Protein Synthesis and Degradation
- Translation regulation largely occurs during initiation, which features ribosome assembly onto mRNAs and selection of the translation start site. Short, upstream ORFs (uORFs) located in the 5′-leader of the mRNA can be selected for translation. Multiple transcripts associated with stress amelioration are preferentially translated through uORF-mediated mechanisms during activation of the integrated stress response (ISR) in which phosphorylation of the α subunit of eIF2 results in a coincident global reduction in translation initiation.
- 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.
- Upon exposure to environmental stress, phosphorylation of the α subunit of eIF2 (eIF2α-P) represses global protein synthesis, coincident with preferential translation of gene transcripts that mitigate stress damage or alternatively trigger apoptosis. Because there are multiple mammalian eIF2 kinases, each responding to different stress arrangements, this translational control scheme is referred to as the integrated stress response (ISR). Included among the preferentially translated mRNAs induced by eIF2α-P is that encoding the transcription factor CHOP (DDIT3/GADD153).
- Background: eIF2α-P induced GADD34 and constitutively expressed CReP target PP1c to dephosphorylate eIF2α-P to dictate translation control of the ISR.Results: Differential expression of GADD34 and CReP is regulated by upstream ORF (uORF)-mediated ribosome reinitiation.Conclusion: uORFs regulate differential expression of GADD34 and CReP and are important for cell adaptation to stress.Significance: Regulation of eIF2α-P is central for protein homeostasis and cell viability.