Elevated ATF4 Expression, in the Absence of Other Signals, Is Sufficient for Transcriptional Induction via CCAAT Enhancer-binding Protein-activating Transcription Factor Response Elements

Abstract

Protein limitation in vivo or amino acid deprivation of cells in culture causes a signal transduction cascade consisting of activation of the kinase GCN2 (general control nonderepressible 2), phosphorylation of eukaryotic initiation factor 2, and increased synthesis of activating transcription factor (ATF) 4 by a translational control mechanism. In a self-limiting transcriptional program, ATF4 transiently activates a wide range of downstream target genes involved in transport, cellular metabolism, and other cell functions. Simultaneous activation of other signal transduction pathways by amino acid deprivation led to the question of whether or not the increased abundance of ATF4 alone was sufficient to trigger the transcriptional control mechanisms. Using 293 cells that ectopically express ATF4 in a tetracycline-inducible manner showed that ATF4 target genes were activated in the absence of amino acid deprivation. Ectopic expression of ATF4 alone resulted in effective recruitment of the general transcription machinery, but some reduction in histone modification was observed. These data document that ATF4 alone is sufficient to trigger the amino acid-responsive transcriptional control program. However, the absolute amount of ectopic ATF4 required to achieve the same degree of transcriptional activation observed after amino acid limitation was greater, suggesting that other factors may serve to enhance ATF4 function.

A Mitogen-activated Protein Kinase/Extracellular Signal-regulated Kinase Kinase (MEK)-dependent Transcriptional Program Controls Activation of the Early Growth Response 1 (EGR1) Gene during Amino Acid Limitation

“…2B). As we have reported previously (32), Tet-induced ATF4 caused a significant increase in ASNS expression. However, despite immunoblot evidence for a large increase in ATF4 protein in response to the Tet, no effect of ATF4 overexpression alone was observed on the EGR1 mRNA level.…”

Auto-activation of c-JUN Gene by Amino Acid Deprivation of Hepatocellular Carcinoma Cells Reveals a Novel c-JUN-mediated Signaling Pathway

“…Tetracycline treatment of these cells results in increased ATF4 protein and, consequently, increased transcriptional activation of the ASNS, C/EBP␤, ATF3, and other ATF4-responsive genes (47). In contrast to the AA-responsive genes just mentioned, a tetracycline-induced increase in ATF4 protein caused little or no effect on c-JUN expression (Fig.…”

Cellular and animal indispensable amino acid limitation responses and health promotion. Can the two be linked? A critical review

“…These auxiliary pathways are best understood for ER stress responses in which PERK and ATF6 are also key factors (Deval et al 2009). So, even though amino acid deprivation and other stresses that activate mammalian eIF2a kinases commonly trigger increased ATF4 synthesis, a somewhat distinct subset of genes is activated in response to different types of cellular stress, perhaps due to eIF2a kinaseindependent signalling, which, among other things, may lead to induction of different C/EBP family members (Wek et al 1995;Deval et al 2009;Shan et al 2009). It is also likely that some of the long-term responses to sustained induction of eIF2a may simply be consequences of the global repression of translation and/or of stress granule formation.…”

“…The ATF family members heterodimerize within the ATF family as well as with members of another bZIP subgroup, the CCAAT/enhancer-binding protein (C/EBP) family Sikalidis and Stipanuk 2010). Many of the genes known to be transcriptionally up-regulated by amino acid deprivation or the eIF2a-P/ATF4-mediated stress response pathway, contain C/EBP -ATF composite sites that are also known as amino acid response elements (AAREs) or CCAAT/EBP-activating transcription factor response elements (Harding et al 2000;Kilberg et al 2009;Shan et al 2009). …”