Ca2+/calmodulin-dependent protein kinase IV stimulates nuclear factor-kappa B transactivation via phosphorylation of the p65 subunit

Involvement of calmodulin-dependent protein kinase I in the regulation of the expression of connexin 43 in MA-10 tumor Leydig cells

Connexin 43 (Cx43, also known as Gja1) is the most abundant testicular gap junction protein. It has a crucial role in the support of spermatogenesis by Sertoli cells in the seminiferous tubules as well as in androgen synthesis by Leydig cells. The multifunctional family of Ca²⁺/calmodulin-dependent protein kinases (CaMK) is composed of CaMK I, II, and IV and each can serve as a mediator of nuclear Ca²⁺ signals. These kinases can control gene expression by phosphorylation of key regulatory sites on transcription factors. Among these, AP-1 members cFos and cJun are interesting candidates that seem to cooperate with CaMKs to regulate Cx43 expression in Leydig cells. In this study, the Cx43 promoter region important for CaMK-dependent activation is characterized using co-transfection of plasmid reporter-constructs with different plasmids coding for CaMKs and/or AP-1 members in MA-10 Leydig cells. Here we report that the activation of Cx43 expression by cFos and cJun is increased by CaMKI. Furthermore, results from chromatin immunoprecipitation suggest that the recruitment of AP-1 family members to the proximal region of the Cx43 promoter may involve another uncharacterized AP-1 DNA regulatory element and/or protein-protein interactions with other partners. Thus, our data provide new insights into the molecular regulatory mechanisms that control mouse Cx43 transcription in testicular Leydig cells.

Transcription factors regulated by cAMP in smooth muscle of the myometrium at human parturition

Cyclic adenosine monophosphate (cAMP) contributes to maintenance of a quiescent (relaxed) state in the myometrium (i.e. uterine smooth muscle) during pregnancy, which most commonly has been attributed to activation of protein kinase A (PKA). PKA-mediated phosphorylation of cytosolic contractile apparatus components in myometrial smooth muscle cells (mSMCs) are known to promote relaxation. Additionally, PKA also regulates nuclear transcription factor (TF) activity to control expression of genes important to the labour process; these are mostly involved in actin-myosin interactions, cell-to-cell connectivity and inflammation, all of which influence mSMC transition from a quiescent to a contractile (pro-labour) phenotype. This review focuses on the evidence that cAMP modulates the activity of TFs linked to pro-labour gene expression, predominantly cAMP response element (CRE) binding TFs, nuclear factor κB (NF-κB), activator protein 1 (AP-1) family and progesterone receptors (PRs). This review also considers the more recently described exchange protein directly activated by cAMP (EPAC) that may oppose the pro-quiescent effects of PKA, as well as explores findings from other cell types that have the potential to be of novel relevance to cAMP action on TF function in the myometrium.

Inhibition of calmodulin increases intracellular survival of Salmonella in chicken macrophage cells

Calcium (Ca²⁺) is a pivotal intracellular second messenger and calmodulin (CaM) acts as a multifunctional Ca²⁺-binding protein that regulates downstream Ca²⁺ dependent signaling. Together they play an important role in regulating various cellular functions, including gene expression, maturation of phagolysosome, apoptosis, and immune response. Intracellular Ca²⁺ has been shown to play a critical role in Toll-like receptor-mediated immune response to microbial agonists in the HD11 chicken macrophage cell line. The role of that the Ca²⁺/CaM pathway plays in the intracellular survival of Salmonella in chicken macrophages has not been reported. In this study, kinome peptide array analysis indicated that the Ca²⁺/CaM pathway was significantly activated when chicken macrophage HD11 cells were infected with S. Enteritidis or S. Heidelberg. Further study demonstrated that treating cells with a pharmaceutical CaM inhibitor W-7, which disrupts the formation of Ca²⁺/CaM, significantly inhibited macrophages to produce nitric oxide and weaken the control of intracellular Salmonella replication. These results strongly indicate that CaM plays an important role in the innate immune response of chicken macrophages and that the Ca²⁺/CaM mediated signaling pathway is critically involved in the host cell response to Salmonella infection.

STIM- and Orai-mediated calcium entry controls NF-κB activity and function in lymphocytes

The central role of Ca²⁺ signaling in the development of functional immunity and tolerance is well established. These signals are initiated by antigen binding to cognate receptors on lymphocytes that trigger store operated Ca²⁺ entry (SOCE). The underlying mechanism of SOCE in lymphocytes involves TCR and BCR mediated activation of Stromal Interaction Molecule 1 and 2 (STIM1/2) molecules embedded in the ER membrane leading to their activation of Orai channels in the plasma membrane. STIM/Orai dependent Ca²⁺ signals guide key antigen induced lymphocyte development and function principally through direct regulation of Ca²⁺ dependent transcription factors. The role of Ca²⁺ signaling in NFAT activation and signaling is well known and has been studied extensively, but a wide appreciation and mechanistic understanding of how Ca²⁺ signals also shape the activation and specificity of NF-κB dependent gene expression has lagged. Here we discuss and interpret what is known about Ca²⁺ dependent mechanisms of NF-kB activation, including what is known and the gaps in our understanding of how these signals control lymphocyte development and function.

Evidence of vanillin binding to CAMKIV explains the anti-cancer mechanism in human hepatic carcinoma and neuroblastoma cells

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV) is a member of Ser/Thr kinase family, and is associated with different types of cancer and neurodegenerative diseases. Vanillin is a natural compound, a primary component of the extract of the vanilla bean which possesses varieties of pharmacological features including anti-oxidant, anti-inflammatory, anti-bacterial and anti-tumor. Here, we have investigated the binding mechanism and affinity of vanillin to the CAMKIV which is being considered as a potential drug target for cancer and neurodegenerative diseases. We found that vanillin binds strongly to the active site cavity of CAMKIV and stabilized by a large number of non-covalent interactions. We explored the utility of vanillin as anti-cancer agent and found that it inhibits the proliferation of human hepatocyte carcinoma (HepG2) and neuroblastoma (SH-SY5Y) cells in a dose-dependent manner. Furthermore, vanillin treatment resulted into the significant reduction in the mitochondrial membrane depolarization and ROS production that eventually leads to apoptosis in HepG2 and SH-SY5Y cancer cells. These findings may offer a novel therapeutic approach by targeting the CAMKIV using natural product and its derivative with a minimal side effect.

Binding studies and biological evaluation of β-carotene as a potential inhibitor of human calcium/calmodulin-dependent protein kinase IV

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV), a member of Ser/Thr kinase family, is associated with cancer, cerebral hypoxia and neurodegenerative diseases. β-carotene is a colored organic compound, abundant in plants and fruits and is used in cancer prevention. Here, we report a strong binding affinity of β-carotene with CAMKIV using molecular docking, fluorescence binding and isothermal titration calorimetry methods. Furthermore, β-carotene also reduces the enzyme activity of CAMKIV moderately as observed during ATPase assay. To see the role of β-carotene on cell proliferation and apoptosis, cancerous cells (HeLa, HuH7and MCF-7) and normal (HEK-293-T) cell lines were used. Admirable anticancer activity of β-carotene was observed. We further performed propidium iodide and DAPI (4',6-diamidino-2-phenylindole) assays to understand the mechanism of anticancer activity of β-carotene at molecular level. Our findings provide a newer insight into the use of β-carotene in cancer prevention and protection via inhibition of CAMKIV by regulating the signaling pathways.

T Cell Receptor-induced Nuclear Factor κB (NF-κB) Signaling and Transcriptional Activation Are Regulated by STIM1- and Orai1-mediated Calcium Entry

T cell activation following antigen binding to the T cell receptor (TCR) involves the mobilization of intracellular Ca(2+) to activate the key transcription factors nuclear factor of activated T lymphocytes (NFAT) and NF-κB. The mechanism of NFAT activation by Ca(2+) has been determined. However, the role of Ca(2+) in controlling NF-κB signaling is poorly understood, and the source of Ca(2+) required for NF-κB activation is unknown. We demonstrate that TCR- but not TNF-induced NF-κB signaling upstream of IκB kinase activation absolutely requires the influx of extracellular Ca(2+) via STIM1-dependent Ca(2+) release-activated Ca(2+)/Orai channels. We further show that Ca(2+) influx controls phosphorylation of the NF-κB protein p65 on Ser-536 and that this posttranslational modification controls its nuclear localization and transcriptional activation. Notably, our data reveal that this role for Ca(2+) is entirely separate from its upstream control of IκBα degradation, thereby identifying a novel Ca(2+)-dependent distal step in TCR-induced NF-κB activation. Finally, we demonstrate that this control of distal signaling occurs via Ca(2+)-dependent PKCα-mediated phosphorylation of p65. Thus, we establish the source of Ca(2+) required for TCR-induced NF-κB activation and define a new distal Ca(2+)-dependent checkpoint in TCR-induced NF-κB signaling that has broad implications for the control of immune cell development and T cell functional specificity.

