TRE-dependent transcription activation by JDP2-CHOP10 association

Research progress on activation transcription factor 3: A promising cardioprotective molecule

Activation transcription factor 3 (ATF3), a member of the ATF/cyclic adenosine monophosphate response element binding family, can be induced by a variety of stresses. Numerous studies have indicated that ATF3 plays multiple roles in the development and progression of cardiovascular diseases, including atherosclerosis, hypertrophy, fibrosis, myocardial ischemia-reperfusion, cardiomyopathy, and other cardiac dysfunctions. In past decades, ATF3 has been demonstrated to be detrimental to some cardiac diseases. Current studies have indicated that ATF3 can function as a cardioprotective molecule in antioxidative stress, lipid metabolic metabolism, energy metabolic regulation, and cell death modulation. To unveil the potential therapeutic role of ATF3 in cardiovascular diseases, we organized this review to explore the protective effects and mechanisms of ATF3 on cardiac dysfunction, which might provide rational evidence for the prevention and cure of cardiovascular diseases.

Phylogenetic and Expression Analysis of Fos Transcription Factors in Zebrafish

Members of the FOS protein family regulate gene expression responses to a multitude of extracellular signals and are dysregulated in several pathological states. Whilst mouse genetic models have provided key insights into the tissue-specific functions of these proteins in vivo, little is known about their roles during early vertebrate embryonic development. This study examined the potential of using zebrafish as a model for such studies and, more broadly, for investigating the mechanisms regulating the functions of Fos proteins in vivo. Through phylogenetic and sequence analysis, we identified six zebrafish FOS orthologues, fosaa, fosab, fosb, fosl1a, fosl1b, and fosl2, which show high conservation in key regulatory domains and post-translational modification sites compared to their equivalent human proteins. During embryogenesis, zebrafish fos genes exhibit both overlapping and distinct spatiotemporal patterns of expression in specific cell types and tissues. Most fos genes are also expressed in a variety of adult zebrafish tissues. As in humans, we also found that expression of zebrafish FOS orthologs is induced by oncogenic BRAF-ERK signalling in zebrafish melanomas. These findings suggest that zebrafish represent an alternate model to mice for investigating the regulation and functions of Fos proteins in vertebrate embryonic and adult tissues, and cancer.

Candidate plasticity gene 16 and jun dimerization protein 2 are involved in the suppression of insulin gene expression in rat pancreatic INS-1 β-cells

Chronic hyperglycemia causes pancreatic β-cell dysfunction, impaired insulin secretion and the suppression of insulin gene expression. This phenomenon is referred to as glucotoxicity, and is a critical component of the pathogenesis of type 2 diabetes. We previously reported that the expression of candidate plasticity gene 16 (CPG16) was higher in rat pancreatic INS-1 β-cells under glucotoxic conditions and CPG16 suppressed insulin promoter activity. However, the molecular mechanisms of the CPG16-mediated suppression of insulin gene expression are unclear. In this study, we found that CPG16 directly bound and phosphorylated jun dimerization protein 2 (JDP2), an AP-1 family transcription factor. CPG16 co-localized with JDP2 in the nucleus of INS-1 cells. JDP2 bound to the G1 element of the insulin promoter and up-regulated promoter activity. Finally, CPG16 suppressed the up-regulation of insulin promoter activity by JDP2 in a kinase activity-dependent manner. These results suggest that CPG16 suppresses insulin promoter activity by phosphorylating JDP2.

Prevention of tumor risk associated with the reprogramming of human pluripotent stem cells

Human pluripotent embryonic stem cells have two special features: self-renewal and pluripotency. It is important to understand the properties of pluripotent stem cells and reprogrammed stem cells. One of the major problems is the risk of reprogrammed stem cells developing into tumors. To understand the process of differentiation through which stem cells develop into cancer cells, investigators have attempted to identify the key factors that generate tumors in humans. The most effective method for the prevention of tumorigenesis is the exclusion of cancer cells during cell reprogramming. The risk of cancer formation is dependent on mutations of oncogenes and tumor suppressor genes during the conversion of stem cells to cancer cells and on the environmental effects of pluripotent stem cells. Dissecting the processes of epigenetic regulation and chromatin regulation may be helpful for achieving correct cell reprogramming without inducing tumor formation and for developing new drugs for cancer treatment. This review focuses on the risk of tumor formation by human pluripotent stem cells, and on the possible treatment options if it occurs. Potential new techniques that target epigenetic processes and chromatin regulation provide opportunities for human cancer modeling and clinical applications of regenerative medicine.

