关键词： AMPK   ATF3   CHOP   ER stress   IL-6   NF-kappa B   Oleate   Palmitate   PPAR   XBP1   ENDOPLASMIC-RETICULUM STRESS   ACTIVATED PROTEIN-KINASE   NF-KAPPA-B   GLUCOSE-HOMEOSTASIS   METABOLIC SYNDROME   DIABETES-MELLITUS   BETA-CELLS   IN-VIVO   PALMITATE   DIET  

摘要： Although the substitution of saturated fatty acids with oleate has been recommended in the management of type 2 diabetes mellitus, the mechanisms by which oleate improves insulin resistance in skeletal muscle cells are not completely known. Here, we examined whether oleate, through activation of AMP-activated protein kinase (AMPK), prevented palmitate-induced endoplasmic reticulum (ER) stress, which is involved in the link between lipid-induced inflammation and insulin resistance. Studies were conducted in mouse C2C12 myotubes and in the human myogenic cell line LHCN-M2. To analyse the involvement of AMPK, activators and inhibitors of this kinase and overexpression of a dominant negative AMPK construct (K45R) were used. Palmitate increased the levels of ER stress markers, whereas oleate did not. In palmitate-exposed cells incubated with a lower concentration of oleate, the effects of palmitate were prevented. The induction of ER stress markers by palmitate was prevented by the presence of the AMPK activators AICAR and A-769662. Moreover, the ability of oleate to prevent palmitate-induced ER stress and inflammation (nuclear factor-kappa B [NF-kappa B] DNA-binding activity and expression and secretion of IL6) as well as insulin-stimulated Akt phosphorylation and 2-deoxyglucose uptake was reversed in the presence of the AMPK inhibitor compound C or by overexpression of a dominant negative AMPK construct. Finally, palmitate reduced phospho-AMPK levels, whereas this was not observed in oleate-exposed cells or in palmitate-exposed cells supplemented with oleate. Overall, these findings indicate that oleate prevents ER stress, inflammation and insulin resistance in palmitate-exposed skeletal muscle cells by activating AMPK.

关键词： Agrp   ATF3   Energy expenditure   Food intake   FoxO1   Hypothalamus   AGOUTI-RELATED PROTEIN   INSULIN-RECEPTOR SUBSTRATE-2   VASCULAR ENDOTHELIAL-CELLS   ACTIVATING TRANSCRIPTION   BETA-CELLS   CAUSES OBESITY   GENE   EXPRESSION   BRAIN   REPRESSION  

摘要： The pancreas and hypothalamus are critical for maintaining nutrient and energy homeostasis, and combined disorders in these organs account for the onset of the metabolic syndrome. Activating transcription factor 3 (ATF3) is an adaptive response transcription factor. The physiological role of ATF3 in the pancreas has been controversial, and its role in the hypothalamus remains unknown. To elucidate the roles of ATF3 in these organs, we generated pancreas- and hypothalamus-specific Atf3 knockout (PHT-Atf3-KO) mice in this study. We crossed mice bearing floxed Atf3 alleles with Pdx1-cre mice, in which cre is specifically expressed in the pancreas and hypothalamus, and analysed metabolic variables, pancreatic morphology, food intake, energy expenditure and sympathetic activity in adipose tissue. We also used a hypothalamic cell line to investigate the molecular mechanism by which ATF3 regulates transcription of the gene encoding agouti-related protein (Agrp). Although PHT-Atf3-KO mice displayed better glucose tolerance, neither plasma glucagon nor insulin level was altered in these mice. However, these mice exhibited higher insulin sensitivity, which was accompanied by a leaner phenotype due to decreased food intake and increased energy expenditure. We also observed decreased hypothalamic Agrp expression in PHT-Atf3-KO mice. Importantly, an increase in ATF3 levels is induced by fasting or low glucose in the hypothalamus. We also showed that ATF3 interacts with forkhead box-containing protein, O subfamily 1 (FoxO1) on the Agrp promoter and activates Agrp transcription. Our results suggest that ATF3 plays an important role in the control of glucose and energy metabolism by regulating Agrp.

