The role of basic leucine zipper protein-mediated transcription in physiological and pathological myocardial hypertrophy

Spexin Diminishes Atrial Fibrillation Vulnerability by Acting on Galanin Receptor 2

BACKGROUND

G protein-coupled receptors play a critical role in atrial fibrillation (AF). Spexin is a novel ligand of galanin receptors (GALRs). In this study, we investigated the regulation of spexin and GALRs on AF and the underlying mechanisms.

METHODS

Global spexin knockout (SPX-KO) and cardiomyocyte-specific GALRs knockout (GALR-cKO) mice underwent burst pacing electrical stimulation. Optical mapping was used to determine atrial conduction velocity and action potential duration. Atrial myocyte action potential duration and inward rectifying K+ current (IK1) were recorded using whole-cell patch clamps. Isolated cardiomyocytes were stained with Fluo-3/AM dye, and intracellular Ca2+ handling was examined by CCD camera. A mouse model of AF was established by Ang-II (angiotensin II) infusion.

RESULTS

Spexin plasma levels in patients with AF were lower than those in subjects without AF, and knockout of spexin increased AF susceptibility in mice. In the atrium of SPX-KO mice, potassium inwardly rectifying channel subfamily J member 2 (KCNJ2) and sarcolipin (SLN) were upregulated; meanwhile, IK1 current was increased and Ca2+ handling was impaired in isolated atrial myocytes of SPX-KO mice. GALR2-cKO mice, but not GALR1-cKO and GALR3-cKO mice, had a higher incidence of AF, which was associated with higher IK1 current and intracellular Ca2+ overload. The phosphorylation level of CREB (cyclic AMP responsive element binding protein 1) was upregulated in atrial tissues of SPX-KO and GALR2-cKO mice. Chromatin immunoprecipitation confirmed the recruitment of p-CREB to the proximal promoter regions of KCNJ2 and SLN. Finally, spexin treatment suppressed CREB signaling, decreased IK1 current and decreased intracellular Ca2+ overload, which thus reduced the inducibility of AF in Ang-II-infused mice.

CONCLUSIONS

Spexin reduces atrial fibrillation susceptibility by inhibiting CREB phosphorylation and thus downregulating KCNJ2 and SLN transcription by GALR2 receptor. The spexin/GALR2/CREB signaling pathway represents a novel therapeutic avenue in the development of agents against atrial fibrillation.

Activating Transcription Factor 3 Stimulates Follicle-Stimulating Hormone-β Expression In Vitro But Is Dispensable for Follicle-Stimulating Hormone Production in Murine Gonadotropes In Vivo

Follicle-stimulating hormone (FSH), a dimeric glycoprotein produced by pituitary gonadotrope cells, regulates spermatogenesis in males and ovarian follicle growth in females. Hypothalamic gonadotropin-releasing hormone (GnRH) stimulates FSHβ subunit gene (Fshb) transcription, though the underlying mechanisms are poorly understood. To address this gap in knowledge, we examined changes in pituitary gene expression in GnRH-deficient mice (hpg) treated with a regimen of exogenous GnRH that increases pituitary Fshb but not luteinizing hormone β (Lhb) messenger RNA levels. Activating transcription factor 3 (Atf3) was among the most upregulated genes. Activating transcription factor 3 (ATF3) can heterodimerize with members of the activator protein 1 family to regulate gene transcription. Co-expression of ATF3 with JunB stimulated murine Fshb, but not Lhb, promoter-reporter activity in homologous LβT2b cells. ATF3 also synergized with a constitutively active activin type I receptor to increase endogenous Fshb expression in these cells. Nevertheless, FSH production was intact in gonadotrope-specific Atf3 knockout [conditional knockout (cKO)] mice. Ovarian follicle development, ovulation, and litter sizes were equivalent between cKOs and controls. Testis weights and sperm counts did not differ between genotypes. Following gonadectomy, increases in LH secretion were enhanced in cKO animals. Though FSH levels did not differ between genotypes, post-gonadectomy increases in pituitary Fshb and gonadotropin α subunit expression were more pronounced in cKO than control mice. These data indicate that ATF3 can selectively stimulate Fshb expression in vitro but is not required for FSH production in vivo.

A novel function of ATF3 in suppression of ferroptosis in mouse heart suffered ischemia/reperfusion

INTRODUCTION

Ferroptosis, a newly identified type of programmed cell death type, has been proven to contribute to the progression of myocardial ischemia/reperfusion (I/R) injury. However, little is known about ferroptosis regulation in I/R injury.