JDP2 and ATF3 deficiencies dampen maladaptive cardiac remodeling and preserve cardiac function

c-Jun dimerization protein (JDP2) and Activating Transcription Factor 3 (ATF3) are closely related basic leucine zipper proteins. Transgenic mice with cardiac expression of either JDP2 or ATF3 showed maladaptive remodeling and cardiac dysfunction. Surprisingly, JDP2 knockout (KO) did not protect the heart following transverse aortic constriction (TAC). Instead, the JDP2 KO mice performed worse than their wild type (WT) counterparts. To test whether the maladaptive cardiac remodeling observed in the JDP2 KO mice is due to ATF3, ATF3 was removed in the context of JDP2 deficiency, referred as double KO mice (dKO). Mice were challenged by TAC, and followed by detailed physiological, pathological and molecular analyses. dKO mice displayed no apparent differences from WT mice under unstressed condition, except a moderate better performance in dKO male mice. Importantly, following TAC the dKO hearts showed low fibrosis levels, reduced inflammatory and hypertrophic gene expression and a significantly preserved cardiac function as compared with their WT counterparts in both genders. Consistent with these data, removing ATF3 resumed p38 activation in the JDP2 KO mice which correlates with the beneficial cardiac function.

Collectively, mice with JDP2 and ATF3 double deficiency had reduced maladaptive cardiac remodeling and lower hypertrophy following TAC. As such, the worsening of the cardiac outcome found in the JDP2 KO mice is due to the elevated ATF3 expression. Simultaneous suppression of both ATF3 and JDP2 activity is highly beneficial for cardiac function in health and disease.

ATF3 and JDP2 deficiency in cancer associated fibroblasts promotes tumor growth via SDF-1 transcription

The activating transcription factor 3 (ATF3) and the c-Jun dimerization protein 2 (JDP2) are members of the basic leucine zipper (bZIP) family of transcription factors. These proteins share a high degree of homology and both can activate or repress transcription. Deficiency of either one of them in the non-cancer host cells was shown to reduce metastases. As ATF3 and JDP2 compensate each other's function, we studied the double deficiency of ATF3 and JDP2 in the stromal tumor microenvironment. Here, we show that mice with ATF3 and JDP2 double deficiency (designated thereafter dKO) developed larger tumors with high vascular perfusion and increased cell proliferation rate compared to wild type (WT) mice. We further identify that the underlying mechanism involves tumor associated fibroblasts which secrete high levels of stromal cell-derived factor 1 (SDF-1) in dKO fibroblasts. SDF-1 depletion in dKO fibroblasts dampened tumor growth and blood vessel perfusion. Furthermore, ATF3 and JDP2 were found to regulate SDF-1 transcription and secretion in fibroblasts, a phenomenon that is potentiated in the presence of cancer cells. Collectively, our results suggest that ATF3 and JDP2 regulate the expression of essential tumor promoting factors expressed by fibroblasts within the tumor microenvironment, and thus restrain tumor growth.

Zebrafish disease models in hematology: Highlights on biological and translational impact

Zebrafish (Danio rerio) has proven to be a versatile and reliable in vivo experimental model to study human hematopoiesis and hematological malignancies. As vertebrates, zebrafish has significant anatomical and biological similarities to humans, including the hematopoietic system. The powerful genome editing and genome-wide forward genetic screening tools have generated models that recapitulate human malignant hematopoietic pathologies in zebrafish and unravel cellular mechanisms involved in these diseases. Moreover, the use of zebrafish models in large-scale chemical screens has allowed the identification of new molecular targets and the design of alternative therapies. In this review we summarize the recent achievements in hematological research that highlight the power of the zebrafish model for discovery of new therapeutic molecules. We believe that the model is ready to give an immediate translational impact into the clinic.

Role of activating transcription factor 3 and its interacting proteins under physiological and pathological conditions

Activating transcription factor 3 (ATF3) is a stress-responsive factor that belongs to the activator protein 1 (AP-1) family of transcription factors. ATF3 expression is stimulated by various factors such as hypoxia, cytokines, and chemotherapeutic and DNA damaging agents. Upon stimulation, ATF3 can form homodimers or heterodimers with other members of the AP-1 family to repress or activate transcription. Under physiological conditions, ATF3 expression is transient and plays a pivotal role in controlling the expression of cell-cycle regulators and tumor suppressor, DNA repair, and apoptosis genes. However, under pathological conditions such as those during breast cancer, a sustained and prolonged expression of ATF3 has been observed. In this review, the structure and function of ATF3, its posttranslational modifications (PTM), and its interacting proteins are discussed with a special emphasis on breast cancer metastasis.

JDP2: An oncogenic bZIP transcription factor in T cell acute lymphoblastic leukemia

A substantial subset of patients with T cell acute lymphoblastic leukemia (T-ALL) develops resistance to steroids and succumbs to their disease. JDP2 encodes a bZIP protein that has been implicated as a T-ALL oncogene from insertional mutagenesis studies in mice, but its role in human T-ALL pathogenesis has remained obscure. Here we show that JDP2 is aberrantly expressed in a subset of T-ALL patients and is associated with poor survival. JDP2 is required for T-ALL cell survival, as its depletion by short hairpin RNA knockdown leads to apoptosis. Mechanistically, JDP2 regulates prosurvival signaling through direct transcriptional regulation of MCL1. Furthermore, JDP2 is one of few oncogenes capable of initiating T-ALL in transgenic zebrafish. Notably, thymocytes from rag2:jdp2 transgenic zebrafish express high levels of mcl1 and demonstrate resistance to steroids in vivo. These studies establish JDP2 as a novel oncogene in high-risk T-ALL and implicate overexpression of MCL1 as a mechanism of steroid resistance in JDP2-overexpressing cells.

