Structural determinants for transcriptional activation by cAMP-responsive DNA elements

Transcription factors, metabolic dysfunction-associated fatty liver disease, and therapeutic implications

Metabolic dysfunction-associated fatty liver disease (MAFLD) encompasses a spectrum of liver diseases ranging from metabolic dysfunction-associated fatty liver to metabolic dysfunction-associated steatohepatitis, which may progress to liver cirrhosis and hepatocellular carcinoma. Several mechanisms, including obesity, insulin resistance, dyslipidemia, inflammation, apoptosis, mitochondrial dysfunction, and reactive oxygen species, have been proposed to underlie the progression of MAFLD. Transcription factors are proteins that specifically bind to DNA sequences to regulate the transcription of target genes. Numerous transcription factors regulate MAFLD by modulating the transcription of genes involved in steatosis, inflammation, apoptosis, and fibrosis. Here, we review the pathological factors associated with MAFLD, with a particular emphasis on the transcription factors that contribute to the progression of MAFLD and their therapeutic implications.

Transcriptome analysis of mammary epithelial cell between Sewa sheep and East FriEsian sheep from different localities

Mammary epithelial cells, the only milk-producing cell type in the mammary gland, undergo dynamic proliferation and differentiation during pregnancy, culminating in lactation postpartum. The East FriEsian sheep ranks among the world's most prolific dairy breeds, while the Sewa sheep, a unique dual-purpose breed autochthonous to the Qinghai-Tibet Plateau, exhibits significantly lower milk production. Employing tissue culture methods, we successfully established mammary epithelial cell lines from both breeds. Morphological assessment of mammary epithelial cells and immunofluorescence identification of Cytokeratin 7 and Cytokeratin 8 confirmed the epithelial identity of the isolated cells. Subsequent RNA-seq analysis of these in vitro epithelial cell lines revealed 1813 differentially expressed genes (DEGs). Among these, 1108 were significantly up-regulated and 705 were down-regulated in Sewa epithelial sheep cells compared to East FriEsian epithelial cells. KEGG enrichment analysis identified cellular processes, environmental information processing, human diseases, metabolism, and organismal systems as the primary functional categories associated with DEGs. Gene ontology (GO) terms annotation, categorized into molecular function, biological processes, and cellular component, yielded "binding and catalytic activity," "molecular function regulator activity," and "cellular process," "biological regulation," and "regulation of biological process" as the top three terms within each domain, respectively. Clusters of Orthologous Groups of proteins (KOG) classification further revealed that "signal transduction mechanisms" accounted for the largest proportion of DEGs among all KOG categories. Finally, based on these analyses, ATF3 and MPP7 were identified as promising candidate genes for regulating lactation.

Variation within the non-coding genome influences genetic and epigenetic regulation of the human leukocyte antigen genes

Variation within the non-coding genome may influence the regulation and expression of important genes involved in immune control such as the human leukocyte antigen (HLA) system. Class I and Class II HLA molecules are essential for peptide presentation which is required for T lymphocyte activation. Single nucleotide polymorphisms within non-coding regions of HLA Class I and Class II genes may influence the expression of these genes by affecting the binding of transcription factors and chromatin modeling molecules. Furthermore, an interplay between genetic and epigenetic factors may also influence HLA expression. Epigenetic factors such as DNA methylation and non-coding RNA, regulate gene expression without changing the DNA sequence. However, genetic variation may promote or allow genes to escape regulation by epigenetic factors, resulting in altered expression. The HLA system is central to most diseases, therefore, understanding the role of genetics and epigenetics on HLA regulation will tremendously impact healthcare. The knowledge gained from these studies may lead to novel and cost-effective diagnostic approaches and therapeutic interventions. This review discusses the role of non-coding variants on HLA regulation. Furthermore, we discuss the interplay between genetic and epigenetic factors on the regulation of HLA by evaluating literature based on polymorphisms within DNA methylation and miRNA regulatory sites within class I and Class II HLA genes. We also provide insight into the importance of the HLA non-coding genome on disease, discuss ethnic-specific differences across the HLA region and provide guidelines for future HLA studies.

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.

Methylation-Mediated Silencing of ATF3 Promotes Thyroid Cancer Progression by Regulating Prognostic Genes in the MAPK and PI3K/AKT Pathways

Background: Aberrant expression of oncogenes and/or tumor suppressor genes (TSGs) drives the tumorigenesis and development of thyroid cancer. We investigated the expression and function of a member of the activating transcription factor (ATF)/cAMP-responsive element-binding protein (CREB) transcription factor (TF) family, ATF3, in thyroid cancer. Methods: Data from 80 patients with papillary thyroid cancer (PTC) in the First Affiliated Hospital of Sun Yat-sen University and 510 PTC samples in The Cancer Genome Atlas thyroid cancer database were utilized for gene expression and prognosis analyses. The survival data were analyzed by Kaplan-Meier curves and Cox regression with adjustment for age, sex, multilocality, extrathyroidal extension, lymph metastases, and history of neoadjuvant treatment. DNA methylation was analyzed by methylation-specific polymerase chain reaction (PCR) and bisulfite sequencing PCR. TFs binding to ATF3 promoter were identified by DNA pull-down combined with mass spectrum assay, and confirmed by quantitative PCR (qPCR), luciferase reporter assay, and chromatin immunoprecipitation (ChIP)-qPCR. We conducted functional assays in vitro and in a xenograft mouse model to evaluate the function of ATF3 in thyroid cancer. Integrated analyses based on RNA sequencing, ChIP-seq, and CUT&Tag assays were performed to explore the mechanisms underlying the function of ATF3. Results: ATF3 was significantly downregulated in PTC and patients with low ATF3 expression had reduced progression-free survival (adjusted hazard ratio = 0.50 [CI 0.26-0.98], p = 0.043). DNA hypermethylation in ATF3 promoter disrupted the binding of SP1 and MYC-MAX, leading to inactivation of the gene. ATF3 functioned as a TSG by inhibiting the proliferation and mobility of thyroid cancer cells. And ATF3 regulated the expression of a number of genes by binding to the regulatory elements of them, particularly for genes in MAPK and PI3K/AKT pathways. Among these target genes, filamin C was positively regulated by ATF3 and associated with a more favorable thyroid cancer prognosis, while dual specificity phosphatase 10, fibronectin-1, tenascin C, and CREB5 were negatively regulated by ATF3 and associated with a poorer prognosis. Conclusions: We observed that the promoter DNA hypermethylation decreased the expression of ATF3, which in turn promoted the progression of thyroid cancer, at least partially, by directly regulating prognosis-related genes in the MAPK and PI3K/AKT pathways.

Identification of ATF3 as a novel protective signature of quiescent colorectal tumor cells

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of death in the world. In most cases, drug resistance and tumor recurrence are ultimately inevitable. One obstacle is the presence of chemotherapy-insensitive quiescent cancer cells (QCCs). Identification of unique features of QCCs may facilitate the development of new targeted therapeutic strategies to eliminate tumor cells and thereby delay tumor recurrence. Here, using single-cell RNA sequencing, we classified proliferating and quiescent cancer cell populations in the human colorectal cancer spheroid model and identified ATF3 as a novel signature of QCCs that could support cells living in a metabolically restricted microenvironment. RNA velocity further showed a shift from the QCC group to the PCC group indicating the regenerative capacity of the QCCs. Our further results of epigenetic analysis, STING analysis, and evaluation of TCGA COAD datasets build a conclusion that ATF3 can interact with DDIT4 and TRIB3 at the transcriptional level. In addition, decreasing the expression level of ATF3 could enhance the efficacy of 5-FU on CRC MCTS models. In conclusion, ATF3 was identified as a novel marker of QCCs, and combining conventional drugs targeting PCCs with an option to target QCCs by reducing ATF3 expression levels may be a promising strategy for more efficient removal of tumor cells.

