Human CCAAT/enhancer-binding protein beta gene expression is activated by endoplasmic reticulum stress through an unfolded protein response element downstream of the protein coding sequence (original) (raw)
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Journal of Biological Chemistry, 2004
CCAAT/enhancer-binding protein  (C/EBP) is a member of the bZIP family of transcription factors that contribute to the regulation of a wide range of important cellular processes. The data in the present study document that transcription from the human C/EBP gene is induced in response to endoplasmic reticulum stress, such as glucose deprivation, or treatment of cells with tunicamycin or thapsigargin. Transient transfection of C/EBP genomic fragments linked to a luciferase reporter gene demonstrated that the C/EBP promoter plays no major regulatory role. Instead, by deletion analysis it was discovered that a 46-bp region, located at a genomic site that corresponds to the 3-untranslated region of the C/EBP mRNA, harbored an element that was required for the stress response. Mutagenesis demonstrated that a cis-regulatory element located at nt ؉1614 -1621 (5-TGACGCAA-3) is responsible for activation of the C/EBP gene. Electrophoresis mobility shift analysis revealed that proteins are bound to this element and that the amount of binding is increased following glucose deprivation. This element is homologous to a previously reported mammalian unfolded protein response element that binds XBP-1. Consistent with those data, overexpression of XBP-1 caused an increase in transcription that was mediated by the C/EBP mammalian unfolded protein response element.
Journal of Biological Chemistry, 2008
The accumulation of unfolded proteins in the endoplasmic reticulum (ER) triggers a stress response program that protects cells early in the response and can lead to apoptosis during prolonged stress. The basic leucine zipper transcription factor, CCAAT/enhancer-binding protein  (C/EBP), is one of the genes with increased expression during ER stress. Translation of the C/EBP mRNA from different initiation codons leads to the synthesis of two transcriptional activators (LAP-1 and-2) and a transcriptional repressor (LIP). The LIP/LAP ratio is a critical factor in C/EBP-mediated gene transcription. It is shown here that the LIP/LAP ratio decreased by 5-fold during the early phase of ER stress and increased by 20-fold during the late phase, mostly because of changes in LIP levels. The early decrease in LIP required degradation via the proteasome pathway and phosphorylation of the translation initiation factor, eIF2␣. The increased LIP levels during the late phase were due to increased synthesis and increased stability of the protein. It is proposed that regulation of synthesis and degradation rates during ER stress controls the LIP/LAP ratio. The importance of C/EBP in the ER-stress response program was demonstrated using C/EBP-deficient mouse embryonic fibroblasts. It is shown that C/EBP attenuates expression of pro-survival ATF4 target genes in late ER stress and enhances expression of cell death-associated genes downstream of CHOP. The inhibitory effect of LIP on ATF4-induced transcription was demonstrated for the cat-1 amino acid transporter gene. We conclude that regulation of LIP/LAP ratios during ER stress is a novel mechanism for modulating the cellular stress response.
The Biochemical journal, 2005
For animals, dietary protein is critical for the nutrition of the organism and, at the cellular level, protein nutrition translates into amino acid availability. Amino acid deprivation triggers the AAR (amino acid response) pathway, which causes enhanced transcription from specific target genes. The present results show that C/EBPbeta (CCAAT/enhancer-binding protein beta) mRNA and protein content were increased following the deprivation of HepG2 human hepatoma cells of a single amino acid. Although there was a modest increase in mRNA half-life following histidine limitation, the primary mechanism for the elevated steady-state mRNA was increased transcription. Transient transfection documented that C/EBPbeta genomic fragments containing the 8451 bp 5' upstream of the transcription start site did not contain amino-acid-responsive elements. However, deletion analysis of the genomic region located 3' downstream of the protein coding sequence revealed that a 93 bp fragment contai...
CCAAT/Enhancer Binding Protein β in relation to ER Stress, Inflammation, and Metabolic Disturbances
BioMed research international, 2015
The prevalence of the metabolic syndrome and underlying metabolic disturbances increase rapidly in developed countries. Various molecular targets are currently under investigation to unravel the molecular mechanisms that cause these disturbances. This is done in attempt to counter or prevent the negative health consequences of the metabolic disturbances. Here, we reviewed the current knowledge on the role of C/EBP-β in these metabolic disturbances. C/EBP-β deletion in mice resulted in downregulation of hepatic lipogenic genes and increased expression of β-oxidation genes in brown adipose tissue. Furthermore, C/EBP-β is important in the differentiation and maturation of adipocytes and is increased during ER stress and proinflammatory conditions. So far, studies were only conducted in animals and in cell systems. The results found that C/EBP-β is an important transcription factor within the metabolic disturbances of the metabolic system. Therefore, it is interesting to examine the pot...
