Genome-wide analysis of CREB target genes reveals a core promoter requirement for cAMP responsiveness

Loss of glucose-stimulated β-cell Nr4a1 expression impairs insulin secretion and glucose homeostasis

A central aspect of type 2 diabetes is decreased functional β-cell mass. The orphan nuclear receptor Nr4a1 is critical for fuel utilization, but little is known regarding its regulation and function in the β-cell. Nr4a1 expression is decreased in type 2 diabetes rodent β-cells and type 2 diabetes patient islets. We have shown that Nr4a1-deficient mice have reduced β-cell mass and that Nr4a1 knockdown impairs glucose-stimulated insulin secretion (GSIS) in INS-1 832/13 β-cells. Here, we demonstrate that glucose concentration directly regulates β-cell Nr4a1 expression. We show that 11 mM glucose increases Nr4a1 expression in INS-1 832/13 β-cells and primary mouse islets. We show that glucose functions through the cAMP/PKA/CREB pathway to regulate Nr4a1 mRNA and protein expression. Using Nr4a1-/- animals, we show that Nr4a1 is necessary for GSIS and systemic glucose handling. Using RNA-seq, we define Nr4a1-regulated pathways in response to glucose in the mouse islet, including Glut2 expression. Our data suggest that Nr4a1 plays a critical role in the β-cells response to the fed state.NEW & NOTEWORTHY Nr4a1 has a key role in fuel metabolism and β-cell function, but its exact role is unclear. Nr4a1 expression is regulated by glucose concentration using cAMP/PKA/CREB pathway. Nr4a1 regulates Glut2, Ndufa4, Ins1, In2, Sdhb, and Idh3g expression in response to glucose treatment. These results suggest that Nr4a1 is necessary for proper insulin secretion both through glucose uptake and metabolism machinery.

The transition state for coupled folding and binding of a disordered DNA binding domain resembles the unbound state

The basic zippers (bZIPs) are one of two large eukaryotic families of transcription factors whose DNA binding domains are disordered in isolation but fold into stable α-helices upon target DNA binding. Here, we systematically disrupt pre-existing helical propensity within the DNA binding region of the homodimeric bZIP domain of cAMP-response element binding protein (CREB) using Ala-Gly scanning and examine the impact on target binding kinetics. We find that the secondary structure of the transition state strongly resembles that of the unbound state. The residue closest to the dimerization domain is largely folded within both unbound and transition states; dimerization apparently propagates additional helical propensity into the basic region. The results are consistent with electrostatically-enhanced DNA binding, followed by rapid folding from the folded zipper outwards. Fly-casting theory suggests that protein disorder can accelerate binding. Interestingly however, we did not observe higher association rate constants for mutants with lower levels of residual structure in the unbound state.

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.

The role of aging and brain-derived neurotrophic factor signaling in expression of base excision repair genes in the human brain

DNA damage is a central contributor to the aging process. In the brain, a major threat to the DNA is the considerable amount of reactive oxygen species produced, which can inflict oxidative DNA damage. This type of damage is removed by the base excision repair (BER) pathway, an essential DNA repair mechanism, which contributes to genome stability in the brain. Despite the crucial role of the BER pathway, insights into how this pathway is affected by aging in the human brain and the underlying regulatory mechanisms are very limited. By microarray analysis of four cortical brain regions from humans aged 20-99 years (n = 57), we show that the expression of core BER genes is largely downregulated during aging across brain regions. Moreover, we find that expression of many BER genes correlates positively with the expression of the neurotrophin brain-derived neurotrophic factor (BDNF) in the human brain. In line with this, we identify binding sites for the BDNF-activated transcription factor, cyclic-AMP response element-binding protein (CREB), in the promoter of most BER genes and confirm the ability of BDNF to regulate several BER genes by BDNF treatment of mouse primary hippocampal neurons. Together, these findings uncover the transcriptional landscape of BER genes during aging of the brain and suggest BDNF as an important regulator of BER in the human brain.

Targeting gut-brain axis by dietary flavonoids ameliorate aging-related cognition decline: Evidences and mechanisms

Aging-related cognitive impairment, mainly Alzheimer's disease (AD), has been widely studied. However, effective prevention and treatment methods are still lacking. In recent years, researchers have observed beneficial effects of plant-based supplements, such as flavonoids, on cognitive protection. This provides a new clue for the prevention of cognitive dysfunction. Studies have shown that dietary flavonoids have neuroprotective effects, but the mechanism is not clear. In this review, we systematically reviewed the research progress on the effects of dietary flavonoids on gut microbes and their metabolites, and concluded that flavonoids could improve cognitive function through the gut-brain axis. Flavonoids can be absorbed through the intestine, cross the blood-brain barrier, and enter the brain tissue. Flavonoids can inhibit the expression and secretion of inflammatory factors in brain tissue, reduce the damage caused by oxidative stress, clear neural damage proteins and inhibit neuronal apoptosis, thereby ameliorating age-related cognitive disorders. Future work will continue to explore the gut-brain axis and target genes regulated by flavonoids. In addition, clinical research and its mechanisms need to be further explored to provide solutions or advise for patients with cognitive impairment.

Prenatal low-dose methylmercury exposure causes premature neuronal differentiation and autism-like behaviors in a rodent model

Aberrant neurodevelopment is a core deficit of autism spectrum disorder (ASD). Here we ask whether a non-genetic factor, prenatal exposure to the environmental pollutant methylmercury (MeHg), is a contributing factor in ASD onset. We showed that adult mice prenatally exposed to non-apoptotic MeHg exhibited key ASD characteristics, including impaired communication, reduced sociability, and increased restrictive repetitive behaviors, whereas in the embryonic cortex, prenatal MeHg exposure caused premature neuronal differentiation. Further single-cell RNA sequencing (scRNA-seq) analysis disclosed that prenatal exposure to MeHg resulted in cortical radial glial precursors (RGPs) favoring asymmetric differentiation to directly generate cortical neurons, omitting the intermediate progenitor stage. In addition, MeHg exposure in cultured RGPs increased CREB phosphorylation and enhanced the interaction between CREB and CREB binding protein (CBP). Intriguingly, metformin, an FDA-approved drug, can reverse MeHg-induced premature neuronal differentiation via CREB/CBP repulsion. These findings provide insights into ASD etiology, its underlying mechanism, and a potential therapeutic strategy.

Activation of the CREB Coactivator CRTC2 by Aberrant Mitogen Signaling promotes oncogenic functions in HPV16 positive head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer worldwide and incidence rates are continuing to rise globally. Patients often present with locally advanced disease and a staggering 50% chance of relapse following treatment. Aberrant activation of adaptive response signaling pathways, such as the cAMP/PKA pathway, induce an array of genes associated with known cancer pathways that promote tumorigenesis and drug resistance. We identified the cAMP Regulated Transcription Coactivator 2 (CRTC2) to be overexpressed and constitutively activated in HNSCCs and this confers poor prognosis. CRTCs are regulated through their subcellular localization and we show that CRTC2 is exclusively nuclear in HPV(+) HNSCC, thus constitutively active, due to non-canonical Mitogen-Activated Kinase Kinase 1 (MEKK1)-mediated activation via a MEKK1-p38 signaling axis. Loss-of-function and pharmacologic inhibition experiments decreased CRTC2/CREB transcriptional activity by reducing nuclear CRTC2 via nuclear import inhibition and/or by eviction of CRTC2 from the nucleus. This shift in localization was associated with decreased proliferation, migration, and invasion. Our results suggest that small molecules that inhibit nuclear CRTC2 and p38 activity may provide therapeutic benefit to patients with HPV(+) HNSCC.