New Synthesized Activating Transcription Factor 3 Inducer SW20.1 Suppresses Resistin-Induced Metabolic Syndrome

Obesity is an emerging concern globally with increasing prevalence. Obesity is associated with many diseases, such as cardiovascular disease, dyslipidemia, and cancer. Thus, effective new antiobesity drugs should be urgently developed. We synthesized SW20.1, a compound that induces activating transcription factor 3 (ATF3) expression. The results of Oil Red O staining and quantitative real-time polymerase chain reaction revealed that SW20.1 was more effective in reducing lipid accumulation in 3T3-L1 preadipocytes than the previously synthesized ST32db, and that it inhibited the expression of the genes involved in adipogenesis and lipogenesis. A chromatin immunoprecipitation assay indicated that SW20.1 inhibited adipogenesis and lipogenesis by binding to the upstream promoter region of resistin at two sites (-2861/-2854 and -241/-234). In mice, the intraperitoneal administration of SW20.1 reduced body weight, white adipocyte weight in different regions, serum cholesterol levels, adipogenesis-related gene expression, hepatic steatosis, and serum resistin levels. Overall, SW20.1 exerts antiobesity effects by inhibiting resistin through the ATF3 pathway. Our study results indicate that SW20.1 is a promising therapeutic drug for diet-induced obesity.

Transcriptional responses to injury of regenerative lung alveolar epithelium

The significance of alveolar epithelial type 2 (AT2) cell proliferation for lung alveolar epithelial homeostasis and regeneration after injury has been widely accepted. However, the heterogeneity of AT2 cell population for cell proliferation capacity remains disputed. By single-cell RNA sequencing and genetic lineage labeling using the Ki67 knock-in mouse model, we map all proliferative AT2 cells in homeostatic and regenerating murine lungs after injury induced by Streptococcus pneumoniae infection. The proliferative AT2 cell population displays a unique transcriptional program, which is regulated by activating transcription factor 3 (ATF3) and thyroid hormone receptor alpha (THRA) transcription factors. Overexpression of these two transcription factors in AT2 cells promoted AT2 cell proliferation and improved lung function after injury. These results indicate that increased expression of ATF3 and THRA at the onset of lung epithelial regeneration is required to permit rapid AT2 cell proliferation and hence progression through the recovery of lung epithelium.

Identifying of miRNA–mRNA Regulatory Networks Associated with Acute Kidney Injury by Weighted Gene Co-Expression Network Analysis

Background

Acute kidney injury (AKI) is a clinical emergency characterized by a dramatic decline in renal function and the accumulation of metabolic waste products in the body, with a high morbidity and mortality rate. The pathogenesis of AKI remains unclear and there are no effective treatment options.

Methods

We aimed to identify critical genes involved in the pathogenesis of AKI and construct a miRNA–mRNA regulatory network using gene expression data downloaded from Gene Expression Omnibus (GSE85957) for 38 kidneys of AKI and 19 control rats and cisplatin treated kidneys of 3 AKI and 3 control rats. Data in GSE85957 were processed using weighted gene co-expression network analysis (WGCNA), and biological function analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used to analyze the functions associated with critical genes.

Results

Twenty-eight modules in the GSE85957 dataset were identified by WGCNA, of which 103 genes in the orange module and 30 genes in the black module were closely associated with AKI and dose. Biological function analysis of genes in the orange and black modules revealed that skeletal muscle cell differentiation, tissue development and organ development were involved in the pathological changes of AKI. Combining with our experimentally processed AKI rat kidney data, eight genes (Atf3, Egr1, Egr2, Fos, Fosb, Gdf15, Serpine1 and Nr1d1) were identified as potential biomarkers of AKI, and miRNA–mRNA regulatory networks were constructed based on the above eight critical genes. Further tissue validation revealed that Egr1 and Fos were highly expressed in AKI.

Conclusion

Our study identified potential biomarkers of AKI and constructed an associated miRNA–mRNA regulatory network, which may provide new insights into the molecular pathogenesis of AKI.

The ATF3 inducer protects against diet-induced obesity via suppressing adipocyte adipogenesis and promoting lipolysis and browning

In this study, we investigated whether the activating transcription factor 3 (ATF3) inducer ST32db, a synthetic compound with a chemical structure similar to that of native Danshen compounds, exerts an anti-obesity effect in 3T3-L1 white preadipocytes, D16 beige cells, and mice with obesity induced by a high-fat diet (HFD). The results showed that ST32db inhibited 3T3-L1 preadipocyte differentiation by inhibiting adipogenesis/lipogenesis-related gene (and protein levels) and enhancing lipolysis-related gene (and protein levels) via the activation of β3-adrenoceptor (β3-AR)/PKA/p38, AMPK, and ERK pathways. Furthermore, ST32db inhibited triacylglycerol accumulation in D16 adipocytes by suppressing adipogenesis/lipogenesis-related gene (and protein levels) and upregulating browning gene expression by suppressing the β3-AR/PKA/p38, and AMPK pathways. Intraperitoneally injected ST32db (1 mg kg-1 twice weekly) inhibited body weight gain and reduced the weight of inguinal white adipose tissue (iWAT), epididymal WAT (eWAT), and mesenteric WAT, with no effects on food intake by the obese mice. The adipocyte diameter and area of iWAT and eWAT were decreased in obese mice injected with ST32db compared with those administered only HFD. In addition, ST32db significantly suppressed adipogenesis and activated lipolysis, browning, mitochondrial oxidative phosphorylation, and β-oxidation-related pathways by suppressing the p38 pathway in the iWAT of the obese mice. These results indicated that the ATF3 inducer ST32db has therapeutic potential for reducing obesity.

Multi-Target Effects of Novel Synthetic Coumarin Derivatives Protecting Aβ-GFP SH-SY5Y Cells against Aβ Toxicity

Alzheimer's disease (AD) is a common neurodegenerative disease presenting with progressive memory and cognitive impairments. One of the pathogenic mechanisms of AD is attributed to the aggregation of misfolded amyloid β (Aβ), which induces neurotoxicity by reducing the expression of brain-derived neurotrophic factor (BDNF) and its high-affinity receptor tropomyosin-related kinase B (TRKB) and increasing oxidative stress, caspase-1, and acetylcholinesterase (AChE) activities. Here, we have found the potential of two novel synthetic coumarin derivatives, ZN014 and ZN015, for the inhibition of Aβ and neuroprotection in SH-SY5Y neuroblastoma cell models for AD. In SH-SY5Y cells expressing the GFP-tagged Aβ-folding reporter, both ZN compounds reduced Aβ aggregation, oxidative stress, activities of caspase-1 and AChE, as well as increased neurite outgrowth. By activating TRKB-mediated extracellular signal-regulated kinase (ERK) and AKT serine/threonine kinase 1 (AKT) signaling, these two ZN compounds also upregulated the cAMP-response-element binding protein (CREB) and its downstream BDNF and anti-apoptotic B-cell lymphoma 2 (BCL2). Knockdown of TRKB attenuated the neuroprotective effects of ZN014 and ZN015. A parallel artificial membrane permeability assay showed that ZN014 and ZN015 could be characterized as blood-brain barrier permeable. Our results suggest ZN014 and ZN015 as novel therapeutic candidates for AD and demonstrate that ZN014 and ZN015 reduce Aβ neurotoxicity via pleiotropic mechanisms.

Testicular localization of activating transcription factor 1 and its potential function during spermatogenesis

Activating transcription factor 1 (ATF1), belonging to the CREB/ATF family of transcription factors, is highly expressed in the testes. However, its role in spermatogenesis has not yet been established. Here, we aimed to elucidate the impact of ATF1 in spermatogenesis by examining the expression pattern of ATF1 in mice and the effect of ATF1 knockdown in the mouse testes. We found that ATF1 is expressed in various organs, with very high levels in the testes. Immunohistochemical staining showed that ATF1 was localized in the nuclei of spermatogonia and co-localized with proliferating cell nuclear antigen. In ATF1-deficient mice, the seminiferous tubules of the testis contained cells at all developmental stages; however, the number of spermatocytes was decreased. Proliferating cell nuclear antigen expression was decreased and apoptotic cells were rare in the seminiferous tubules. These results indicate that ATF1 plays a role in male germ cell proliferation and sperm production.

