The 5′-untranslated region regulates ATF5 mRNA stability via nonsense-mediated mRNA decay in response to environmental stress

We previously reported that activating transcription factor5 (ATF5) mRNA increases in response to amino acid limitation, and that this increase is dependent on mRNA stabilization. The ATF5 gene allows transcription of mRNAs with two alternative 5-UTRs, 5-UTR and 5-UTR, derived from exon1 and exon1. 5-UTR contains the upstream open reading frames uORF1 and uORF2. Phosphorylation of eukaryotic initiation factor2 during the integrated stress response had been previously shown to lead to bypassing of uORF2 translation and production of ATF5 protein. Translation of uORF2 is expected to result in translational termination at a position 125 nucleotides upstream of the exon junction, and this fits the criterion of a nonsense-mediated decay target mRNA. We investigated the potential role of 5-UTR in the control of mRNA stabilization, and found that 5-UTR reduced the stability of ATF5 mRNA. 5-UTR-regulated destabilization of mRNA was suppressed by knockdown of the nonsense-mediated decay factors Upf1 and Upf2. Mutation of the downstream AUG (uAUG2) rendered mRNA refractory to Upf1 and Upf2 knockdown. Moreover, 5-UTR-regulated down-regulation was hindered by amino acid limitation and tunicamycin treatment, and stress-induced phosphorylation of eukaryotic initiation factor2 was involved in stabilization of ATF5 mRNA. These studies show that ATF5 mRNA is a naturally occurring normal mRNA target of nonsense-mediated decay, and provide evidence for linkage between stress-regulated translational regulation and the mRNA decay pathway. This linkage constitutes a mechanism that regulates expression of stress response genes.