Role of the CCAAT/enhancer-binding protein NFATc2 transcription factor cascade in the induction of secretory phospholipase A2

CEBPB is Required for NRF2-Mediated Drug Resistance in NRF2-Activated Non-Small Cell Lung Cancer Cells

NRF2 is a transcription activator that plays a key role in cytoprotection against oxidative stress. While increased NRF2 activity is principally beneficial for our health, NRF2 activation in cancer cells is detrimental, as it drives their malignant progression. We previously found that CEBPB cooperates with NRF2 in NRF2-activated lung cancer and enhances tumor-initiating activity by promoting NOTCH3 expression. However, the general contribution of CEBPB in lung cancer is rather controversial, probably because the role of CEBPB depends on cooperating transcription factors in each cellular context. To understand how NRF2 shapes the function of CEBPB in NRF2-activated lung cancers and its biological consequence, we comprehensively explored NRF2-CEBPB-coregulated genes and found that genes involved in drug metabolism and detoxification were characteristically enriched. Indeed, CEBPB and NRF2 cooperatively contribute to the drug resistance. We also found that CEBPB is directly regulated by NRF2, which is likely to be advantageous for the coexpression and cooperative function of NRF2 and CEBPB. These results suggest that drug resistance of NRF2-activated lung cancers is achieved by the cooperative function of NRF2 and CEBPB.

Functional regulation of phospholipase D expression in cancer and inflammation

Phospholipase D (PLD) regulates downstream effectors by generating phosphatidic acid. Growing links of dysregulation of PLD to human disease have spurred interest in therapeutics that target its function. Aberrant PLD expression has been identified in multiple facets of complex pathological states, including cancer and inflammatory diseases. Thus, it is important to understand how the signaling network of PLD expression is regulated and contributes to progression of these diseases. Interestingly, small molecule PLD inhibitors can suppress PLD expression as well as enzymatic activity of PLD and have been shown to be effective in pathological mice models, suggesting the potential for use of PLD inhibitors as therapeutics against cancer and inflammation. Here, we summarize recent scientific developments regarding the regulation of PLD expression and its role in cancer and inflammatory processes.

CCAAT enhancer binding protein and nuclear factor of activated T cells regulate HIV-1 LTR via a novel conserved downstream site in cells of the monocyte-macrophage lineage

Transcriptional control of the human immunodeficiency virus type 1 (HIV-1) promoter, the long terminal repeat (LTR), is achieved by interactions with cis-acting elements present both upstream and downstream of the start site. In silico transcription factor binding analysis of the HIV-1 subtype B LTR sequences revealed a potential downstream CCAAT enhancer binding protein (C/EBP) binding site. This binding site (+158 to+172), designated DS3, was found to be conserved in 67% of 3,858 unique subtype B LTR sequences analyzed in terms of nucleotide sequence as well as physical location in the LTR. DS3 was found to be well represented in other subtypes as well. Interestingly, DS3 overlaps with a previously identified region that bind members of the nuclear factor of activated T cells (NFAT) family of proteins. NFATc2 exhibited a higher relative affinity for DS3 as compared with members of the C/EBP family (C/EBP α and β). DS3 was able to compete efficiently with the low-affinity upstream C/EBP binding site I with respect to C/EBP binding, suggesting utilization of both NFAT and C/EBP. Moreover, cyclosporine A treatment, which has been shown to prevent dephosphorylation and nuclear translocation of NFAT isoforms, resulted in enhanced C/EBPα binding. The interactions at DS3 were also validated in an integrated HIV-1 LTR in chronically infected U1 cells. A binding knockout of DS3 demonstrated reduced HIV-1 LTR-directed transcription under both basal and interleukin-6-stimulated conditions only in cells of the monocyte-macrophage lineage cells and not in cells of T-cell origin. Thus, the events at DS3 positively regulate the HIV-1 promoter in cells of the monocyte-macrophage lineage.