OBJECTIVES

We identified activating transcription factor 3 (ATF3) as a vital regulator of I/R induced ferroptosis and investigated the effects and potential mechanism of ATF3 in cardiac ferroptosis.

METHODS

In this study, the dynamic RNA-sequencing (RNA-seq) analysis were performed on mouse hearts exposed to different I/R schedules to identify that ATF3 represents an important modulatory molecule in myocardial I/R injury. Then knockout, rescue and overexpression methods were used in mice and neonatal mouse cells (NMCs) to illustrate the effect of ATF3 on myocardial I/R injury. Loss/gain of function techniques were used both in vivo and in vitro to explore the effects of ATF3 on ferroptosis in I/R injury. Furthermore, chromatin immunoprecipitation sequence (ChIP-seq) analysis was performed in the AC16 human cardiomyocyte cell line to investigate potential genes regulated by ATF3.

RESULTS

ATF3 expression reached highest level at early stage of reperfusion, knockout of ATF3 significantly aggravated I/R injury, which could be rescued by ATF3 re-expression. Knockout and the re-expression of ATF3 changed the transcription levels of multiple ferroptosis genes. In addition, results showed that overexpression of ATF3 inhibits cardiomyocyte ferroptosis triggered by erastin and RSL3. Lastly, ChIP-seq and dual luciferase activity analysis revealed ATF3 could bind to the transcription start site of Fanconi anaemia complementation group D2 (FANCD2) and increased the FANCD2 promoter activity. Furthermore, we first demonstrated that overexpression of FANCD2 exerts significant anti-ferroptosis and cardioprotective effect on AC16 cell H/R injury.

CONCLUSION

ATF3 inhibits cardiomyocyte ferroptotic death in I/R injury, which might be related with regulating FANCD2. Our study provides new insight into the molecular target for the therapy of myocardial I/R injury.

The Role of the CREB Protein Family Members and the Related Transcription Factors in Radioresistance Mechanisms

In the framework of space flight, the risk of radiation carcinogenesis is considered a "red" risk due to the high likelihood of occurrence as well as the high potential impact on the quality of life in terms of disease-free survival after space missions. The cyclic AMP response element-binding protein (CREB) is overexpressed both in haematological malignancies and solid tumours and its expression and function are modulated following irradiation. The CREB protein is a transcription factor and member of the CREB/activating transcription factor (ATF) family. As such, it has an essential role in a wide range of cell processes, including cell survival, proliferation, and differentiation. Among the CREB-related nuclear transcription factors, NF-κB and p53 have a relevant role in cell response to ionising radiation. Their expression and function can decide the fate of the cell by choosing between death or survival. The aim of this review was to define the role of the CREB/ATF family members and the related transcription factors in the response to ionising radiation of human haematological malignancies and solid tumours.

Homozygous CREM-IbΔC-X Overexpressing Mice Are a Reliable and Effective Disease Model for Atrial Fibrillation

Background: Atrial fibrillation (AF) is a significant cause of morbidity and mortality with foreseeably increasing prevalence. While large animal models of the disease are well established but resource intensive, transgenic AF mouse models are not yet widely used to develop or validate novel therapeutics for AF. Hemizygous mice with a cardiomyocyte-specific overexpression of the human cAMP response element modulator (CREM) isoform IbΔC-X spontaneously develop AF on grounds of an arrhythmogenic substrate consisting of alterations in structure, conduction, and calcium handling.

Objective: We investigated if homozygous expression of the CREM-IbΔC-X transgene in mice alters the time course of AF development, and if homozygous CREM-IbΔC-X transgenics could be suitable as a disease model of AF.

Methods: Southern Blot, quantitative real-time PCR, and immunoblotting were used to identify and verify homozygous transgenics. Cardiac gravimetry, quantitative real-time RT-PCR, histology, survival analysis, and repeated ECG recordings allowed assessment of phenotypic development and effects of antiarrhythmic drugs.

Results: Homozygous animals could be identified by Southern blot and quantitative PCR, showing a strong trend to increased transgenic protein expression. In homozygous animals, atrial hypertrophy appeared earlier and more pronounced than in hemizygous animals, going along with an earlier onset of spontaneous AF, while no increased early mortality was observed. Application of a rate-controlling drug (esmolol) led to the expected result of a decreased heart rate. Application of a rhythm-controlling drug (flecainide) showed effects on heart rate variability, but did not lead to a definitive conversion to sinus rhythm.

Conclusion: We suggest homozygous CREM-IbΔC-X overexpressing mice as a reliable model of early onset, rapidly progressive AF.

