Uncovering a Dual Regulatory Role for Caspases During Endoplasmic Reticulum Stress-induced Cell Death

Abstract

Many diseases are associated with endoplasmic reticulum (ER) stress, which results from an accumulation of misfolded proteins. This triggers an adaptive response called the “unfolded protein response” (UPR), and prolonged exposure to ER stress leads to cell death. Caspases are reported to play a critical role in ER stress-induced cell death but the underlying mechanisms by which they exert their effect continue to remain elusive. To understand the role caspases play during ER stress, a systems level approach integrating analysis of the transcriptome, proteome, and proteolytic substrate profile was employed. This quantitative analysis revealed transcriptional profiles for most human genes, provided information on protein abundance for 4476 proteins, and identified 445 caspase substrates. Based on these data sets many caspase substrates were shown to be downregulated at the protein level during ER stress suggesting caspase activity inhibits their cellular function. Additionally, RNA sequencing revealed a role for caspases in regulation of ER stress-induced transcriptional pathways and gene set enrichment analysis showed expression of multiple gene targets of essential transcription factors to be upregulated during ER stress upon inhibition of caspases. Furthermore, these transcription factors were degraded in a caspase-dependent manner during ER stress. These results indicate that caspases play a dual role in regulating the cellular response to ER stress through both post-translational and transcriptional regulatory mechanisms. Moreover, this study provides unique insight into progression of the unfolded protein response into cell death, which may help identify therapeutic strategies to treat ER stress-related diseases.

Kaempferol mitigates Endoplasmic Reticulum Stress Induced Cell Death by targeting caspase 3/7

“…A very recent study showed that ZVAD-FMK also inhibited ER stress. Furthermore, it has been demonstrated in the same study that ER stress downregulated many caspase substrates at the protein level; caspases influenced ER stress pathway both by directly cleaving its substrates and also by deactivating transcription factors essential for upregulation of genes involved in cell fate decisions 58 .…”

Caspases and their substrates

“…These functional differences are particularly evident in apoptosis, where some cleavage events drive apoptosis through gain-of-function, such as the activation of caspases themselves, whereas most of the cleaved substrates, such as inhibitor of the caspase-activated DNAse (ICAD), have undergone a loss-of-function. 54 For example, Anania et al 55 used a systems-level approach combining transcriptomics, proteomics, and N-terminomics to study the role of caspases during the unfolded protein response caused by endoplasmic reticulum stress. This study showed that caspase activation not only controls post-translational protein expression of direct caspase substrates, but also regulates transcription of genes involved Rank order in cell fate decisions in response to endoplasmic reticulum stress.…”

iNrich, Rapid and Robust Method to Enrich N-Terminal Proteome in a Highly Multiplexed Platform

“…Therefore, we set up a TMT-compatible version of iNrich by replacing acetic anhydride with TMT and validated the method via a quantitative analysis of HCT116 cells treated with TM or TG (Figure A). The two reagents are known to induce ER stress and consequently a cellular response to the stress of unfolded proteins or unfolded protein response (UPR) . Using a 6-plex TMT reagent, 100 μg proteins of cells treated with TG, TM, and DMSO for 0 and 48 h, respectively, were labeled, and the iNrich-enriched N-terminomes were analyzed.…”