关键词： TRANSCRIPTION FACTOR-3   LIVER DYSFUNCTION   GENE-EXPRESSION   BETA-CATENIN   ENDODERM   ATF3   ENDOCRINE   FATE   DOWNSTREAM   PROTEIN  

摘要： How cells integrate multiple patterning signals to achieve early endoderm regionalization remains largely unknown. Between gastrulation and neurulation, retinoic acid (RA) signaling is required, while Wnt/beta-catenin signaling has to be repressed for the specification of the pancreas, oesophagus, stomach, and duodenum primordia in Xenopus embryos. In attempt to screen for RA regulated genes in Xenopus endoderm, we identified a direct RA target gene, N-myc downstream regulated gene 1a (ndrg1a) that showed expression early in the archenteron roof endoderm and late in the developing pancreas, oesophagus, stomach, and duodenum. Both antisense morpholino oligonucleotide mediated knockdown of ndrg1a in Xenopus laevis and the transcription activator-like effector nucleases (TALEN) mediated disruption of ndrg1 in Xenopus tropicalis demonstrate that like RA signaling, Ndrg1a is specifically required for the specification of Xenopus pancreas, oesophagus, stomach, and duodenum primordia. Immunofluorescence data suggest that RA-activated Ndrg1a suppresses Wnt/beta-catenin signaling in Xenopus archenteron roof endoderm cells. Blocking Wnt/beta-catenin signaling rescued Ndrg1a knockdown phenotype. Furthermore, overexpression of the putative Wnt/beta-catenin target gene Atf3 phenocopied knockdown of Ndrg1a or inhibition of RA signaling, while Atf3 knockdown can rescue Ndrg1a knockdown phenotype. Lastly, the pancreas/stomach/duodenum transcription factor Pdx1 was able to rescue Atf3 overexpression or Ndrg1a knockdown phenotype. Together, we conclude that RA activated Ndrg1a represses Wnt/beta-catenin signaling to allow the specification of pancreas, oesophagus, stomach, and duodenum progenitor cells in Xenopus embryos.

关键词： Parkinson's   MPP+   UPR   p53   PUMA   ATF3   UNFOLDED PROTEIN RESPONSE   ACTIVATING TRANSCRIPTION FACTOR-3   ENDOPLASMIC-RETICULUM STRESS   PARKINSONS-DISEASE   DOPAMINERGIC-NEURONS   IN-VIVO   MOUSE MODEL   DNA-DAMAGE   ER STRESS   MPTP  

摘要： Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra (SN) and depletion of striatal dopamine (DA), leading to a range of motor symptoms, including resting tremor, rigidity, bradykinesia and postural abnormalities. The neurotoxin (MPTP) and its active metabolite, 1-methyl-4-phenylpyridinium (MPP+), cause dopaminergic cell loss in a variety of animal species and produce symptoms similar to those seen in PD. Our lab has shown that MPP+ activates cell stress pathways, including the unfolded protein response (UPR) in mouse primary mesencephalic cultures. The BH3-only protein, PUMA (p53 upregulated mediator of apoptosis), has been shown to be activated in response to many cellular stresses, including endoplasmic reticulum (ER) stress and UPR, and to induce cell death. Therefore, we hypothesized that PUMA may mediate MPP+ toxicity. To test this hypothesis, we compared the response of primary mesencephalic cultures from wild-type and PUMA deficient (-/-) mice to MPP+. We also utilized cultures from p53 -/- and activating transcription factor 3 (ATF3) -/- mice to further elucidate the pathways involved. These studies revealed that PUMA and p53, but not ATF3, are required for MPP+-induced cell death, suggesting that UPR activation is parallel to the induction of MPP+-induced cell death. (C) 2013 Elsevier Ireland Ltd. All rights reserved.

关键词： TUMOR-SUPPRESSOR GENES   GROWTH-FACTOR RECEPTOR   SELF-RENEWAL   FUNCTIONAL IDENTIFICATION   GLIOBLASTOMA   DIFFERENTIATION   TRANSFORMATION   PROLIFERATION   EXPRESSION   ATF3  

摘要： In mouse and human neural progenitor and glioblastonna "stem-like" cells, we identified key targets of the Polycomb-group protein BMI1 by combining ChIP-seq with in vivo RNAi screening. We discovered that Bmi1 is important in the cellular response to the transforming growth factor-beta/bone morphogenetic protein (TGF-beta/BMP) and endoplasmic reticulum (ER) stress pathways, in part converging on the Atf3 transcriptional repressor. We show that Atf3 is a tumor-suppressor gene inactivated in human glioblastoma multiforme together with Cbx7 and a few other candidates. Acting downstream of the ER stress and BMP pathways, ATF3 binds to cell-type-specific accessible chromatin preloaded with AP1 and participates in the inhibition of critical oncogenic networks. Our data support the feasibility of combining ChIP-seq and RNAi screens in solid tumors and highlight multiple p16(INK4a)/p(19ARF)-independent functions for Bmi1 in development and cancer.