The Activating Transcription Factor 3 (Atf3) Homozygous Knockout Mice Exhibit Enhanced Conditioned Fear and Down Regulation of Hippocampal GELSOLIN

The genetic and molecular basis underlying fear memory formation is a key theme in anxiety disorder research. Because activating transcription factor 3 (ATF3) is induced under stress conditions and is highly expressed in the hippocampus, we hypothesize that ATF3 plays a role in fear memory formation. We used fear conditioning and various other paradigms to test Atf3 knockout mice and study the role of ATF3 in processing fear memory. The results demonstrated that the lack of ATF3 specifically enhanced the expression of fear memory, which was indicated by a higher incidence of the freeze response after fear conditioning, whereas the occurrence of spatial memory including Morris Water Maze and radial arm maze remained unchanged. The enhanced freezing behavior and normal spatial memory of the Atf3 knockout mice resembles the fear response and numbing symptoms often exhibited by patients affected with posttraumatic stress disorder. Additionally, we determined that after fear conditioning, dendritic spine density was increased, and expression of Gelsolin, the gene encoding a severing protein for actin polymerization, was down-regulated in the bilateral hippocampi of the Atf3 knockout mice. Taken together, our results suggest that ATF3 may suppress fear memory formation in mice directly or indirectly through mechanisms involving modulation of actin polymerization.

Identification of Novel SCIRR69-Interacting Proteins During ER Stress Using SILAC-Immunoprecipitation Quantitative Proteomics Approach

Spinal cord injury and regeneration-related protein #69 (SCIRR69),also known as cAMP-responsive element-binding protein 3-like 2, belongs to the CREB/ATF family, some members of which play significant roles in ER stress. However, it is still not fully elucidated whether SCIRR69 involves in ER stress and its biochemical and functional roles during ER stress. In this study, we firstly treated fetal rat spinal cord neuron cells (SCN) and PC12 cells with ER stress activator thapsigargin (TG) or tunicamycin (TM) and then detected the expression pattern of SCIRR69 in response to ER stress at mRNA and protein levels using real-time PCR assay and immunoblotting. Results showed that the expression pattern of SCIRR69 was largely consistent with those of ER stress marker (ATF6, BIP and CHOP) at either mRNA level or protein level, implying that SCIRR69 may play important roles in ER stress. Subsequently, we used stable isotope labeling by amino acids in cell culture (SILAC)-immunoprecipitation quantitative proteomics to identify interaction partners of SCIRR69 during TG-induced ER stress in PC12 cells and found that transitional endoplasmic reticulum ATPase (TERA) and sideroflexin-1 (SFXN1) were potential SCIRR69-interacting proteins. The interaction between SCIRR69 and TERA or SFXN1 was validated using co-immunoprecipitation. Those results provide some clues for novel signaling nexuses that made by interactions between SCIRR69 and TERA or SFXN1. Our findings may facilitate a better understanding of the fundamental functions of SCIRR69 during ER stress.

ATF3-dependent cross-talk between cardiomyocytes and macrophages promotes cardiac maladaptive remodeling

RATIONALE

Pressure overload induces adaptive remodeling processes in the heart. However, when pressure overload persists, adaptive changes turn into maladaptive alterations leading to cardiac hypertrophy and heart failure. ATF3 is a stress inducible transcription factor that is transiently expressed following neuroendocrine stimulation. However, its role in chronic pressure overload dependent cardiac hypertrophy is currently unknown.

OBJECTIVE

The objective of the study was to study the role of ATF3 in chronic pressure overload dependent cardiac remodeling processes.

METHODS AND RESULTS

Pressure overload was induced by phenylephrine (PE) mini-osmotic pumps in various mice models of whole body, cardiac specific, bone marrow (BM) specific and macrophage specific ATF3 ablations. We show that ATF3-KO mice exhibit a significantly reduced expression of cardiac remodeling markers following chronic pressure overload. Consistently, the lack of ATF3 specifically in either cardiomyocytes or BM derived cells blunts the hypertrophic response to PE infusion. A unique cross-talk between cardiomyocytes and macrophages was identified. Cardiomyocytes induce an ATF3 dependent induction of an inflammatory response leading to macrophage recruitment to the heart. Adoptive transfer of wild type macrophages, but not ATF3-KO derived macrophages, into wild type mice potentiates maladaptive response to PE infusion.

