Conserved and distinct modes of CREB/ATF transcription factor regulation by PP2A/B56gamma and genotoxic stress

The role of Nrf2 in immune cells and inflammatory autoimmune diseases: a comprehensive review

INTRODUCTION

Nrf2 regulates mild stress, chronic inflammation, and metabolic changes by regulating different immune cells via downstream signaling. Collection of information about the role of Nrf2 in inflammatory autoimmune diseases will better understand the therapeutic potential of targeting Nrf2 in these diseases.

AREAS COVERED

In this review, we comprehensively discussed biological function of Nrf2 in different immune cells, including Nrf2 preventing oxidative tissue injury, affecting apoptosis of immune cells and inflammatory cytokine production. Moreover, we discussed the role of Nrf2 in the development of inflammatory autoimmune diseases.

EXPERT OPINION

Nrf2 binds to downstream signaling molecules and then provides durable protection against different cellular and organ stress. It has emerged as an important target for inflammatory autoimmune diseases. Development of Nrf2 modulator drugs needs to consider factors such as target specificity, short/long term safety, disease indication identification, and the extent of variation in Nrf2 activity. We carefully discussed the dual role of Nrf2 in some diseases, which helps to better target Nrf2 in the future.

Multi-faceted regulation of CREB family transcription factors

cAMP response element-binding protein (CREB) is a ubiquitously expressed nuclear transcription factor, which can be constitutively activated regardless of external stimuli or be inducibly activated by external factors such as stressors, hormones, neurotransmitters, and growth factors. However, CREB controls diverse biological processes including cell growth, differentiation, proliferation, survival, apoptosis in a cell-type-specific manner. The diverse functions of CREB appear to be due to CREB-mediated differential gene expression that depends on cAMP response elements and multi-faceted regulation of CREB activity. Indeed, the transcriptional activity of CREB is controlled at several levels including alternative splicing, post-translational modification, dimerization, specific transcriptional co-activators, non-coding small RNAs, and epigenetic regulation. In this review, we present versatile regulatory modes of CREB family transcription factors and discuss their functional consequences.

Safety, efficacy and determinants of response of allogeneic CD19-specific CAR-NK cells in CD19+ B cell tumors: a phase 1/2 trial

There is a pressing need for allogeneic chimeric antigen receptor (CAR)-immune cell therapies that are safe, effective and affordable. We conducted a phase 1/2 trial of cord blood-derived natural killer (NK) cells expressing anti-CD19 chimeric antigen receptor and interleukin-15 (CAR19/IL-15) in 37 patients with CD19+ B cell malignancies. The primary objectives were safety and efficacy, defined as day 30 overall response (OR). Secondary objectives included day 100 response, progression-free survival, overall survival and CAR19/IL-15 NK cell persistence. No notable toxicities such as cytokine release syndrome, neurotoxicity or graft-versus-host disease were observed. The day 30 and day 100 OR rates were 48.6% for both. The 1-year overall survival and progression-free survival were 68% and 32%, respectively. Patients who achieved OR had higher levels and longer persistence of CAR-NK cells. Receiving CAR-NK cells from a cord blood unit (CBU) with nucleated red blood cells ≤ 8 × 107 and a collection-to-cryopreservation time ≤ 24 h was the most significant predictor for superior outcome. NK cells from these optimal CBUs were highly functional and enriched in effector-related genes. In contrast, NK cells from suboptimal CBUs had upregulation of inflammation, hypoxia and cellular stress programs. Finally, using multiple mouse models, we confirmed the superior antitumor activity of CAR/IL-15 NK cells from optimal CBUs in vivo. These findings uncover new features of CAR-NK cell biology and underscore the importance of donor selection for allogeneic cell therapies. ClinicalTrials.gov identifier: NCT03056339 .