Regulation of Hepatic Metabolism and Cell Growth by the ATF/CREB Family of Transcription Factors

The liver is a major metabolic organ that regulates the whole-body metabolic homeostasis and controls hepatocyte proliferation and growth. The ATF/CREB family of transcription factors integrates nutritional and growth signals to the regulation of metabolism and cell growth in the liver, and deregulated ATF/CREB family signaling is implicated in the progression of type 2 diabetes, nonalcoholic fatty liver disease, and cancer. This article focuses on the roles of the ATF/CREB family in the regulation of glucose and lipid metabolism and cell growth and its importance in liver physiology. We also highlight how the disrupted ATF/CREB network contributes to human diseases and discuss the perspectives of therapeutically targeting ATF/CREB members in the clinic.

Master Regulator Activating Transcription Factor 3 (ATF3) in Metabolic Homeostasis and Cancer

Activating transcription factor 3 (ATF3) is a stress-induced transcription factor that plays vital roles in modulating metabolism, immunity, and oncogenesis. ATF3 acts as a hub of the cellular adaptive-response network. Multiple extracellular signals, such as endoplasmic reticulum (ER) stress, cytokines, chemokines, and LPS, are connected to ATF3 induction. The function of ATF3 as a regulator of metabolism and immunity has recently sparked intense attention. In this review, we describe how ATF3 can act as both a transcriptional activator and a repressor. We then focus on the role of ATF3 and ATF3-regulated signals in modulating metabolism, immunity, and oncogenesis. The roles of ATF3 in glucose metabolism and adipose tissue regulation are also explored. Next, we summarize how ATF3 regulates immunity and maintains normal host defense. In addition, we elaborate on the roles of ATF3 as a regulator of prostate, breast, colon, lung, and liver cancers. Further understanding of how ATF3 regulates signaling pathways involved in glucose metabolism, adipocyte metabolism, immuno-responsiveness, and oncogenesis in various cancers, including prostate, breast, colon, lung, and liver cancers, is then provided. Finally, we demonstrate that ATF3 acts as a master regulator of metabolic homeostasis and, therefore, may be an appealing target for the treatment of metabolic dyshomeostasis, immune disorders, and various cancers.

The Phosphorylation of CREB at Serine 133 Is a Key Event for Circadian Clock Timing and Entrainment in the Suprachiasmatic Nucleus

Within the suprachiasmatic nucleus (SCN)-the locus of the master circadian clock- transcriptional regulation via the CREB/CRE pathway is implicated in the functioning of the molecular clock timing process, and is a key conduit through which photic input entrains the oscillator. One event driving CRE-mediated transcription is the phosphorylation of CREB at serine 133 (Ser¹³³). Indeed, numerous reporter gene assays have shown that an alanine point mutation in Ser¹³³ reduces CREB-mediated transcription. Here, we sought to examine the contribution of Ser¹³³ phosphorylation to the functional role of CREB in SCN clock physiology in vivo. To this end, we used a CREB knock-in mouse strain, in which Ser¹³³ was mutated to alanine (S/A CREB). Under a standard 12 h light-dark cycle, S/A CREB mice exhibited a marked alteration in clock-regulated wheel running activity. Relative to WT mice, S/A CREB mice had highly fragmented bouts of locomotor activity during the night phase, elevated daytime activity, and a delayed phase angle of entrainment. Further, under free-running conditions, S/A CREB mice had a significantly longer tau than WT mice and reduced activity amplitude. In S/A CREB mice, light-evoked clock entrainment, using both Aschoff type 1 and 6 h "jet lag" paradigms, was markedly reduced relative to WT mice. S/A CREB mice exhibited attenuated transcriptional drive, as assessed by examining both clock-gated and light-evoked gene expression. Finally, SCN slice culture imaging detected a marked disruption in cellular clock phase synchrony following a phase-resetting stimulus in S/A CREB mice. Together, these data indicate that signaling through CREB phosphorylation at Ser¹³³ is critical for the functional fidelity of both SCN timing and entrainment.

Beta-2 adrenergic receptors increase TREG cell suppression in an OVA-induced allergic asthma mouse model when mice are moderate aerobically exercised

Background

The potency of T regulatory (TREG) cells to inhibit T helper (Th)-driven immune cell responses has been linked to increased intracellular cyclic-AMP (cAMP) levels of TREG cells. In an ovalbumin (OVA)-driven allergic asthma mouse model, moderate aerobic exercise increases TREG cell function in a contact-dependent manner that leads to a significant reduction in chronic inflammation and restoration of lung function. However, the mechanism, whereby exercise increases TREG function, remains unknown and was the focus of these investigations. Exercise can communicate with TREG cells by their expression of β2-adrenergic receptors (β2-AR). Activation of these receptors results in an increase in intracellular levels of cyclic-AMP, potentially creating a potent inhibitor of Th cell responses.

Results

For the allergic asthma model, female wildtype BALB/c mice were challenged with OVA, and exercised (13.5 m/min for 45 min) 3×/week for 4 weeks. TREG cells were isolated from all mouse asthma/exercise groups, including β2-AR^−/− mice, to test suppressive function and intracellular cAMP levels. In these studies, cAMP levels were increased in TREG cells isolated from exercised mice. When β2-AR expression was absent on TREG cells, cAMP levels were significantly decreased. Correlatively, their suppressive function was compromised. Next, TREG cells from all mouse groups were tested for suppressive function after treatment with either a pharmaceutical β2-adrenergic agonist or an effector-specific cAMP analogue. These experiments showed TREG cell function was increased when treated with either a β2-adrenergic agonist or effector-specific cAMP analogue. Finally, female wildtype BALB/c mice were antibody-depleted of CD25⁺CD4⁺ TREG cells (anti-CD25). Twenty-four hours after TREG depletion, either β2-AR^−/− or wildtype TREG cells were adoptively transferred. Recipient mice underwent the asthma/exercise protocols. β2-AR^−/− TREG cells isolated from these mice showed no increase in TREG function in response to moderate aerobic exercise.

Conclusion

These studies offer a novel role for β2-AR in regulating cAMP intracellular levels that can modify suppressive function in TREG cells.

Lipotoxic brain microvascular injury is mediated by activating transcription factor 3-dependent inflammatory and oxidative stress pathways

Dysfunction of the cerebrovasculature plays an important role in vascular cognitive impairment (VCI). Lipotoxic injury of the systemic endothelium in response to hydrolyzed triglyceride-rich lipoproteins (TGRLs; TGRL lipolysis products) or a high-fat Western diet (WD) suggests similar mechanisms may be present in brain microvascular endothelium. We investigated the hypothesis that TGRL lipolysis products cause lipotoxic injury to brain microvascular endothelium by generating increased mitochondrial superoxide radical generation, upregulation of activating transcription factor 3 (ATF3)-dependent inflammatory pathways, and activation of cellular oxidative stress and apoptotic pathways. Human brain microvascular endothelial cells were treated with human TGRL lipolysis products that induced intracellular lipid droplet formation, mitochondrial superoxide generation, ATF3-dependent transcription of proinflammatory, stress response, and oxidative stress genes, as well as activation of proapoptotic cascades. Male apoE knockout mice were fed a high-fat/high-cholesterol WD for 2 months, and brain microvessels were isolated by laser capture microdissection. ATF3 gene transcription was elevated 8-fold in the hippocampus and cerebellar brain region of the WD-fed animals compared with chow-fed control animals. The microvascular injury phenotypes observed in vitro and in vivo were similar. ATF3 plays an important role in mediating brain microvascular responses to acute and chronic lipotoxic injury and may be an important preventative and therapeutic target for endothelial dysfunction in VCI.