Emerging Role of CREB in Epithelial to Mesenchymal Plasticity of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive solid malignancy with a high rate of metastasis and therapeutic resistance as its major hallmarks. Although a defining mutational event in pancreatic cancer initiation is the presence of oncogenic KRAS, more advanced PDAC lesions accumulate additional genomic alterations, including loss of tumor suppressor gene TP53. Co-occurrence of mutant KRAS and TP53 in PDAC promotes hyperactivation of cancer cell signaling pathways driving epithelial to mesenchymal plasticity (EMP). The cellular process of EMP influences the biological behavior of cancer cells by increasing their migratory and invasive properties, thus promoting metastasis. Our previous work has demonstrated that oncogenic KRAS-mediated activation of cyclic AMP response element-binding protein 1 (CREB) is one of the critical drivers of PDAC aggressiveness. The therapeutic approach of targeting this key transcription factor attenuates tumor burden in genetically engineered mouse models (GEMMs) of this disease. Herein, we discuss the significant role of CREB in perpetuating disease aggressiveness and therapeutic resistance through the EMP process. Furthermore, this review updates the therapeutic implications of targeting CREB, highlighting the challenges and emerging approaches in PDAC.

Design, Synthesis and Biological Evaluation of Prodrugs of 666-15 as Inhibitors of CREB-Mediated Gene Transcription

cAMP-response element binding protein (CREB) is a transcription factor involved in multiple cancers. Chemical inhibitors of CREB represent potential anticancer agents. We previously identified 666-15 as a potent CREB inhibitor. While 666-15 showed efficacious anticancer activity in vivo through intraperitoneal (IP) injection, its oral bioavailability is limited. To increase its oral bioavailability, we describe synthesis and evaluation of prodrugs based on 666-15. The amino acid esters were attempted, but they were not stable for detailed characterization. The corresponding sulfate and phosphates were prepared. The sulfate of 666-15 was too stable to release 666-15 while the phosphates were converted into 666-15 with half-lives of ∼2 h. Phosphate 3 was also a potent CREB inhibitor with anti-breast cancer activity. Furthermore, compound 3 showed much improved oral bioavailability at 38%. These studies support that 3 can be used as an oral CREB inhibitor while IP administration of 666-15 is preferred for in vivo applications.

Melanocortin 1 receptor activation protects against alpha-synuclein pathologies in models of Parkinson's disease

Background

Epidemiological studies suggest a link between the melanoma-related pigmentation gene melanocortin 1 receptor (MC1R) and risk of Parkinson’s disease (PD). We previously showed that MC1R signaling can facilitate nigrostriatal dopaminergic neuron survival. The present study investigates the neuroprotective potential of MC1R against neurotoxicity induced by alpha-synuclein (αSyn), a key player in PD genetics and pathogenesis.

Methods

Nigral dopaminergic neuron toxicity induced by local overexpression of aSyn was assessed in mice that have an inactivating mutation of MC1R, overexpress its wild-type transgene, or were treated with MC1R agonists. The role of nuclear factor erythroid 2-related factor 2 (Nrf2) in MC1R-mediated protection against αSyn was characterized in vitro. Furthermore, MC1R expression was determined in human postmortem midbrain from patients with PD and unaffected subjects.

Results

Targeted expression of αSyn in the nigrostriatal pathway induced exacerbated synuclein pathologies in MC1R mutant mice, which were accompanied by neuroinflammation and altered Nrf2 responses, and reversed by the human MC1R transgene. Two MC1R agonists were neuroprotective against αSyn-induced dopaminergic neurotoxicity. In vitro experiments showed that Nrf2 was a necessary mediator of MC1R effects. Lastly, MC1R was present in dopaminergic neurons in the human substantia nigra and appeared to be reduced at the tissue level in PD patients.

Conclusion

Our study supports an interaction between MC1R and αSyn that can be mediated by neuronal MC1R possibly through Nrf2. It provides evidence for MC1R as a therapeutic target and a rationale for development of MC1R-activating strategies for PD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-022-00520-4.

Systematical analysis reveals a strong cancer relevance of CREB1-regulated genes

The transcription factor cyclic-AMP response element-binding protein 1 (CREB1) responds to cAMP level and controls the expression of target genes, which regulates nutrition partitioning. The promoters of CREB1-targeted genes responsive to cAMP have been extensively investigated and characterized with the presence of both cAMP response element and TATA box. Compelling evidence demonstrates that CREB1 also plays an essential role in promoting tumor development. However, only very few genes required for cell survival, proliferation and migration are known to be constitutively regulated by CREB1 in tumors. Their promoters mostly do not harbor any cAMP response element. Thus, it is very likely that CREB1 regulates the expressions of distinct sets of target genes in normal tissues and tumors. The whole gene network constitutively regulated by CREB1 in tumors has remained unrevealed. Here, we employ a systematical and integrative approach to decipher this gene network in the context of both tissue cultured cancer cells and patient samples. We combine transcriptomic, Rank-Rank Hypergeometric Overlap, and Chipseq analysis, to define and characterize CREB1-regulated genes in a multidimensional fashion. A strong cancer relevance of those top-ranked targets, which meet the most stringent criteria, is eventually verified by overall survival analysis of cancer patients. These findings strongly suggest the importance of genes constitutively regulated by CREB1 for their implicative involvement in promoting tumorigenesis.

Fibroblast growth factor receptor 3 activates a network of profibrotic signaling pathways to promote fibrosis in systemic sclerosis

Aberrant activation of fibroblasts with progressive deposition of extracellular matrix is a key feature of systemic sclerosis (SSc), a prototypical idiopathic fibrotic disease. Here, we demonstrate that the profibrotic cytokine transforming growth factor β selectively up-regulates fibroblast growth factor receptor 3 (FGFR3) and its ligand FGF9 to promote fibroblast activation and tissue fibrosis, leading to a prominent FGFR3 signature in the SSc skin. Transcriptome profiling, in silico analysis and functional experiments revealed that FGFR3 induces multiple profibrotic pathways including endothelin, interleukin-4, and connective tissue growth factor signaling mediated by transcription factor CREB (cAMP response element-binding protein). Inhibition of FGFR3 signaling by fibroblast-specific knockout of FGFR3 or FGF9 or pharmacological inhibition of FGFR3 blocked fibroblast activation and attenuated experimental skin fibrosis in mice. These findings characterize FGFR3 as an upstream regulator of a network of profibrotic mediators in SSc and as a potential target for the treatment of fibrosis.

Diel rhythm of urotensin I mRNA expression and its involvement in the locomotor activity and appetite regulation in olive flounder Paralichthys olivaceus

Urotensin I (UI), a member of the corticotropin-releasing hormone family of peptides, regulates a diverse array of physiological functions, including appetite regulation, defensive behavior and stress response. In this study, firstly, the tissue-specific distribution of UI mRNA in olive flounder (Paralichthys olivaceus) was characterized and we found that UI mRNA was highly expressed in caudal neurosecretory system (CNSS) tissue. Secondly, alignment analysis found that a conserved cAMP response binding (CREB) site and a TATA element were located in the proximal promoter of UI gene. In addition, treatment of forskolin activatated cAMP-CREB pathway and induced the up-regulation of UI mRNA in cultured CNSS, suggesting the role of CREB in regulating the UI mRNA expression. Furthermore, plasma UI concentration and UI mRNA in CNSS showed obvious daily rhythm, with higher values in the daytime while lower values in the nighttime. Thirdly, using bold personality (BP) and shy personality (SP) flounder as an animal model, we found that flounder exhibited significantly higher locomotor activity in the nighttime than in the daytime (P < 0.001), and BP flounder showed significantly higher locomotor activity (P < 0.001) compared with SP flounder both in the daytime and nighttime. Analysis of feeding behavior revealed that BP flounder showed a shorter latency to feed and more attacks to prey. Furthermore, the qPCR and immunohistochemistry results showed that BP flounder expressed significantly lower level of UI mRNA and protein in CNSS tissue. Collectively, our study suggested that the UI plays an important role in locomotor activity and appetite regulation, which provides a basis for understanding the mechanism of defensive behavior and animal personality in flounder.