Host JDP2 expression in the bone marrow contributes to metastatic spread

The c-Jun Dimerization Protein 2, JDP2, is a basic leucine zipper protein member of the activator protein-1 (AP-1) family of transcription factors. JDP2 typically suppresses gene transcription through multiple mechanisms and plays a dual role in multiple cellular processes, including cell differentiation and proliferation which is dependent on AP-1 function. Whereas the role of JDP2 expression within cancer cells has been studied, its role in stromal cells at the tumor microenvironment is largely unknown. Here we show that mice lacking JDP2 (JDP2−/−) display a reduced rate of metastasis in Lewis lung carcinoma (LLC) and polyoma middle T-antigen (PyMT) breast carcinoma mouse models. The replacement of wild-type bone marrow derived cells (BMDCs) with JDP2-deficient BMDCs recapitulates the metastatic phenotype of JDP2−/− tumor-bearing mice. In vitro, conditioned medium of wild-type BMDCs significantly potentiates the migration and invasion capacity of LLC cells as compared to that of JDP2−/− BMDCs. Furthermore, wild-type BMDCs secrete CCL5, a chemokine known to contribute to metastasis, to a greater extent than JDP2−/− BMDCs. The supplementation of CCL5 in JDP2−/− BMDC conditioned medium was sufficient to potentiate the invasion capacity of LLC. Overall, this study suggests that JDP2-expressing BMDCs within the tumor microenvironment contribute to metastatic spread.

Multiple functions of the histone chaperone Jun dimerization protein 2

The Jun dimerization protein 2 (JDP2) is part of the family of stress-responsible transcription factors such as the activation protein-1, and binds the 12-O-tetradecanoylphorbol-13-acetateresponse element and the cAMP response element. It also plays a role as a histone chaperone and participates in diverse processes, such as cell-cycle arrest, cell differentiation, apoptosis, senescence, and metastatic spread, and functions as an oncogene and anti-oncogene, and as a cellular reprogramming factor. However, the molecular mechanisms underlying these multiple functions of JDP2 have not been clarified. This review summarizes the structure and function of JDP2, highlighting the specific role of JDP2 in cellular-stress regulation and prevention.

Sympathoexcitation in Rats With Chronic Heart Failure Depends on Homeobox D10 and MicroRNA-7b Inhibiting GABBR1 Translation in Paraventricular Nucleus

BACKGROUND

Chronic heart failure (CHF) increases sympathoexcitation through angiotensin II (ANG II) receptors (AT1R) in the paraventricular nucleus (PVN). Recent publications indicate both γ-aminobutyric acid B-type receptor 1 (GABBR1) and microRNA-7b (miR-7b) are expressed in the PVN. We hypothesized that ANG II regulates sympathoexcitation through homeobox D10 (HoxD10), which regulates miR-7b in other tissues.

METHODS AND RESULTS

Ligation of the left anterior descendent coronary artery in rats caused CHF and sympathoexcitation. PVN expression of AT1R, HoxD10, and miR-7b was increased, whereas GABBR1 was lower in CHF. Infusion of miR-7b in the PVN caused sympathoexcitation in control animals and enhanced the changes in CHF. Antisense miR-7b infused in PVN normalized GABBR1 expression while attenuating CHF symptoms, including sympathoexcitation. A luciferase reporter assay detected miR-7b binding to the 3' untranslated region of GABBR1 that was absent after targeted mutagenesis. ANG II induced HoxD10 and miR-7b in NG108 cells, effects blocked by AT1R blocker losartan and by HoxD10 silencing. miR-7b transfection into NG108 cells decreased GABBR1 expression, which was inhibited by miR-7b antisense. In vivo PVN knockdown of AT1R attenuated the symptoms of CHF, whereas HoxD10 overexpression exaggerated them. Finally, in vivo PVN ANG II infusion caused dose-dependent sympathoexcitation that was abrogated by miR-7b antisense and exaggerated by GABBR1 silencing.

CONCLUSIONS

There is an ANG II/AT1R/HoxD10/miR-7b/GABBR1 pathway in the PVN that contributes to sympathoexcitation and deterioration of cardiac function in CHF.

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.

