PERK-dependent gene expression programs of the acute and chronic cellular response to ER stress

The UPR (Unfolded Protein Response) is a well-orchestrated response to ER protein folding and processing overload, integrating both transcriptional and translational outputs. Its three arms in mammalian cells, the PERK translational response arm, together with the ATF6 and IRE1-mediated transcriptional arms, have been thoroughly investigated. Using ribosome footprint profiling, we performed a deep characterization of the gene expression programs involved in the acute and adaptive ER stress responses. We utilized MEFs (Mouse Embryonic Fibroblasts) treated with Thapsigargin for different durations, that were wither WT or PERK knockouts, to determine the role of PERK in the acute and chronic UPR. We characterized three major gene expression programs: acute induction, chronic induction, and repression, and found that they were all PERK dependent. All three programs were recapitulated in publicly available data and in NIH3T3 cells. While PERK -/- cells did not recapitulate these responses in the acute timepoints, late timepoints showed an extremely weak induction/repression, suggesting that the chronic responses in WT cells are largely PERK dependent as well. We found that most ER target proteins were significantly repressed; including transmembrane proteins, glycoproteins, and proteins with disulfide bonds. We further demonstrate the downregulation of cyclins, while the expression of the amino acid biosynthesis pathway was enhanced. Overall design: We utilized MEFs (Mouse Embryonic Fibroblasts) treated with Thapsigargin for different durations (1h, 2h, 5h, 8h), that were wither WT or PERK knockouts, to determine the role of PERK in the acute and chronic UPR. Thapsigargin was applied also with NIH 3t3 cells within two differet time-points (2h 7h) as well.