Mucosal acidosis elicits a unique molecular signature in epithelia and intestinal tissue mediated by GPR31-induced CREB phosphorylation

Metabolic changes associated with tissue inflammation result in significant extracellular acidosis (EA). Within mucosal tissues, intestinal epithelial cells (IEC) have evolved adaptive strategies to cope with EA through the up-regulation of SLC26A3 to promote pH homeostasis. We hypothesized that EA significantly alters IEC gene expression as an adaptive mechanism to counteract inflammation. Using an unbiased RNA sequencing approach, we defined the impact of EA on IEC gene expression to define molecular mechanisms by which IEC respond to EA. This approach identified a unique gene signature enriched in cyclic AMP response element-binding protein (CREB)-regulated gene targets. Utilizing loss- and gain-of-function approaches in cultured epithelia and murine colonoids, we demonstrate that EA elicits prominent CREB phosphorylation through cyclic AMP-independent mechanisms that requires elements of the mitogen-activated protein kinase signaling pathway. Further analysis revealed that EA signals through the G protein-coupled receptor GPR31 to promote induction of FosB, NR4A1, and DUSP1. These studies were extended to an in vivo murine model in conjunction with colonization of a pH reporter Escherichia coli strain that demonstrated significant mucosal acidification in the TNFΔARE model of murine ileitis. Herein, we observed a strong correlation between the expression of acidosis-associated genes with bacterial reporter sfGFP intensity in the distal ileum. Finally, the expression of this unique EA-associated gene signature was increased during active inflammation in patients with Crohn's disease but not in the patient control samples. These findings establish a mechanism for EA-induced signals during inflammation-associated acidosis in both murine and human ileitis.

Mud Loss Restricts Yki-Dependent Hyperplasia in Drosophila Epithelia

Tissue development demands precise control of cell proliferation and organization, which is achieved through multiple conserved signaling pathways and protein complexes in multicellular animals. Epithelia are a ubiquitous tissue type that provide diverse functions including physical protection, barrier formation, chemical exchange, and secretory activity. However, epithelial cells are also a common driver of tumorigenesis; thus, understanding the molecular mechanisms that control their growth dynamics is important in understanding not only developmental mechanisms but also disease. One prominent pathway that regulates epithelial growth is the conserved Hippo/Warts/Yorkie network. Hippo/Warts inactivation, or activating mutations in Yorkie that prevent its phosphorylation (e.g., YkiS168A), drive hyperplastic tissue growth. We recently reported that loss of Mushroom body defect (Mud), a microtubule-associated protein that contributes to mitotic spindle function, restricts YkiS168A-mediated growth in Drosophila imaginal wing disc epithelia. Here we show that Mud loss alters cell cycle progression and triggers apoptosis with accompanying Jun kinase (JNK) activation in YkiS168A-expressing discs. To identify additional molecular insights, we performed RNAseq and differential gene expression profiling. This analysis revealed that Mud knockdown in YkiS168A-expressing discs resulted in a significant downregulation in expression of core basement membrane (BM) and extracellular matrix (ECM) genes, including the type IV collagen gene viking. Furthermore, we found that YkiS168A-expressing discs accumulated increased collagen protein, which was reduced following Mud knockdown. Our results suggest that ECM/BM remodeling can limit untoward growth initiated by an important driver of tumor growth and highlight a potential regulatory link with cytoskeleton-associated genes.

CB1R regulates soluble leptin receptor levels via CHOP, contributing to hepatic leptin resistance

The soluble isoform of leptin receptor (sOb-R), secreted by the liver, regulates leptin bioavailability and bioactivity. Its reduced levels in diet-induced obesity (DIO) contribute to hyperleptinemia and leptin resistance, effects that are regulated by the endocannabinoid (eCB)/CB₁R system. Here we show that pharmacological activation/blockade and genetic overexpression/deletion of hepatic CB₁R modulates sOb-R levels and hepatic leptin resistance. Interestingly, peripheral CB₁R blockade failed to reverse DIO-induced reduction of sOb-R levels, increased fat mass and dyslipidemia, and hepatic steatosis in mice lacking C/EBP homologous protein (CHOP), whereas direct activation of CB₁R in wild-type hepatocytes reduced sOb-R levels in a CHOP-dependent manner. Moreover, CHOP stimulation increased sOb-R expression and release via a direct regulation of its promoter, while CHOP deletion reduced leptin sensitivity. Our findings highlight a novel molecular aspect by which the hepatic eCB/CB₁R system is involved in the development of hepatic leptin resistance and in the regulation of sOb-R levels via CHOP.

When the human body has stored enough energy from food, it releases a hormone called leptin that travels to the brain and stops feelings of hunger. This hormone moves through the bloodstream and can affect other organs, such as the liver, which also help control our body’s energy levels. Most people with obesity have very high levels of leptin in their blood, but are resistant to its effects and will therefore continue to feel hungry despite having stored enough energy.

One of the proteins that controls the levels of leptin is a receptor called sOb-R, which is released by the liver and binds to leptin as it travels in the blood. Individuals with high levels of this receptor often have less free leptin in their bloodstream and a lower body weight. Another protein that helps the body to regulate its energy levels is the cannabinoid-1 receptor, or CB1R for short. In people with obesity, this receptor is overactive and has been shown to contribute to leptin resistance, which is when the brain becomes less receptive to leptin. Previous work in mice showed that blocking CB1R reduced the levels of leptin and allowed mice to react to this hormone normally again, but it remained unclear whether CB1R affects how other organs, such as the liver, respond to leptin.

To answer this question, Drori et al. blocked the CB1R receptor in the liver of mice eating a high-fat diet, either by using a drug or by deleting the gene that codes for this protein. This caused mice to have higher levels of sOb-R circulating in their bloodstream. Further experiments showed that this change in sOb-R was caused by the levels of a protein called CHOP increasing in the liver when CB1R was blocked. Drori et al. found that inhibiting CB1R caused these obese mice to lose weight and have healthier, less fatty livers as a result of their livers no longer being resistant to the effects of leptin.

Scientists, doctors and pharmaceutical companies are trying to develop new strategies to combat obesity. The results from these experiments suggest that blocking CB1R in the liver could allow this organ to react to leptin appropriately again. Drugs blocking CB1R, including the one used in this study, will be tested in clinical trials and could provide a new approach for treating obesity.

Engineering a Synthesis-Friendly Constitutive Promoter for Mammalian Cell Expression

Since cell-based therapies require the constitutive and stable expression of therapeutic transgenes, lentiviral infection is commonly used to integrate gene material regulated by standard constitutive promoters. Unfortunately, none of the standard or synthetic constitutive promoters can be easily synthesized at low cost due to the presence of repeated subsequences. Thus, in this paper, we designed a synthetic constitutive promoter (named SFCp) that can drive the expression of fluorescent proteins that subsequently trafficked to intended subcellular localizations and the expression of synthetic proteins that rewired the cellular response of Ca²⁺ to cell morphology changes. Furthermore, SFCp can be used to avoid sequence homology that can theoretically result in loss of genetic material by homologous recombination in tandem constructs. As gene synthesis becomes an indispensable tool in the arsenal of synthetic biology, it is essential to develop a toolbox of gene synthesis friendly components for cell engineering such as constitutive promoters.

Effect of the neuropeptide phoenixin and its receptor GPR173 during folliculogenesis

Folliculogenesis is a complex process, defined by the growth and development of follicles from the primordial population. Granulosa cells (GCs) play a vital role in every stage of follicular growth through proliferation, acquisition of gonadotropic responsiveness, steroidogenesis and production of autocrine/paracrine factors. A recently discovered hypothalamic neuropeptide phoenixin is involved in the regulation of the reproductive system. Phoenixin acts through its receptor, G protein-coupled receptor 173 (GPR173), to activate the cAMP/PKA pathway leading to the phosphorylation of CREB (pCREB). Here, we demonstrated the expression patterns of phoenixin and GPR173 in human ovary and explored its role in folliculogenesis. Phoenixin and GPR173 were both expressed in the human ovarian follicle, with increased expression in GCs as the follicle grows. Phoenixin treatment at 100 nM for 24 h induced the proliferation of human non-luteinized granulosa cell line, HGrC1 and significantly increased the expression levels of CYP19A1, FSHR, LHR and KITL, but decreased NPPC expression levels. These effects were suppressed by GPR173 siRNA. The expression level of CREB1, pCREB and estradiol (E2) production in the culture medium was significantly enhanced by phoenixin treatment in a concentration-dependent manner. Phoenixin also significantly increased the follicular area in a murine ovarian tissue culture model, leading to an increased number of ovulated oocytes with a higher level of maturation. Taken together, our data demonstrate that phoenixin is an intraovarian factor that promotes follicular growth through its receptor GPR173 by accelerating proliferation of GCs, inducing E2 production and increasing the expression of genes related to follicle development.

