptosis induced by type 2 stress. These findings may be relevant to the problem of hypoxia-induced resistance to cancer chemotherapy.

MEKK4 sequesters RIP2 to dictate NOD2 signal specificity

The Crohn's-disease-susceptibility protein, NOD2, coordinates signaling responses upon intracellular exposure to bacteria. Although NOD2 is known to activate NFkappaB, little is known about the molecular mechanisms by which NOD2 coordinates functionally separate signaling pathways such as NFkappaB, JNK, and p38 to regulate cytokine responses. Given that one of the characteristics of Crohn's disease is an altered cytokine response to normal bacterial flora, the coupling of signaling pathways could be important for Crohn's-disease pathophysiology. We find that a MAP3K, MEKK4, binds to RIP2 to sequester RIP2 from the NOD2 signaling pathway. This MEKK4:RIP2 complex dissociates upon exposure to the NOD2 agonist, MDP, allowing NOD2 to bind to RIP2 and activate NFkappaB. MEKK4 thus sequesters RIP2 to inhibit the NOD2:RIP2 complex from activating NFkappaB signaling pathways, and Crohn's-disease-associated NOD2 polymorphisms cannot compete with MEKK4 for RIP2 binding. Lastly, we find that MEKK4 helps dictate signal specificity downstream of NOD2 activation as knockdown of MEKK4 in macrophages exposed to MDP causes increased NFkappaB activity, absent p38 activity, and hyporesponsiveness to TLR2 and TLR4 agonists. These biochemical findings suggest that basal inhibition of the NOD2-driven NFkappaB pathway by MEKK4 could be important in the pathogenesis of Crohn's disease.