ATF4 Is a Mediator of the Nutrient-sensing Response Pathway That Activates the Human Asparagine Synthetase Gene

Abstract

Transcription from the asparagine synthetase (A.S.) gene is increased in response to either amino acid (amino acid response) or glucose (endoplasmic reticulum stress response) deprivation. These two independent pathways converge on the same set of genomic cis-elements within the A.S. promoter referred to as nutrientsensing response elements (NSRE) 1 and 2, both of which are necessary for gene activation. The NSRE-1 sequence was used to screen ATF/CREB family members by electrophoresis mobility shift assays and supershift by specific antibodies. The results indicated that ATF4 binds to the NSRE-1 sequence and that the amount of the ATF4 complex was increased when extracts from amino acid-deprived or glucose-deprived cells were tested. Using electrophoresis mobility shift assay experiments and a probe that contained both NSRE-1 and NSRE-2, mutation of the NSRE-1 sequence completely prevented formation of the ATF4-containing complexes, whereas mutation of the NSRE-2 sequence did not. Overexpression of ATF4 increased A.S. promoter-driven transcription, whereas an inhibitory dominant negative ATF4 mutant blocked both basal and starvation-enhanced transcription. Collectively, the results provide both in vitro and in vivo evidence for a role of ATF4 in the transcriptional activation of the A.S. gene in response to nutrient deprivation.

Nonsense surveillance regulates expression of diverse classes of mammalian transcripts and mutes genomic noise

“…We also observed upregulation of two transcription factors that coordinate cellular responses to amino acid starvation (ATF3 and ATF4; refs. 19,20). Depletion of amino acids inhibits translation 21 , and as NMD requires ongoing translation, regulation of these transcripts by nonsense surveillance probably couples their expression level to translational efficiency.…”

Upregulation of tryptophanyl-tRNA synthethase adapts human cancer cells to nutritional stress caused by tryptophan degradation

“…eIF2α phosphorylation enhances translation 28 and transcription of ATF4 29 . In line, ATF4 protein (Figure 4L) and ATF4 mRNA (Fig.…”

“…Trp shortage mediates WARS upregulation by signaling via the GCN2-peIF2a-ATF4 axis (Figure 4), as low levels of Trp result in the accumulation of uncharged tRNAs, which activate the stress kinase GCN2 10 . GCN2 then phosphorylates its substrate, eIF2a leading to reduced global protein synthesis, but increased translation of specific mRNAs such as ATF4 27,28 . Our results reveal that expression of GCN2 and ATF4 as well as phosphorylation of eIF2a are each required for the induction of WARS upon Trp degradation (Figure 4).…”

Circulating tumour cells demonstrate an altered response to hypoxia and an aggressive phenotype

“…The ATF3 is a gene with a known role in metastasis, and has been described to induce genes relevant to epithelial-to-mesenchymal transition (Yin et al, 2008), a histological feature of invading cells (Guarino et al, 2007). Activating transcription factor 4 is involved in drug resistance (Igarashi et al, 2007) and is a major factor in nutrition sensing, regulating the expression of ASNS (Siu et al, 2002). Under conditions of hypoxia and/or glucose deprivation, cells can switch to ATF4-mediated ASNS expression as a protective mechanism (Cui et al, 2007).…”