The small molecule C-6 is selectively cytotoxic against breast cancer cells and its biological action is characterized by mitochondrial defects and endoplasmic reticulum stress

INTRODUCTION

The establishment of drug resistance following treatment with chemotherapeutics is strongly associated with poor clinical outcome in patients, and drugs that target chemoresistant tumors have the potential to increase patient survival. In an effort to identify biological pathways of chemoresistant breast cancers that can be targeted therapeutically, a small molecule screen utilizing metastatic patient-derived breast cancer cells was conducted; from this previous report, the cytotoxic small molecule, C-6, was identified for its ability to selectively kill aggressive breast cancer cells in a caspase-independent manner. Here, we describe the cellular and molecular pathways induced following C-6 treatment in both normal and breast cancer cell lines.

METHODS

Transcriptome analyses and protein expression experiments were used to measure endoplasmic reticulum (ER) stress following C-6 treatment. Studies utilizing transmission electron microscopy and metabolomic profiling were conducted to characterize mitochondrial morphology and function in C-6-treated cells. Oxygen consumption rates and oxidative stress were also measured in breast cancer and normal mammary epithelial cells following treatment with the small molecule. Finally, structural modifications were made to the molecule and potency and cancer selectivity were evaluated.

RESULTS

Treatment with C-6 resulted in ER stress in both breast cancer cells and normal mammary epithelial cells. Gross morphological defects were observed in the mitochondria and these aberrations were associated with metabolic imbalances and a diminished capacity for respiration. Following treatment with C-6, oxidative stress was observed in three breast cancer cell lines but not in normal mammary epithelial cells. Finally, synthetic modifications made to the small molecule resulted in the identification of the structural components that contribute to C-6's cancer-selective phenotype.

CONCLUSIONS

The data reported here implicate mitochondrial and ER stress as a component of C-6's biological activity and provide insight into non-apoptotic cell death mechanisms; targeting biological pathways that induce mitochondrial dysfunction and ER stress may offer new strategies for the development of therapeutics that are effective against chemoresistant breast cancers.

Jun dimerization protein 2 is a critical component of the Nrf2/MafK complex regulating the response to ROS homeostasis

Oxidative stress and reactive oxygen species (ROS) are associated with diseases such as cancer, cardiovascular complications, inflammation and neurodegeneration. Cellular defense systems must work constantly to control ROS levels and to prevent their accumulation. We report here that the Jun dimerization protein 2 (JDP2) has a critical role as a cofactor for transcription factors nuclear factor-erythroid 2-related factor 2 (Nrf2) and small Maf protein family K (MafK) in the regulation of the antioxidant-responsive element (ARE) and production of ROS. Chromatin immunoprecipitation–quantitative PCR (qPCR), electrophoresis mobility shift and ARE-driven reporter assays were carried out to examine the role of JDP2 in ROS production. JDP2 bound directly to the ARE core sequence, associated with Nrf2 and MafK (Nrf2–MafK) via basic leucine zipper domains, and increased DNA-binding activity of the Nrf2–MafK complex to the ARE and the transcription of ARE-dependent genes. In mouse embryonic fibroblasts from Jdp2-knockout (Jdp2 KO) mice, the coordinate transcriptional activation of several ARE-containing genes and the ability of Nrf2 to activate expression of target genes were impaired. Moreover, intracellular accumulation of ROS and increased thickness of the epidermis were detected in Jdp2 KO mice in response to oxidative stress-inducing reagents. These data suggest that JDP2 is required to protect against intracellular oxidation, ROS activation and DNA oxidation. qPCR demonstrated that several Nrf2 target genes such as heme oxygenase-1, glutamate–cysteine ligase catalytic and modifier subunits, the notch receptor ligand jagged 1 and NAD(P)H dehydrogenase quinone 1 are also dependent on JDP2 for full expression. Taken together, these results suggest that JDP2 is an integral component of the Nrf2–MafK complex and that it modulates antioxidant and detoxification programs by acting via the ARE.

Preeclamptic plasma induces transcription modifications involving the AP-1 transcriptional regulator JDP2 in endothelial cells

Preeclampsia is a pregnancy disorder characterized by hypertension and proteinuria. In preeclampsia, the placenta releases factors into the maternal circulation that cause a systemic endothelial dysfunction. Herein, we investigated the effects of plasma from women with preeclamptic and normal pregnancies on the transcriptome of an immortalized human umbilical vein endothelial cell line. The cells were exposed for 24 hours to preeclamptic or normal pregnancy plasma and their transcriptome was analyzed using Agilent microarrays. A total of 116 genes were found differentially expressed: 71 were up-regulated and 45 were down-regulated. In silico analysis revealed significant consistency and identified four functional categories of genes: mitosis and cell cycle progression, anti-apoptotic, fatty acid biosynthesis, and endoplasmic reticulum stress effectors. Moreover, several genes involved in vasoregulation and endothelial homeostasis showed modified expression, including EDN1, APLN, NOX4, and CBS. Promoter analysis detected, among the up-regulated genes, a significant overrepresentation of genes containing activation protein-1 regulatory sites. This correlated with down-regulation of JDP2, a gene encoding a repressor of activation protein-1. The role of JDP2 in the regulation of a subset of genes in the human umbilical vein endothelial cells was confirmed by siRNA inhibition. We characterized transcriptional changes induced by preeclamptic plasma on human umbilical vein endothelial cells, and identified, for the first time to our knowledge, JDP2 as a regulator of a subset of genes modified by preeclamptic plasma.