Activating transcription factor 3 SUMOylation is involved in angiotensin II-induced endothelial cell inflammation and dysfunction

Activating transcription factor 3 (ATF3) is an adaptive-response protein induced by various environmental stresses and is implicated in the pathogenesis of many disease states. However, the role of ATF3 SUMOylation in hypertension-induced vascular injury remains poorly understood. Here we investigated the function of ATF3 SUMOylation in vascular endothelial cells (ECs). The expression of ATF3 and small ubiquitin-like modifier 1 (SUMO1) was increased in angiotensin II (Ang II)-induced human umbilical vein endothelial cells (HUVECs). Microscopic analyses further revealed that the expression of ATF3 and SUMO1 is upregulated and colocalized in the endothelium of thoracic aortas from Ang II-induced hypertensive mice. However, Ang II-induced upregulation of ATF3 and SUMO1 in vitro and in vivo was blocked by Ang II type I receptor antagonist olmesartan. Moreover, Ang II induced ATF3 SUMOylation at lysine 42, which is SUMO1 dependent. ATF3 SUMOylation attenuated ATF3 ubiquitination and in turn promoted ATF3 protein stability. ATF3 or SUMO1 knockdown inhibited Ang II-induced expression of inflammatory molecules such as tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-8. Wild type ATF3 but not ATF3-K42R (SUMOylation defective mutant) reduced the production of nitric oxide (NO), a key indicator of EC function. Consistently, ginkgolic acid, an inhibitor of SUMOylation, increased NO production in HUVECs and significantly improved vasodilatation of aorta from Ang II-induced hypertensive mice. Our findings demonstrated that ATF3 SUMOylation is involved in Ang II-induced EC inflammation and dysfunction in vitro and in vivo through inhibiting ATF3 ubiquitination and increasing ATF3 protein stability.

Aromatase induction in tamoxifen-resistant breast cancer: Role of phosphoinositide 3-kinase-dependent CREB activation

Estrogens are important for the development and growth of estrogen receptor (ER)-positive breast cancer, for which anti-estrogen therapy is one of the most effective treatments. However, its efficacy can be limited by either de novo or acquired resistance. Aromatase is a key enzyme for the biosynthesis of estrogens, and inhibition of this enzyme leads to profound hypoestrogenism. Here, we found that the basal expression and activity of aromatase were significantly increased in tamoxifen (TAM)-resistant human breast cancer (TAMR-MCF-7) cells compared to control MCF-7 cells. We further revealed that aromatase immunoreactivity in tumor tissues was increased in recurrence group after TAM therapy compared to non-recurrence group after TAM therapy. Phosphorylation of Akt, extracellular signal-regulated kinase (ERK), and p38 kinase were all increased in TAMR-MCF-7 cells. Inhibition of phosphoinositide 3-kinase (PI3K) suppressed the transactivation of the aromatase gene and its enzyme activity. Furthermore, we have also shown that PI3K/Akt-dependent cAMP-response element binding protein (CREB) activation was required for the enhanced expression of aromatase in TAMR-MCF-7 cells. Our findings suggest that aromatase expression is up-regulated in TAM-resistant breast cancer via PI3K/Akt-dependent CREB activation.

Apicidin F: characterization and genetic manipulation of a new secondary metabolite gene cluster in the rice pathogen Fusarium fujikuroi

The fungus F. fujikuroi is well known for its production of gibberellins causing the ‘bakanae’ disease of rice. Besides these plant hormones, it is able to produce other secondary metabolites (SMs), such as pigments and mycotoxins. Genome sequencing revealed altogether 45 potential SM gene clusters, most of which are cryptic and silent. In this study we characterize a new non-ribosomal peptide synthetase (NRPS) gene cluster that is responsible for the production of the cyclic tetrapeptide apicidin F (APF). This new SM has structural similarities to the known histone deacetylase inhibitor apicidin. To gain insight into the biosynthetic pathway, most of the 11 cluster genes were deleted, and the mutants were analyzed by HPLC-DAD and HPLC-HRMS for their ability to produce APF or new derivatives. Structure elucidation was carried out be HPLC-HRMS and NMR analysis. We identified two new derivatives of APF named apicidin J and K. Furthermore, we studied the regulation of APF biosynthesis and showed that the cluster genes are expressed under conditions of high nitrogen and acidic pH in a manner dependent on the nitrogen regulator AreB, and the pH regulator PacC. In addition, over-expression of the atypical pathway-specific transcription factor (TF)-encoding gene APF2 led to elevated expression of the cluster genes under inducing and even repressing conditions and to significantly increased product yields. Bioinformatic analyses allowed the identification of a putative Apf2 DNA-binding (“Api-box”) motif in the promoters of the APF genes. Point mutations in this sequence motif caused a drastic decrease of APF production indicating that this motif is essential for activating the cluster genes. Finally, we provide a model of the APF biosynthetic pathway based on chemical identification of derivatives in the cultures of deletion mutants.

Flaviviral regulation of the unfolded protein response: can stress be beneficial?

Members of the Flaviviridae family remain some of the most significant human viral pathogens, with few vaccines or antivirals commercially available for therapeutic use. Thus, understanding the intracellular events of replication and how these viruses modulate signaling within an infected cell is of great importance. The ER is central to replication within the Flaviviridae family, as the site of viral protein translation and processing, as a source of membranes for replication complex formation and as a site of virus assembly. This places a large burden upon the organelle, resulting in the induction of ER stress responses, in particular the unfolded protein response. In turn, unfolded protein response signaling induced in infected cells is tightly modulated by the virus in order to maintain an optimal environment for replication. The loss of various components of the stress response can have either beneficial or detrimental effects, presenting intriguing targets for antiviral discovery.

Activating transcription factor 4 confers a multidrug resistance phenotype to gastric cancer cells through transactivation of SIRT1 expression

BACKGROUND

Multidrug resistance (MDR) in gastric cancer remains a major challenge to clinical treatment. Activating transcription factor 4 (ATF4) is a stress response gene involved in homeostasis and cellular protection. However, the expression and function of ATF4 in gastric cancer MDR remains unknown. In this study, we investigate whether ATF4 play a role in gastric cancer MDR and its potential mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrated that ATF4 overexpression confered the MDR phenotype to gastric cancer cells, while knockdown of ATF4 in the MDR variants induced re-sensitization. In this study we also showed that the NAD(+)-dependent histone deacetylase SIRT1 was required for ATF4-induced MDR effect in gastric cancer cells. We demonstrated that ATF4 facilitated MDR in gastric cancer cells through direct binding to the SIRT1 promoter, resulting in SIRT1 up-regulation. Significantly, inhibition of SIRT1 by small interfering RNA (siRNA) or a specific inhibitor (EX-527) reintroduced therapeutic sensitivity. Also, an increased Bcl-2/Bax ratio and MDR1 expression level were found in ATF4-overexpressing cells.

CONCLUSIONS/SIGNIFICANCE

We showed that ATF4 had a key role in the regulation of MDR in gastric cancer cells in response to chemotherapy and these findings suggest that targeting ATF4 could relieve therapeutic resistance in gastric cancer.

CO(2)-cAMP-responsive cis-elements targeted by a transcription factor with CREB/ATF-like basic zipper domain in the marine diatom Phaeodactylum tricornutum

Expression controls of the carbon acquisition system in marine diatoms in response to environmental factors are an essential issue to understand the changes in marine primary productivity. A pyrenoidal β-carbonic anhydrase, PtCA1, is one of the most important candidates to investigate the control mechanisms of the CO(2) acquisition system in the marine diatom Phaeodactylum tricornutum. A detailed functional assay was carried out on the putative core regulatory region of the ptca1 promoter using a β-glucuronidase reporter in P. tricornutum cells under changing CO(2) conditions. A set of loss-of-function assays led to the identification of three CO(2)-responsive elements, TGACGT, ACGTCA, and TGACGC, at a region -86 to -42 relative to the transcription start site. Treatment with a cyclic (c)AMP analog, dibutyryl cAMP, revealed these three elements to be under the control of cAMP; thus, we designated them, from 5' to 3', as CO(2)-cAMP-Responsive Element1 (CCRE1), CCRE2, and CCRE3. Because the sequence TGACGT is known to be a typical target of human Activating Transcription Factor6 (ATF6), we searched for genes containing a basic zipper (bZIP) region homologous to that of ATF6 in the genome of P. tricornutum. Gel-shift assays using CCRE pentamers as labeled probes showed that at least one candidate of bZIP proteins, PtbZIP11, bound specifically to CCREs. A series of gain-of-function assays with CCREs fused to a minimal promoter strongly suggested that the alternative combination of CCRE1/2 or CCRE2/3 at proper distances from the minimal promoter is required as a potential target of PtbZIP11 for an effective CO(2) response of the ptca1 gene.

