Differences in the molecular mechanisms involved in the transcriptional activation of the CHOP and asparagine synthetase genes in response to amino acid deprivation or activation of the unfolded protein response.

A promoter element called the amino acid response element (AARE), which is essential for the induction of CHOP (a CCAAT/enhancer-binding protein-related gene) transcription by amino acid depletion, has been previously characterized. Conversely, the human asparagine synthetase (AS) promoter contains two cis-acting elements termed nutrient-sensing response elements (NSRE-1 and NSRE-2) that are required to activate the gene by either amino acid deprivation or the endoplasmic reticulum stress response. The results reported here document the comparison between CHOP and AS transcriptional control elements used by the amino acid pathway. We first establish that the AS NSRE-1 sequence shares nucleotide sequence and functional similarities with the CHOP AARE. However, we demonstrate that the CHOP AARE can function independently, whereas AS NSRE-1 is functionally weak by itself and instead requires the presence of NSRE-2. Furthermore, AS NSRE-2 can confer endoplasmic reticulum stress responsiveness to the CHOP AARE. Using activating transcription factor-2-deficient mouse embryonic fibroblasts, we also show that lack of this transcription factor does not abolish the amino acid inducibility of AS transcription, but this transcription factor is necessary to obtain the full AS response to amino acid starvation. Collectively, these results document that there are significant differences in the molecular mechanisms involved in the transcriptional activation of CHOP and AS by amino acid limitation.