Control of Oxidative Stress and Generation of Induced Pluripotent Stem Cell-like Cells by Jun Dimerization Protein 2

We report here that the Jun dimerization protein 2 (JDP2) plays a critical role as a cofactor for the transcription factors nuclear factor-erythroid 2-related factor 2 (Nrf2) and MafK in the regulation of the antioxidants and production of reactive oxygen species (ROS). JDP2 associates with Nrf2 and MafK (Nrf2-MafK) to increase the transcription of antioxidant response element-dependent genes. Oxidative-stress-inducing reagent led to an increase in the intracellular accumulation of ROS and cell proliferation in Jdp2 knock-out mouse embryonic fibroblasts. In Jdp2-Cre mice mated with reporter mice, the expression of JDP2 was restricted to granule cells in the brain cerebellum. The induced pluripotent stem cells (iPSC)-like cells were generated from DAOY medulloblastoma cell by introduction of JDP2, and the defined factor OCT4. iPSC-like cells expressed stem cell-like characteristics including alkaline phosphatase activity and some stem cell markers. However, such iPSC-like cells also proliferated rapidly, became neoplastic, and potentiated cell malignancy at a later stage in SCID mice. This study suggests that medulloblastoma cells can be reprogrammed successfully by JDP2 and OCT4 to become iPSC-like cells. These cells will be helpful for studying the generation of cancer stem cells and ROS homeostasis.

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.

Identification and analysis of a novel dimerization domain shared by various members of c-Jun N-terminal kinase (JNK) scaffold proteins

Mitogen-activated protein kinases (MAPKs) form a kinase tier module in which MAPK, MAP2K, and MAP3K are held by scaffold proteins. The scaffold proteins serve as a protein platform for selective and spatial kinase activation. The precise mechanism by which the scaffold proteins function has not yet been fully explained. WDR62 is a novel scaffold protein of the c-Jun N-terminal kinase (JNK) pathway. Recessive mutations within WDR62 result in severe cerebral cortical malformations. One of the WDR62 mutant proteins found in a patient with microcephaly encodes a C-terminal truncated protein that fails to associate efficiently with JNK and MKK7β1. The present article shows that the WDR62 C-terminal region harbors a novel dimerization domain composed of a putative loop-helix domain that is necessary and sufficient for WDR62 dimerization and is critical for its scaffolding function. The loop-helix domain is highly conserved between orthologues and is also shared by the JNK scaffold protein, JNKBP1/MAPKBP1. Based on the high sequence conservation of the loop-helix domain, our article shows that MAPKBP1 homodimerizes and heterodimerizes with WDR62. Endogenous WDR62 and MAPKBP1 co-localize to stress granules following arsenite treatment, but not during mitosis. This study proposes another layer of complexity, in which coordinated activation of signaling pathways is mediated by the association between the different JNK scaffold proteins depending on their biological function.

The bZIP repressor proteins, c-Jun dimerization protein 2 and activating transcription factor 3, recruit multiple HDAC members to the ATF3 promoter

JDP2, is a basic leucine zipper (bZIP) protein displaying a high degree of homology with the stress inducible transcription factor, ATF3. Both proteins bind to cAMP and TPA response elements and repress transcription by multiple mechanisms. Histone deacetylases (HDACs) play a key role in gene inactivation by deacetylating lysine residues on histones. Here we describe the association of JDP2 and ATF3 with HDACs 1, 2-6 and 10. Association of HDAC3 and HDAC6 with JDP2 and ATF3 occurs via direct protein-protein interactions. Only part of the N-terminal bZIP motif of JDP2 and ATF3 basic domain is necessary and sufficient for the interaction with HDACs in a manner that is independent of coiled-coil dimerization. Class I HDACs associate with the bZIP repressors via the DAC conserved domain whereas the Class IIb HDAC6 associates through its C-terminal unique binder of ubiquitin Zn finger domain. Both JDP2 and ATF3 are known to bind and repress the ATF3 promoter. MEF cells treated with histone deacetylase inhibitor, trichostatin A (TSA) display enhanced ATF3 transcription. ATF3 enhanced transcription is significantly reduced in MEF cells lacking both ATF3 and JDP2. Collectively, we propose that the recruitment of multiple HDAC members to JDP2 and ATF3 is part of their transcription repression mechanism.