Molecular Mechanisms Underlying TNFα-Induced Mitochondrial Biogenesis in Human Airway Smooth Muscle

Proinflammatory cytokines such as TNFα mediate airway inflammation. Previously, we showed that TNFα increases mitochondrial biogenesis in human ASM (hASM) cells, which is associated with increased PGC1α expression. We hypothesized that TNFα induces CREB and ATF1 phosphorylation (pCREBS133 and pATF1S63), which transcriptionally co-activate PGC1α expression. Primary hASM cells were dissociated from bronchiolar tissue obtained from patients undergoing lung resection, cultured (one-three passages), and then differentiated by serum deprivation (48 h). hASM cells from the same patient were divided into two groups: TNFα (20 ng/mL) treated for 6 h and untreated controls. Mitochondria were labeled using MitoTracker green and imaged using 3D confocal microscopy to determine mitochondrial volume density. Mitochondrial biogenesis was assessed based on relative mitochondrial DNA (mtDNA) copy number determined by quantitative real-time PCR (qPCR). Gene and/or protein expression of pCREBS133, pATF1S63, PCG1α, and downstream signaling molecules (NRFs, TFAM) that regulate transcription and replication of the mitochondrial genome, were determined by qPCR and/or Western blot. TNFα increased mitochondrial volume density and mitochondrial biogenesis in hASM cells, which was associated with an increase in pCREBS133, pATF1S63 and PCG1α expression, with downstream transcriptional activation of NRF1, NRF2, and TFAM. We conclude that TNFα increases mitochondrial volume density in hASM cells via a pCREBS133/pATF1S63/PCG1α-mediated pathway.

Impaired myocellular Ca2+ cycling in protein phosphatase PP2A-B56α knockout mice is normalized by β-adrenergic stimulation

The activity of protein phosphatase 2A (PP2A) is determined by the expression and localization of the regulatory B-subunits. PP2A-B56α is the dominant isoform of the B′-family in the heart. Its role in regulating the cardiac response to β-adrenergic stimulation is not yet fully understood. We therefore generated mice deficient in B56α to test the functional cardiac effects in response to catecholamine administration versus corresponding WT mice. We found the decrease in basal PP2A activity in hearts of KO mice was accompanied by a counter-regulatory increase in the expression of B′ subunits (β and γ) and higher phosphorylation of sarcoplasmic reticulum Ca²⁺ regulatory and myofilament proteins. The higher phosphorylation levels were associated with enhanced intraventricular pressure and relaxation in catheterized KO mice. In contrast, at the cellular level, we detected depressed Ca²⁺ transient and sarcomere shortening parameters in KO mice at basal conditions. Consistently, the peak amplitude of the L-type Ca²⁺ current was reduced and the inactivation kinetics of I_CaL were prolonged in KO cardiomyocytes. However, we show β-adrenergic stimulation resulted in a comparable peak amplitude of Ca²⁺ transients and myocellular contraction between KO and WT cardiomyocytes. Therefore, we propose higher isoprenaline-induced Ca²⁺ spark frequencies might facilitate the normalized Ca²⁺ signaling in KO cardiomyocytes. In addition, the application of isoprenaline was associated with unchanged L-type Ca²⁺ current parameters between both groups. Our data suggest an important influence of PP2A-B56α on the regulation of Ca²⁺ signaling and contractility in response to β-adrenergic stimulation in the myocardium.

Metabolic consequences of PGC-1α dysregulation in adult zebrafish muscle

The peroxisome proliferator activated receptor gamma co-activator 1 alpha (PGC-1α) is central to the regulation of cellular and mitochondrial energy homeostasis in mammals, but its role in other vertebrates remains unclear. Indeed, previous work suggests extensive structural and functional divergence of PGC-1α in teleosts but this remains to be directly tested. Here, we describe the initial characterization of heterozygous PGC-1α mutant zebrafish lines created by CRISPR-Cas9 disruptions of an evolutionarily conserved regulatory region of the PGC-1α proximal promoter. Using qPCR, we confirmed the disruption of PGC-1α gene expression in striated muscle, leading to a simultaneous 4-fold increase in mixed skeletal muscle PGC-1α mRNA levels and an opposite 4-fold downregulation in cardiac muscle. In mixed skeletal muscle, most downstream effector genes were largely unaffected yet two mitochondrial lipid transporters, carnitine palmitoyltransferase 1 and 2, were strongly induced. Conversely, PGC-1α depression in cardiac muscle reduced the expression of several transcriptional regulators (estrogen related receptor alpha, nuclear respiratory factor 1 and PGC-1β) without altering metabolic gene expression. Using high resolution respirometry, we determined that white muscle exhibited increased lipid oxidative capacity with little difference in markers of mitochondrial abundance. Finally, using whole animal intermittent respirometry, we show that mutant fish exhibit a 2-fold higher basal metabolism than their wildtype counterparts. Altogether, this new model confirms a central but complex role for PGC-1α in mediating energy utilization in zebrafish and we propose its use as a valuable tool to explore the intricate regulatory pathways of energy homeostasis in a popular biomedical model.