Effect of pH on the structure, function, and stability of human calcium/calmodulin-dependent protein kinase IV: combined spectroscopic and MD simulation studies

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV) is a member of Ser/Thr protein kinase family. It is regulated by the calcium-calmodulin dependent signal through a secondary messenger, Ca(2+), which leads to the activation of its autoinhibited form. The over-expression and mutation in CAMKIV as well as change in Ca(2+) concentration is often associated with numerous neurodegenerative diseases and cancers. We have successfully cloned, expressed, and purified a functionally active kinase domain of human CAMKIV. To observe the effect of different pH conditions on the structural and functional properties of CAMKIV, we have used spectroscopic techniques such as circular diachroism (CD) absorbance and fluorescence. We have observed that within the pH range 5.0-11.5, CAMKIV maintained both its secondary and tertiary structures, along with its function, whereas significant aggregation was observed at acidic pH (2.0-4.5). We have also performed ATPase activity assays under different pH conditions and found a significant correlation between the structure and enzymatic activities of CAMKIV. In-silico validations were further carried out by modeling the 3-dimensional structure of CAMKIV and then subjecting it to molecular dynamics (MD) simulations to understand its conformational behavior in explicit water conditions. A strong correlation between spectroscopic observations and the output of molecular dynamics simulation was observed for CAMKIV.

Curcumin specifically binds to the human calcium-calmodulin-dependent protein kinase IV: fluorescence and molecular dynamics simulation studies

Calcium-calmodulin-dependent protein kinase IV (CAMK4) plays significant role in the regulation of calcium-dependent gene expression, and thus, it is involved in varieties of cellular functions such as cell signaling and neuronal survival. On the other hand, curcumin, a naturally occurring yellow bioactive component of turmeric possesses wide spectrum of biological actions, and it is widely used to treat atherosclerosis, diabetes, cancer, and inflammation. It also acts as an antioxidant. Here, we studied the interaction of curcumin with human CAMK4 at pH 7.4 using molecular docking, molecular dynamics (MD) simulations, fluorescence binding, and surface plasmon resonance (SPR) methods. We performed MD simulations for both neutral and anionic forms of CAMK4-curcumin complexes for a reasonably long time (150 ns) to see the overall stability of the protein-ligand complex. Molecular docking studies revealed that the curcumin binds in the large hydrophobic cavity of kinase domain of CAMK4 through several hydrophobic and hydrogen-bonded interactions. Additionally, MD simulations studies contributed in understanding the stability of protein-ligand complex system in aqueous solution and conformational changes in the CAMK4 upon binding of curcumin. A significant increase in the fluorescence intensity at 495 nm was observed (λexc = 425 nm), suggesting a strong interaction of curcumin to the CAMK4. A high binding affinity (KD = 3.7 × 10(-8) ± .03 M) of curcumin for the CAMK4 was measured by SPR further indicating curcumin as a potential ligand for the CAMK4. This study will provide insights into designing a new inspired curcumin derivatives as therapeutic agents against many life-threatening diseases.

De novo expression of connexin hemichannels in denervated fast skeletal muscles leads to atrophy

Denervation of skeletal muscles induces atrophy, preceded by changes in sarcolemma permeability of causes not yet completely understood. Here, we show that denervation-induced Evans blue dye uptake in vivo of fast, but not slow, myofibers was acutely inhibited by connexin (Cx) hemichannel/pannexin1 (Panx1) channel and purinergic ionotropic P2X7 receptor (P2X7R) blockers. Denervated myofibers showed up-regulation of Panx1 and de novo expression of Cx39, Cx43, and Cx45 hemichannels as well as P2X7Rs and transient receptor potential subfamily V, member 2, channels, all of which are permeable to small molecules. The sarcolemma of freshly isolated WT myofibers from denervated muscles also showed high hemichannel-mediated permeability that was slightly reduced by blockade of Panx1 channels or the lack of Panx1 expression, but was completely inhibited by Cx hemichannel or P2X7R blockers, as well as by degradation of extracellular ATP. However, inhibition of transient receptor potential subfamily V, member 2, channels had no significant effect on membrane permeability. Moreover, activation of the transcription factor NFκB and higher mRNA levels of proinflammatory cytokines (TNF-α and IL-1β) were found in denervated WT but not Cx43/Cx45-deficient muscles. The atrophy observed after 7 d of denervation was drastically reduced in Cx43/Cx45-deficient but not Panx1-deficient muscles. Therefore, expression of Cx hemichannels and P2X7R promotes a feed-forward mechanism activated by extracellular ATP, most likely released through hemichannels, that activates the inflammasome. Consequently, Cx hemichannels are potential targets for new therapeutic agents to prevent or reduce muscle atrophy induced by denervation of diverse etiologies.

β-Transducin repeat-containing protein 1 (β-TrCP1)-mediated silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) protein degradation promotes tumor necrosis factor α (TNFα)-induced inflammatory gene expression

Cytokine modulation of the endothelium is considered an important contributor to the inflammation response. TNFα is an early response gene during the initiation of inflammation. However, the detailed mechanism by which TNFα induces proinflammatory gene expression is not completely understood. In this report, we demonstrate that silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) represses the expression of a subset of TNFα target genes in human umbilical vein endothelial cells. Upon TNFα stimulation, we observed an increase in the E3 ubiquitin ligase β-TrCP1 and a decrease in SMRT protein levels. We show that β-TrCP1 interacts with SMRT in a phosphorylation-independent manner and cooperates with the E2 ubiquitin-conjugating enzyme E2D2 to promote ubiquitination-dependent SMRT degradation. Knockdown of β-TrCP1 increases SMRT protein accumulation, increases SMRT association with its targeted promoters, and decreases SMRT target gene expression. Taken together, our results support a model in which TNFα-induced β-TrCP1 accumulation promotes SMRT degradation and the subsequent induction of proinflammatory gene expression.

Knockdown of PLC-gamma-2 and calmodulin 1 genes sensitizes human cervical adenocarcinoma cells to doxorubicin and paclitaxel

Background

RNA interference (RNAi) is a powerful approach in functional genomics to selectively silence messenger mRNA (mRNA) expression and can be employed to rapidly develop potential novel drugs against a complex disease like cancer. However, naked siRNA being anionic is unable to cross the anionic cell membrane through passive diffusion and therefore, delivery of siRNA remains a major hurdle to overcome before the potential of siRNA technology can fully be exploited in cancer. pH-sensitive carbonate apatite has recently been developed as an efficient tool to deliver siRNA into the mammalian cells by virtue of its high affinity interaction with the siRNA and the desirable size distribution of the resulting siRNA-apatite complex for effective cellular endocytosis. Moreover, internalized siRNA was found to escape from the endosomes in a time-dependent manner and efficiently silence gene expression.

Results

Here we show that carbonate apatite-mediated delivery of siRNA against PLC-gamma-2 (PLCG2) and calmodulin 1 (CALM1) genes has led to the sensitization of a human cervical cancer cell line to doxorubicin- and paclitaxel depending on the dosage of the individual drug whereas no such enhancement in cell death was observed with cisplatin irrespective of the dosage following intracellular delivery of the siRNAs.

Conclusion

Thus, PLCG2 and CALM1 genes are two potential targets for gene knockdown in doxorubicin and paclitaxel-based chemotherapy of cervical cancer.