The transcription factor network associated with the amino acid response in mammalian cells

Mammals exhibit multiple adaptive mechanisms that sense and respond to fluctuations in dietary nutrients. Consumption of reduced total dietary protein or a protein diet that is deficient in 1 or more of the essential amino acids triggers wide-ranging changes in feeding behavior and gene expression. At the level of individual cells, dietary protein deficiency is manifested as amino acid (AA) deprivation, which activates the AA response (AAR). The AAR is composed of a collection of signal transduction pathways that terminate in specific transcriptional programs designed to catalyze adaptation to the nutrient stress or, ultimately, undergo apoptosis. Independently of the AAR, endoplasmic reticulum stress activates 3 signaling pathways, collectively referred to as the unfolded protein response. The transcription factor activating transcription factor 4 is one of the terminal transcriptional mediators for both the AAR and the unfolded protein response, leading to a significant degree of overlap with regard to the target genes for these stress pathways. Over the past 5 y, research has revealed that the basic leucine zipper superfamily of transcription factors plays the central role in the AAR. Formation of both homo- and heterodimers among the activating transcription factor, CCAAT enhancer-binding protein, and FOS/JUN families of basic leucine zipper proteins forms the nucleus of a highly integrated transcription factor network that determines the initiation, magnitude, and duration of the cellular response to dietary protein or AA limitation.

Stress-induced C/EBP homology protein (CHOP) represses MyoD transcription to delay myoblast differentiation

When mouse myoblasts or satellite cells differentiate in culture, the expression of myogenic regulatory factor, MyoD, is downregulated in a subset of cells that do not differentiate. The mechanism involved in the repression of MyoD expression remains largely unknown. Here we report that a stress-response pathway repressing MyoD transcription is transiently activated in mouse-derived C2C12 myoblasts growing under differentiation-promoting conditions. We show that phosphorylation of the α subunit of the translation initiation factor 2 (eIF2α) is followed by expression of C/EBP homology protein (CHOP) in some myoblasts. ShRNA-driven knockdown of CHOP expression caused earlier and more robust differentiation, whereas its constitutive expression delayed differentiation relative to wild type myoblasts. Cells expressing CHOP did not express the myogenic regulatory factors MyoD and myogenin. These results indicated that CHOP directly repressed the transcription of the MyoD gene. In support of this view, CHOP associated with upstream regulatory region of the MyoD gene and its activity reduced histone acetylation at the enhancer region of MyoD. CHOP interacted with histone deacetylase 1 (HDAC1) in cells. This protein complex may reduce histone acetylation when bound to MyoD regulatory regions. Overall, our results suggest that the activation of a stress pathway in myoblasts transiently downregulate the myogenic program.

Suppression of FoxO1 activity by long-chain fatty acyl analogs

OBJECTIVE

Overactivity of the Forkhead transcription factor FoxO1 promotes diabetic hyperglycemia, dyslipidemia, and acute-phase response, whereas suppression of FoxO1 activity by insulin may alleviate diabetes. The reported efficacy of long-chain fatty acyl (LCFA) analogs of the MEDICA series in activating AMP-activated protein kinase (AMPK) and in treating animal models of diabesity may indicate suppression of FoxO1 activity.

RESEARCH DESIGN AND METHODS

The insulin-sensitizing and anti-inflammatory efficacy of a MEDICA analog has been verified in guinea pig and in human C-reactive protein (hCRP) transgenic mice, respectively. Suppression of FoxO1 transcriptional activity has been verified in the context of FoxO1- and STAT3-responsive genes and compared with suppression of FoxO1 activity by insulin and metformin.

RESULTS

Treatment with MEDICA analog resulted in total body sensitization to insulin, suppression of lipopolysaccharide-induced hCRP and interleukin-6-induced acute phase reactants and robust decrease in FoxO1 transcriptional activity and in coactivation of STAT3. Suppression of FoxO1 activity was accounted for by its nuclear export by MEDICA-activated AMPK, complemented by inhibition of nuclear FoxO1 transcriptional activity by MEDICA-induced C/EBPβ isoforms. Similarly, insulin treatment resulted in nuclear exclusion of FoxO1 and further suppression of its nuclear activity by insulin-induced C/EBPβ isoforms. In contrast, FoxO1 suppression by metformin was essentially accounted for by its nuclear export by metformin-activated AMPK.

CONCLUSIONS

Suppression of FoxO1 activity by MEDICA analogs may partly account for their antidiabetic anti-inflammatory efficacy. FoxO1 suppression by LCFA analogs may provide a molecular rational for the beneficial efficacy of carbohydrate-restricted ketogenic diets in treating diabetes.