The CCAAT/enhancer binding protein beta (C/EBPbeta) cooperates with NFAT to control expression of the calcineurin regulatory protein RCAN1-4

Regulator of calcineurin 1 (RCAN1) inhibits the protein phosphatase calcineurin and is required for appropriate immune responses, synaptic plasticity, vascular tone, angiogenesis, and cardiac remodeling. Expression of the RCAN1-4 isoform is under the control of the calcineurin-responsive transcription factor NFAT. Typically, NFATs act in cooperation with other transcription factors to achieve maximal activation of gene expression. In this study, we identify the CCAAT/enhancer binding protein beta (C/EBPbeta) as an NFAT binding partner that cooperates with NFAT to regulate RCAN1-4 expression. Numerous C/EBPbeta binding sites are conserved in the RCAN1-4 proximal promoter. Overexpression of C/EBPbeta increased activity of both the endogenous mouse Rcan1-4 gene and a human RCAN1-4 luciferase reporter. Binding of C/EBPbeta to multiple sites in the promoter was verified using electrophoretic mobility shift assays and chromatin immunoprecipitation. A direct interaction between C/EBPbeta and NFAT was demonstrated by co-immunoprecipitation of proteins and complex formation at NFAT-C/EBPbeta composite sites. Depletion of endogenous C/EBPbeta decreased maximal activation of RCAN1-4 expression by calcineurin, whereas inhibition of calcineurin did not alter the ability of C/EBPbeta to activate RCAN1-4 expression. Together, these findings suggest that calcineurin/NFAT activation of RCAN1-4 expression is in part dependent upon C/EBPbeta, whereas activation by C/EBPbeta is not dependent on calcineurin and may provide a calcineurin-independent pathway for regulating RCAN1-4 expression. Importantly, nuclear localization, C/EBPbeta DNA binding activity and occupancy of the Rcan1-4 promoter increased in mouse models of heart failure demonstrating in vivo activation of this pathway to regulate Rcan1-4 expression and ultimately shape the dynamics of calcineurin-dependent signaling.

The effects of IL-6 on CD4 T cell responses

Cytokines have long been known to profoundly influence the adaptive immune response by determining CD4 T cell differentiation. Although IL-6 has been initially characterized as a B cell growth factor and inducer of antibody production research from our lab and others has revealed over the last years that IL-6 also plays a significant role in CD4 T cell differentiation. This review highlights the variety of ways in which IL-6 affects CD4 effector functions and how this may contribute to different types of diseases.

Interleukin-1beta-dependent signaling between astrocytes and neurons depends critically on astrocytic calcineurin/NFAT activity

Interleukin-1beta (IL-1beta) and the Ca(2+)/calmodulin-dependent protein phosphatase, calcineurin, have each been shown to play an important role in neuroinflammation. However, whether these signaling molecules interact to coordinate immune/inflammatory processes and neurodegeneration has not been investigated. Here, we show that exogenous application of IL-1beta (10 ng/ml) recruited calcineurin/NFAT (nuclear factor of activated T cells) activation in primary astrocyte-enriched cultures within minutes, through a pathway involving IL-1 receptors and L-type Ca(2+) channels. Adenovirus-mediated delivery of the NFAT inhibitor, VIVIT, suppressed the IL-1beta-dependent induction of several inflammatory mediators and/or markers of astrocyte activation, including tumor necrosis factor alpha, granulocyte/macrophage colony-stimulating factor, and vimentin. Expression of an activated form of calcineurin in one set of astrocyte cultures also triggered the release of factors that, in turn, stimulated NFAT activity in a second set of "naive" astrocytes. This effect was prevented when calcineurin-expressing cultures co-expressed VIVIT, suggesting that the calcineurin/NFAT pathway coordinates positive feedback signaling between astrocytes. In the presence of astrocytes and neurons, 48-h delivery of IL-1beta was associated with several excitotoxic effects, including NMDA receptor-dependent neuronal death, elevated extracellular glutamate, and hyperexcitable synaptic activity. Each of these effects were reversed or ameliorated by targeted delivery of VIVIT to astrocytes. IL-1beta also caused an NFAT-dependent reduction in excitatory amino acid transporter levels, indicating a possible mechanism for IL-1beta-mediated excitotoxicity. Taken together, the results have potentially important implications for the propagation and maintenance of neuroinflammatory signaling processes associated with many neurodegenerative conditions and diseases.