The glucose-regulated proteins: stress induction and clinical applications
Trends in Biochemical Sciences, 2001
A protective mechanism used by cells to adapt to stress of the endoplasmic reticulum (ER) is the induction of members of the glucose-regulated protein (Grp) family. The induction of mammalian Grp proteins in response to ER stress involves a complex network of regulators and novel mechanisms. The elucidation of Grp function and regulation opens up new therapeutic approaches to diseases associated with ER stress and cancer.
The Journal of Biological Chemistry, 1999
The gene for the amino acid biosynthetic activity asparagine synthetase (AS) is induced by both amino acid and glucose deprivation of cells. The data reported here document that the human AS gene is induced following activation of the Unfolded Response Pathway (UPR), also known as the Endoplasmic Reticulum Stress Response (ERSR) in mammals. Increased AS transcription occurs in response to glucose deprivation, tunicamycin, or azetidine-2-carboxylate, all known to activate the UPR/ERSR pathway. Previously identified ERSR target genes contain multiple copies of a single highly conserved cis-element. In contrast, the human AS gene does not contain the ERSR element, as it has been described for other responsive genes. Instead, AS induction requires an Sp1-like sequence, a sequence previously shown to be associated with amino acid control of transcription, and possibly, a third region containing no consensus sequences for known transcription factors. Oligonucleotides covering each of these regions form DNA-protein complexes in vitro, and for some the amount of these complexes is greater when nuclear extracts from glucose-starved cells are tested. These results document that a wider range of metabolic activities are activated by the UPR/ERSR pathway than previously recognized and that genomic elements other than those already described can serve to enhance transcription of specific target genes.
CCAAT/Enhancer Binding Proteins: Structure, Function and Regulation
Biochemical Journal, 2002
CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that all contain a highly conserved, basic-leucine zipper domain at the C-terminus that is involved in dimerization and DNA binding. At least six members of the family have been isolated and characterized to date (C/EBPα—C/EBPζ), with further diversity produced by the generation of different sized polypeptides, predominantly by differential use of translation initiation sites, and extensive protein—protein interactions both within the family and with other transcription factors. The function of the C/EBPs has recently been investigated by a number of approaches, including studies on mice that lack specific members, and has identified pivotal roles of the family in the control of cellular proliferation and differentiation, metabolism, inflammation and numerous other responses, particularly in hepatocytes, adipocytes and haematopoietic cells. The expression of the C/EBPs is regulated at multiple levels duri...
EMBO reports, 2015
The accumulation of misfolded proteins in the endoplasmic reticulum (ER) activates the Unfolded Protein Response (UPR ER ) to restore ER homeostasis. The AAA + ATPase p97/CDC-48 plays key roles in ER stress by promoting both ER protein degradation and transcription of UPR ER genes. Although the mechanisms associated with protein degradation are now well established, the molecular events involved in the regulation of gene transcription by p97/CDC-48 remain unclear. Using a reporter-based genome-wide RNAi screen in combination with quantitative proteomic analysis in Caenorhabditis elegans, we have identified RUVB-2, a AAA + ATPase, as a novel repressor of a subset of UPR ER genes. We show that degradation of RUVB-2 by CDC-48 enhances expression of ER stress response genes through an XBP1-dependent mechanism. The functional interplay between CDC-48 and RUVB-2 in controlling transcription of select UPR ER genes appears conserved in human cells. Together, these results describe a novel role for p97/CDC-48, whereby its role in protein degradation is integrated with its role in regulating expression of ER stress response genes.
Nucleic Acids Research, 1993
The promoter region of the mouse CCAAT-Enhancer Binding Protein (C/EBPa) gene is capable of directing high levels of expression of reporter constructs in various cell lines, albeit even in cells that do not express their endogenous C/EBPa gene. To understand the molecular mechanisms underlying this ubiquitous expression, we have characterized the promoter region of the mouse C/EBPa gene by a variety of in vitro and in vivo methods. We show that three sites related in sequence to USF, BTE and C/EBP binding sites and present in promoter region -350/+ 3, are recognized by proteins from rat liver nuclear extracts. The sequence of the C/EBPa promoter that Includes the USF binding site Is also capable of forming stable complexes with purified Myc + Max heterodimers and mutation of this site drastically reduces transcription of C/EBPa promoter luciferase constructs both in liver and non liver cell lines. In addition, we identify three novel protein-binding sites two of which display similarity to NF-1 and a NFxB binding sites. The region located between nucleotides -197 and -178 forms several heat-stable complexes with liver nuclear proteins in vitro which are recognized mainly by antibodies specific for C/EBPa. Furthermore, transient expression of C/EBPco and to a lesser extent C/EBPJ expression vectors, results in transactivation of a cotransfected C/EBPat promoterluciferase reporter construct. These experiments support the notion that