Translation Regulation of the Glutamyl-prolyl-tRNA Synthetase Gene EPRS through Bypass of Upstream Open Reading Frames with Noncanonical Initiation Codons

• Published in: The Journal of biological chemistry Vol. 291; no. 20; pp. 10824 - 10835
• Main Authors: Young, Sara K., Baird, Thomas D., Wek, Ronald C.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 13.05.2016; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acyl-tRNA Synthetases - biosynthesis; Amino Acyl-tRNA Synthetases - genetics; aminoacyl tRNA synthetase; Animals; Codon, Initiator - genetics; Codon, Initiator - metabolism; endoplasmic reticulum stress (ER stress); EPRS; eukaryotic initiation factor 2 (eIF2); Eukaryotic Initiation Factor-2 - genetics; Eukaryotic Initiation Factor-2 - metabolism; Gene Expression Regulation, Enzymologic - physiology; Gene Regulation; integrated stress response; Mice; Mice, Knockout; Open Reading Frames; Protein Biosynthesis - physiology; stress response; translation control; translation initiation; uORF; stress response; aminoacyl tRNA synthetase; eukaryotic initiation factor 2 (eIF2); translation initiation; uORF; endoplasmic reticulum stress (ER stress); translation control; EPRS; integrated stress response
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M116.722256

In the integrated stress response, phosphorylation of eIF2α (eIF2α-P) reduces protein synthesis while concomitantly promoting preferential translation of specific transcripts associated with stress adaptation. Translation of the glutamyl-prolyl-tRNA synthetase gene EPRS is enhanced in response to eIF2α-P. To identify the underlying mechanism of translation control, we employed biochemical approaches to determine the regulatory features by which upstream ORFs (uORFs) direct downstream translation control and expression of the EPRS coding region. Our findings reveal that translation of two inhibitory uORFs encoded by noncanonical CUG and UUG initiation codons in the EPRS mRNA 5′-leader serve to dampen levels of translation initiation at the EPRS coding region. By a mechanism suggested to involve increased translation initiation stringency during stress-induced eIF2α-P, we observed facilitated ribosome bypass of these uORFs, allowing for increased translation of the EPRS coding region. Importantly, EPRS protein expression is enhanced through this preferential translation mechanism in response to multiple known activators of eIF2α-P and likely serves to facilitate stress adaptation in response to a variety of cellular stresses. The rules presented here for the regulated ribosome bypass of noncanonical initiation codons in the EPRS 5′-leader add complexity into the nature of uORF-mediated translation control mechanisms during eIF2α-P and additionally illustrate the roles that previously unexamined uORFs with noncanonical initiation codons can play in modulating gene expression.