CONCLUSIONS

Collectively, this study places ATF3 as a key regulator in promoting pressure overload induced cardiac hypertrophy through a cross-talk between cardiomyocytes and macrophages. Inhibiting this cross-talk may serve as a useful approach to blunt maladaptive remodeling processes in the heart.

Gene expression profiling reveals potential prognostic biomarkers associated with the progression of heart failure

Background

Heart failure (HF) is the most common cause of morbidity and mortality in developed countries. Here, we identify biologically relevant transcripts that are significantly altered in the early phase of myocardial infarction and are associated with the development of post-myocardial infarction HF.

Methods

We collected peripheral blood samples from patients with ST-segment elevation myocardial infarction (STEMI): n = 111 and n = 41 patients from the study and validation groups, respectively. Control groups comprised patients with a stable coronary artery disease and without a history of myocardial infarction. Based on plasma NT-proBNP level and left ventricular ejection fraction parameters the STEMI patients were divided into HF and non-HF groups. Microarrays were used to analyze mRNA levels in peripheral blood mononuclear cells (PBMCs) isolated from the study group at four time points and control group. Microarray results were validated by RT-qPCR using whole blood RNA from the validation group.

Results

Samples from the first three time points (admission, discharge, and 1 month after AMI) were compared with the samples from the same patients collected 6 months after AMI (stable phase) and with the control group. The greatest differences in transcriptional profiles were observed on admission and they gradually stabilized during the follow-up. We have also identified a set of genes the expression of which on the first day of STEMI differed significantly between patients who developed HF after 6 months of observation and those who did not. RNASE1, FMN1, and JDP2 were selected for further analysis and their early up-regulation was confirmed in HF patients from both the study and validation groups. Significant correlations were found between expression levels of these biomarkers and clinical parameters. The receiver operating characteristic (ROC) curves indicated a good prognostic value of the genes chosen.

Conclusions

This study demonstrates an altered gene expression profile in PBMCs during acute myocardial infarction and through the follow-up. The identified gene expression changes at the early phase of STEMI that differentiated the patients who developed HF from those who did not could serve as a convenient tool contributing to the prognosis of heart failure.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-015-0149-z) contains supplementary material, which is available to authorized users.

Activating transcription factor 3 protects against pressure-overload heart failure via the autophagy molecule Beclin-1 pathway

Activating transcription factor 3 (ATF3), a cAMP response element-binding protein/ATF family transcription factors member, has been implicated in the cardiovascular and inflammatory system and is rapidly induced by ischemic-reperfusion injuries. We performed transverse aortic banding (TAB) experiments using ATF3 gene-deleted mice (ATF3(-/-)) and wild-type (WT) mice to determine what effect it might have on heart failure induced by pressure overloading. Compared with the WT mice, ATF3(-/-) mice were found by echocardiography to have decreased left ventricular contractility with loss of normal cardiac hypertrophic remodeling. The ATF3(-/-) mice had greater numbers of terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine nick-end labeling-positive cells and higher levels of activated caspase-3, as well as more apoptosis. Restoration of ATF3 expression in the heart of ATF3(-/-) mice by adenovirus-induced ATF3 treatment significantly improved cardiac contractility after TAB. The results from molecular and biochemical analyses, including chromatin immune-precipitation and in vitro /in vivo promoter assays, showed that ATF3 bound to the ATF/cAMP response element of the Beclin-1 promoter and that ATF3 reduced autophagy via suppression of the Beclin-1-dependent pathway. Furthermore, infusion of tert-butylhydroquinone (tBHQ), a selective ATF3 inducer, increased the expression of ATF3 via the nuclear factor erythroid 2-related transcriptional factor, inhibited TAB-induced cardiac dilatation, and increased left ventricular contractility, thereby rescuing heart failure. Our study identified a new epigenetic regulation mediated by the stress-inducible gene ATF3 on TAB-induced cardiac dysfunction. These findings suggest that the ATF3 activator tBHQ may have therapeutic potential for the treatment of pressure-overload heart failure induced by chronic hypertension or other pressure overload mechanisms.