Dietary Flavonoids Interaction with CREB-BDNF Pathway: An Unconventional Approach for Comprehensive Management of Epilepsy

cAMP response element binding protein (CREB) is a key transcriptional regulator that regulates the transcription of genes related with neuronal differentiation, synaptic plasticity, learning and memory. Brain derived neurotrophic factor (BDNF), is a CREB dependent gene which plays a pivotal role in the pathogenesis of epilepsy and central comorbid conditions associated with epilepsy. However, the beneficial or detrimental consequences of CREB-BDNF activation on the induction and/or progression of seizures depend specifically on the region of brain involved and the time of activation. The bioactive molecules that alter the activity of CREB in a way to have specialized effects in different brain regions and neural circuits involved could potentially be utilized for therapeutic purposes. Flavonoids are the polyphenolic compounds which lead to phosphorylation of CREB in the hippocampus, followed by increase in extracellular signal regulated kinase (ERK) and BDNF. Several members of flavonoid family have also showed suppression of epileptic seizures via interaction with CREB/BDNF pathway. Moreover, epilepsy is often accompanied by a number of behavioural and psychological comorbid conditions that further gets aggravated by the use of conventional antiepileptic drug therapy. Multiple studies have also supported the beneficial effects of flavonoids in cognitive and memory impairments by upregulation of CREB-BDNF pathway. The current review is an attempt to collate the available preclinical and clinical studies to establish the therapeutic potential of various dietary flavonoids in comprehensive management of epilepsy with relation to CREB-BDNF pathway.

Regulation of dopaminergic neuronal phenotypes by the estrogen-related receptor gamma ligand GSK4716 via the activation of CREB signaling

Midbrain dopaminergic (DAergic) neurotransmission plays a crucial role in regulating motor, cognitive, and emotional functions. The orphan nuclear receptor estrogen-related receptor gamma (ERRγ) is highly expressed in the adult brain and in the developing fetal brain. Our previous study showed the relevance of ERRγ in the regulation of the DAergic neuronal phenotype with the upregulation of dopamine synthesizing tyrosine hydroxylase (TH) and dopamine transporter (DAT) and the possibility that ERRγ could be a novel target for regulating DAergic neuronal differentiation. In this study, we examined whether ERRγ ligands could be small molecule regulators of DAergic phenotypes. The ERRγ agonist GSK4716 increased DAT and TH expression, and the ERRγ inverse agonist GSK5182 attenuated the retinoic acid-induced upregulation of DAT and TH in differentiated SH-SY5Y cells. We found that biphasic activation of the protein kinase A/cyclic AMP response element-binding (CREB) protein signaling pathway was involved in the GSK4716-induced increase in the DAergic phenotype in SH-SY5Y cells. CREB signaling activated as early as 3 h after GSK4716 treatment in an ERRγ-independent manner, but increased following ERRγ activation after 3 days. Protein kinase A inhibitor H-89 attenuated GSK4716-induced DAT and TH upregulation. In primary cultured DAergic neurons, GSK4716 increased neurite length and the number of DAT and TH-double-positive (DAT + TH+) neurons compared to that in control cells. These findings suggest that ERRγ ligands could serve as useful chemical tools for obtaining a better understanding of the regulation of DAergic phenotypes and might facilitate the development of small molecule therapeutics to treat DA-related neurological diseases.

Adaptation to inflammatory acidity through neutrophil-derived adenosine regulation of SLC26A3

Acute intestinal inflammation includes the early accumulation of neutrophils (PMN). Based on recent evidence that PMN infiltration "imprints" changes in the local tissue environment through local oxygen depletion and the release of adenine nucleotides, we hypothesized that the interaction between transmigrating PMN and intestinal epithelial cells (IECs) results in inflammatory acidification of the tissue. Using newly developed tools, we revealed that active PMN transepithelial migration (TEM) significantly acidifies the local microenvironment, a decrease of nearly 2 pH units. Using unbiased approaches, we sought to define acid-adaptive pathways elicited by PMN TEM. Given the significant amount of adenosine (Ado) generated during PMN TEM, we profiled the influence of Ado on IECs gene expression by microarray and identified the induction of SLC26A3, the major apical Cl^-/HCO₃^- exchanger in IECs. Utilizing loss- and gain-of-function approaches, as well as murine and human colonoids, we demonstrate that Ado-induced SLC26A3 promotes an adaptive IECs phenotype that buffers local pH during active inflammation. Extending these studies, chronic murine colitis models were used to demonstrate that SLC26A3 expression rebounds during chronic DSS-induced inflammation. In conclusion, Ado signaling during PMN TEM induces an adaptive tissue response to inflammatory acidification through the induction of SLC26A3 expression, thereby promoting pH homeostasis.

In Vivo Imaging of the Coupling between Neuronal and CREB Activity in the Mouse Brain

Sensory experiences cause long-term modifications of neuronal circuits by modulating activity-dependent transcription programs that are vital for regulation of long-term synaptic plasticity and memory. However, it has not been possible to precisely determine the interaction between neuronal activity patterns and transcription factor activity. Here we present a technique using two-photon fluorescence lifetime imaging (2pFLIM) with new FRET biosensors to chronically image in vivo signaling of CREB, an activity-dependent transcription factor important for synaptic plasticity, at single-cell resolution. Simultaneous imaging of the red-shifted CREB sensor and GCaMP permitted exploration of how experience shapes the interplay between CREB and neuronal activity in the neocortex of awake mice. Dark rearing increased the sensitivity of CREB activity to Ca²⁺ elevations and prolonged the duration of CREB activation to more than 24 h in the visual cortex. This technique will allow researchers to unravel the transcriptional dynamics underlying experience-dependent plasticity in the brain.

Discovery of a Synergistic Inhibitor of cAMP-Response Element Binding Protein (CREB)-Mediated Gene Transcription with -

CREB is a transcription factor implicated in the pathogenesis of multiple cancers. Targeting CREB is a promising strategy to develop potential cancer therapeutics. Previously, we identified 666-15 as a potent CREB inhibitor. Herein, we designed an ester prodrug of 666-15 through a long-range O,N-acyl transfer reaction for improved aqueous solubility. Unexpectedly, we discovered a small molecule 11 (653-47) that can potentiate the CREB inhibitory activity of 666-15 although 653-47 alone does not inhibit CREB.

Exclusive Temporal Stimulation of IL-10 Expression in LPS-Stimulated Mouse Macrophages by cAMP Inducers and Type I Interferons

Expression of the key anti-inflammatory cytokine IL-10 in lipopolysaccharide (LPS)-stimulated macrophages is mediated by a delayed autocrine/paracrine loop of type I interferons (IFN) to ensure timely attenuation of inflammation. We have previously shown that cAMP synergizes with early IL-10 expression by LPS, but is unable to amplify the late type I IFN-dependent activity. We now examined the mechanism of this synergistic transcription in mouse macrophages at the promoter level, and explored the crosstalk between type I IFN signaling and cAMP, using the β-adrenergic receptor agonist, isoproterenol, as a cAMP inducer. We show that silencing of the type I IFN receptor enables isoproterenol to synergize with LPS also at the late phase, implying that autocrine type I IFN activity hinders synergistic augmentation of LPS-stimulated IL-10 expression by cAMP at the late phase. Furthermore, IL-10 expression in LPS-stimulated macrophages is exclusively stimulated by either IFNα or isoproterenol. We identified a set of two proximate and inter-dependent cAMP response element (CRE) sites that cooperatively regulate early IL-10 transcription in response to isoproterenol-stimulated CREB and that further synergize with a constitutive Sp1 site. At the late phase, up-regulation of Sp1 activity by LPS-stimulated type I IFN is correlated with loss of function of the CRE sites, suggesting a mechanism for the loss of synergism when LPS-stimulated macrophages switch to type I IFN-dependent IL-10 expression. This report delineates the molecular mechanism of cAMP-accelerated IL-10 transcription in LPS-stimulated murine macrophages that can limit inflammation at its onset.