MyD88 mediated inflammatory signaling leads to CaMKII oxidation, cardiac hypertrophy and death after myocardial infarction

The toll-like receptors (TLR) and myocardial infarction (MI) promote NF-κB-dependent inflammatory transcription and oxidative injury in myocardium. The multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is activated by oxidation and contributes to NF-κB-dependent transcription, myocardial hypertrophy and post-MI death. The myeloid differentiation protein 88 (MyD88) is an adapter protein critical for many TLR functions, but downstream targets for TLR/MyD88 signaling in MI are not well understood. We asked if CaMKII and TLR/MyD88 pathways are interconnected and if TLR/MyD88 contributes to adverse outcomes after MI. Here we show that TLR-4 activation by lipopolysaccharide (LPS) induces CaMKII oxidation (ox-CaMKII) in cardiomyocytes. MI enhances ox-CaMKII in wild type (WT) hearts but not in MyD88(-/-) hearts that are defective in MyD88-dependent TLR signaling. In post-MI WT hearts expression of pro-inflammatory genes TNF-α (Tnfa), complement factor B (Cfb), myocyte death and fibrosis were significantly increased, but increases were significantly less in MyD88(-/-) hearts after MI. MyD88(-/-) cardiomyocytes were defective in NF-κB activation by LPS but not by the MyD88-independent TLR agonist poly(I:C). In contrast, TNF-α induced Cfb gene expression was not deficient in MyD88(-/-) cardiomyocytes. Several hypertrophy marker genes were upregulated in both WT and MyD88(-/-) hearts after MI, but Acta1 was significantly attenuated in MyD88(-/-) hearts, suggesting that MyD88 selectively affects expression of hypertrophic genes. Post-MI cardiac hypertrophy, inflammation, apoptosis, ox-CaMKII expression and mortality were significantly reduced in MyD88(-/-) compared to WT littermates. These data suggest that MyD88 contributes to CaMKII oxidation and is important for adverse hypertrophic and inflammatory responses to LPS and MI.

Is CaMKII a link between inflammation and hypertrophy in heart?

Myocardial infarction is a major cause of morbidity and mortality in the developing and developed world. Although current interventions have been successful in prolonging life, they are inadequate because mortality is still high among MI patients. The multifunctional Ca(2+)/calmodulin-dependent protein kinase (CaMKII) plays a key role in the structure and contractility of the myocardium. CaMKII activity is increased in MI hearts and CaMKII promotes cardiac hypertrophy and inflammation, processes consistently activated by myocardial injury. Hypertrophy and inflammation are also related to neurohumoral and redox signaling which uncouple CaMKII activation from Ca(2+)/calmodulin dependence. Thus, CaMKII may act as a nodal point for integrating hypertrophic and inflammatory signaling in myocardium.

Transducin β-like protein 1 recruits nuclear factor κB to the target gene promoter for transcriptional activation

Nuclear factor κB (NF-κB) signaling controls a wide range of cellular functions such as tumor progression and invasion by inducing gene expression. Upon stimulation, NF-κB is translocated to the nucleus and binds to its target gene promoters to activate transcription by recruiting transcription coactivators. Although significant progress has been made in understanding NF-κB-mediated transactivation, little is known about how NF-κB is recruited to its target gene promoters. Here, we report that transducin β-like protein 1 (TBL1) controls the expression of NF-κB target genes by directly binding with NF-κB and facilitating its recruitment to target gene promoters. Tumor necrosis factor alpha stimulation triggered the formation of an NF-κB and TBL1 complex and subsequent target gene promoter binding. Knockdown of TBL1 impaired the recruitment of NF-κB to its target gene promoters. Interestingly, analysis of the Oncomine database revealed that TBL1 mRNA levels were significantly higher in invasive breast cancer tissues than in breast adenocarcinoma tissue. Consistently, TBL1 knockdown significantly reduced the invasive potential of breast cancer cells by inhibiting NF-κB. Our results reveal a new mechanism for the regulation of NF-κB activation, with important implications for the development of novel strategies for cancer therapy by targeting NF-κB.

Tetra-O-methyl nordihydroguaiaretic acid (Terameprocol) inhibits the NF-κB-dependent transcription of TNF-α and MCP-1/CCL2 genes by preventing RelA from binding its cognate sites on DNA

Background

Tetra-O-methyl nordihydroguaiaretic acid, also known as terameprocol (TMP), is a naturally occurring phenolic compound found in the resin of the creosote bush. We have shown previously that TMP will suppress production of certain inflammatory cytokines, chemokines and lipids from macrophages following stimulation with LPS or infection with H1N1 influenza virus. In this study our goal was to elucidate the mechanism underlying TMP-mediated suppression of cytokine and chemokine production. We focused our investigations on the response to LPS and the NF-κB protein RelA, a transcription factor whose activity is critical to LPS-responsiveness.

Methods

Reporter assays were performed with HEK293 cells overexpressing either TLR-3, -4, or -8 and a plasmid containing the luciferase gene under control of an NF-κB response element. Cells were then treated with LPS, poly(I:C), or resiquimod, and/or TMP, and lysates measured for luciferase activity.

RAW 264.7 cells treated with LPS and/or TMP were used in ChIP and EMSA assays. For ChIP assays, chromatin was prepared and complexes precipitated with anti-NF-κB RelA Ab. Cross-links were reversed, DNA purified, and sequence abundance determined by Q-PCR. For EMSA assays, nuclear extracts were incubated with radiolabeled probes, analyzed by non-denaturing PAGE and visualized by autoradiography.

RAW 264.7 cells treated with LPS and/or TMP were also used in fluorescence microscopy and western blot experiments. Translocation experiments were performed using a primary Ab to NF-κB RelA and a fluorescein-conjugated secondary Ab. Western blots were performed using Abs to IκB-α and phospho-IκB-α. Bands were visualized by chemiluminescence.

Results

In reporter assays with TLR-3, -4, and -8 over-expressing cells, TMP caused strong inhibition of NF-κB-dependent transcription.

ChIP assays showed TMP caused virtually complete inhibition of RelA binding in vivo to promoters for the genes for TNF-α, MCP-1/CCL2, and RANTES/CCL5 although the LPS-dependent synthesis of IκB-α was not inhibited. EMSA assays did not reveal an effect of TMP on the binding of RelA to naked DNA templates in vitro.

TMP did not inhibit the nuclear translocation of NF-κB RelA nor the phosphorylation of IκB-α.

Conclusion

TMP acts indirectly as an inhibitor of NF-κB-dependent transcription by preventing RelA from binding the promoters of certain key cytokine and chemokine genes.

PLC/CAMK IV-NF-kappaB involved in the receptor for advanced glycation end products mediated signaling pathway in human endothelial cells

Advanced glycation end products (AGEs) and their interaction with the receptor for advanced glycation end products (RAGE) play an important role in diabetic vascular complications. The current study demonstrated that AGEs significantly increased RAGE expression and the release of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) in human umbilical vein endothelial cell-derived line ECV304 cells. RAGE antisense RNA partially inhibited the expression of TNF-alpha and IL-6 induced by AGEs. Oligonucleotide microarray was used to identify the genes that respond to RAGE activation. Phospholipase C beta 1 (PLC beta 1), phospholipase C beta 4 (PLC beta 4) and calcium/calmodulin-dependent protein kinase IV (CAMK IV) which associated with Ca(2+) signaling were upregulated. The rise of intracellular calcium and the NF-kappaB promoter activity induced by AGEs were suppressed by RAGE antisense RNA, PLC inhibitor U73122 and dominant negative CAMK IV, respectively. These findings suggest that PLC/CAMK IV-NF-kappaB is involved in RAGE mediated signaling pathway in human endothelial cells.

Interaction of calmodulin with Bcl10 modulates NF-kappaB activation

Calcium signals resulting from antigen receptor activation are important in determining the responses of a T or B lymphocyte to an antigen. Calmodulin (CaM), a multi-functional sensor of intracellular calcium (Ca(2+)) signals in cells, is required in the pathway from the T cell receptor (TCR) to activation of the key transcription factor NF-kappaB. Here we searched for a partner in direct interaction with CaM in the pathway, and found that CaM interacts specifically with the signaling adaptor Bcl10. The binding is Ca(2+) dependent and of high affinity, with a K(d) of approximately 160 nM. Proximity of CaM and Bcl10 in vivo is induced by increases in the intracellular Ca(2+) level. The interaction is localized to the CARD domain of Bcl10, which interacts with the CARD domain of the upstream signaling partner Carma1. Binding of CaM to Bcl10 is shown to inhibit the ability of Bcl10 to interact with Carma1, an interaction that is required for signaling from the TCR to NF-kappaB. Furthermore, a mutant of Bcl10 with reduced binding to CaM shows increased activation of an NF-kappaB reporter, which is further enhanced by activating stimuli. We propose a novel mechanism whereby the Ca(2+) sensor CaM regulates T cell responses to antigens by binding to Bcl10, thereby modulating its interaction with Carma1 and subsequent activation of NF-kappaB.