Transcription factor SCIRR69 involved in the activation of brain-derived neurotrophic factor gene promoter II in mechanically injured neurons

The spinal cord injury and regeneration-related gene #69 (SCIRR69), which was identified in our screen for genes upregulated after spinal cord injury, encode a protein belonging to the cAMP response element-binding protein (CREB)/ATF family of transcription factors. Our previous study showed that SCIRR69 functions as a transcriptional activator. However, the target gene regulated by SCIRR69 and its roles in injured neurons remain unknown. In this study, we showed that SCIRR69 is widely distributed in the central nervous system. Full-length SCIRR69 is an endoplasmic reticulum-bound protein. Following mechanical injury to neurons, SCIRR69 was induced and proteolytically cleaved by site-1 and site-2 proteases, and the proteolytically cleaved SCIRR69 (p60-SCIRR69) was translocated to the nucleus where it bound to brain-derived neurotrophic factor (BDNF) gene promoter II. In addition, loss- and gain-of-function studies confirmed that SCIRR69 is involved in the regulation of BDNF expression in injured neurons. As expected, the culture supernatants of PC12 cells stably expressing p60-SCIRR69 contained higher levels of BDNF, and more remarkably promoted neurite outgrowth in a spinal cord slice culture model in vitro than the supernatants of control cells. These results suggest that SCIRR69 is a novel regulator of the BDNF gene and may play an important role in the repair and/or regeneration of damaged neural tissues by specifically activating BDNF promoter II.

Adult cardiac expression of the activating transcription factor 3, ATF3, promotes ventricular hypertrophy

Cardiac hypertrophy is an adaptive response to various mechanophysical and pathophysiological stresses. However, when chronic stress is sustained, the beneficial response turns into a maladaptive process that eventually leads to heart failure. Although major advances in the treatment of patients have reduced mortality, there is a dire need for novel treatments for cardiac hypertrophy. Accordingly, considerable efforts are being directed towards developing mice models and understanding the processes that lead to cardiac hypertrophy. A case in point is ATF3, an immediate early transcription factor whose expression is induced in various cardiac stress models but has been reported to have conflicting functional significance in hypertrophy. To address this issue, we generated a transgenic mouse line with tetracycline-regulated ATF3 cardiac expression. These mice allowed us to study the consequence of ATF3 expression in the embryo or during the adult period, thus distinguishing the effect of ATF3 on development versus pathogenesis of cardiac dysfunction. Importantly, ATF3 expression in adult mice resulted in rapid ventricles hypertrophy, heart dysfunction, and fibrosis. When combined with a phenylephrine-infusion pressure overload model, the ATF3 expressing mice displayed a severe outcome and heart dysfunction. In a complementary approach, ATF3 KO mice displayed a lower level of heart hypertrophy in the same pressure overload model. In summary, ectopic expression of ATF3 is sufficient to promote cardiac hypertrophy and exacerbates the deleterious effect of chronic pressure overload; conversely, ATF3 deletion protects the heart. Therefore, ATF3 may serve as an important drug target to reduce the detrimental consequences of heart hypertrophy.

Human SNF2L gene is regulated constitutively and inducibly in neural cells via a cAMP-response element

PURPOSE

SNF2L belongs to Imitation Switch family and plays an essential role in neural tissues and gonads. In our previous studies, we have demonstrated that the basal transcription of human SNF2L gene is regulated by two cis-elements, cAMP response element (CRE)- and Sp1-binding sites. Recent studies suggested that cyclic adenosine monophosphate (cAMP) stimulation significantly up-regulated SNF2L expression in ovarian granulose cells. These data suggested that protein kinase-mediated signal pathways might also regulate SNF2L expression in neural cells. We therefore investigated the effects of agents that activate protein kinases A on SNF2L gene expression in neural cells.

MATERIALS AND METHODS

To increase intracellular cAMP levels, all neural cells were treated with forskolin and dbcAMP, two cAMP response activators. We exmined the effects of cAMP on the promoter activity of human SNF2L gene by luciferase reporter gene assays, and further examined the effects of cAMP on endogenous SNF2L mRNA levels by qPCR.

RESULTS

Transient expression of a luciferase fusion gene under the control of the SNF2L promoter was significantly increased by treatment of rat primary neurons with forskolin or dbcAMP, but not PC12, C6 and SH-SY5Y cells. Consistently, treatment with forskolin or dbcAMP could enhance endogenous SNF2L mRNA levels also only in rat primary neurons.

CONCLUSION

These results suggest that the CRE consensus sequence in the SNF2L proximal promoter most likely confers constitutive activation and regulation by cAMP in neural cells.