Phosphorylation of JDP2 on threonine-148 by the c-Jun N-terminal kinase targets it for proteosomal degradation

JDP2 (c-Jun dimerization protein 2) is a member of the basic leucine zipper family of transcription factors that is ubiquitously expressed in all examined cell types. JDP2 is phosphorylated on Thr148 by JNK (c-Jun N-terminal kinase) and p38 kinase, although the functional role of its phosphorylation is unknown. In the present paper we show that the JDP2 protein level is dramatically reduced in response to serum stimulation, anisomycin treatment, ultraviolet light irradiation and cycloheximide treatment, all of which activate the JNK pathway. In addition, endogenous and overexpressed JDP2 are phosphorylated in response to these stimuli. Replacement of Thr148 with an alanine residue stabilizes ectopically expressed JDP2 in the presence of the stimuli; conversely, substitution with glutamic acid destabilizes it. Serum-induced phosphorylation and degradation of JDP2 are specific to JNK activation since a JNK inhibitor (SP600125) abolishes these effects, whereas p38 and MEK inhibitors (SB203580 and UO126) have no effect. In the presence of cycloheximide, JDP2 is rapidly phosphorylated and degraded due to the combined effects of protein synthesis inhibition and activation of JNK. Pre-treatment of cells with SP600125 prior to cycloheximide treatment significantly prolongs the half-life of JDP2 that is found mainly in the unphosphorylated form. Lastly, the proteasome inhibitor (MG132) rescues JDP2 degradation following cycloheximide treatment and increases the expression of the JDP2 phospho-mimetic T148E mutant. Collectively, these results suggest that phosphorylation of JDP2 on thr148 by JNK targets it to the proteasome for degradation.

Involvement of Jun dimerization protein 2 (JDP2) in the maintenance of Epstein-Barr virus latency

Reactivation of the Epstein-Barr virus from latency is dependent on expression of the BZLF1 viral immediate-early protein. The BZLF1 promoter (Zp) normally exhibits only low basal activity but is activated in response to chemical inducers such as 12-O-tetradecanoylphorbol-13-acetate and calcium ionophore. We found that Jun dimerization protein 2 (JDP2) plays a significant role in suppressing Zp activity. Reporter, EMSA, and ChIP assays of a Zp mutant virus revealed JDP2 association with Zp at the ZII cis-element, a binding site for CREB/ATF/AP-1. Suppression of Zp activity by JDP2 correlated with HDAC3 association and reduced levels of histone acetylation. Although introduction of point mutations into the ZII element of the viral genome did not increase the level of BZLF1 production, silencing of endogenous JDP2 gene expression by RNA interference increased the levels of viral early gene products and viral DNA replication. These results indicate that JDP2 plays a role as a repressor of Zp and that its replacement by CREB/ATF/AP-1 at ZII is crucial to triggering reactivation from latency to lytic replication.

Suppression of cell-cycle progression by Jun dimerization protein-2 (JDP2) involves downregulation of cyclin-A2

We report here a novel role for Jun dimerization protein-2 (JDP2) as a regulator of the progression of normal cells through the cell cycle. To determine the role of JDP2 in vivo, we generated Jdp2-knockout (Jdp2KO) mice by targeting exon-1 to disrupt the site of initiation of transcription. The epidermal thickening of skin from the Jdp2KO mice after treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) proceeded more rapidly than that of control mice, and more proliferating cells were found at the epidermis. Fibroblasts derived from embryos of Jdp2KO mice proliferated faster and formed more colonies than fibroblasts from wild-type mice. JDP2 was recruited to the promoter of the gene for cyclin-A2 (ccna2) at the AP-1 site. Cells lacking Jdp2 had elevated levels of cyclin-A2 mRNA. Furthermore, reintroduction of JDP2 resulted in the repression of transcription of ccna2 and of cell-cycle progression. Thus, transcription of the gene for cyclin-A2 appears to be a direct target of JDP2 in the suppression of cell proliferation.

Epigenetic regulation of p16Ink4a and Arf by JDP2 in cellular senescence

In response to accumulating cellular stress, cells protect themselves from abnormal growth by entering the senescent stage. Senescence is controlled mainly by gene products from the p16Ink4a/Arf locus. In mouse cells, the expression of p16Ink4a and Arf increases continuously during proliferation in cell culture. Transcription from the locus is under complex control. p16Ink4a and Arf respond independently to positive and negative signals, and the entire locus is epigenetically suppressed by histone methylation that depends on the Polycomb repressive complex-1 and -2 (PRC1 and PRC2). In fact, the PRCs associate with the p16Ink4a/Arf locus in young proliferating cells and dissociate in aged senescent cells. Thus, it seems that chromatin-remodeling factors that regulate association and dissociation of PRCs might be important players in the senescence program. Here, we summarize the molecular mechanisms that mediate cellular aging and introduce the Jun dimerization protein 2 (JDP2) as a factor that regulates replicative senescence by mediating dissociation of PRCs from the p16Ink4a/Arf locus.