Nuclear factor kappa B-dependent gene transcription in cholecystokinin- and tumor necrosis factor-alpha-stimulated isolated acinar cells is regulated by p38 mitogen-activated protein kinase

BACKGROUND

Mitogen-activated protein (MAP) kinases and nuclear factor kappa B (NF-kappaB) are implicated in early stages of acute pancreatitis pathogenesis. We investigated the relationship between the p38 MAP kinase and NF-kappaB in isolated acinar cells.

METHODS

Isolated rodent acinar cells were stimulated with agonists after infection with an adenovector containing a luciferase promoter driven only by NF-kappaB and an adenovector containing the dominant negative (DN) form of p38 (empty vector in controls).

RESULTS

Initial immunoblots confirmed that the agonist stimulated p38 activation in acinar cells was substantially attenuated by DN p38 overexpression. Stimulation of native cholecystokinin (CCK)-A receptors or tumor necrosis factor-alpha (TNF-alpha) receptors promoted a significant increase in NF-kappaB-dependent gene transcription in cells infected with the empty vector, while overexpression of DN p38 significantly abrogated NF-kappaB-dependent luciferase activity.

CONCLUSIONS

These findings support our hypothesis that p38 is involved in the activation of proinflammatory nuclear transcription factors such as NF-kappaB in pancreatic exocrine cells.

FIP-fve stimulates interferon-gamma production via modulation of calcium release and PKC-alpha activation

Fungal immunomodulatory protein, FIP-fve, has been isolated from Flammulina velutipes, and its immunomodulatory effects are believed to be associated with the enhanced activation of IFN-gamma-releasing Th1 cells. However, the mechanisms of FIP-fve-mediated signal transduction in the regulation of interferon-gamma (IFN-gamma) gene expression in human peripheral blood mononuclear cells (PBMCs) are still poorly understood. Using fluo-3 AM, we found that FIP-fve induces a rapid elevation in calcium concentration. ELISA, RT-PCR and Western blot assays demonstrated significant increases in the production and mRNA expression of IFN-gamma and protein kinase C-alpha (PKC-alpha) activation in activated PBMCs, which were abolished by EGTA, nifedipine and GO6976. In conclusion, Ca2+ release and PKC-alpha activation are required for IFN-gamma production induced by FIP-fve in PBMCs.

The orphan nuclear receptor SHP inhibits apoptosis during the monocytic differentiation by inducing p21WAF1

Small heterodimer partner (SHP) is an atypical member of nuclear receptor superfamily that lacks a DNA-binding domain. In previous study, we showed that SHP, c-jun, p65 of NF-gammaB subunits, and p21WAF1 expression was increased during monocytic differentiaton with the exposure of human leukemia cells to a differentiation agent, PMA. In this study, c-Jun and p65 were shown to mediate the transcriptional activation of the SHP promoter. In addition, SHP induced the cell cycle regulatory protein levels and cooperatively increased an induction of p21WAF1 expression with p65. Furthermore, SHP protected differentiated cells from etoposide-induced cellular apoptosis through the induction and cytoplasmic sequestration of p21WAF1. Complex formation between SHP and p21WAF1 was demonstrated by means of coimmunoprecipitation. These results suggest that SHP prolongs a cellular survival of differentiating monocytes through the transcriptional regulation of target genes of cell survival and differentiation.

Ca2+/calmodulin-dependent kinase II triggers cell membrane injury by inducing complement factor B gene expression in the mouse heart

Myocardial Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibition improves cardiac function following myocardial infarction (MI), but the CaMKII-dependent pathways that participate in myocardial stress responses are incompletely understood. To address this issue, we sought to determine the transcriptional consequences of myocardial CaMKII inhibition after MI. We performed gene expression profiling in mouse hearts with cardiomyocyte-delimited transgenic expression of either a CaMKII inhibitory peptide (AC3-I) or a scrambled control peptide (AC3-C) following MI. Of the 8,600 mRNAs examined, 156 were substantially modulated by MI, and nearly half of these showed markedly altered responses to MI with CaMKII inhibition. CaMKII inhibition substantially reduced the MI-triggered upregulation of a constellation of proinflammatory genes. We studied 1 of these proinflammatory genes, complement factor B (Cfb), in detail, because complement proteins secreted by cells other than cardiomyocytes can induce sarcolemmal injury during MI. CFB protein expression in cardiomyocytes was triggered by CaMKII activation of the NF-kappaB pathway during both MI and exposure to bacterial endotoxin. CaMKII inhibition suppressed NF-kappaB activity in vitro and in vivo and reduced Cfb expression and sarcolemmal injury. The Cfb-/- mice were partially protected from the adverse consequences of MI. Our findings demonstrate what we believe is a novel target for CaMKII in myocardial injury and suggest that CaMKII is broadly important for the genetic effects of MI in cardiomyocytes.

A P2X ion channel-triggered NF-kappaB pathway enhances TNF-alpha-induced IL-8 expression in airway epithelial cells

Extracellular ATP, acting at P2Y and P2X receptors, has recently been shown to contribute to airway inflammation. The aim of our study was to investigate the molecular mechanisms involved in the ATP-dependent regulation of IL-8 production by airway epithelial cells. Treatment of human normal tracheal (NT)-1 cells with ATP or its two analogs, alpha,beta-methylene ATP (alpha,beta-meATP) and 2'- and 3'-O-(4-benzoyl-benzoyl)-ATP (BzATP) activated NF-kappaB through the IkappaB kinase (IKK) complex, a process requiring Ca(2+), calmodulin (CaM), and Ca(2+)/CaM-dependent kinase (CaMK), but independent from phospholipase C. alpha,beta-meATP-induced IKK activation also occurred in the alveolar A549 cell line. Real-time RT-PCR revealed that NT-1 and A549 cells expressed P2X(4), P2X(5),and P2X(6) subtype mRNAs, whereas P2X(7) mRNAs were only detected in NT-1 cells. Polarized human primary nasal epithelial cells expressed all four P2X subtypes. Both alpha,beta-meATP and BzATP caused Ca(2+)-dependent binding of phosphorylated p65 (S536) NF-kappaB subunit to the endogenous IL-8 gene promoter in NT-1 cells. Although these agonists did not induce significant IL-8 gene expression by these cells, they markedly enhanced TNF-alpha-induced NF-kappaB activation, resulting in increased IL-8 expression and release. Application of alpha,beta-meATP or BzATP at the apical side of polarized human primary nasal epithelial cells sufficed to cause CaMK-dependent IL-8 release by these cells. Thus, ATP promotes TNF-alpha-elicited IL-8 expression through P2X ion channel-triggered Ca(2+) entry, leading to CaMK-dependent IKK activation and binding of active p65 to IL-8 gene promoter.

Ca2+ entry via TRPC channels is necessary for thrombin-induced NF-kappaB activation in endothelial cells through AMP-activated protein kinase and protein kinase Cdelta

The transient receptor potential canonical (TRPC) family channels are proposed to be essential for store-operated Ca2+ entry in endothelial cells. Ca2+ signaling is involved in NF-kappaB activation, but the role of store-operated Ca2+ entry is unclear. Here we show that thrombin-induced Ca2+ entry and the resultant AMP-activated protein kinase (AMPK) activation targets the Ca2+-independent protein kinase Cdelta (PKCdelta) to mediate NF-kappaB activation in endothelial cells. We observed that thrombin-induced p65/RelA, AMPK, and PKCdelta activation were markedly reduced by knockdown of the TRPC isoform TRPC1 expressed in human endothelial cells and in endothelial cells obtained from Trpc4 knock-out mice. Inhibition of Ca2+/calmodulin-dependent protein kinase kinase beta downstream of the Ca2+ influx or knockdown of the downstream Ca2+/calmodulin-dependent protein kinase kinase beta target kinase, AMPK, also prevented NF-kappaB activation. Further, we observed that AMPK interacted with PKCdelta and phosphorylated Thr505 in the activation loop of PKCdelta in thrombin-stimulated endothelial cells. Expression of a PKCdelta-T505A mutant suppressed the thrombin-induced but not the TNF-alpha-induced NF-kappaB activation. These findings demonstrate a novel mechanism for TRPC channels to mediate NF-kappaB activation in endothelial cells that involves the convergence of the TRPC-regulated signaling at AMPK and PKCdelta and that may be a target of interference of the inappropriate activation of NF-kappaB associated with thrombosis.