Cyclic mechanical strain causes cAMP-response element binding protein activation by different pathways in cardiac fibroblasts

The transcription factor cAMP-response element binding protein (CREB) mediates the mechanical strain-induced gene expression in the heart. This study investigated which signaling pathways are involved in the straininduced CREB activation using cultured ventricular fibroblasts from adult rat hearts. CREB phosphorylation was analyzed by immunocytochemistry and ELISA. Cyclic mechanical strain (1 Hz and 5% elongation) for 15 min induced CREB phosphorylation in all CREB-positive fibroblasts. Several signaling transduction pathways can contribute to strain-induced CREB activation. The inhibition of PKA, PKC, MEK, p38-MAPK or PI3-kinase partially reduced the strain-induced CREB phosphorylation. Activation of PKA by forskolin or PKC by PMA resulted in a level of CREB phosphorylation comparable to the reduced level of the strain-induced CREB phosphorylation in the presence of PKA or PKC inhibitors. Signaling pathways involving PKC, MEK, p38-MAPK or PI3-kinase seem to converge during strain-induced CREB activation. PKA interacted additively with the investigated signaling pathways. The strain-induced c-Fos expression can be reduced by PKC inhibition but not by PKA inhibition. Our results suggest that the complete strain-induced CREB phosphorylation involves several signaling pathways that have a synergistic effect. The influence on gene expression is dependent on the level and the time of CREB stimulation. These wide-ranging possibilities of CREB activation provide a graduated control system.

Activating transcription factor 3 deficiency promotes cardiac hypertrophy, dysfunction, and fibrosis induced by pressure overload

Activating transcription factor 3 (ATF3), which is encoded by an adaptive-response gene induced by various stimuli, plays an important role in the cardiovascular system. However, the effect of ATF3 on cardiac hypertrophy induced by a pathological stimulus has not been determined. Here, we investigated the effects of ATF3 deficiency on cardiac hypertrophy using in vitro and in vivo models. Aortic banding (AB) was performed to induce cardiac hypertrophy in mice. Cardiac hypertrophy was estimated by echocardiographic and hemodynamic measurements and by pathological and molecular analysis. ATF3 deficiency promoted cardiac hypertrophy, dysfunction and fibrosis after 4 weeks of AB compared to the wild type (WT) mice. Furthermore, enhanced activation of the MEK-ERK1/2 and JNK pathways was found in ATF3-knockout (KO) mice compared to WT mice. In vitro studies performed in cultured neonatal mouse cardiomyocytes confirmed that ATF3 deficiency promotes cardiomyocyte hypertrophy induced by angiotensin II, which was associated with the amplification of MEK-ERK1/2 and JNK signaling. Our results suggested that ATF3 plays a crucial role in the development of cardiac hypertrophy via negative regulation of the MEK-ERK1/2 and JNK pathways.

Spontaneous high-frequency action potential

Action potential, which is the foundation of physiology and electrophysiology, is most vital in physiological research. This work starts by detecting cardiac electrophysiology (tachyarrhythmias), combined with all spontaneous discharge phenomena in vivo such as wound currents and spontaneous neuropathic pain, elaborates from generation, induction, initiation, to all of the features of spontaneous high-frequency action potential-SSL action potential mechanism, i.e., connecting-end hyperpolarization initiates spontaneous depolarization and action potential in somatic membrane. This work resolves the conundrums of in vivo spontaneous discharge in tachyarrhythmias, wounds, denervation supersensitivity, neurogenic pain (hyperalgesia and allodynia), epileptic discharge and diabetic pain in pathophysiological and clinical researches that have puzzled people for a hundred years.

Angiotensin II signaling up-regulates the immediate early transcription factor ATF3 in the left but not the right atrium

The atria respond to various pathological stimuli including pressure and volume overload with remodeling and dilatation. Dilatation of the left atrium is associated with atrial fibrillation. The mechanisms involved in chamber-specific hypertrophy are largely unknown. Angiotensin II is hypothesized to take part in mediating this response. ATF3 is an immediate early gene found at the receiving end of multiple stress and growth stimuli. Here we characterize ATF3 as a direct target gene for angiotensin II. ATF3 expression is regulated by angiotensin receptor-mediated signaling in vivo and in vitro at the transcriptional level. ATF3 induction is mediated by cooperation between both the AT(1A) and AT₂ receptor subtypes. While AT₂R blocker (PD123319) efficiently blocks ATF3 induction in response to angiotensin II injection, it results in an increase in blood pressure indicating that the effect of angiotensin II on ATF3 is independent of its effect on blood pressure. In contrast to adrenergic stimulation that induces ATF3 in all heart chambers, ATF3 induction in response to angiotensin II occurs primarily in the left chambers. We hypothesize that the activation of differential signaling pathways accounts for the chamber-specific induction of ATF3 expression in response to angiotensin II stimulation. Angiotensin II injection rapidly activates the EGFR-dependent pathways including ERK and PI3K-AKT in the left but not the right atrium. EGF receptor inhibitor (Gefitinib/Iressa) as well as the AKT inhibitor (Triciribine) significantly abrogates ATF3 induction by angiotensin II in the left chambers. Collectively, our data strongly place ATF3 as a unique nuclear protein target in response to angiotensin II stimulation in the atria. The spatial expression of ATF3 may add to the understanding of the signaling pathways involved in cardiac response to neuro-hormonal stimulation, and in particular to the understanding of left atrial-generated pathology such as atrial fibrillation.