The AP-1 repressor protein, JDP2, potentiates hepatocellular carcinoma in mice

Background

The AP-1 transcription factor plays a major role in cell proliferation, apoptosis, differentiation and developmental processes. AP-1 proteins are primarily considered to be oncogenic. Gene disruption studies placed c-Jun as an oncogene at the early stage of a mouse model of hepatocellular carcinoma. Mice lacking c-Jun display reduced number and size of hepatic tumors attributed to elevated p53 expression and increased apoptosis. This suggests that c-Jun inhibition may serve as a therapeutic target for liver cancer. The c-Jun dimerization protein 2, JDP2 is an AP-1 repressor protein that potently inhibits AP-1 transcription. On the other hand, the JDP2 locus was found at a recurring viral integration site in T-cell lymphoma. We sought to examine the potential of JDP2 to inhibit c-Jun/AP-1 oncogenic activity in mice. Towards this end, we generated a tetracycline inducible transgenic mouse expressing JDP2 specifically in the liver. We used diethylnitrosamine (DEN) injection to initiate liver cancer in mice and assessed the extent of liver cancer in JDP2-transgenic and wild type control mice by biochemical and molecular biology techniques.

Results

JDP2-transgenic mice display normal liver function. JDP2-transgenic mice displayed potentiation of liver cancer, higher mortality and increased number and size of tumors. The expression of JDP2 at the promotion stage was found to be the most critical for enhancing liver cancer severity.

Conclusions

This study suggests that JDP2 expression may play a critical role in liver cancer development by potentiating the compensatory proliferative response and increased inflammation in the DEN liver cancer model.

Expression profiling after activation of amino acid deprivation response in HepG2 human hepatoma cells

Dietary protein malnutrition is manifested as amino acid deprivation of individual cells, which activates an amino acid response (AAR) that alters cellular functions, in part, by regulating transcriptional and posttranscriptional mechanisms. The AAR was activated in HepG2 human hepatoma cells, and the changes in mRNA content were analyzed by microarray expression profiling. The results documented that 1,507 genes were differentially regulated by P < 0.001 and by more than twofold in response to the AAR, 250 downregulated and 1,257 upregulated. The spectrum of altered genes reveals that amino acid deprivation has far-reaching implications for gene expression and cellular function. Among those cellular functions with the largest numbers of altered genes were cell growth and proliferation, cell cycle, gene expression, cell death, and development. Potential biological relationships between the differentially expressed genes were analyzed by computer software that generates gene networks. Proteins that were central to the most significant of these networks included c-myc, polycomb group proteins, transforming growth factor β1, nuclear factor (erythroid-derived 2)-like 2-related factor 2, FOS/JUN family members, and many members of the basic leucine zipper superfamily of transcription factors. Although most of these networks contained some genes that were known to be amino acid responsive, many new relationships were identified that underscored the broad impact that amino acid stress has on cellular function.

Activation of alternative Jdp2 promoters and functional protein isoforms in T-cell lymphomas by retroviral insertion mutagenesis

Retroviral insertional mutagenesis has been instrumental for the identification of genes important in cancer development. The molecular mechanisms involved in retroviral-mediated activation of proto-oncogenes influence the distribution of insertions within specific regions during tumorigenesis and hence may point to novel gene structures. From a retroviral tagging screen on tumors of 1767 SL3-3 MLV-infected BALB/c mice, intron 2 of the AP-1 repressor Jdp2 locus was found frequently targeted by proviruses resulting in upregulation of non-canonical RNA subspecies. We identified several promoter regions within 1000 bp upstream of exon 3 that allowed for the production of Jdp2 protein isoforms lacking the histone acetylase inhibitory domain INHAT present in canonical Jdp2. The novel Jdp2 isoforms localized to the nucleus and over-expression in murine fibroblast cells induced cell death similar to canonic Jdp2. When expressed in the context of oncogenic NRAS both full length Jdp2 and the shorter isoforms increased anchorage-independent growth. Our results demonstrate a biological function of Jdp2 lacking the INHAT domain and suggest a post-genomic application for the use of retroviral tagging data in identifying new gene products with a potential role in tumorigenesis.

JDP2 (Jun Dimerization Protein 2)-deficient mouse embryonic fibroblasts are resistant to replicative senescence

JDP2 (Jun dimerization protein 2, an AP-1 transcription factor) is involved in the regulation of the differentiation and proliferation of cells. We report here that JDP2-deficient mouse embryonic fibroblasts (Jdp2(-/-) MEF) are resistant to replicative senescence. In the absence of JDP2, the level of expression of p16(Ink4a), which is known to rise as normal fibroblasts age, fell significantly when cells were cultured for more than 2 months. Conversely, the overexpression of JDP2 induced the expression of genes for p16(Ink4a) and p19(Arf). Moreover, at the promoter of the gene for p16(Ink4a) in Jdp2(-/-) MEF, the extent of methylation of lysine 27 of histone H3 (H3K27), which is important for gene silencing, increased. Polycomb-repressive complexes (PRC-1 and PRC-2), which are responsible for histone methylation, bound efficiently to the promoter to repress the expression of the gene for p16(Ink4a). As a result, JDP2-deficient MEF became resistant to replicative senescence. Our results indicate that JDP2 is involved in the signaling pathway for senescence via epigenetic regulation of the expression of the gene for p16(Ink4a).

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.