Adeno-associated virus (AAV)-mediated suppression of Ca2+/calmodulin kinase IV activity in the nucleus accumbens modulates emotional behaviour in mice

Background

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) controls activity-dependent gene transcription by regulating the activity of the cyclic AMP response element binding protein (CREB). This signaling pathway is involved in gating emotional responses in the CNS but previous studies did not address the potential roles of CaMKIV in discrete brain regions. In the present study, we aimed at specifically dissecting the role of CaMKIV in the nucleus accumbens of adult mice.

Results

We used recombinant adeno-associated virus (rAAV)-mediated gene transfer of a dominant-negative CaMKIV variant (rAAV-dnCaMKIV) to inhibit endogenous CaMKIV in the nucleus accumbens. rAAV-dnCaMKIV treated animals were subjected to a battery of tests including, prepulse inhibition of the acoustic startle response, open field, social interaction and anxiety-related behaviour. We found that basal locomotor activity in the open field, and prepulse inhibition or startle performance were unaltered in mice infected with rAAV-dnCaMKIV in the nucleus accumbens. However, anxiogenic effects were revealed in social interaction testing and the light/dark emergence test.

Conclusion

Our findings suggest a modulatory role of CaMKIV in the nucleus accumbens in anxiety-like behaviour but not sensorimotor gating.

MYBBP1a is a Novel Repressor of NF-κB

NF-kappaB is an inducible transcription factor activated in many different cell types by inflammatory and stress signals. The transcription of a wide variety of NF-kappaB genes is regulated by the coordinated action of transcription co-activators and co-repressors. Previously we identified Myb binding protein 1a (MYBBP1a) as an interaction partner of the transcription activation domain of RelA/p65. MYBBP1a has been shown by others to regulate various transcription factors, through largely unknown mechanisms. Here we present evidence that MYBBP1a is a novel co-repressor of NF-kappaB. MYBBP1a interacted directly with RelA/p65 and expression of MYBBP1a in cells repressed NF-kappaB dependent reporter expression but did affect neither RelA/p65 nuclear translocation nor its DNA binding activity. In vitro, MYBBP1a inhibited transcription from chromatinized templates at a step before pre-initiation complex formation. MYBBP1a was found to compete with the histone acetyl transferase co-activator, p300, for interaction with the transcription activation domain of RelA/p65. Expression levels of MYBBP1a are dependent on the cell type, and are particularly high in Jurkat T cells. These results indicate that MYBBP1a is a novel NF-kappaB co-repressor of transcription that competes with p300 and may function to regulate cell type specific genes.

Nuclear IKK activity leads to dysregulated notch-dependent gene expression in colorectal cancer

Nuclear functions for IkappaB kinase (IKK), including phosphorylation of histone H3 and nuclear corepressors, have been recently described. Here, we show that IKK is activated in colorectal tumors concomitant with the presence of phosphorylated SMRT (silencing mediator of retinoic acid and thyroid hormone receptor) corepressor that is aberrantly localized in the cytoplasm. In these tumors, IKKalpha associates to the chromatin of specific Notch targets, leading to the release of SMRT. Abrogation of IKK activity by BAY11-7082 or by expressing dominant negative IKKalpha restores the association of SMRT with Notch target genes, resulting in specific gene repression. Finally, BAY11-7082 significantly reduces tumor size in colorectal cancer xenografts (CRC-Xs) implanted in nude mice.

Ca2+/calmodulin-dependent protein kinase II is a modulator of CARMA1-mediated NF-kappaB activation

CARMA1 is a central regulator of NF-kappaB activation in lymphocytes. CARMA1 and Bcl10 functionally interact and control NF-kappaB signaling downstream of the T-cell receptor (TCR). Computational analysis of expression neighborhoods of CARMA1-Bcl10MALT 1 for enrichment in kinases identified calmodulin-dependent protein kinase II (CaMKII) as an important component of this pathway. Here we report that Ca(2+)/CaMKII is redistributed to the immune synapse following T-cell activation and that CaMKII is critical for NF-kappaB activation induced by TCR stimulation. Furthermore, CaMKII enhances CARMA1-induced NF-kappaB activation. Moreover, we have shown that CaMKII phosphorylates CARMA1 on Ser109 and that the phosphorylation facilitates the interaction between CARMA1 and Bcl10. These results provide a novel function for CaMKII in TCR signaling and CARMA1-induced NF-kappaB activation.

Functional link between TNF biosynthesis and CaM-dependent activation of inducible nitric oxide synthase in RAW 264.7 macrophages

Inflammatory responses stimulated by bacterial endotoxin LPS involve Ca2+-mediated signaling, yet the cellular sensors that determine cell fate in response to LPS remain poorly understood. We report that exposure of RAW 264.7 macrophage-like cells to LPS induces a rapid increase in CaM abundance, which is associated with the modulation of the inflammatory response. Increases in CaM abundance precede nuclear localization of key transcription factors (i.e., NF-κB p65 subunit, phospho-c-Jun, Sp1) and subsequent increases in the proinflammatory cytokine TNF-α and inducible nitric oxide synthase (iNOS). Cellular apoptosis after LPS challenge is blocked upon inhibition of iNOS activity using the pharmacological inhibitor 1400W. LPS-mediated iNOS expression and apoptosis also were inhibited by siRNA-mediated silencing of TNF induction, indicating TNF induction both precedes and is necessary for subsequent regulation of iNOS expression. Increasing the level of cellular CaM by stable transfection results in reductions in LPS-induced expression of TNF and iNOS, along with reduced activation of their transcriptional regulators and concomitant protection against apoptosis. Thus the level of CaM available for Ca2+-dependent signaling regulation plays a key role in determining the expression of the proinflammatory and proapoptotic cascade during cellular activation by LPS. These results indicate a previously unrecognized central role for CaM in maintaining cellular homeostasis in response to LPS such that, under resting conditions, cellular concentrations of CaM are sufficient to inhibit the biosynthesis of proinflammatory mediators associated with macrophage activation. Although CaM and iNOS protein levels are coordinately increased as part of the oxidative burst, limiting cellular concentrations of CaM due to association with iNOS (and other high-affinity binders) commit the cell to an unchecked inflammatory cascade leading to apoptosis.

Novel Anti-inflammatory Role for Glycogen Synthase Kinase-3β in the Inhibition of Tumor Necrosis Factor-α- and Interleukin-1β-induced Inflammatory Gene Expression

Glycogen synthase kinase-3beta (GSK-3beta) is a serine/threonine kinase with a broad array of cellular targets, such as cytoskeletal proteins and transcription factors. Recent studies with GSK-3beta-null mice showed impaired NFkappaB-mediated survival responses. Because NFkappaB serves a dual role as a key regulator of cytokine-induced inflammatory gene expression and apoptosis, we investigated whether modulation of GSK-3beta expression affects cytokine-induced and NFkappaB-mediated inflammatory gene expression. We observed that tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) treatment of primary cultures of human microvascular cells reduced net endogenous active GSK-3beta protein levels while inducing inflammatory cytokine (IL-6 and monocyte chemoattractant protein-1 (MCP-1)) expression. Interestingly, inhibition of GSK-3beta by antisense oligonucleotides or pharmacological agent (10 mm lithium) potentiated TNF-induced expression of IL-6 and MCP-1 by 2-6-fold suggesting that inhibition of GSK-3beta under inflammatory conditions (exposure to TNF-alpha and IL-1beta) may contribute to enhanced cytokine expression. Overexpression of GSK-3beta in endothelial cells, in contrast, significantly inhibited (by 70%, p < 0.01) both TNF-alpha and IL-1beta-induced expression of IL-6, MCP-1, and vascular cell adhesion molecule-1. Using adenoviruses in lipopolysaccharide-stimulated mice, overexpression of GSK-3beta significantly decreased TNF-alpha expression in lung and heart tissues (38 and 15%, respectively), further confirming the anti-inflammatory role of GSK-3beta. Overexpression of GSK-3beta did not affect the TNF-alpha-induced nuclear translocation of NFkappaB but reduced the nuclear half-life of TNF-alpha-induced NFkappaB considerably (by as much as 9 h) and enhanced phosphorylation (by as much as 33%). Interestingly, neither endothelial cell survival nor NFkappaB-mediated expression of anti-apoptotic genes was affected by GSK-3beta overexpression. We conclude that GSK-3beta selectively regulates NFkappaB-mediated inflammatory gene expression by controlling the flow of NFkappaB activity between transcription of inflammatory and survival genes.