The Possible Pathogenesis of Idiopathic Pulmonary Fibrosis considering MUC5B

Background

Overexpression of the MUC5B protein is associated with idiopathic pulmonary fibrosis (IPF), but little information is available regarding the pathogenic effects and regulatory mechanisms of overexpressed MUC5B in IPF.

Main Body

The overexpression of MUC5B in terminal bronchi and honeycomb cysts produces mucosal host defensive dysfunction in the distal airway which may play an important role in the development of IPF. This review addresses the possible association of overexpression of MUC5B, with MUC5B promoter polymorphism, MUC5B gene epigenetic changes, effects of some transcriptional factors, and inflammatory mediators in IPF. In addition, the associated signaling pathways which may influence the expression of MUC5B are also discussed.

Conclusion

This work has important implications for further exploration of the mechanisms of overexpression of MUC5B in IPF, and future personalized treatment.

Anabolic and Pro-metabolic Functions of CREB-CRTC in Skeletal Muscle: Advantages and Obstacles for Type 2 Diabetes and Cancer Cachexia

cAMP is one of the earliest described mediators of hormone action in response to physiologic stress that allows acute stress responses and adaptation in every tissue. The classic role of cAMP signaling in metabolic tissues is to regulate nutrient partitioning. In response to acute stress, such as epinephrine released during strenuous exercise or fasting, intramuscular cAMP liberates glucose from glycogen and fatty acids from triglycerides. In the long-term, activation of Gs-coupled GPCRs stimulates muscle growth (hypertrophy) and metabolic adaptation through multiple pathways that culminate in a net increase of protein synthesis, mitochondrial biogenesis, and improved metabolic efficiency. This review focuses on regulation, function, and transcriptional targets of CREB (cAMP response element binding protein) and CRTCs (CREB regulated transcriptional coactivators) in skeletal muscle and the potential for targeting this pathway to sustain muscle mass and metabolic function in type 2 diabetes and cancer. Although the muscle-autonomous roles of these proteins might render them excellent targets for both conditions, pharmacologic targeting must be approached with caution. Gain of CREB-CRTC function is associated with excess liver glucose output in type 2 diabetes, and growing evidence implicates CREB-CRTC activation in proliferation and invasion of different types of cancer cells. We conclude that deeper investigation to identify skeletal muscle specific regulatory mechanisms that govern CREB-CRTC transcriptional activity is needed to safely take advantage of their potent effects to invigorate skeletal muscle to potentially improve health in people with type 2 diabetes and cancer.

Mechanistic role of the CREB-regulated transcription coactivator 1 in cardiac hypertrophy

The sympathetic nervous system is the main stimulator of cardiac function. While acute activation of the β-adrenoceptors exerts positive inotropic and lusitropic effects by increasing cAMP and Ca²⁺, chronically enhanced sympathetic tone with changed β-adrenergic signaling leads to alterations of gene expression and remodeling. The CREB-regulated transcription coactivator 1 (CRTC1) is activated by cAMP and Ca²⁺. In the present study, the regulation of CRTC1 in cardiomyocytes and its effect on cardiac function and growth was investigated. In cardiomyocytes, isoprenaline induced dephosphorylation, and thus activation of CRTC1, which was prevented by propranolol. Crtc1-deficient mice exhibited left ventricular dysfunction, hypertrophy and enlarged cardiomyocytes. However, isoprenaline-induced contractility of isolated trabeculae or phosphorylation of cardiac troponin I, cardiac myosin-binding protein C, phospholamban, and ryanodine receptor were not altered, suggesting that cardiac dysfunction was due to the global lack of Crtc1. The mRNA and protein levels of the Gα_q GTPase activating protein regulator of G-protein signaling 2 (RGS2) were lower in hearts of Crtc1-deficient mice. Chromatin immunoprecipitation and reporter gene assays showed stimulation of the Rgs2 promoter by CRTC1. In Crtc1-deficient cardiomyocytes, phosphorylation of the Gα_q-downstream kinase ERK was enhanced. CRTC1 content was higher in cardiac tissue from patients with aortic stenosis or hypertrophic cardiomyopathy and from two murine models mimicking these diseases. These data suggest that increased CRTC1 in maladaptive hypertrophy presents a compensatory mechanism to delay disease progression in part by enhancing Rgs2 gene transcription. Furthermore, the present study demonstrates an important role of CRTC1 in the regulation of cardiac function and growth.

3-Aminobenzamide Prevents Concanavalin A-Induced Acute Hepatitis by an Anti-inflammatory and Anti-oxidative Mechanism

BACKGROUND AND AIMS

Concanavalin A is known to activate T cells and to cause liver injury and hepatitis, mediated in part by secretion of TNFα from macrophages. Poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors have been shown to prevent tissue damage in various animal models of inflammation. The objectives of this study were to evaluate the efficacy and mechanism of the PARP-1 inhibitor 3-aminobenzamide (3-AB) in preventing concanavalin A-induced liver damage.

METHODS

We tested the in vivo effects of 3-AB on concanavalin A-treated mice, its effects on lipopolysaccharide (LPS)-stimulated macrophages in culture, and its ability to act as a scavenger in in vitro assays.

RESULTS

3-AB markedly reduced inflammation, oxidative stress, and liver tissue damage in concanavalin A-treated mice. In LPS-stimulated RAW264.7 macrophages, 3-AB inhibited NFκB transcriptional activity and subsequent expression of TNFα and iNOS and blocked NO production. In vitro, 3-AB acted as a hydrogen peroxide scavenger. The ROS scavenger N-acetylcysteine (NAC) and the ROS formation inhibitor diphenyleneiodonium (DPI) also inhibited TNFα expression in stimulated macrophages, but unlike 3-AB, NAC and DPI were unable to abolish NFκB activity. PARP-1 knockout failed to affect NFκB and TNFα suppression by 3-AB in stimulated macrophages.

CONCLUSIONS

Our results suggest that 3-AB has a therapeutic effect on concanavalin A-induced liver injury by inhibiting expression of the key pro-inflammatory cytokine TNFα, via PARP-1-independent NFκB suppression and via an NFκB-independent anti-oxidative mechanism.

The Past, Present, and Future of Phosphodiesterase-4 Modulation for Age-Induced Memory Loss

The purpose of this chapter is to highlight the state of progress for phosphodiesterase-4 (PDE4) modulation as a potential therapeutic for psychiatric illness, and to draw attention to particular hurdles and obstacles that must be overcome in future studies to develop PDE4-mediated therapeutics. Pathological and non-pathological related memory loss will be the focus of the chapter; however, we will at times also touch upon other psychiatric illnesses like anxiety and depression. First, we will provide a brief background of PDE4, and the rationale for its extensive study in cognition. Second, we will explore fundamental differences in individual PDE4 subtypes, and then begin to address differences between pathological and non-pathological aging. Alterations of cAMP/PDE4 signaling that occur within normal vs. pathological aging, and the potential for PDE4 modulation to combat these alterations within each context will be described. Finally, we will finish the chapter with obstacles that have hindered the field, and future studies and alternative viewpoints that need to be addressed. Overall, we hope this chapter will demonstrate the incredible complexity of PDE4 signaling in the brain, and will be useful in forming a strategy to develop future PDE4-mediated therapeutics for psychiatric illnesses.