Differential expression of secretory phospholipases A2 in normal and malignant prostate cell lines: regulation by cytokines, cell signaling pathways, and epigenetic mechanisms

Upregulation of group IIA phospholipase A(2) (sPLA(2)-IIA) correlates with prostate tumor progression suggesting prooncogenic properties of this protein. Here, we report data on expression of three different sPLA(2) isozymes (groups IIA, V, and X) in normal (PrEC) and malignant (DU-145, PC-3, and LNCaP) human prostate cell lines. All studied cell lines constitutively expressed sPLA(2)-X, whereas sPLA(2)-V transcripts were identified only in malignant cells. In contrast, no expression of sPLA(2)-IIA was found in PrEC and DU-145 cells, but it was constitutively expressed by IFN-gamma in LNCaP and PC-3 cells. Expression of sPLA(2)-IIA is upregulated in PC-3 and in PrEC cell in a signal transducer and activator of transcription-1-dependent manner, but not in LNCaP cell. Additional signaling pathways regulating sPLA(2)-IIA expression include cAMP/protein kinase A, p38 mitogen-activated protein kinase, protein kinase C, Rho-kinase, and mitogen-activated/extracellular response protein kinase / extracellular signal-regulated kinase. No deletions were revealed in the sPLA(2)-IIA gene from DU-145 cells lacking the expression of sPLA(2)-IIA. Reexpression of sPLA(2)-IIA was induced by 5-aza-2'-deoxycytidine demonstrating that DNA methylation is implicated in the regulation of sPLA(2)-II. Together, these data suggest that sPLA(2)-IIA and sPLA(2)-V, but not sPLA(2)-X, are differentially expressed in normal and malignant prostate cells under the control of proinflammatory cytokines; epigenetic mechanisms appear involved in the regulation of sPLA(2)-IIA expression, at least in DU-145 cells.

Histamine receptor H1 is required for TCR-mediated p38 MAPK activation and optimal IFN-gamma production in mice

Histamine receptor H1 (H1R) is a susceptibility gene in both experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune orchitis (EAO), 2 classical T cell-mediated models of organ-specific autoimmune disease. Here we showed that expression of H1R in naive CD4+ T cells was required for maximal IFN-gamma production but was dispensable for proliferation. Moreover, H1R signaling at the time of TCR ligation was required for activation of p38 MAPK, a known regulator of IFN-gamma expression. Importantly, selective reexpression of H1R in CD4+ T cells fully complemented both the IFN-gamma production and the EAE susceptibility of H1R-deficient mice. These data suggest that the presence of H1R in CD4+ T cells and its interaction with histamine regulates early TCR signals that lead to Th1 differentiation and autoimmune disease.

Role of transcription factor NFAT in glucose and insulin homeostasis

Compromised immunoregulation contributes to obesity and complications in metabolic pathogenesis. Here, we demonstrate that the nuclear factor of activated T cell (NFAT) group of transcription factors contributes to glucose and insulin homeostasis. Expression of two members of the NFAT family (NFATc2 and NFATc4) is induced upon adipogenesis and in obese mice. Mice with the Nfatc2-/- Nfatc4-/- compound disruption exhibit defects in fat accumulation and are lean. Nfatc2-/- Nfatc4-/- mice are also protected from diet-induced obesity. Ablation of NFATc2 and NFATc4 increases insulin sensitivity, in part, by sustained activation of the insulin signaling pathway. Nfatc2-/- Nfatc4-/- mice also exhibit an altered adipokine profile, with reduced resistin and leptin levels. Mechanistically, NFAT is recruited to the transcription loci and regulates resistin gene expression upon insulin stimulation. Together, these results establish a role for NFAT in glucose/insulin homeostasis and expand the repertoire of NFAT function to metabolic pathogenesis and adipokine gene transcription.