CREB influences timing and entrainment of the SCN circadian clock

The transcriptional feedback circuit, which is at the core of the suprachiasmatic nucleus (SCN) circadian (i.e., 24 h) clock, is tightly coupled to both external entrainment cues, such as light, as well as rhythmic cues that arise on a system-wide level within the SCN. One potential signaling pathway by which these cues are conveyed to the molecular clock is the CREB/CRE transcriptional cascade. In this study, we employed a tetracycline-inducible CREB repressor mouse strain, in which approximately 60% of the SCN neurons express the transgene, to test CREB functionality in the clock and its effects on overt rhythmicity. We show that attenuated CREB signaling in the SCN led to a significant reduction in light-evoked clock entrainment. An examination of circadian timing revealed that CREB repressor mice exhibited normal free-running rhythms in the absence of external lighting cues. However, under conditions of constant light, which typically leads to a lengthening of the circadian period, CREB repressor mice exhibited a dramatic arrhythmic phenotype, which could be reversed with doxycycline. At a cellular level, the repression of CREB led to a significant reduction in both the expression of the circadian clock proteins PERIOD1 and PERIOD2 and the clock output hormones AVP and VIP. Together, these data support the idea that the CRE transcriptional pathway orchestrates transcriptional events that are essential for both the maintenance of SCN timing and light entrainment of the circadian clock.

Endoplasmic reticulum stress-induced activation of activating transcription factor 6 decreases cAMP-stimulated hepatic gluconeogenesis via inhibition of CREB

The expression of genes encoding key hepatic gluconeogenic enzymes, including phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), is regulated at the transcriptional level by a network of transcription factors and cofactors, including cAMP response element-binding protein (CREB). It has been suggested that increased endoplasmic reticulum (ER) stress in the liver impairs hepatic glucose metabolism. However, the direct effect of ER stress on hepatic gluconeogenesis is still not clear. Here, we investigated whether ER stress influences hepatic gluconeogenesis and whether this process is mediated by activating transcription factor 6 (ATF6) through the inhibition of cAMP-mediated activation of CREB. A cAMP stimulant, forskolin, and 8-bromoadenosine-cAMP increased PEPCK and G6Pase mRNA expression in H4IIE rat hepatoma cells, and ER stress induced by tunicamycin or thapsigargin decreased the expression of these genes in forskolin or 8-bromoadenosine-cAMP-treated cells. In a transient transfection study, ATF6 inhibited the PEPCK and G6Pase promoters. Also, adenovirus-mediated overexpression of ATF6 in H4IIE cells decreased forskolin-stimulated PEPCK and G6Pase gene expression. Moreover, the inhibition of endogenous ATF6 expression by small interfering RNAs restored the ER stress-induced suppression of PEPCK and G6Pase gene expression. Transient transfection of ATF6 inhibited transactivation by CREB on the PEPCK and G6Pase promoters, and a gel shift assay showed that Ad-ATF6 inhibits forskolin-stimulated CREB DNA-binding activity. Finally, we found that expression of ATF6 decreased fasting-induced PEPCK, G6Pase mRNA expression, and blood glucose levels in mice. Taken together, these data extend our understanding of ER stress and the regulation of liver gluconeogenesis by ATF6.

Function and regulation of the glutathione peroxidase homologous gene GPXH/GPX5 in Chlamydomonas reinhardtii

When exposed to strong sunlight, photosynthetic organisms encounter photooxidative stress by the increased production of reactive oxygen species causing harmful damages to proteins and membranes. Consequently, a fast and specific induction of defense mechanisms is required to protect the organism from cell death. In Chlamydomonas reinhardtii, the glutathione peroxidase homologous gene GPXH/GPX5 was shown to be specifically upregulated by singlet oxygen formed during high light conditions presumably to prevent the accumulation of lipid hydroperoxides and membrane damage. We now showed that the GPXH protein is a thioredoxin-dependent peroxidase catalyzing the reduction of hydrogen peroxide and organic hydroperoxides.Furthermore, the GPXH gene seems to encode a dual-targeted protein, predicted to be localized both in the chloroplast and the cytoplasm, which is active with either plastidic TRXy or cytosolic TRXh1. Putative dual-targeting is achieved by alternative transcription and translation start sites expressed independently from either a TATA-box or an Initiator core promoter. Expression of both transcripts was upregulated by photooxidative stress even though with different strengths. The induction required the presence of the core promoter sequences and multiple upstream regulatory elements including a Sp1-like element and an earlier identified CRE/AP-1 homologous sequence. This element was further characterized by mutation analysis but could not be confirmed to be a consensus CRE or AP1 element. Instead, it rather seems to be another member of the large group of TGAC-transcription factor binding sites found to be involved in the response of different genes to oxidative stress.

ATF3 transcription factor and its emerging roles in immunity and cancer

Activating transcription factor 3 (ATF3) is a member of the ATF/cyclic AMP response element-binding (ATF/CREB) family of transcription factors. It is an adaptive-response gene that participates in cellular processes to adapt to extra- and/or intracellular changes, where it transduces signals from various receptors to activate or repress gene expression. Advances made in understanding the immunobiology of Toll-like receptors have recently generated new momentum for the study of ATF3 in immunity. Moreover, the role of ATF3 in the regulation of the cell cycle and apoptosis has important implications for understanding susceptibility to and progression of several cancers.

Lipopolysaccharide stimulation of trophoblasts induces corticotropin-releasing hormone expression through MyD88

OBJECTIVE

We hypothesized that intrauterine infection may lead to placental corticotrophin-releasing hormone (CRH) expression via Toll-like receptor signaling.

STUDY DESIGN

To test this hypothesis JEG3 cells were stimulated with lipopolysaccharide (LPS), chlamydial heat shock protein 60, and interleukin (IL)-1. CRH expression was assessed by reverse transcription polymerase chain reaction (RT-PCR). The signaling mechanisms that were involved were examined in transient transfection experiments with beta-galactosidase, CRH-luciferase, cyclic adenosine monophosphate (AMP) response element-luciferase, dominant-negative (DN)-myeloid differentiation primary response gene (MyD88) and DN-toll-IL-1-receptor domain containing adapter inducing interferon (TRIF) vectors. Luciferase activity was determined by luciferase assay. Beta-galactosidase assay was performed to determine transfection efficiency.

RESULTS

LPS, chlamydial heat shock protein 60, and IL-1 stimulation led to CRH expression in the JEG3 cells. LPS-induced CRH expression was not due to the autocrine effect of LPS-induced IL-1 because the supernatant from LPS-conditioned JEG3 cells did not induce CRH expression in the naïve cells. DN-MyD88, but not DN-TRIF, blocked the LPS-induced CRH expression. The cAMP response element did not play a role in LPS-induced CRH expression.

CONCLUSION

Toll-like receptor signaling 4 may induce placental CRH expression through MyD88.

A comparative genomics approach to identifying the plasticity transcriptome

Background

Neuronal activity regulates gene expression to control learning and memory, homeostasis of neuronal function, and pathological disease states such as epilepsy. A great deal of experimental evidence supports the involvement of two particular transcription factors in shaping the genomic response to neuronal activity and mediating plasticity: CREB and zif268 (egr-1, krox24, NGFI-A). The gene targets of these two transcription factors are of considerable interest, since they may help develop hypotheses about how neural activity is coupled to changes in neural function.

Results

We have developed a computational approach for identifying binding sites for these transcription factors within the promoter regions of annotated genes in the mouse, rat, and human genomes. By combining a robust search algorithm to identify discrete binding sites, a comparison of targets across species, and an analysis of binding site locations within promoter regions, we have defined a group of candidate genes that are strong CREB- or zif268 targets and are thus regulated by neural activity. Our analysis revealed that CREB and zif268 share a disproportionate number of targets in common and that these common targets are dominated by transcription factors.

Conclusion

These observations may enable a more detailed understanding of the regulatory networks that are induced by neural activity and contribute to the plasticity transcriptome. The target genes identified in this study will be a valuable resource for investigators who hope to define the functions of specific genes that underlie activity-dependent changes in neuronal properties.