Roles of constitutive and signal-dependent protein phosphatase 2A docking motifs in burst attenuation of the cyclic AMP response element-binding protein

The cAMP response element-binding protein (CREB) is an important regulator of cell growth, metabolism, and synaptic plasticity. CREB is activated through phosphorylation of an evolutionarily conserved Ser residue (S133) within its intrinsically disordered kinase-inducible domain (KID). Phosphorylation of S133 in response to cAMP, Ca²⁺, and other stimuli triggers an association of the KID with the KID-interacting (KIX) domain of the CREB-binding protein (CBP), a histone acetyl transferase (HAT) that promotes transcriptional activation. Here we addressed the mechanisms of CREB attenuation following bursts in CREB phosphorylation. We show that phosphorylation of S133 is reversed by protein phosphatase 2A (PP2A), which is recruited to CREB through its B56 regulatory subunits. We found that a B56-binding site located at the carboxyl-terminal boundary of the KID (BS2) mediates high-affinity B56 binding, while a second binding site (BS1) located near the amino terminus of the KID mediates low affinity binding enhanced by phosphorylation of adjacent casein kinase (CK) phosphosites. Mutations that diminished B56 binding to BS2 elevated both basal and stimulus-induced phosphorylation of S133, increased CBP interaction with CREB, and potentiated the expression of CREB-dependent reporter genes. Cells from mice harboring a homozygous Creb^E153D mutation that disrupts BS2 exhibited increased S133 phosphorylation stoichiometry and elevated transcriptional bursts to cAMP. These findings provide insights into substrate targeting by PP2A holoenzymes and establish a new mechanism of CREB attenuation that has implications for understanding CREB signaling in cell growth, metabolism, synaptic plasticity, and other physiologic contexts.

What turns CREB on? And off? And why does it matter?

Altered expression and function of the transcription factor cyclic AMP response-binding protein (CREB) has been identified to play an important role in cancer and is associated with the overall survival and therapy response of tumor patients. This review focuses on the expression and activation of CREB under physiologic conditions and in tumors of distinct origin as well as the underlying mechanisms of CREB regulation by diverse stimuli and inhibitors. In addition, the clinical relevance of CREB is summarized, including its use as a prognostic and/or predictive marker as well as a therapeutic target.

Polymorphism in the 3'-UTR of LIF but Not in the ATF6B Gene Associates with Schizophrenia Susceptibility: a Case-Control Study and In Silico Analyses

Schizophrenia (SCZ) is a multifactorial disorder caused by environmental and genetic factors. Studies have shown that various single-nucleotide polymorphisms (SNPs) in the binding sites of microRNAs contribute to the risk of developing SCZ. We aimed to investigate whether the variants located in the 3'-UTR region of LIF (rs929271T>G) and ATF6B (rs8283G>A) were associated with increased susceptibility to SCZ in a population from the south-east of Iran. In this case-control study, a total of 396 subjects were recruited. SNPs were genotyped via polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Genotyping results showed that the G allele of rs929271 significantly increased the risk of SCZ (OR = 1.58 95%CI = 1.19-2.10, p = 0.001). As for rs929271, the GG genotype of co-dominant (OR = 2.54 95%CI = 1.39-4.64, p = 0.002) and recessive (OR = 2.91 95%CI = 1.77-4.80, p < 0.001) models were strongly linked to SCZ. No significant differences were observed between rs8283 polymorphism and predisposition to SCZ. In silico analyses predicted that rs929271 might alter the binding sites of microRNAs, which was believed to have an unclear role in the development of SCZ. Moreover, rs929271 polymorphism changed the LIF-mRNA folding structure. These findings provide fine pieces of evidence regarding the possible effects of LIF polymorphism in the development of SCZ and regulation of the LIF gene targeted by microRNAs.