alpha5beta1 integrin stimulates Bcl-2 expression and cell survival through Akt, focal adhesion kinase, and Ca2+/calmodulin-dependent protein kinase IV

CHO cells expressing alpha5beta1 integrin are more resistant to apoptosis and express more Bcl-2 than the same cells engineered to express alphavbeta1 or cytoplasmically truncated alpha5Deltacbeta1 integrin as their main fibronectin receptor. The Bcl-2 up-regulation by alpha5beta1 is mediated, at least in part, by the focal adhesion kinase (FAK) and phosphatidylinositol-3 kinase (PI3K)/Akt pathways. Here, we show that integrin-mediated activation of Ca2+/calmodulin-dependent protein kinase (CaMK) IV, and the NF-kappaB and CREB transcription factors also enhance the integrin-dependent regulation of Bcl-2 expression in the alpha5beta1cells. A forkhead transcription factor, which is inactivated by Akt, blocked Bcl-2 expression. The FAK pathway was found to be defective in both the alphavbeta1 and alpha5Deltacbeta1 cells. These cell lines differed from one another in two Bcl-2-regulating pathways: adhesion through alphavbeta1 failed to activate Akt, allowing forkhead to suppress Bcl-2 transcription, whereas alpha5Deltacbeta1 did not activate NF-kappaB and CREB, presumably because CaMK IV was not activated. Our results indicate that three pathways, the FAK, PI3K/Akt, and CaMK IV mediate the survival-supporting activity of alpha5beta1 integrin.

Ca2+/calmodulin-dependent protein kinase IV activates cysteine-rich protein 1 through adjacent CRE and CArG elements

Smooth muscle-specific transcription is controlled by a multitude of transcriptional regulators that cooperate to drive expression in a temporospatial manner. Previous analysis of the cysteine-rich protein 1 ( CRP1/Csrp) gene revealed an intronic enhancer that is sufficient for expression in arterial smooth muscle cells and requires a serum response factor-binding CArG element for activity. The presence of a CArG box in smooth muscle regulatory regions is practically invariant; however, it stands to reason that additional elements contribute to the modulation of transcription in concert with the CArG. Because of the potential importance of other regulatory elements for expression of the CRP1 gene, we sought to identify additional motifs within the enhancer that are necessary for expression. In this effort, we identified a conserved cAMP response element (CRE) that, when mutated, diminishes the expression of the enhancer in cultured vascular smooth muscle cells. Using transfection and electrophoretic mobility shift assays, we have shown that the CRE binds the cAMP response element-binding protein (CREB) and is activated by Ca2+/calmodulin-dependent protein kinase IV (CaMKIV), but not by CaMKII. Furthermore, our data demonstrate that CaMKIV stimulates CRP1 expression not only through the CRE but also through the CArG box. These findings represent evidence of a functional CRE within a smooth muscle-specific gene and provide support for a mechanism in which CREB functions as a smooth muscle determinant through CaMKIV activation.

Nuclear Ca2+ and CaM kinase IV specify hormonal- and Notch-responsiveness

Many neuronal processes require gene activation by synaptically evoked Ca(2+) transients. Ca(2+)-dependent signal pathways activate some transcription factors outright, but here we report that such signals also potentiate the activation of nuclear receptors by their cognate hormone, and of CBF1 by Notch, transcription factors hitherto not thought to be Ca(2+)-responsive. This potentiation is occluded by histone deacetylase inhibition, indicating a mechanism involving inactivation of co-repressors associated with these transcription factors. Synaptic activity, acting via the nuclear Ca(2+)-dependent activation of CaM kinase IV, triggers the disruption of subnuclear domains containing class II histone deacetylases (HDACs) and silencing mediator of retinoic acid and thyroid hormone receptors (SMRT), a broad-specificity co-repressor which represses nuclear hormone receptors and CBF1. The sequential loss of class II HDACs and SMRT from the subnuclear domains, followed by nuclear export, is associated with disruption of SMRT interaction with its target transcription factors and sensitization of these factors to their activating signal. Counterbalancing these changes, protein phosphatase 1 promotes nuclear localization of SMRT and inactivation of nuclear receptors and CBF1. Thus, the synaptically controlled kinase-phosphatase balance of the neuron determines the efficacy of SMRT-mediated repression and the signal-responsiveness of a variety of transcription factors.

Post-translational modification of RelA(p65) NF-kappaB

Stimulation with diverse agents activates the NF-kappaB (nuclear factor kappaB) transcription factor, affecting inflammatory and immune responses, proliferation, differentiation, apoptosis and tumourigenesis. Determining how NF-kappaB elicits such distinct responses is essential to understanding NF-kappaB function in diseased tissues. Recent developments illustrating that post-translational modification of NF-kappaB subunits influences their nuclear role are discussed. These observations suggest that diagnosis and new therapies based on reprogramming NF-kappaB activity could be more efficient than total NF-kappaB inhibition.

Tyrosine nitration on p65: a novel mechanism to rapidly inactivate nuclear factor-kappaB

NO is an important factor that induces post-translational modifications of proteins by cellular reduction and oxidation mechanism: cysteinyl-nitrosylation or Tyr nitration. Nuclear factor (NF)-kappaB activity can be rapidly suppressed by sodium nitroprusside, a NO donor. This effect was effectively reversed by peroxynitrite scavenger deferoxamine, suggesting a Tyr nitration-mediated mechanism. Western blot with nitrotyrosine-specific antibody demonstrated that the p65 subunit of NF-kappaB was predominantly nitrated on Tyr residues. Tyr nitration of p65 induced its dissociation from p50, its association with IkappaBalpha, and subsequent sequestration of p65 in the cytoplasm by IkappaBalpha-mediated export. Liquid chromatography-coupled nanoelectrospray mass spectrometry revealed specific nitration on Tyr-66 and Tyr-152 residues of p65. Mutation studies confirmed that both Tyr-66 and Tyr-152 residues were important for the direct effects of NO on p65, which resulted in more p65 export and inactivation of NF-kappaB activity. This study identified a novel and efficient pathway where NO rapidly inactivated NF-kappaB activity by inducing Tyr nitration on p65.

DNA binding of repressor nuclear factor-kappaB p50/p50 depends on phosphorylation of Ser337 by the protein kinase A catalytic subunit

The NF-kappaB p50/p50 homodimer is mainly associated with transcriptional repression. Previously, we demonstrated that phosphorylation of NF-kappaB p50 Ser(337) is critical for DNA binding. Here, we report that p50 Ser(337) is constitutively phosphorylated by the protein kinase A catalytic subunit (PKAc) in three different cell types, which may account for the constant binding of p50/p50 to DNA in unstimulated cells. This was demonstrated first by showing that treatment of cells with PKAc-specific inhibitors blocked p50/p50 DNA binding. Second, phosphorylation of p50 by PKAc was prevented by substitution of Ser(337) to alanine. Third, both p50 and PKAc proteins as well as kinase activity that phosphorylates p50 were found to co-fractionate following gel filtration chromatography. Finally, PKAc and p50 were shown to be able to reciprocally co-immunoprecipitate one another, and their physical association was blocked by a PKA catalytic site inhibitory peptide. This indicates that phosphorylation of p50 Ser(337) involves direct contact with the PKAc catalytic center. In contrast to the dramatic elevation of nuclear p50/p65 heterodimers induced by tumor necrosis factor alpha, DNA binding of p50/p50 homodimers was not greatly altered. Taken together, these findings reveal for the first time that there is a direct interaction between PKAc and p50 that accounts for constitutive phosphorylation of p50 Ser(337) and the existence of DNA bound p50/p50 in the nuclei of most resting cells. This mechanism of DNA binding by p50/p50 following phosphorylation of Ser(337) by PKAc may represent an important means for maintaining stable negative regulation of NF-kappaB gene expression in the absence of extracellular stimulation.

cis-Acting Element-specific Transcriptional Activity of Differentially Phosphorylated Nuclear Factor-κB

Phosphorylation of nuclear factor-kappa B (NF-kappa B) subunits emerges as a mechanism by which transcriptional activity of nuclear NF-kappa B complexes is regulated in an inhibitor kappa B-independent fashion. As the main transactivator, the p65 subunit of NF-kappa B has an outstanding position in the hierarchy of NF-kappa B proteins. p65 is a multiply phosphorylated protein with phosphorylation sites in the C-terminal transactivation domain and the N-terminal Rel homology domain (RHD). In this study, we describe two previously non-reported phospho-acceptor sites within the p65 RHD. We show that differential phosphorylation of serine residues within the RHD modulates transcriptional activity in a cis-acting element and promoter-specific context, thus leading to a phosphorylation state-dependent gene expression profile. RelA(-/-) mouse embryonic fibroblasts reconstituted with wild-type p65 or p65 phosphorylation-deficient mutants showed a distinctive expression profile of synthetic kappa B-dependent reporters as well as endogenous genes. Hypophosphorylated p65 did not display cis-acting element-specific changes in DNA binding or dimerization behavior. This study shows for the first time that site-specific phosphorylation can target a transcription factor to a particular subset of genes.