Upregulation of lactate dehydrogenase a by 14-3-3ζ leads to increased glycolysis critical for breast cancer initiation and progression

Metabolic reprogramming is a hallmark of cancer. Elevated glycolysis in cancer cells switches the cellular metabolic flux to produce more biological building blocks, thereby sustaining rapid proliferation. Recently, new evidence has emerged that metabolic dysregulation may occur at early-stages of neoplasia and critically contribute to cancer initiation. Here, our bioinformatics analysis of microarray data from early-stages breast neoplastic lesions revealed that 14-3-3ζ expression is strongly correlated with the expression of canonical glycolytic genes, particularly lactate dehydrogenase A (LDHA). Experimentally, increasing 14-3-3ζ expression in human mammary epithelial cells (hMECs) up-regulated LDHA expression, elevated glycolytic activity, and promoted early transformation. Knockdown of LDHA in the 14-3-3ζ-overexpressing hMECs significantly reduced glycolytic activity and inhibited transformation. Mechanistically, 14-3-3ζ overexpression activates the MEK-ERK-CREB axis, which subsequently up-regulates LDHA. In vivo, inhibiting the activated the MEK/ERK pathway in 14-3-3ζ-overexpressing hMEC-derived MCF10DCIS.COM lesions led to effective inhibition of tumor growth. Therefore, targeting the MEK/ERK pathway could be an effective strategy for intervention of 14-3-3ζ-overexpressing early breast lesions. Together, our data demonstrate that overexpression of 14-3-3ζ in early stage pre-cancerous breast epithelial cells may trigger an elevated glycolysis and transcriptionally up-regulating LDHA, thereby contributes to human breast cancer initiation.

CRTC1 mediates preferential transcription at neuronal activity-regulated CRE/TATA promoters

Gene expression mediated by the transcription factor cAMP-responsive element-binding protein (CREB) is essential for a wide range of brain processes. The transcriptional coactivartor CREB-regulated transcription coactivator-1 (CRTC1) is required for efficient induction of CREB target genes during neuronal activity. However, the mechanisms regulating induction of specific CREB/CRTC1-dependent genes during neuronal activity remain largely unclear. Here, we investigated the molecular mechanisms regulating activity-dependent gene transcription upon activation of the CREB/CRTC1 signaling pathway in neurons. Depolarization and cAMP signals induce preferential transcription of activity-dependent genes containing promoters with proximal CRE/TATA sequences, such as c-fos, Dusp1, Nr4a1, Nr4a2 and Ptgs2, but not genes with proximal CRE/TATA-less promoters (e.g. Nr4a3, Presenilin-1 and Presenilin-2). Notably, biochemical and chromatin immunoprecipitation analyses reveal constitutive binding of CREB to target gene promoters in the absence of neuronal activity, whereas recruitment of CRTC1 to proximal CRE/TATA promoters depends on neuronal activity. Neuronal activity induces rapid CRTC1 dephosphorylation, nuclear translocation and binding to endogenous CREB. These results indicate that neuronal activity induces a preferential binding of CRTC1 to the transcriptional complex in CRE/TATA-containing promoters to engage activity-dependent transcription in neurons.

Linking CREB function with altered metabolism in murine fibroblast-based model cell lines

The cAMP-responsive element binding protein CREB is frequently overexpressed and activated in tumors of distinct histology, leading to enhanced proliferation, migration, invasion and angiogenesis as well as reduced apoptosis. The de-regulated expression of CREB might be linked with transcriptional as well as post-transcriptional regulation mechanisms. We show here that altered CREB expression levels and function are associated with changes in the cellular metabolism. Using comparative proteome-based analysis an altered expression pattern of proteins involved in the cellular metabolism in particular in glycolysis was found upon CREB down-regulation in HER-2/neu-transfected cell lines. This was associated with diminished expression levels of the glucose transporter 1, reduced glucose uptake and reduced glycolytic activity in HER-2/neu-transfected cells with down-regulated CREB when compared to HER-2/neu⁺ cells. Furthermore, hypoxia-induced CREB activity resulted in changes of the metabolism in HER-2/neu transfected cells. Low pH values in the supernatant of HER-2/neu transformants were restored by CREB down-regulation, but further decreased by hypoxia. The altered intracellular pH values were associated with a distinct expression of lactate dehydrogenase, and its substrate lactate. Moreover, enhanced phosphorylation of CREB on residue Ser133 was accompanied by a down-regulation of pERK and an up-regulation of pAKT. CREB promotes the detoxification of ROS by catalase, therefore protecting the mitochondrial activity under oxidative stress. These data suggest that there might exists a link between CREB function and the altered metabolism in HER-2/neu-transformed cells. Thus, targeting these altered metabolic pathways might represent an attractive therapeutic approach at least for the treatment of patients with HER-2/neu overexpressing tumors.

MSK1 regulates transcriptional induction of Arc/Arg3.1 in response to neurotrophins

The immediate early gene activity‐regulated cytoskeletal protein (Arc)/Arg3.1 and the neurotrophin brain‐derived neurotrophic factor (BDNF) play important roles in synaptic plasticity and learning and memory in the mammalian brain. However, the mechanisms by which BDNF regulates the expression of Arc/Arg3.1 are unclear. In this study, we show that BDNF acts via the ERK1/2 pathway to activate the nuclear kinase mitogen‐ and stress‐activated protein kinase 1 (MSK1). MSK1 then induces Arc/Arg3.1 expression via the phosphorylation of histone H3 at the Arc/Arg3.1 promoter. MSK1 can also phosphorylate the transcription factor cyclic‐AMP response element‐binding protein (CREB) on Ser133. However, this is not required for BDNF‐induced Arc.Arg3.1 transcription as a Ser133Ala knockin mutation had no effect on Arc/Arg3.1 induction. In parallel, ERK1/2 directly activates Arc/Arg3.1 mRNA transcription via at least one serum response element on the promoter, which bind a complex of the Serum Response Factor (SRF) and a Ternary Complex Factor (TCF).

Context and Auditory Fear are Differentially Regulated by HDAC3 Activity in the Lateral and Basal Subnuclei of the Amygdala

Histone acetylation is a fundamental epigenetic mechanism that is dynamically regulated during memory formation. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) compete to modulate histone acetylation, allowing for rapid changes in acetylation in response to a learning event. HDACs are known to be powerful negative regulators of memory formation, but it is not clear whether this function depends on HDAC enzymatic activity per se. Here, we tested whether the enzymatic activity of an individual Class I HDAC, HDAC3, has a role in fear memory formation in subregions of the hippocampus and amygdala. We found that fear conditioning drove expression of the immediate early genes cFos and Nr4a2 in the hippocampus, which coincided with reduced HDAC3 occupancy at these promoters. Using a dominant-negative, deacetylase-dead point mutant virus (AAV-HDAC3(Y298H)-v5), we found that selectively blocking HDAC3 deacetylase activity in either the dorsal hippocampus or basal nucleus of the amygdala enhanced context fear without affecting tone fear. Blocking HDAC3 activity in the lateral nucleus of the amygdala, on the other hand, enhanced tone, but not context fear memory. These results show for the first time that the enzymatic activity of HDAC3 functions to negatively regulate fear memory formation. Further, HDAC3 activity regulates different aspects of fear memory in the basal and lateral subregions of the amygdala. Thus, the deacetylase activity of HDAC3 is a powerful negative regulator of fear memory formation in multiple subregions of the fear circuit.

Transient CREB-mediated transcription is key in direct neuronal reprogramming

Combinations of neuronal determinants and/or small-molecules such as Forskolin (Fk) can be used to convert different cell types into neurons. As Fk is known to activate cAMP-dependent pathways including CREB-activity, we aimed here to determine the role of CREB in reprogramming – including its temporal profile. We show that transient expression of the dominant-positive CREB-VP16 followed by its inactivation mediated by the dominant-negative ICER improves neuronal conversion of astrocytes mediated by the neurogenic determinant Ascl1. Contrarily, persistent over-activation by CREB-VP16 or persistent inhibition by ICER interferes with neuronal reprogramming, with the latter enhancing cell death. Taken together our work shows transient CREB activation as a key effector in neuronal reprogramming.