Increased mAb production in amplified CHO cell lines is associated with increased interaction of CREB1 with transgene promoter

Most therapeutic monoclonal antibodies in biopharmaceutical processes are produced in Chinese hamster ovary (CHO) cells. Technological advances have rendered the selection procedure for higher producers a robust protocol. However, information on molecular mechanisms that impart the property of hyper-productivity in the final selected clones is currently lacking. In this study, an IgG-producing industrial cell line and its methotrexate (MTX)-amplified progeny cell line were analyzed using transcriptomic, proteomic, phosphoproteomic, and chromatin immunoprecipitation (ChIP) techniques. Computational prediction of transcription factor binding to the transgene cytomegalovirus (CMV) promoter by the Transcription Element Search System and upstream regulator analysis of the differential transcriptomic data suggested increased in vivo CMV promoter-cAMP response element binding protein (CREB1) interaction in the higher producing cell line. Differential nuclear proteomic analysis detected 1.3-fold less CREB1 in the nucleus of the high productivity cell line compared with the parental cell line. However, the differential abundance of multiple CREB1 phosphopeptides suggested an increase in CREB1 activity in the higher producing cell line, which was confirmed by increased association of the CMV promotor with CREB1 in the high producer cell line. Thus, we show here that the nuclear proteome and phosphoproteome have an important role in regulating final productivity of recombinant proteins from CHO cells, and that CREB1 may play a role in transcriptional enhancement. Moreover, CREB1 phosphosites may be potential targets for cell engineering for increased productivity.

Structural Basis for Graded Inhibition of CREB:DNA Interactions by Multisite Phosphorylation

Phosphorylation of the kinase inducible domain (KID) of the cyclic AMP response element binding transcription factor (CREB) regulates its function through several mechanisms. Transcriptional activation occurs following phosphorylation at serine 133, but multisite phosphorylation in a neighboring region termed the CK cassette, residues 108-117, results in inhibition of CREB-mediated transcription. A molecular-level understanding of the mechanism of these opposing reactions has been lacking, in part because of the difficulty of preparing multiply phosphorylated CREB in vitro. By substituting a single residue, we have generated an engineered mammalian CREB in which the CK cassette can be phosphorylated in vitro by casein kinases and have characterized its interactions with cyclic AMP response element DNA. Phosphorylation of the CK cassette promotes an intramolecular interaction between the KID domain and the site of DNA binding, the basic region of the C-terminal basic leucine zipper (bZip) domain. Competition between the phosphorylated KID domain and DNA for bZip binding results in a decreased affinity of CREB for DNA. The binding free energy calculated from the dissociation constant is directly proportional to the number of phosphate groups in the CK cassette, indicating that the DNA binding is regulated by a rheostat-like mechanism. The rheostat is modulated by variation of the concentration of cations such as Mg2+ and by alternative isoforms such as the natural CREB isoform that lacks residues 162-272. Multisite phosphorylation of CREB represents a versatile mechanism by which transcription can be tuned to meet the variable needs of the cell.

miR-30a radiosensitizes non-small cell lung cancer by targeting ATF1 that is involved in the phosphorylation of ATM

Increasing number of studies report that microRNAs play important roles in radiosensitization. miR-30a has been proved to perform many functions in the development and treatment of cancer, and it is downregulated in non-small cell lung cancer (NSCLC) tissues and cells. This study was conducted to understand if miR-30a plays a role in the radiosensitivity of NSCLC cells. Radiosensitivity was examed by colony survival assay and tumor volume changing in vitro and in vivo, respectively. Bioinformatic analysis and luciferase reporter assays were used to distinguish the candidate target of miR-30a. qRT-PCR and western blotting were carried out to detect the relative expression of mRNAs and proteins. Cell cycle and cell apoptosis were determined by flow cytometry. Our results illustrated miR-30a could increase the radiosensitivity of NSCLC, especially in A549 cell line. In vivo experiment also showed the potential radiosensitizing possibility of miR-30a. Further exploration validated that miR-30a was directly targeting activating transcription factor 1 (ATF1). In studying the ataxia-telangiectasia mutated (ATM) associated effects on cell radiosensitivity, we found that miR-30a could reduce radiation induced G2/M cell cycle arrest and may also affect radiation induced apoptosis. Together, our results demonstrated that miR-30a may modulate the radiosensitivity of NSCLC through reducing the function of ATF1 in phosphorylation of ATM and have potential therapeutic value.