SMRT derepression by the IkappaB kinase alpha: a prerequisite to NF-kappaB transcription and survival

Understanding how signaling cascades stimulate chromatin-remodeling events through derepression is one of the foremost questions in the transcription field. Here, we demonstrate that NF-kappaB transcription requires IKKalpha to phosphorylate SMRT on chromatin, stimulating the exchange of corepressor for coactivator complexes. IKKalpha-induced phosphorylation coincides with a loss of chromatin-associated SMRT and HDAC3 and with nuclear export of the SMRT corepressor, events required for expression of the NF-kappaB-regulated cIAP-2 and IL-8 genes. Although SMRT derepression corresponds with the recruitment of TBL1/TBLR1, this complex alone is insufficient to relieve repression. Using a nonphosphorylatable SMRT protein, we demonstrate that IKKalpha-induced phosphorylation is required to recruit 14-3-3epsilon and Ubc5 for SMRT derepression. Failure of IKKalpha to stimulate the removal of SMRT from chromatin inhibits the recruitment of NF-kappaB to promoters, blocking transcription and sensitizing cells to apoptosis. Our work provides evidence that IKKalpha orchestrates SMRT derepression, a prerequisite for NF-kappaB transcription and survival.

SMRT and N-CoR corepressors are regulated by distinct kinase signaling pathways

N-CoR and SMRT are corepressor paralogs that partner with and mediate transcriptional repression by a wide variety of metazoan transcription factors, including nuclear hormone receptors. Although encoded by distinct genetic loci, N-CoR and SMRT share substantial sequence interrelatedness, form analogous assemblies with histone deacetylases and auxiliary factors, can interact with overlapping sets of transcription factor partners, and exert overlapping functions in cells. SMRT is subject to negative regulation by MAPK signaling pathways operating downstream of growth factor and stress signaling pathways. We report here that whereas activation of MEKK1 leads to phosphorylation of SMRT, its dissociation from its transcription factor partners in vivo and in vitro, and its redistribution from the cell nucleus to a cytoplasmic compartment, N-CoR is refractory to all these forms of regulation. In contrast to this MAPK cascade, other signal transduction pathways operating downstream of growth factor/cytokine receptors appear able to affect both corepressor paralogs. Our results indicate that SMRT and N-CoR are embedded in distinct regulatory networks and that the two corepressors interpret growth factor, cytokine, differentiation, and prosurvival signals differently.

African swine fever virus proteins involved in evading host defence systems

African swine fever virus (ASFV) can cause an acutely fatal haemorrhagic fever in domestic pigs although in its natural hosts, warthogs, bushpigs and the soft tick vector, Ornithodoros moubata, ASFV causes inapparent persistent infections. The virus is a large, cytoplasmic, double-stranded DNA virus which has a tropism for macrophages. As it is the only member of the Asfarviridae family, ASFV encodes many novel genes not encoded by other virus families. The ability of the virus to persist in its natural hosts and in domestic pigs, which recover from infection with less virulent isolates, shows that the virus has effective mechanisms to evade host defence systems. This review focuses on recent progress made in understanding the function of ASFV-encoded proteins, which are involved in modulating the host response to infection. Growing evidence suggests that a major strategy used by the virus is to modulate signalling pathways in infected macrophages, thus interfering with the expression of a large number of immunomodulatory genes. One potent immunomodulatory protein, A238L, inhibits both activation of the host NFkappaB transcription factor and inhibits calcineurin phosphatase activity. Calcineurin-dependent pathways, including activation of the NFAT transcription factor, are therefore inhibited. Another ASFV-encoded protein, CD2v, resembles the host CD2 protein, which is expressed on T cells and NK cells. This virus protein causes the adsorption of red blood cells around virus-infected cells and extracellular virus particles. Expression of the CD2v protein aids virus dissemination in pigs and the protein also has a role in impairing bystander lymphocyte function. This may be mediated either by a direct interaction of CD2v extracellular domain with ligands on lymphocytes or by an indirect mechanism involving interaction of the CD2v cytoplasmic tail with host proteins involved in signalling or trafficking pathways. Two ASFV proteins, an IAP and a Bcl2 homologue, inhibit apoptosis in infected cells and thus facilitate production of progeny virions. The prediction is that half to two-thirds of the approximately 150 genes encoded by ASFV are not essential for replication in cells but have an important role for virus survival and transmission in its hosts. These genes provide an untapped repository, and will be valuable tools for deciphering not only how the virus manipulates the host response to infection to avoid elimination, but also useful for understanding important host anti-viral mechanisms. In addition, they may provide leads for discovery of novel immunomodulatory drugs.

Immunosuppressive activity of endovanilloids: N-arachidonoyl-dopamine inhibits activation of the NF-kappa B, NFAT, and activator protein 1 signaling pathways

Endogenous N-acyl dopamines such as N-arachidonoyldopamine (NADA) and N-oleoyldopamine have been recently identified as a new class of brain neurotransmitters sharing endocannabinoid and endovanilloid biological activities. As endocannabinoids show immunomodulatory activity, and T cells play a key role in the onset of several diseases that affect the CNS, we have evaluated the immunosuppressive activity of NADA and N-oleoyldopamine in human T cells, discovering that both compounds are potent inhibitors of early and late events in TCR-mediated T cell activation. Moreover, we found that NADA specifically inhibited both IL-2 and TNF-alpha gene transcription in stimulated Jurkat T cells. To further characterize the inhibitory mechanisms of NADA at the transcriptional level, we examined the DNA binding and transcriptional activities of NF-kappaB, NF-AT, and AP-1 transcription factors in Jurkat cells. We found that NADA inhibited NF-kappaB-dependent transcriptional activity without affecting either degradation of the cytoplasmic NF-kappaB inhibitory protein, IkappaBalpha, or DNA binding activity. However, phosphorylation of the p65/RelA subunit was clearly inhibited by NADA in stimulated cells. In addition, NADA inhibited both binding to DNA and the transcriptional activity of NF-AT and AP-1, as expected from the inhibition of NF-AT1 dephosphorylation and c-Jun N-terminal kinase activation in stimulated T cells. Finally, overexpression of a constitutively active form of calcineurin demonstrated that this phosphatase may represent one of the main targets of NADA. These findings provide new mechanistic insights into the anti-inflammatory activities of NADA and highlight their potential to design novel therapeutic strategies to manage inflammatory diseases.

The role of corepressors in transcriptional regulation by nuclear hormone receptors

Nuclear receptors (also known as nuclear hormone receptors) are hormone-regulated transcription factors that control many important physiological and developmental processes in animals and humans. Defects in receptor function result in disease. The diverse biological roles of these receptors reflect their surprisingly versatile transcriptional properties, with many receptors possessing the ability to both repress and activate target gene expression. These bipolar transcriptional properties are mediated through the interactions of the receptors with two distinct classes of auxiliary proteins: corepressors and coactivators. This review focuses on how corepressors work together with nuclear receptors to repress gene transcription in the normal organism and on the aberrations in this process that lead to neoplasia and endocrine disorders. The actions of coactivators and the contributions of the same corepressors to the functions of nonreceptor transcription factors are also touched on.