关键词： ATF3   SUMOylation   prostate cancer   CCND   proliferation   ACTIVATING TRANSCRIPTION FACTOR-3   CYCLIN D1   DNA-DAMAGE   SUMO   ANDROGEN   GENE   UBIQUITIN   PROTEIN   CONJUGATION   SUPPRESSES  

摘要： SUMOylation plays an important role in regulating a wide range of cellular processes. Previously, we showed that ATF3, a stress response mediator, can be SUMOylated and lysine 42 is the major SUMO site. However, the significance of ATF3 SUMOylation in biological processes is still poorly understood. In the present study, we investigated the role of ATF3 SUMOylation on CCND activity and cellular proliferation in human prostate cancer cells. First, we showed that ATF3 can be SUMOylated endogenously in the overexpression system, and lysine 42 is the major SUMO site. Unlike normal prostate tissue and androgen-responsive LNCaP cancer cells, androgen-independent PC3 and DU145 cancer cells did not express ATF3 endogenously. Overexpression of ATF3 increased CCND1/2 expression in PC3 and DU145 cancer cells. Interestingly, we observed that SUMOylation is essential for ATF3-mediated CCND1/2 activation. Finally, we observed that SUMOylation plays a functional role in ATF3-mediated cellular proliferation in PC3 and DU145 cells. Taken together, our results demonstrate that SUMO modification of ATF3 influences CCND1/2 activity and cellular proliferation of prostate cancer PC3 and DU145 cells and explains at least in part how ATF3 functions to regulate cancer development.

关键词： DIM   ATF3   ATF4   Colon cancer   ENDOPLASMIC-RETICULUM STRESS   EARLY GROWTH RESPONSE-1   COLON-CANCER   INDUCED APOPTOSIS   CYCLE ARREST   TUMOR-SUPPRESSOR   INDOLE-3-CARBINOL   EXPRESSION   RECEPTOR   GENE  

摘要： 3,3 '-Diindolylmethane (DIM) is a major in vivo condensation product of indole-3-carbinol, which is present in cruciferous vegetables. Although these compounds have been widely implicated in antitumorigenic and proapoptotic properties in animal as well as in vitro models of cancer, the underlying cellular mechanisms regulated by DIM are only partially understood. Activating transcription factor 3 (ATF3) is a member of the ATF/c-AMP response element-binding (CREB) subfamily of the basic-region leucine zipper family and has been known to induce apoptosis in human colorectal cancer (CRC) cells. The present study was performed to elucidate the molecular mechanism of ATF3 induction by DIM in human CRC cells. The DIM treatment induced apoptosis and induced ATF3 gene expression at protein and messenger RNA levels. DIM increased ATF3 promoter activity, and the region of 84 to +34 within ATF3 promoter was responsible for promoter activation by DIM. This region contained an ATF binding site. Deletion and point mutation of the ATF binding site ( 23 to 16) abolished ATF3 promoter activation by DIM, and overexpression of ATF4 enhanced ATF3 transactivation. Chromatin immunoprecipitation assay confirmed the binding of ATF4 in the ATF3 promoter. Inhibition of ATF4 expression by small interference RNA results in repression of DIM-induced ATF3 expression. The current study demonstrates that DIM stimulates ATF3 expression through ATF4-mediated pathway and subsequently induces apoptosis in human CRC cells. (C) 2013 Elsevier Inc. All rights reserved.

关键词： ATF3   SUMOylation   p53   TRANSCRIPTIONAL ACTIVITY   SUMO E3 LIGASE   ACTIVATING TRANSCRIPTION   PROTEIN SUMOYLATION   ENDOTHELIAL-CELLS   PROSTATE-CANCER   NUCLEAR-BODIES   COMPLEX   UBIQUITIN   FACTOR-3   P53  

