Induction of CHOP Expression by Amino Acid Limitation Requires Both ATF4 Expression and ATF2 Phosphorylation

Abstract

The CHOP gene is transcriptionally induced by amino acid starvation. We have previously identified a genomic cis-acting element (amino acid response element (AARE)) involved in the transcriptional activation of the human CHOP gene by leucine starvation and shown that it binds the activating transcription factor 2 (ATF2). The present study was designed to identify other transcription factors capable of binding to the CHOP AARE and to establish their role with regard to induction of the gene by amino acid deprivation. Electrophoretic mobility shift assay and transient transfection experiments show that several transcription factors that belong to the C/EBP or ATF families bind the AARE sequence and activate transcription. Among all these transcription factors, only ATF4 and ATF2 are involved in the amino acid control of CHOP expression. We show that inhibition of ATF2 or ATF4 expression impairs the transcriptional activation of CHOP by amino acid starvation. The transacting capacity of ATF4 depends on its expression level and that of ATF2 on its phosphorylation state. In response to leucine starvation, ATF4 expression and ATF2 phosphorylation are increased. However, induction of ATF4 expression by the endoplasmic reticulum stress pathway does not fully activate the AARE-dependent transcription. Taken together our results demonstrate that at least two pathways, one leading to ATF4 induction and one leading to ATF2 phosphorylation, are necessary to induce CHOP expression by amino acid starvation. This work was extended to the regulation of other amino acid regulated genes and suggests that ATF4 and ATF2 are key components of the amino acid control of gene expression.

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

“…Moreover, there is adequate precedent that starvation-induced translational inhibition can be associated with an increased translational yield for selected transcripts, including ATF3 and ATF4 (refs. 19,22).…”

ATF3 and p15PAF are novel gatekeepers of genomic integrity upon UV stress

“…To characterize ATF3 function after UV stress, knockdown experiments were performed, using a previously described siRNA (siATF3) 12 . The efficiency of this siRNA in HaCaT and HeLa cells has been shown in an earlier study.…”

Cyclophilin B is involved in p300-mediated degradation of CHOP in tumor cell adaptation to hypoxia

“…It has been reported that ATF4 is overexpressed under hypoxia, 14 and that it can directly upregulate CHOP transcription through its binding to the CHOP promoter region. 5,6 Thus, we tested whether hypoxia increases ATF4 and CHOP expression in our cell lines. Both ATF4 and CHOP protein levels began to increase after 3 h in hypoxia (Figure 4a), and continuously increased for up to 12 h (experimental endpoint).…”

“…1,2 It is a leucine-zipper transcription factor that is present at low levels under normal conditions but is highly upregulated in ER stress by ATF4. [3][4][5][6] Increased expression of CHOP promotes cell death, but the deletion of the CHOP gene leads to an attenuation in cell death induced by ER stress. 2,7 Also, the accumulation of CHOP protein during ER stress has been reported to be regulated through modulation of its degradation by the proteasome.…”