Reduction of spermatogenesis but not fertility in Creb3l4-deficient mice

Creb3l4 belongs to the CREB/ATF family of transcription factors that are involved in mediating transcription in response to intracellular signaling. This study shows that Creb3l4 is expressed at low levels in all organs and in different stages of embryogenesis but is present at very high levels in the testis, particularly in postmeiotic male germ cells. In contrast to CREB3L4 in the human prostate, of which specific expression was detected, Creb3l4 transcripts in the mouse prostate could be detected only by RT-PCR. To identify the physiological function of Creb3l4, the murine gene was inactivated by replacement with the gene encoding green fluorescent protein. Surprisingly, Creb3l4-deficient mice were born at expected ratios, were healthy, and displayed normal long-term survival rates. Despite a significant reduction in the number of spermatozoa in the epididymis of Creb3l4(-)(/)(-) mice, the breeding of mutant males with wild-type females was productive and the average litter size was not significantly altered in comparison to wild-type littermates. Further analyses revealed that the seminiferous tubules of Creb3l4(-)(/)(-) mice contained all of the developmental stages, though there was evidence for increased apoptosis of meiotic/postmeiotic germ cells. These results suggest that Creb3l4 plays a role in male germ cell development, but its loss is insufficient to completely compromise the production of spermatozoa.

Transactivation of the parathyroid hormone promoter by specificity proteins and the nuclear factor Y complex

We previously identified a highly conserved specificity protein 1 (Sp1) DNA element in mammalian PTH promoters that acted as an enhancer of gene transcription and bound Sp1 and Sp3 proteins present in parathyroid gland nuclear extracts. More recently, a nuclear factor (NF)-Y element (NF-Y(prox)) was also described by our group, which was located approximately 30 bp downstream from the Sp1 site in the human PTH (hPTH) promoter and by itself acted as a weak enhancer of gene transcription. We now report that Sp proteins and NF-Y can synergistically enhance transcription of a minimal hPTH promoter construct. Positioning of the Sp1 DNA element appears to be critical for this synergism because deviations of one half of a helical turn caused an approximate 60% decrease in transactivation. Finally, examination of the bovine PTH (bPTH) promoter also revealed Sp1/NF-Y synergism, in conjunction with the identification of an analogous NF-Y binding site similarly positioned downstream from the bPTH Sp1 element. In summary, synergistic transactivation of the hPTH and bPTH promoters is observed by Sp proteins and the NF-Y complex. The conservation of this transactivation in the human and bovine promoters suggests that this may be a principle means of enhancing PTH gene transcription.

A Distal Region Involving Hepatocyte Nuclear Factor 4α and CAAT/Enhancer Binding Protein Markedly Potentiates the Protein Kinase A Stimulation of the Glucose-6-Phosphatase Promoter

Glucose-6-phosphatase (Glc6Pase) is the last enzyme of gluconeogenesis and is only expressed in the liver, kidney, and small intestine. In these tissues, the mRNA and its activity are increased when cAMP levels increased (e.g. in fasting or diabetes). We first report that a proximal region (within −200 bp relative to the transcription start site) and a distal region (−694/−500 bp) are both required for a potent cAMP and a protein kinase A (PKA) responsiveness of the Glc6Pase promoter. Using different molecular approaches, we demonstrate that hepatocyte nuclear factor (HNF4α), CAAT/ enhancer-binding protein-α (C/EBPα), C/EBPβ, and cAMP response element-binding protein (CREB) are involved in the potentiated PKA responsiveness: in the distal region, via one HNF4α- and one C/EBP-binding sites, and in the proximal region, via two HNF4α and two CREB-binding sites. We also show that HNF4α, C/EBPα, and C/EBPβ are constitutively bound to the endogenous Glc6Pase gene, whereas CREB and CREB-binding protein (CBP) will be bound to the gene upon stimulation by cAMP. These data strongly suggest that the cAMP responsiveness of the Glc6Pase promoter requires a tight cooperation between a proximal and a distal region, which depends on the presence of several HNF4α-, C/EBP-, and CREB-binding sites, therefore involving an intricate association of hepatic and ubiquitous transcription factors.

Cyclin D3 interacts with human activating transcription factor 5 and potentiates its transcription activity

The Cyclin D3 protein is a member of the D-type cyclins. Besides serving as cell cycle regulators, D-type cyclins have been reported to be able to interact with several transcription factors and modulate their transcriptional activations. Here we report that human activating transcription factor 5 (hATF5) is a new interacting partner of Cyclin D3. The interaction was confirmed by in vivo coimmunoprecipitation and in vitro binding analysis. Neither interaction between Cyclin D1 and hATF5 nor interaction between Cyclin D2 and hATF5 was observed. Confocal microscopy analysis showed that Cyclin D3 could colocalize with hATF5 in the nuclear region. Cyclin D3 could potentiate hATF5 transcriptional activity independently of its Cdk4 partner. But Cyclin D1 and Cyclin D2 had no effect on hATF5 transcriptional activity. These data provide a new clue to understand the new role of Cyclin D3 as a transcriptional regulator.

Suppression of the human parathyroid hormone promoter by vitamin D involves displacement of NF-Y binding to the vitamin D response element

An earlier report in the literature indicated the vitamin D response element (VDRE) in the human parathyroid hormone (hPTH) promoter could be specifically bound by an unidentified transcription factor in addition to the vitamin D receptor (VDR) complex. We confirmed that OK and HeLa cell nuclear extracts formed a specific complex with the hPTH VDRE that was insensitive to competition with other VDRE sequences. However, this factor could be competed for by a consensus NF-Y DNA-binding site, and an anti-NF-Y antibody was able to supershift the bound band. Mutational analysis indicated that the NF-Y-binding site partially overlapped the 3' portion of the VDRE. Transfection studies using an hPTH promoter construct in Drosophila SL2 cells demonstrated strong synergistic transactivation by NF-Y interactions with both the VDRE site and a previously described distal NF-Y-binding site. Finally, mobility shift studies indicated that the VDR heterodimer competed with NF-Y for binding to the VDRE sequence, and NF-Y-stimulated activity of the hPTH promoter could be suppressed in a hormone-dependent manner when the VDR heterodimer complex was coexpressed in SL2 cells. In summary, these findings establish the presence of a proximal NF-Y-binding site in the hPTH promoter and highlight the potential for synergism between distal and proximal NF-Y DNA elements to strongly enhance transcription. Furthermore, findings suggest that the repressive effects of vitamin D on hPTH gene transcription may involve displacement of NF-Y binding to the proximal site by the VDR heterodimer, which subsequently attenuates synergistic transactivation.

Molecular cloning and characterization of three adult rat beta-globin gene promoters

We analyzed the promoter regions of the adult rat beta (IIbeta, IIIbeta, and 0beta)-globin genes. The results indicated that (1) the activities of the minimal promoters of these three genes are proportional to the gene expression levels in vivo, and (2) erythroid-specific repressor regions are located immediately upstream of the minimal promoter sequences and are regulated by the same transcription factor.

CPTF1, a CREB-like transcription factor, is involved in the oxidative stress response in the phytopathogen Claviceps purpurea and modulates ROS level in its host Secale cereale

CPTF1, a transcription factor with significant homology to ATF/CREB bZIP factors, was identified during an expressed sequence tag (EST) analysis of in planta-expressed genes of the phytopathogen Claviceps purpurea. Using a gene-replacement approach, deletion mutants of cptf1 were created. Expression studies in axenic culture showed that the H2O2-inducible gene cpcat1 (encoding a secreted catalase) had a reduced basal expression level and no longer responded to oxidative stress in the delta cptf1 mutant. Biochemical analyses indicated that CPTF1 is a general regulator of catalase activity. Delta cptf1 mutants showed significantly reduced virulence on rye. Electron microscopical in situ localization revealed significant amounts of H2O2 in delta cptf1-infected rye epidermal tissues, indicating that the plant tissue displayed an oxidative burst-like reaction, an event not detected in wild-type infections. These data indicate that CPTF1 is involved not only in oxidative stress response in the fungus but also in modulation of the plant's defense reactions.