Jun dimerization protein 2 controls senescence and differentiation via regulating histone modification

Transcription factor, Jun dimerization protein 2 (JDP2), binds directly to histones and DNAs and then inhibits the p300-mediated acetylation both of core histones and of reconstituted nucleosomes that contain JDP2 recognition DNA sequences. JDP2 plays a key role as a repressor of adipocyte differentiation by regulation of the expression of the gene C/EBPδ via inhibition of histone acetylation. Moreover, JDP2-deficient mouse embryonic fibroblasts (JDP2^−/− MEFs) are resistant to replicative senescence. JDP2 inhibits the recruitment of polycomb repressive complexes (PRC1 and PRC2) to the promoter of the gene encoding p16^Ink4a, resulting from the inhibition of methylation of lysine 27 of histone H3 (H3K27). Therefore, it seems that chromatin-remodeling factors, including the PRC complex controlled by JDP2, may be important players in the senescence program. The novel mechanisms that underline the action of JDP2 in inducing cellular senescence and suppressing adipocyte differentiation are reviewed.

Role of basic leucine zipper proteins in transcriptional regulation of the steroidogenic acute regulatory protein gene

The regulation of steroidogenic acute regulatory protein (StAR) gene transcription by cAMP-dependent mechanisms occurs in the absence of a consensus cAMP response element (CRE, TGACGTGA). This regulation is coordinated by multiple transcription factors that bind to sequence-specific elements located approximately 150 bp upstream of the transcription start site. Among the proteins that bind within this region, the basic leucine zipper (bZIP) family of transcription factors, i.e. CRE binding protein (CREB)/CRE modulator (CREM)/activating transcription factor (ATF), activator protein 1 (AP-1; Fos/Jun), and CCAAT enhancer binding protein beta (C/EBPbeta), interact with an overlapping region (-81/-72 bp) in the StAR promoter, mediate stimulus-transcription coupling of cAMP signaling and play integral roles in regulating StAR gene expression. These bZIP proteins are structurally similar and bind to DNA sequences as dimers; however, they exhibit discrete transcriptional activities, interact with several transcription factors and other properties that contribute in their regulatory functions. The 5'-flanking -81/-72 bp region of the StAR gene appears to function as a key element within a complex cAMP response unit by binding to different bZIP members, and the StAR promoter displays variable states of cAMP responsivity contingent upon the occupancy of these cis-elements with these transcription factors. The expression and activities of CREB/CREM/ATF, Fos/Jun and C/EBPbeta have been demonstrated to be mediated by a plethora of extracellular signals, and the phosphorylation of these proteins at several Ser and Thr residues allows recruitment of the transcriptional coactivator CREB binding protein (CBP) or its functional homolog p300 to the StAR promoter. This review will focus on the current level of understanding of the roles of selective bZIP family proteins within the complex series of processes involved in regulating StAR gene transcription.

Regulation of the steroidogenic acute regulatory protein gene expression: present and future perspectives

Steroid hormones are synthesized in the adrenal gland, gonads, placenta and brain and are critical for normal reproductive function and bodily homeostasis. The steroidogenic acute regulatory (StAR) protein regulates the rate-limiting step in steroid biosynthesis, i.e. the delivery of cholesterol from the outer to the inner mitochondrial membrane. The expression of the StAR protein is predominantly regulated by cAMP-dependent mechanisms in the adrenal and gonads. Whereas StAR plays an indispensable role in the regulation of steroid biosynthesis, a complete understanding of the regulation of its expression and function in steroidogenesis is not available. It has become clear that the regulation of StAR gene expression is a complex process that involves the interaction of a diversity of hormones and multiple signaling pathways that coordinate the cooperation and interaction of transcriptional machinery, as well as a number of post-transcriptional mechanisms that govern mRNA and protein expression. However, information is lacking on how the StAR gene is regulated in vivo such that it is expressed at appropriate times during development and is confined to the steroidogenic cells. Thus, it is not surprising that the precise mechanism involved in the regulation of StAR gene has not yet been established, which is the key to understanding the regulation of steroidogenesis in the context of both male and female development and function.