摘要： Cyclic AMP-dependent transcription factor-3 (ATF3), a stress sensor, plays an essential role in cells to maintain homeostasis and has diverse functions in cellular survival and death signal pathways. ATF3 is a novel regulator of p53 protein stability and function. The activities of ATF3 are modulated by post-translational modifications (PTMs), such as ubiquitination, but whether it is modified by small ubiquitin-related modifier (SUMO) remains unknown. The aim of this study was to investigate whether ATF3 is post-translationally modified by SUMO proteins and also to elucidate SUMOylation of ATF3 on TP53 gene activity. Here we report that ATF3 is clearly defined as a SUMO target protein both in vitro SUMOylation assay using recombinant proteins and at the cellular levels. Furthermore, ATF3 interacted with UBE2I, the only SUMO E2 enzyme found so far. In addition, PIAS3 beta (a SUMO E3 ligase) enhanced and SENP2 and SENP7 (two SUMOylation proteases) decreased SUMOylation of ATF3, respectively. Finally, we found that ATF3 is selectively SUMOylated at lysine residue 42 but the SUMOylation does not alter subcellular localization of ATF3. We then characterized the functional role of ATF3 SUMOylation on TP53 gene expression. We found that SUMOylation of ATF3 is required for full repression of TP53 gene. Overall, we provide the first evidence that ATF3 is post-translationally modified by SUMO and SUMOylation of ATF3 plays a functional role in regulation of TP53 gene activity. J. Cell. Biochem. 114: 589598, 2013. (C) 2012 Wiley Periodicals, Inc.

关键词： Obesity   Adipose tissue hypoxia   Activating transcription factor (ATF3)   Mitochondrial dysfunction   Nuclear respiratory factor 1 (NRF-1)   ADIPOSE-TISSUE HYPOXIA   INSULIN   EXPRESSION   INFLAMMATION   BIOGENESIS  

摘要： Obesity-associated adipose tissue hypoxia plays a pivotal role in insulin resistance via impaired adipocyte dysfunction including mitochondria dysfunction. In this study, we investigated the involvement of hypoxia-inducible ATF3 in adipocyte hypoxia-mediated mitochondrial dysfunction. While HIF-1 alpha and ATF3 were increased in white adipose tissue of high fat diet (HFD) obese mice compared with control lean mice, mitochondria-related genes were significantly reduced. Treatment with hypoxia mimetics CoCl2 or incubation with 2% O-2 impaired mitochondria function as demonstrated by decreases in ATP production, NADH dehydrogenase activity, mitochondrial membrane potential, and reduced expression of mitochondria-related genes including NRF-1, PGC-1 alpha, COX1 and SOD in 3T3-L1 adipocyte cells. Furthermore, overexpression of ATF3 in 3T3-L1 cells also decreased mitochondria function as well as expression of mitochondria-related genes. ATF3 knockdown in 3T3-L1 cells partly prevented the hypoxia-mediated decrease in mitochondria function and expression of mitochondria-related genes. The mitochondria-related genes were decreased in white adipose tissue of ATF3-overexpressing mice compared with wild-type mice. These results suggest that ATF3 may play a role in adipocyte hypoxia-mediated mitochondrial dysfunction in obesity. (C) 2013 Elsevier Inc. All rights reserved.

关键词： ATF4   nutrition   amino acid limitation   gene expression   liver   ASPARAGINE SYNTHETASE GENE   C-JUN   STRESS   DEPRIVATION   BINDING   PROTEIN   CELLS   BETA   INHIBITOR   SURVIVAL  

摘要： Fu L, Kilberg MS. Elevated cJUN expression and an ATF/CRE site within the ATF3 promoter contribute to activation of ATF3 transcription by the amino acid response. Physiol Genomics 45: 127-137, 2013. First published December 26, 2012; doi: 10.1152/physiolgenomics.00160.2012.-Mammalian cells respond to amino acid deprivation through multiple signaling pathways referred to as the amino acid response (AAR). Transcription factors mediate the AAR after their activation by several mechanisms; examples include translational control (activating transcription factor 4, ATF4), phosphorylation (p-cJUN), and transcriptional control (ATF3). ATF4 induces ATF3 transcription through a promoter-localized C/EBP-ATF response element (CARE). The present report characterizes an ATF/CRE site upstream of the CARE that also contributes to AAR-induced ATF3 transcription. ATF4 binds to the ATF/CRE and CARE sequences and both are required for a maximal response to ATF4 induction. ATF3, which antagonizes ATF4 and represses its own gene, also exhibited binding activity to the ATF/CRE and CARE sequences. The AAR resulted in elevated total cJUN and p-cJUN protein levels and both forms exhibited binding activity to the ATF/CRE and CARE ATF3 sequences. Knockdown of AAR-enhanced cJUN expression blocked induction of the ATF3 gene and mutation of either the ATF/CRE or the CARE site prevented the cJUN-dependent increase in ATF3-driven luciferase activity. The results indicate that both increased cJUN and the cisacting ATF/CRE sequence within the ATF3 promoter contribute to the transcriptional activation of the gene during the AAR.