Cyclic AMP mediated GSTP1 gene activation in tumor cells involves the interaction of activated CREB-1 with the GSTP1 CRE: a novel mechanism of cellular GSTP1 gene regulation

The human GSTP1 gene is frequently over-expressed in many human cancers and the expression increases with tumor progression and is associated with a more aggressive biology, poor patient survival, and resistance to therapy. The molecular regulation of the human GSTP1 gene during malignancy is, however, still not well understood. Recently, we reported the presence of a cAMP response element (CRE) in the 5'-region of the human GSTP1 gene, raising the possibility that the cAMP signaling pathway, frequently aberrant in human cancers, may play an important role in the transcriptional activation of the GSTP1 gene in human tumors. In this study, we report that the GSTP1 gene is an early cAMP response gene. Treatment of cells of the human lung carcinoma cell line, Calu-6, with 25 microM forskolin to activate the cAMP pathway resulted in a rapid and significant (sevenfold after 30 min) increase in GSTP1 gene transcripts, which peaked at 12-fold after 4 h. The forskolin-activated GSTP1 transcription in Calu-6 cells was suppressed dose-dependently by a 2-h pre-treatment with 0.1, 1.0, and 10 microM of the adenylate cyclase inhibitor, 2', 5'-dideoxyadenosine. Western blot analysis showed a rapid, fivefold increase, in GSTP1 protein levels after treatment with 25 microM forskolin, with a peak at 2 h post-treatment. The levels of phosphorylated CRE (Ser133) binding protein-1 (CREB-1) increased rapidly, sevenfold at 30 min, and reached 10-fold at 4 h following forskolin treatment. Intracellular cAMP levels also increased rapidly reaching 12-fold at 30 min. Gel mobility shift and supershift assays and DNase/footprinting analyses demonstrated that CREB-1 bZIP and CREB-containing nuclear extracts recognized the GSTP1 CRE with high affinity and specificity. Binding of CREB-1 bZIP to the GSTP1 CRE was abolished when the GSTP1 CRE sequence 5'-CGTCA-3', was mutated at the core nucleotides. Finally, transfection studies using luciferase plasmid constructs showed the GSTP1 CRE to be required for the cAMP-activated gene expression. Together, these findings describe a novel cAMP- and CREB-1-mediated mechanism of transcriptional regulation of the GSTP1 gene and suggest that this may be an important mechanism underlying the increased GSTP1 expression observed in tumors with an aberrant cAMP signaling pathway and in normal cells under conditions of stress, associated with increased intracellular cAMP.

NF-kappaB and TNF-alpha stimulate androgen receptor expression in Sertoli cells

Germ cell development within the mammalian testis requires testosterone stimulation of somatic Sertoli cells via interaction with intracellular androgen receptors (AR). AR expression levels undergo marked changes during spermatogenesis suggesting that the modulation of AR expression is an important mechanism to regulate Sertoli cell responsiveness to testosterone. An analysis of the AR gene promoter revealed three kappaB enhancer elements that interacted with Sertoli cell p50 and RelA NF-kappaB proteins, and the overexpression of these NF-kappaB subunits in Sertoli cells stimulated AR promoter activity. Moreover, TNF-alpha, a secretory product of round spermatids, stimulated NF-kappaB binding to the AR promoter, induced AR promoter activity, and increased endogenous AR expression in primary cultures of Sertoli cells. Given the requirement of testosterone for spermatogenesis and the importance of AR in mediating Sertoli cell responsiveness to testosterone, the stimulation of AR expression by NF-kappaB and TNF-alpha may represent an important regulatory mechanism required to maintain efficient spermatogenesis.

Nopp140 is a mediator of the protein kinase A signaling pathway that activates the acute phase response alpha1-acid glycoprotein gene

The acute phase response (APR) in liver during inflammation is one of the well known examples for elucidating the signaling pathways that lead to the combinatorial regulation of gene expression. The APR is exemplified by alpha(1)-acid glycoprotein gene (agp) expression. A number of transcription factors, including CCAAT/enhancer-binding protein beta (C/EBPbeta), glucocorticoid receptor, cAMP-response element-binding protein (CREB), and Nopp140, are known to participate in its induction. The underlying mechanism of Nopp140 and other factors for regulating agp expression remains unclear. Here we demonstrate that protein kinase A (PKA)-dependent phosphorylation of Nopp140, together with C/EBPbeta, induces agp gene expression synergistically. The cooperative activation of the agp gene by Nopp140 and forskolin is sensitive to inhibition by PKI. Results from biochemical and functional characterizations of Nopp140 mutants defective in PKA phosphorylation sites suggest that PKA-dependent Nopp140 phosphorylation is important for its role in agp gene activation. Furthermore, maximal activation of the agp gene by PKA-phosphorylated Nopp140 depends on the presence of CREB and C/EBPbeta. The participation of CREB in the activation is, however, independent of its PKA-mediated phosphorylation. In summary, we demonstrate the existence of a novel Nopp140-mediated PKA signaling pathway that leads to the activation of agp, one of the major acute phase response genes.

AP-2alpha modulates human corticotropin-releasing hormone gene expression in the placenta by direct protein-protein interaction

Since AP-2alpha induces the expression of hPL, hCG and other syncytiotrophoblast-specific marker genes in cytotrophoblast cells during in vitro differentiation, we have examined whether AP-2alpha also induces hCRH gene expression during differentiation of cytotrophoblast cells. Infection of human cytotrophoblast cells in vitro with an adenovirus expressing AP-2alpha resulted in a twofold increase in hCRH mRNA levels, while infection with an adenovirus expressing a dominant/negative mutant of AP-2alpha inhibited basal hCRH mRNA levels by 40% and completely blocked the induction of hCRH mRNA by AP-2alpha. Transient transfection studies in AtT-20 and HepG2 cells indicated that the induction of hCRH mRNA levels was due, at least in part, to transcriptional activation of the hCRH gene. Gel mobility shift and immunoprecipitation assays strongly suggest that AP-2alpha induces hCRH gene expression by interacting with CREB and not by binding directly to the hCRH promoter.

A new polymorphic site located in the human UCP1 gene controls the in vitro binding of CREB-like factor

Uncoupling protein 1 (UCP1) is uniquely expressed in brown adipose tissue (BAT) and generates heat by uncoupling respiration from ATP synthesis. A defect in BAT thermogenesis has been described in different models of rodent obesity. In humans, the implication of BAT in energy expenditure is still under discussion. A BclI polymorphism associated with fat gain over time has been described in the upstream region of the human UCP1 (hUCP1) gene. In this study, a new polymorphic site linked to the BclI site is described which results in a C to A point mutation, 89 bp downstream of the BclI site, ie at position -3737 bp. This site is located in the recently analysed regulatory region of the hUCP1 gene. The mutation disrupts a consensus site for the binding of ATF/CREB transcription factor family and inhibits the factor binding in vitro. However, transient transfection of a rodent brown adipocyte cell line shows that the isoproterenol (ISO) stimulation of the hUCP1 gene transcription is not significantly affected by this mutation. However, we postulate that the C/A substitution, in human, may contribute to a minor defect in the regulation of hUCP1 transcription and that would explain fat gain over time.

Thyroid-stimulating hormone and thyroid-stimulating hormone receptor structure-function relationships

This review focuses on recent advances in the structure-function relationships of thyroid-stimulating hormone (TSH) and its receptor. TSH is a member of the glycoprotein hormone family constituting a subset of the cystine-knot growth factor superfamily. TSH is produced by the pituitary thyrotrophs and released to the circulation in a pulsatile manner. It stimulates thyroid functions using specific membrane TSH receptor (TSHR) that belongs to the superfamily of G protein-coupled receptors (GPCRs). New insights into the structure-function relationships of TSH permitted better understanding of the role of specific protein and carbohydrate domains in the synthesis, bioactivity, and clearance of this hormone. Recent progress in studies on TSHR as well as studies on the other GPCRs provided new clues regarding the molecular mechanisms of receptor activation. Such advances are a result of extensive site-directed mutagenesis, peptide and antibody approaches, detailed sequence analyses, and molecular modeling as well as studies on naturally occurring gain- and loss-of-function mutations. This review integrates expanding information on TSH and TSHR structure-function relationships and summarizes current concepts on ligand-dependent and -independent TSHR activation. Special emphasis has been placed on TSH domains involved in receptor recognition, constitutive activity of TSHR, new insights into the evolution of TSH bioactivity, and the development of high-affinity TSH analogs. Such structural, physiological, pathophysiological, evolutionary, and therapeutic implications of TSH-TSHR structure-function studies are frequently discussed in relation to concomitant progress made in studies on gonadotropins and their receptors.