Tunable regulation of CREB DNA binding activity couples genotoxic stress response and metabolism

cAMP response element binding protein (CREB) is a key regulator of glucose metabolism and synaptic plasticity that is canonically regulated through recruitment of transcriptional coactivators. Here we show that phosphorylation of CREB on a conserved cluster of Ser residues (the ATM/CK cluster) by the DNA damage-activated protein kinase ataxia-telangiectasia-mutated (ATM) and casein kinase1 (CK1) and casein kinase2 (CK2) positively and negatively regulates CREB-mediated transcription in a signal dependent manner. In response to genotoxic stress, phosphorylation of the ATM/CK cluster inhibited CREB-mediated gene expression, DNA binding activity and chromatin occupancy proportional to the number of modified Ser residues. Paradoxically, substoichiometric, ATM-independent, phosphorylation of the ATM/CK cluster potentiated bursts in CREB-mediated transcription by promoting recruitment of the CREB coactivator, cAMP-regulated transcriptional coactivators (CRTC2). Livers from mice expressing a non-phosphorylatable CREB allele failed to attenuate gluconeogenic genes in response to DNA damage or fully activate the same genes in response to glucagon. We propose that phosphorylation-dependent regulation of DNA binding activity evolved as a tunable mechanism to control CREB transcriptional output and promote metabolic homeostasis in response to rapidly changing environmental conditions.

ATF1 modulates the heat shock response by regulating the stress-inducible heat shock factor 1 transcription complex

The heat shock response is an evolutionally conserved adaptive response to high temperatures that controls proteostasis capacity and is regulated mainly by an ancient heat shock factor (HSF). However, the regulation of target genes by the stress-inducible HSF1 transcription complex has not yet been examined in detail in mammalian cells. In the present study, we demonstrated that HSF1 interacted with members of the ATF1/CREB family involved in metabolic homeostasis and recruited them on the HSP70 promoter in response to heat shock. The HSF1 transcription complex, including the chromatin-remodeling factor BRG1 and lysine acetyltransferases p300 and CREB-binding protein (CBP), was formed in a manner that was dependent on the phosphorylation of ATF1. ATF1-BRG1 promoted the establishment of an active chromatin state and HSP70 expression during heat shock, whereas ATF1-p300/CBP accelerated the shutdown of HSF1 DNA-binding activity during recovery from acute stress, possibly through the acetylation of HSF1. Furthermore, ATF1 markedly affected the resistance to heat shock. These results revealed the unanticipated complexity of the primitive heat shock response mechanism, which is connected to metabolic adaptation.

Lactoferrin Promotes Early Neurodevelopment and Cognition in Postnatal Piglets by Upregulating the BDNF Signaling Pathway and Polysialylation

Lactoferrin (Lf) is a sialic acid (Sia)-rich, iron-binding milk glycoprotein that has multifunctional health benefits. Its potential role in neurodevelopment and cognition remains unknown. To test the hypothesis that Lf may function to improve neurodevelopment and cognition, the diet of postnatal piglets was supplemented with Lf from days 3 to 38. Expression levels of selected genes and their cognate protein profiles were quantitatively determined. The importance of our new findings is that Lf (1) upregulated several canonical signaling pathways associated with neurodevelopment and cognition; (2) influenced ~10 genes involved in the brain-derived neurotrophin factor (BDNF) signaling pathway in the hippocampus and upregulated the expression of polysialic acid, a marker of neuroplasticity, cell migration and differentiation of progenitor cells, and the growth and targeting of axons; (3) upregulated transcriptional and translational levels of BDNF and increased phosphorylation of the cyclic adenosine monophosphate (cAMP) response element-binding protein, CREB, a downstream target of the BDNF signaling pathway, and a protein of crucial importance in neurodevelopment and cognition; and (4) enhanced the cognitive function and learning of piglets when tested in an eight-arm radial maze. The finding that Lf can improve neural development and cognition in postnatal piglets has not been previously described.