InFlo: a novel systems biology framework identifies cAMP-CREB1 axis as a key modulator of platinum resistance in ovarian cancer

Characterizing the complex interplay of cellular processes in cancer would enable the discovery of key mechanisms underlying its development and progression. Published approaches to decipher driver mechanisms do not explicitly model tissue-specific changes in pathway networks and the regulatory disruptions related to genomic aberrations in cancers. We therefore developed InFlo, a novel systems biology approach for characterizing complex biological processes using a unique multidimensional framework integrating transcriptomic, genomic and/or epigenomic profiles for any given cancer sample. We show that InFlo robustly characterizes tissue-specific differences in activities of signalling networks on a genome scale using unique probabilistic models of molecular interactions on a per-sample basis. Using large-scale multi-omics cancer datasets, we show that InFlo exhibits higher sensitivity and specificity in detecting pathway networks associated with specific disease states when compared to published pathway network modelling approaches. Furthermore, InFlo's ability to infer the activity of unmeasured signalling network components was also validated using orthogonal gene expression signatures. We then evaluated multi-omics profiles of primary high-grade serous ovarian cancer tumours (N=357) to delineate mechanisms underlying resistance to frontline platinum-based chemotherapy. InFlo was the only algorithm to identify hyperactivation of the cAMP-CREB1 axis as a key mechanism associated with resistance to platinum-based therapy, a finding that we subsequently experimentally validated. We confirmed that inhibition of CREB1 phosphorylation potently sensitized resistant cells to platinum therapy and was effective in killing ovarian cancer stem cells that contribute to both platinum-resistance and tumour recurrence. Thus, we propose InFlo to be a scalable and widely applicable and robust integrative network modelling framework for the discovery of evidence-based biomarkers and therapeutic targets.

MDM2 facilitates adipocyte differentiation through CRTC-mediated activation of STAT3

The ubiquitin ligase MDM2 is best known for balancing the activity of the tumor suppressor p53. We have previously shown that MDM2 is vital for adipocyte conversion through controlling Cebpd expression in a p53-independent manner. Here, we show that the proadipogenic effect of MDM2 relies on activation of the STAT family of transcription factors. Their activation was required for the cAMP-mediated induction of target genes. Interestingly, rather than influencing all cAMP-stimulated genes, inhibition of the kinases directly responsible for STAT activation, namely JAKs, or ablation of MDM2, each resulted in abolished induction of a subset of cAMP-stimulated genes, with Cebpd being among the most affected. Moreover, STATs were able to interact with the transcriptional cofactors CRTC2 and CRTC3, hitherto only reported to associate with the cAMP-responsive transcription factor CREB. Last but not least, the binding of CRTC2 to a transcriptional enhancer that interacts with the Cebpd promoter was dramatically decreased upon JAK inhibition. Our data reveal the existence of an unusual functional interplay between STATs and CREB at the onset of adipogenesis through shared CRTC cofactors.

Knock-in Luciferase Reporter Mice for In Vivo Monitoring of CREB Activity

The cAMP response element binding protein (CREB) is induced during fasting in the liver, where it stimulates transcription of rate-limiting gluconeogenic genes to maintain metabolic homeostasis. Adenoviral and transgenic CREB reporters have been used to monitor hepatic CREB activity non-invasively using bioluminescence reporter imaging. However, adenoviral vectors and randomly inserted transgenes have several limitations. To overcome disadvantages of the currently used strategies, we created a ROSA26 knock-in CREB reporter mouse line (ROSA26-CRE-luc). cAMP-inducing ligands stimulate the reporter in primary hepatocytes and myocytes from ROSA26-CRE-luc animals. In vivo, these animals exhibit little hepatic CREB activity in the ad libitum fed state but robust induction after fasting. Strikingly, CREB was markedly stimulated in liver, but not in skeletal muscle, after overnight voluntary wheel-running exercise, uncovering differential regulation of CREB in these tissues under catabolic states. The ROSA26-CRE-luc mouse line is a useful resource to study dynamics of CREB activity longitudinally in vivo and can be used as a source of primary cells for analysis of CREB regulatory pathways ex vivo.

GSK-3α Is a Novel Target of CREB and CREB-GSK-3α Signaling Participates in Cell Viability in Lung Cancer

Overexpression or activation of cyclic AMP-response element-binding protein (CREB) has been known to be involved in several human malignancies, including lung cancer. Genes regulated by CREB have been reported to suppress apoptosis, induce cell proliferation, inflammation, and tumor metastasis. However, the critical target genes of CREB in lung cancer have not been well understood. Here, we identified GSK-3α as one of the CREB target genes which is critical for the viability of lung cancer cells. The CREB knockdown significantly reduced the expression of GSK-3α and the direct binding of CREB on the promoter of GSK3A was identified. Kaplan-Meier analysis with a public database showed a prognostic significance of aberrant GSK-3α expression in lung cancer. Inhibition of GSK-3α suppressed cell viability, colony formation, and tumor growth. For the first time, we demonstrated that GSK-3α is regulated by CREB in lung cancer and is required for the cell viability. These findings implicate CREB-GSK-3α axis as a novel therapeutic target for lung cancer treatment.

Dietary Polyphenol Supplementation Prevents Alterations of Spatial Navigation in Middle-Aged Mice

Spatial learning and memory deficits associated with hippocampal synaptic plasticity impairments are commonly observed during aging. Besides, the beneficial role of dietary polyphenols has been suggested as potential functional food candidates to prevent this memory decline. Indeed, polyphenols could potentiate the signaling pathways of synaptic plasticity underlying learning and memory. In this study, spatial learning deficits of middle-aged mice were first highlighted and characterized according to their navigation patterns in the Morris water maze task. An eight-week polyphenol-enriched diet, containing a polyphenol-rich extract from grape and blueberry (PEGB; from the Neurophenols Consortium) with high contents of flavonoids, stilbenes and phenolic acids, was then successful in reversing these age-induced effects. The use of spatial strategies was indeed delayed with aging whereas a polyphenol supplementation could promote the occurrence of spatial strategies. These behavioral results were associated with neurobiological changes: while the expression of hippocampal calmodulin kinase II (CaMKII) mRNA levels was reduced in middle-aged animals, the polyphenol-enriched diet could rescue them. Besides, an increased expression of nerve growth neurotrophic factor (NGF) mRNA levels was also observed in supplemented adult and middle-aged mice. Thus these data suggest that supplementation with polyphenols could be an efficient nutritional way to prevent age-induced cognitive decline.

The CREB Transcription Factor Controls Transcriptional Activity of the Human RIC8B Gene

Proper regulation of gene expression is essential for normal development, cellular growth, and differentiation. Differential expression profiles of mRNA coding for vertebrate Ric-8B during embryo and adult stages have been observed. In addition, Ric-8B is expressed in few cerebral nuclei subareas. These facts point to a dynamic control of RIC8B gene expression. In order to understand the transcriptional regulation of this gene, we searched for cis-elements in the sequence of the human RIC8B promoter region, identifying binding sites for the basic/leucine zipper (bZip) CREB transcription factor family (CRE sites) and C/EBP transcription factor family (C/EBP sites). CRE sites were found clustered near the transcription start site, while the C/EBP sites were found clustered at around 300 bp upstream the CRE sites. Here, we demonstrate the ability of CREB1 and C/EBPβ to bind their respective elements identified in the RIC8B promoter. Comparative protein-DNA interaction analyses revealed only the proximal elements as high affinity sites for CREB1 and only the distal elements as high affinity sites for C/EBPβ. Chromatin immunoprecipitation analyses, carried out using a human neuroblastoma cell line, confirmed the preferential association of CREB to the proximal region of the RIC8B promoter. By performing luciferase reporter assays, we found the CRE sites as the most relevant elements for its transcriptional activity. Taken together, these data show the existence of functional CREB and C/EBP binding sites in the human RIC8B gene promoter, a particular distribution of these sites and demonstrate a relevant role of CREB in stimulating transcriptional activity of this gene. J. Cell. Biochem. 117: 1797-1805, 2016. © 2016 Wiley Periodicals, Inc.