The molecular biology and nomenclature of the activating transcription factor/cAMP responsive element binding family of transcription factors: activating transcription factor proteins and homeostasis

The mammalian ATF/CREB family of transcription factors represents a large group of basic region-leucine zipper (bZip) proteins which was originally defined in the late 1980s by their ability to bind to the consensus ATF/CRE site 'TGACGTCA'. Over the past decade, cDNA clones encoding identical or homologous proteins have been isolated by different laboratories and given different names. These proteins can be grouped into subgroups according to their amino acid similarity. In this review, we will briefly describe the classification of these proteins with a historical perspective of their nomenclature. We will then review three members of the ATF/CREB family of proteins: ATF3, ATF4 and ATF6. We will address four issues for each protein: (a) homologous proteins and alternative names, (b) dimer formation with other bZip proteins, (c) transcriptional activity, and (d) potential physiological functions. Although the name Activating Transcription Factor (ATF) implies that they are transcriptional activators, some of these proteins are transcriptional repressors. ATF3 homodimer is a transcriptional repressor and ATF4 has been reported to be either an activator or a repressor. We will review the reports on the transcriptional activities of ATF4, and propose potential explanations for the discrepancy. Although the physiological functions of these proteins are not well understood, some clues can be gained from studies with different approaches. When the data are available, we will address the following questions. (a) How is the expression (at the mRNA level or protein level) regulated? (b) How are the transcriptional activities regulated? (c) What are the interacting proteins (other than bZip partners)? (d) What are the consequences of ectopically expressing the gene (gain-of-function) or deleting the gene (loss-of-function)? Although answers to these questions are far from being complete, together they provide clues to the functions of these ATF proteins. Despite the diversity in the potential functions of these proteins, one common theme is their involvement in cellular responses to extracellular signals, indicating a role for these ATF proteins in homeostasis.

Homeobox protein Hex induces SMemb/nonmuscle myosin heavy chain-B gene expression through the cAMP-responsive element

Recent studies have shown that the homeobox gene Hex plays an important role in inducing differentiation of vascular endothelial cells. In this study, we examined the expression of Hex in vascular smooth muscle cells (VSMCs) in vitro and in vivo. Immunohistochemistry showed a marked induction of Hex protein in neointimal VSMCs after balloon injury in rat aorta. Western and reverse transcriptase-polymerase chain reaction analyses demonstrated that Hex was abundantly expressed in cultured VSMCs, whereas it was undetectable in other cell types or in normal aorta. The expression pattern of Hex was similar to that of SMemb/NMHC-B, a nonmuscle isoform of myosin heavy chain that we have previously reported to be a molecular marker of dedifferentiated VSMCs. We next examined the role of Hex in SMemb gene transcription. Promoter analysis demonstrated that the sequence identical to consensus cAMP-responsive element (CRE) located at -481 of the SMemb promoter was critical for Hex responsiveness. Mutant Hex expression vector, which lacks the homeodomain, failed to stimulate SMemb gene transcription, suggesting the requirement of the homeodomain for its transactivation. Elecrophoretic mobility shift assay showed that Hex binds to a consensus binding sequence for homeobox proteins, but not to CRE. Cotransfection of protein kinase A expression vector increased the ability of Hex to stimulate SMemb promoter activity in a CRE-dependent manner. Overexpression of CRE binding protein (CREB), but not Mut-CREB which contains mutation at Ser133, strongly activated Hex-induced SMemb promoter activity. These results suggest that Hex mediates transcriptional induction of the SMemb/NMHC-B gene via its homeodomain, and Hex can function as a transcriptional modulator of CRE-dependent transcription in VSMCs.

CREB is involved in mouse annexin A1 regulation by cAMP and glucocorticoids

A cAMP and some glucocorticoid response elements have been underlined in the promoter of mouse annexin A1. To analyse the function of these DNA sequences, the role of cAMP and glucocorticoids, as well as the transcription factors involved in their activation, were investigated. A construct containing 1381 bp of the DNA 5'-flanking annexin A1 gene fused to LacZ was used. The level of activation of the reporter gene was analysed by transient transfection of the JEG3 cell line. Activation of beta-galactosidase expression was observed with both dibutyryl cAMP and dexamethasone when compared with cells treated with serum only. Simultaneous addition of dexamethasone and dibutyryl cAMP did not result in a synergistic effect but rather in a competitive one. Gel-shift assays with a probe including the cAMP response element-like element of the annexin A1 promoter revealed a main specific DNA-protein complex when cells were stimulated with dibutyryl cAMP and/or dexamethasone. In all cases CREB protein was identified by supershift analysis. We therefore conclude that this cAMP response element sequence plays a prominent role in the transactivation of the annexin A1 promoter by dibutyryl cAMP and that it is involved in the response to glucocorticoids.

Molecular cloning of the chicken prolactin gene and activation by Pit-1 and cAMP-induced factor in GH3 cells

Transcription of the prolactin (PRL) gene has been reported to be activated by a nuclear factor, Pit-1. However, the precise molecular mechanisms of the Pit-1-mediated PRL gene activation are still unclear. We have cloned the chicken PRL (cPRL) gene and its 5'-flanking region to analyze their structure and transcription-initiating mechanism. In luciferase assay, forskolin activated the proximal promoter region between -248 and -76 to transcribe the cPRL gene in GH3 cells, although there is no canonical cyclic AMP-responsive element in the promoter region. In gel mobility shift assay, a DNA fragment between -104 and -76 containing a putative Pit-1 binding site was bound by nuclear factors from the GH3 cells. Furthermore, it was observed that Pit-1 protein specifically bound to the DNA fragment in the supershift assay. These results indicate that both Pit-1 and cAMP-induced factor(s) associated with the cis element on the proximal promoter region to activate cPRL gene expression in GH3 cells.

Corticotropin-releasing hormone gene expression in primary placental cells is modulated by cyclic adenosine 3',5'-monophosphate

CRH, the principal neuropeptide regulator of pituitary ACTH secretion, is also expressed in placenta. Placental CRH has been linked to the process of human parturition. However, the mechanisms regulating transcription of the CRH gene in placenta remain unclear. cAMP signaling pathways play important roles in regulating the expression of a diverse range of endocrine genes in the placenta. Therefore, we have explored the effect of cAMP on CRH promoter activity in primary cultures of human placental cells. Both forskolin and 8-bromo-cAMP, activators of protein kinase A, can increase CRH promoter activity 5-fold in transiently transfected human primary placental cells, in a manner that parallels the increase in endogenous CRH peptide. Maximal stimulation of CRH promoter activity occurs at 500 micromol/L 8-bromo-cAMP and 10 micromol/L forskolin. Electrophoretic mobility shift assay and mutation analysis combined with transient transfection demonstrate that in placental cells cAMP stimulates CRH gene expression through a cAMP regulatory element in the proximal CRH promoter region and involves a placental nuclear protein interacting specifically with the cAMP regulatory element.

CHOP enhancement of gene transcription by interactions with Jun/Fos AP-1 complex proteins

The transcription factor CHOP (C/EBP homologous protein 10) is a bZIP protein induced by a variety of stimuli that evoke cellular stress responses and has been shown to arrest cell growth and to promote programmed cell death. CHOP cannot form homodimers but forms stable heterodimers with the C/EBP family of activating transcription factors. Although initially characterized as a dominant negative inhibitor of C/EBPs in the activation of gene transcription, CHOP-C/EBP can activate certain target genes. Here we show that CHOP interacts with members of the immediate-early response, growth-promoting AP-1 transcription factor family, JunD, c-Jun, and c-Fos, to activate promoter elements in the somatostatin, JunD, and collagenase genes. The leucine zipper dimerization domain is required for interactions with AP-1 proteins and transactivation of transcription. Analyses by electrophoretic mobility shift assays and by an in vivo mammalian two-hybrid system for protein-protein interactions indicate that CHOP interacts with AP-1 proteins inside cells and suggest that it is recruited to the AP-1 complex by a tethering mechanism rather than by direct binding of DNA. Thus, CHOP not only is a negative or a positive regulator of C/EBP target genes but also, when tethered to AP-1 factors, can activate AP-1 target genes. These findings establish the existence of a new mechanism by which CHOP regulates gene expression when cells are exposed to cellular stress.