TACC3 deregulates the DNA damage response and confers sensitivity to radiation and PARP inhibition

Deregulation of the transforming acidic coiled-coil protein 3 (TACC3), an important factor in the centrosome-microtubule system, has been linked to a variety of human cancer types. We have recently reported on the oncogenic potential of TACC3; however, the molecular mechanisms by which TACC3 mediates oncogenic function remain to be elucidated. In this study, we show that high levels of TACC3 lead to the accumulation of DNA double-strand breaks (DSBs) and disrupt the normal cellular response to DNA damage, at least in part, by negatively regulating the expression of ataxia telangiectasia mutated (ATM) and the subsequent DNA damage response (DDR) signaling cascade. Cells expressing high levels of TACC3 display defective checkpoints and DSB-mediated homologous recombination (HR) and non-homologous end joining (NHEJ) repair systems, leading to genomic instability. Importantly, high levels of TACC3 confer cellular sensitization to radiation and poly(ADP-ribose) polymerase (PARP) inhibition. Overall, our findings provide critical information regarding the mechanisms by which TACC3 contributes to genomic instability, potentially leading to cancer development, and suggest a novel prognostic, diagnostic and therapeutic strategy for the treatment of cancer types expressing high levels of TACC3.

Heme oxygenase-1 regulates dendritic cell function through modulation of p38 MAPK-CREB/ATF1 signaling

Dendritic cells (DCs) are critical for the initiation of immune responses including activation of CD8 T cells. Intracellular reactive oxygen species (ROS) levels influence DC maturation and function. Intracellular heme, a product of catabolism of heme-containing metalloproteins, is a key inducer of ROS. Intracellular heme levels are regulated by heme oxygenase-1 (HO-1), which catalyzes the degradation of heme. Heme oxygenase-1 has been implicated in regulating DC maturation; however, its role in other DC functions is unclear. Furthermore, the signaling pathways modulated by HO-1 in DCs are unknown. In this study, we demonstrate that inhibition of HO-1 activity in murine bone marrow-derived immature DCs (iDCs) resulted in DCs with raised intracellular ROS levels, a mature phenotype, impaired phagocytic and endocytic function, and increased capacity to stimulate antigen-specific CD8 T cells. Interestingly, our results reveal that the increased ROS levels following HO-1 inhibition did not underlie the changes in phenotype and functions observed in these iDCs. Importantly, we show that the p38 mitogen-activated protein kinase (p38 MAPK), cAMP-responsive element binding protein (CREB), and activating transcription factor 1 (ATF1) pathway is involved in the mediation of the phenotypic and functional changes arising from HO-1 inhibition. Furthermore, up-regulation of HO-1 activity rendered iDCs refractory to lipopolysaccharide-induced activation of p38 MAPK-CREB/ATF1 pathway and DC maturation. Finally, we demonstrate that treatment of iDC with the HO-1 substrate, heme, recapitulates the effects that result from HO-1 inhibition. Based on these results, we conclude that HO-1 regulates DC maturation and function by modulating the p38 MAPK-CREB/ATF1 signaling axis.

Protein phosphatase 2A is regulated by protein kinase Cα (PKCα)-dependent phosphorylation of its targeting subunit B56α at Ser41

Protein phosphatase 2A (PP2A) is a family of multifunctional serine/threonine phosphatases consisting of a catalytic C, a structural A, and a regulatory B subunit. The substrate and therefore the functional specificity of PP2A are determined by the assembly of the enzyme complex with the appropriate regulatory B subunit families, namely B55, B56, PR72, or PR93/PR110. It has been suggested that additional levels of regulating PP2A function may result from the phosphorylation of B56 isoforms. In this study, we identified a novel phosphorylation site at Ser(41) of B56α. This phosphoamino acid residue was efficiently phosphorylated in vitro by PKCα. We detected a 7-fold higher phosphorylation of B56α in failing human hearts compared with nonfailing hearts. Purified PP2A dimeric holoenzyme (subunits C and A) was able to dephosphorylate PKCα-phosphorylated B56α. The potency of B56α for PP2A inhibition was markedly increased by PKCα phosphorylation. PP2A activity was also reduced in HEK293 cells transfected with a B56α mutant, where serine 41 was replaced by aspartic acid, which mimics phosphorylation. More evidence for a functional role of PKCα-dependent phosphorylation of B56α was derived from Fluo-4 fluorescence measurements in phenylephrine-stimulated Flp293 cells. The endoplasmic reticulum Ca(2+) release was increased by 23% by expression of the pseudophosphorylated form compared with wild-type B56α. Taken together, our results suggest that PKCα can modify PP2A activity by phosphorylation of B56α at Ser(41). This interplay between PKCα and PP2A represents a new mechanism to regulate important cellular functions like cellular Ca(2+) homeostasis.