Methotrexate-mediated activation of an AMPK-CREB-dependent pathway: a novel mechanism for vascular protection in chronic systemic inflammation

AIMS

Premature cardiovascular events complicate chronic inflammatory conditions. Low-dose weekly methotrexate (MTX), the most widely used disease-modifying drug for rheumatoid arthritis (RA), reduces disease-associated cardiovascular mortality. MTX increases intracellular accumulation of adenosine monophosphate (AMP) and 5-aminoimidazole-4-carboxamide ribonucleotide which activates AMP-activated protein kinase (AMPK). We hypothesised that MTX specifically protects the vascular endothelium against inflammatory injury via induction of AMPK-regulated protective genes.

METHODS/RESULTS

In the (NZW×BXSB)F1 murine model of inflammatory vasculopathy, MTX 1 mg/kg/week significantly reduced intramyocardial vasculopathy and attenuated end-organ damage. Studies of human umbilical vein endothelial cells (HUVEC) and arterial endothelial cells (HAEC) showed that therapeutically relevant concentrations of MTX phosphorylate AMPKα(Thr172), and induce cytoprotective genes including manganese superoxide dismutase (MnSOD) and haem oxygenase-1 (HO-1). These responses were preserved when HUVECs were pretreated with tumour necrosis factor-α to mimic dysfunctional endothelium. Furthermore, MTX protected against glucose deprivation-induced endothelial apoptosis. Mechanistically, MTX treatment led to cyclic AMP response element-binding protein (CREB)(Ser133) phosphorylation, while AMPK depletion attenuated this response and the induction of MnSOD and HO-1. CREB siRNA inhibited upregulation of both cytoprotective genes by MTX, while chromatin immunoprecipitation demonstrated CREB binding to the MnSOD promoter in MTX-treated EC. Likewise, treatment of (NZW×BXSB)F1 mice with MTX enhanced AMPKα(Thr172) phosphorylation and MnSOD, and reduced aortic intercellular adhesion molecule-1 expression.

CONCLUSIONS

These data suggest that MTX therapeutically conditions vascular endothelium via activation of AMPK-CREB. We propose that this mechanism contributes to the protection against cardiovascular events seen in patients with RA treated with MTX.

Gs-coupled GPCR signalling in AgRP neurons triggers sustained increase in food intake

Agouti-related peptide (AgRP) neurons of the hypothalamus play a key role in regulating food intake and body weight, by releasing three different orexigenic molecules: AgRP; GABA; and neuropeptide Y. AgRP neurons express various G protein-coupled receptors (GPCRs) with different coupling properties, including G_s-linked GPCRs. At present, the potential role of G_s-coupled GPCRs in regulating the activity of AgRP neurons remains unknown. Here we show that the activation of G_s-coupled receptors expressed by AgRP neurons leads to a robust and sustained increase in food intake. We also provide detailed mechanistic data linking the stimulation of this class of receptors to the observed feeding phenotype. Moreover, we show that this pathway is clearly distinct from other GPCR signalling cascades that are operative in AgRP neurons. Our data suggest that drugs able to inhibit this signalling pathway may become useful for the treatment of obesity.

Hypothalamic Agouti-related peptide (AgRP) neurons play a key role in regulating food intake. Here, the authors report a novel pathway in which activation of Gs-coupled receptors on AgRP neurons leads to robust, sustained increase in food intake.

CRTC2 Is a Coactivator of GR and Couples GR and CREB in the Regulation of Hepatic Gluconeogenesis

Glucocorticoid hormones play essential roles in the regulation of gluconeogenesis in the liver, an adaptive response that is required for the maintenance of circulating glucose levels during fasting. Glucocorticoids do this by cooperating with glucagon, which is secreted from pancreatic islets to activate the cAMP-signaling pathway in hepatocytes. The cAMP-response element-binding protein (CREB)-regulated transcription coactivator 2 (CRTC2) is a coactivator known to be specific to CREB and plays a central role in the glucagon-mediated activation of gluconeogenesis in the early phase of fasting. We show here that CRTC2 also functions as a coactivator for the glucocorticoid receptor (GR). CRTC2 strongly enhances GR-induced transcriptional activity of glucocorticoid-responsive genes. CRTC2 physically interacts with the ligand-binding domain of the GR through a region spanning amino acids 561-693. Further, CRTC2 is required for the glucocorticoid-associated cooperative mRNA expression of the glucose-6-phosphatase, a rate-limiting enzyme for hepatic gluconeogenesis, by facilitating the attraction of GR and itself to its promoter region already occupied by CREB. CRTC2 is required for the maintenance of blood glucose levels during fasting in mice by enhancing the GR transcriptional activity on both the G6p and phosphoenolpyruvate carboxykinase (Pepck) genes. Finally, CRTC2 modulates the transcriptional activity of the progesterone receptor, indicating that it may influence the transcriptional activity of other steroid/nuclear receptors. Taken together, these results reveal that CRTC2 plays an essential role in the regulation of hepatic gluconeogenesis through coordinated regulation of the glucocorticoid/GR- and glucagon/CREB-signaling pathways on the key genes G6P and PEPCK.

Integrated microfluidic approach for quantitative high-throughput measurements of transcription factor binding affinities

Protein binding to DNA is a fundamental process in gene regulation. Methodologies such as ChIP-Seq and mapping of DNase I hypersensitive sites provide global information on this regulation in vivo In vitro methodologies provide valuable complementary information on protein-DNA specificities. However, current methods still do not measure absolute binding affinities. There is a real need for large-scale quantitative protein-DNA affinity measurements. We developed QPID, a microfluidic application for measuring protein-DNA affinities. A single run is equivalent to 4096 gel-shift experiments. Using QPID, we characterized the different affinities of ATF1, c-Jun, c-Fos and AP-1 to the CRE consensus motif and CRE half-site in two different genomic sequences on a single device. We discovered that binding of ATF1, but not of AP-1, to the CRE half-site is highly affected by its genomic context. This effect was highly correlated with ATF1 ChIP-seq and PBM experiments. Next, we characterized the affinities of ATF1 and ATF3 to 128 genomic CRE and CRE half-site sequences. Our affinity measurements explained that in vivo binding differences between ATF1 and ATF3 to CRE and CRE half-sites are partially mediated by differences in the minor groove width. We believe that QPID would become a central tool for quantitative characterization of biophysical aspects affecting protein-DNA binding.

Renal proximal tubule Na,K-ATPase is controlled by CREB-regulated transcriptional coactivators as well as salt-inducible kinase 1

Sodium reabsorption by the kidney is regulated by locally produced natriuretic and anti-natriuretic factors, including dopamine and norepinephrine, respectively. Previous studies indicated that signaling events initiated by these natriuretic and anti-natriuretic factors achieve their effects by altering the phosphorylation of Na,K-ATPase in the renal proximal tubule, and that protein kinase A (PKA) and calcium-mediated signaling pathways are involved. The same signaling pathways also control the transcription of the Na,K-ATPase β subunit gene atp1b1 in renal proximal tubule cells. In this report, evidence is presented that (1) both the recently discovered cAMP-regulated transcriptional coactivators (CRTCs) and salt-inducible kinase 1 (SIK1) contribute to the transcriptional regulation of atp1b1 in renal proximal tubule (RPT) cells and (2) renal effectors, including norepinephrine, dopamine, prostaglandins, and sodium, play a role. Exogenously expressed CRTCs stimulate atp1b1 transcription. Evidence for a role of endogenous CRTCs includes the loss of transcriptional regulation of atp1b1 by a dominant-negative CRTC, as well as by a CREB mutant, with an altered CRTC binding site. In a number of experimental systems, SIK phosphorylates CRTCs, which are then sequestered in the cytoplasm, preventing their nuclear effects. Consistent with such a role of SIK in primary RPT cells, atp1b1 transcription increased in the presence of a dominant-negative SIK1, and in addition, regulation by dopamine, norepinephrine, and monensin was disrupted by a dominant-negative SIK1. These latter observations can be explained if SIK1 is phosphorylated and inactivated in the presence of these renal effectors. Our results support the hypothesis that Na,K-ATPase in the renal proximal tubule is regulated at the transcriptional level via SIK1 and CRTCs by renal effectors, in addition to the previously reported control of the phosphorylation of Na,K-ATPase.