Identification of a p65 peptide that selectively inhibits NF-kappa B activation induced by various inflammatory stimuli and its role in down-regulation of NF-kappaB-mediated gene expression and up-regulation of apoptosis

Because of the critical role of the nuclear transcription factor NF-kappaB in inflammation, viral replication, carcinogenesis, antiapoptosis, invasion, and metastasis, specific inhibitors of this nuclear factor are being sought and tested as treatments. NF-kappaB activation is known to require p65 phosphorylation at serine residues 276, 529, and 536 before it undergoes nuclear translocation. Small protein domains, termed protein transduction domains (PTDs), which are able to penetrate cell membranes can be used to transport other proteins across the cell membrane. We have identified two peptides from the p65 subunit of NF-kappaB (P1 and P6 were from amino acid residues 271-282 and 525-537, respectively) that, when linked with a PTD derived from the third helix sequence of antennapedia, inhibited tumor necrosis factor (TNF)-induced NF-kappaB activation in vivo. Linkage to the PTD was not, however, required to suppress the binding of the p50-p65-heterodimer to the DNA in vitro. PTD-p65-P1 had no effect on TNF-induced AP-1 activation. PTD-p65-P1 suppressed NF-kappaB activation induced by lipopolysaccharide, interleukin-1, okadaic acid, phorbol 12-myristate 13-acetate, H(2)O(2), and cigarette smoke condensate as well as that induced by TNF. PTD-p65-P1 had no effect on TNF-induced inhibitory subunit of NF-kappaB(IkappaBalpha) phosphorylation, IkappaBalpha degradation, or IkappaBalpha kinase activation, but it blocked TNF-induced p65 phosphorylation and nuclear translocation. NF-kappaB-regulated reporter gene expression induced by TNF, TNF receptor 1, TNF receptor-associated death domain, TNF receptor-associated factor-2, NF-kappaB-inducing kinase, IkappaBalpha kinase, and p65 was also suppressed by these peptides. Suppression of NF-kappaB by PTD-p65-P1 enhanced the apoptosis induced by TNF and chemotherapeutic agents. Overall, our results demonstrate the identification of a p65 peptide that can selectively inhibit NF-kappaB activation induced by various inflammatory stimuli, down-regulate NF-kappaB-mediated gene expression, and up-regulate apoptosis.

Homogeneous Assays for Cellular Protein Degradation Usingβ-Galactosidase Complementation: NF-κB/IκB Pathway Signaling

Activation of cells by the tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) cytokines results in activation of the nuclear factor-kappaB (NF-kappaB) via proteasomal degradation of an associated IkappaB molecule. To monitor cellular IkappaB, the protein was recombinantly expressed as a fusion protein with a novel enzymatic tag, ProLabel (PL). ProLabel is a small 5.5-kDa sequence from the amino-terminal amino acids of beta-galactosidase, possesses a simple ribbon structure, and can be fused to many proteins via the amino or carboxyl terminus. Expression of this construct allows quantitative detection of the recombinant protein in crude lysates by using a method based on beta-galactosidase enzyme fragment complementation (EFC). Transient transfection of IkappaB-PL in HeLa cells generated an EFC signal that was highly correlated with a western analysis of the protein construct. ProLabel expressed alone in the cells did not show any EFC activity, due to rapid proteolytic degradation, indicating a very low background signal from the protein tag. TNF-alpha and IL-1 treatment induced a concentration-dependent degradation of IkappaB-PL, with potency values similar to those reported using other methods. IkappaBM-PL (mutant of IkappaB-PL), in contrast, did not undergo degradation for concentrations up to and including 10 ng/ml TNF-alpha or IL-1, demonstrating that degradation of IkappaB-PL was specific to the NF-kappaB pathway activation. TNF-alpha and IL-1 induced maximal IkappaB-PL degradation within 30 min of induction. This was reversed by several agents that ablate this pathway, including anti-TNF-alpha antibodies and the proteasome inhibitor, MG-132. The assay was amenable to HTS systems, with good precision and reproducibility. Z' values and coefficients of variance for IkappaB-PL degradation were 0.6 and <9%, respectively.

Regulation of c-myc gene by nitric oxide via inactivating NF-kappa B complex in P19 mouse embryonal carcinoma cells

Nitric oxide (NO) may regulate gene expression by directly modifying redox state-sensitive residues of transcription factors. Here we show that the NO donor, sodium nitroprusside (SNP), rapidly represses c-myc gene transcription in a protein synthesis-independent manner in P19 embryonal carcinoma cells by inactivation of NF-kappa B. SNP treatment reduces the DNA binding ability of the constitutively active NF-kappa B heterodimer, p65/p50, and its consequent transactivation of the c-myc promoter. Repression can be blocked by the peroxynitrite scavenger, deferoxamine, but not by dithiothreitol, which triggers reduction of S-nitrosylated residues. In HEK293 cells, where tumor necrosis factor-alpha can activate NF-kappa B, SNP likewise suppresses the binding of the active NF-kappa B complex, restoring the binding of the repressive p50/p50 homodimer complex. This effect of SNP in HEK293 cells is also blocked by deferoxamine. Chromatin immunoprecipitation analysis of SNP-treated P19 cells reveals reduced association of p65, but not of p50, with the promoter region of the endogenous c-myc gene. SNP-induced p65 dissociation was associated with the recruitment of histone deacetylase 1 and 2 to the endogenous c-myc gene promoter and the subsequent deacetylation of its chromatin histone. This study is the first to demonstrate that NO modulates the transcriptional activity of the c-myc gene promoter by dissociating the active form of NF-kappa B and replacing it with a repressive NF-kappa B complex, correlated with the recruitment of gene-silencing histone deacetylases. In light of findings that NF-kappa B stimulates Myc oncoprotein expression in cancers, our findings suggest that NO should be investigated as a prospective therapeutic cancer agent.

Synergy between all-trans retinoic acid and tumor necrosis factor pathways in acute leukemia cells

The nuclear receptor ligand all-trans retinoic acid (ATRA) causes dramatic terminal differentiation of acute promyelocytic leukemia (APL) cells in vitro and in patients, but it is less active in other malignancies. However, downstream mediators of the effects of ATRA are not well understood. We used a cDNA microarray to search for ATRA-regulated genes in the APL cell line NB4 and found that ATRA regulated several members of the tumor necrosis factor (TNF) pathway. Here we show that TNF can synergize with ATRA to induce differentiation, showing monocytic characteristics more typical of differentiation mediated by TNF than by ATRA. ATRA and TNF can also induce differentiation of the non-APL cell line U937. Underlying this response was an increase in TNF-induced nuclear factor-kappaB (NF-kappaB) DNA binding within 2 hours in the presence of ATRA and activation of NF-kappaB DNA binding and transcriptional activity in response to ATRA alone within 48 hours of ATRA treatment. Furthermore, we found a synergistic induction of the NF-kappaB target genes BCL-3, Dif-2, and TNF receptor 2 (TNFR2) in response to the combination of TNF and ATRA. These genes have been previously shown to play a role in TNF signaling, and amplification of such genes may represent a mechanism whereby TNF and ATRA can act synergistically. We propose that ATRA can prime cancer cells for differentiation triggered by TNF and suggest that targeting the TNF pathway in combination with ATRA may represent a novel route to treat leukemias.

Phospholipase Cdelta1 is required for skin stem cell lineage commitment

Phosphoinositide-specific phospholipase C (PLC) is a key enzyme in phosphoinositide turnover and is involved in a variety of physiological functions. Here we report that PLCdelta(1)-deficient mice undergo progressive hair loss in the first postnatal hair cycle. Epidermal hyperplasia was observed, and many hairs in the skin of PLCdelta(1)-deficient mice failed to penetrate the epidermis and became zigzagged owing to occlusion of the hair canal. Two major downstream signals of PLC, calcium elevation and protein kinase C activation, were impaired in the keratinocytes and skin of PLCdelta(1)-deficient mice. In addition, many cysts that had remarkable similarities to interfollicular epidermis, as well as hyperplasia of sebaceous glands, were observed. Furthermore, PLCdelta(1)-deficient mice developed spontaneous skin tumors that had characteristics of both interfollicular epidermis and sebaceous glands. From these results, we conclude that PLCdelta(1) is required for skin stem cell lineage commitment.

Phosphorylation of NF-kappa B by calmodulin-dependent kinase IV activates anti-apoptotic gene expression

We previously presented that calmodulin-dependent kinase IV (CaMKIV) mutually interacts with NF-kappa B and phosphorylates it directly, inducing the increased transcriptional regulation dependent on NF-kappa B target genes [J. Biol. Chem. 276 (2001) 20005]. Here, we show that Ser(535) residue is phosphorylated by CaMKIV. S535A mutant of p65 was specifically defective in transactivation of NF-kappa B target gene expression induced by CaMKIV. While coexpression of active CaMKIV with wild-type p65 led to a recovery from etoposide-induced apoptosis and an increase of Bcl-2 protein in cells, cells expressing S535A mutant did not. Taken together these results suggest that phosphorylated NF-kappa B p65 on Ser(535) by CaMKIV increases NF-kappa B target gene expression, including anti-apoptotic gene, hence leading to inhibition of apoptosis.