Cyclin-dependent kinase 1-dependent phosphorylation of cAMP response element-binding protein decreases chromatin occupancy

The cyclic AMP response element-binding protein (CREB) initiates transcriptional responses to a wide variety of stimuli. CREB activation involves its phosphorylation on Ser-133, which promotes interaction between the CREB kinase-inducible domain (KID) and the KID-interacting domain of the transcriptional coactivator, CREB-binding protein (CBP). The KID also contains a highly conserved phosphorylation cluster, termed the ATM/CK cluster, which is processively phosphorylated in response to DNA damage by the coordinated actions of ataxia-telangiectasia-mutated (ATM) and casein kinases (CKs) 1 and 2. The ATM/CK cluster phosphorylation attenuates CBP binding and CREB transcriptional activity. Paradoxically, it was recently reported that DNA damage activates CREB through homeodomain-interacting protein kinase 2-dependent phosphorylation of Ser-271 near the CREB bZIP DNA binding domain. In this study we sought to further clarify DNA damage-dependent CREB phosphorylation as well as to explore the possibility that the ATM/CK cluster and Ser-271 synergistically or antagonistically modulate CREB activity. We show that, rather than being induced by DNA damage, Ser-270 and Ser-271 of CREB cophosphorylated in a CDK1-dependent manner during G2/M phase. Functionally, we show that phosphorylation of CREB on Ser-270/Ser-271 during mitosis correlated with reduced CREB chromatin occupancy. Furthermore, CDK1-dependent phosphorylation of CREB in vitro inhibited its DNA binding activity. The combined results suggest that CDK1-dependent phosphorylation of CREB on Ser-270/Ser-271 facilitates its dissociation from chromatin during mitosis by reducing its intrinsic DNA binding potential.

Nuclear factor-erythroid 2 (NF-E2) p45-related factor-2 (Nrf2) modulates dendritic cell immune function through regulation of p38 MAPK-cAMP-responsive element binding protein/activating transcription factor 1 signaling

Nrf2 is a redox-responsive transcription factor that has been implicated in the regulation of DC immune function. Loss of Nrf2 results in increased co-stimulatory molecule expression, enhanced T cell stimulatory capacity, and increased reactive oxygen species (ROS) levels in murine immature DCs (iDCs). It is unknown whether altered immune function of Nrf2-deficient DCs (Nrf2^−/− iDCs) is due to elevated ROS levels. Furthermore, it is unclear which intracellular signaling pathways are involved in Nrf2-mediated regulation of DC function. Using antioxidant vitamins to reset ROS levels in Nrf2^−/− iDCs, we show that elevated ROS is not responsible for the altered phenotype and function of these DCs. Pharmacological inhibitors were used to explore the role of key MAPKs in mediating the altered phenotype and function in Nrf2^−/− iDCs. We demonstrate that the increased co-stimulatory molecule expression (MHC II and CD86) and antigen-specific T cell activation capacity observed in Nrf2^−/− iDCs was reversed by inhibition of p38 MAPK but not JNK. Importantly, we provide evidence for increased phosphorylation of cAMP-responsive element binding protein (CREB) and activating transcription factor 1 (ATF1), transcription factors that are downstream of p38 MAPK. The increased phosphorylation of CREB/ATF1 in Nrf2^−/− iDCs was sensitive to p38 MAPK inhibition. We also show data to implicate heme oxygenase-1 as a potential molecular link between Nrf2 and CREB/ATF1. These results indicate that dysregulation of p38 MAPK-CREB/ATF1 signaling axis underlies the altered function and phenotype in Nrf2-deficient DCs. Our findings provide new insights into the mechanisms by which Nrf2 mediates regulation of DC function.

Novel Ser/Thr protein phosphatases in cell death regulation

Cell death is regulated by a myriad of intracellular molecular pathways, with many involving protein phosphorylation and dephosphorylation. In this review, we will focus on Ser/Thr phosphatases-mediated regulation in cell apoptosis as well as on their potential roles in cell necrosis. The emerging functional importance of Ser/Thr protein phosphatases in cell death regulation adds new dimension to the signaling mechanisms of cellular function, physiology, and diseases.