Stress-induced translation of ATF5 mRNA is regulated by the 5′-untranslated region

Activating transcription factor (ATF) 5 is a transcription factor belonging to the ATF/cAMP-response element-binding protein gene family. We previously reported that ATF5 mRNA expression increased in response to amino acid limitation. The ATF5 gene allows transcription of mRNAs with at least two alternative 5 '-untranslated regions (5 '-UTRs), 5 '-UTR alpha and 5 '-UTR beta, derived from exon1 alpha and exon1 beta. 5 '-UTR alpha contains highly conserved sequences, in which the upstream open reading frames (uORFs) uORF1 and uORF2 are found in many species. This study was designed to investigate the potential role of 5 '-UTRs in translational control. These 5 '-UTRs differentially determined translation efficiency from mRNA. The presence of 5 '-UTR alpha or 5 '-UTR beta represses translation from the downstream ATF5 ORF. Moreover, 5 '-UTR alpha-regulated translational repression is released by amino acid limitation or NaAsO2 exposure. This release was not seen for 5 '-UTR beta. Mutation of uAUG2 in the uORF2 of 5 '-UTR alpha restored the basal expression and abolished the positive regulation by amino acid limitation or arsenite exposure. Wedemonstrated that phosphorylation of eukaryotic initiation factor 2 alpha was required for amino acid limitation-induced translational regulation of ATF5. Furthermore, arsenite exposure activated the exogenously expressed heme-regulated inhibitor kinase and induced the phosphorylation of eukaryotic initiation factor 2 alpha in nonerythroid cells. These results suggest that translation of ATF5 is regulated by the alternative 5 '-UTR region of its mRNA, and ATF5 may play a role in protecting cells from amino acid limitation or arsenite-induced oxidative stress.