The ubiquitously expressed bZIP inhibitor, JDP2, suppresses the transcription of its homologue immediate early gene counterpart, ATF3

JDP2 is a ubiquitously expressed bZIP repressor protein. JDP2 binds TPA response element and cyclic AMP response element located within various promoters. JDP2 displays a high degree of homology to the immediate early gene ATF3. ATF3 plays a crucial role in the cellular adaptive response to multiple stress insults as well as growth stimuli. We have identified ATF3 as a potential target gene for JDP2 repression. JDP2 regulates the ATF3 promoter potentially through binding to both the consensus ATF/CRE site and a non-consensus ATF3 auto-repression DNA-binding element. Expression of ATF3 protein in wild-type mouse embryo fibroblast (MEF) cells is below the detectable levels, whereas, JDP2 disrupted MEF cells display noticeable level of ATF3 protein. Following either serum or ER stress stimulation, ATF3 expression is potentiated in JDP2-KO fibroblast cells as compared with wild-type cells. Mice with either JDP2 over-expression or JDP2 disruption display undetectable level of ATF3 protein. However, ATF3 induction in response to either growth or stress signals is dependent on JDP2 expression level. ATF3 induction is attenuated in JDP2 over-expressing mice whereas is potentiated in JDP2-KO mice as compared with the corresponding wild-type mice. Collectively, the data presented strongly suggest that JDP2 plays a role in the determination of the ATF3 adaptive cellular threshold response to different stress insults and growth stimuli.

Activating transcription factor 3 gene expression suggests that tissue stress plays a role in leiomyoma development

OBJECTIVE

To determine whether expression of the stress response gene ATF3 and related members of activator protein complex-1, cJun and cFos, were altered in leiomyoma compared with myometrium, and whether this difference might correlate with leiomyoma size or race.

DESIGN

Laboratory study.

SETTING

University hospital.

PATIENT(S)

Fifteen women undergoing hysterectomy for symptomatic leiomyoma.

INTERVENTION(S)

Tissue procurement, RNA isolation, reverse-transcriptase polymerase chain reaction, real-time reverse-transcriptase polymerase (RT-PCR) chain reaction, immunohistochemistry, Western blot.

MAIN OUTCOME MEASURE(S)

Expression of mRNA and protein in leiomyoma and patient-matched myometrium.

RESULT(S)

mRNA transcripts of ATF3 were decreased in leiomyoma compared with matched myometrium by both RT-PCR and real-time RT-PCR. The decrease was greater than fivefold in a majority of samples. The reduction seen in ATF3 mRNA expression did not show a correlation with race and leiomyoma size. Surprisingly, immunohistochemistry and Western blot analysis demonstrated an elevation of ATF3 protein expression by a mean of 2.9-fold. Transcripts of related AP-1 genes, cJun and cFos, were significantly decreased by a mean of -29.57 for cJun and -23.78 for cFos, but there was no significant change in protein expression of the two transcription factors.

CONCLUSIONS

Alterations in ATF3 gene expression resemble the response to mechanical and ischemic stress reported in other tissues. Results suggested that ATF3 protein expression was increased in leiomyoma, and may reflect increased tissue stress.

TRE-dependent transcription activation by JDP2-CHOP10 association

The c-Jun dimerization protein 2, JDP2, is a member of the activating protein 1 (AP-1) family of transcription factors. Overexpression of JDP2 has been shown to result in repression of AP-1-dependent transcription and inhibition of cellular transformation. Other studies suggested that JDP2 may function as an oncogene. Here we describe the identification of CHOP10, a member of the CCAAT enhancer binding proteins, as a protein associating with JDP2. In contrast to the inhibition of transcription by JDP2, JDP2–CHOP complex strongly enhances transcription from promoters containing TPA response elements (TRE), but not from those containing cyclic AMP response elements (CRE). The association between JDP2 and CHOP10 involves the leucine zipper motifs of both proteins, whereas, the basic domain of CHOP10 contributes to the association of the JDP2–CHOP10 complex with the DNA. DNA binding of JDP2–CHOP complex is observed both in vitro and in vivo. Finally, overexpression of JDP2 results in increased cell viability following ER stress and counteracts CHOP10 pro-apoptotic activity. JDP2 expression may determine the threshold for cell sensitivity to ER stress. This is the first report describing TRE-dependent activation of transcription by JDP2 and thus may provide an explanation for the as yet unexplored oncogenic properties of JDP2.