Mechanisms of ER Stress-Mediated Mitochondrial Membrane Permeabilization

Sanjeev Gupta,Eva Szegezdi,Afshin Samali,Sandra Healy,Susan E Logue,Catherine Neary,Lorraine Cuffe

doi:10.1155/2010/170215

Abstract

During apoptosis, the process of mitochondrial outer membrane permeabilization (MOMP) represents a point-of-no-return as it commits the cell to death. Here we have assessed the role of caspases, Bcl-2 family members and the mitochondrial permeability transition pore on ER stress-induced MOMP and subsequent cell death. Induction of ER stress leads to upregulation of several genes such as Grp78, Edem1, Erp72, Atf4, Wars, Herp, p58ipk, and ERdj4 and leads to caspase activation, release of mitochondrial intermembrane proteins and dissipation of mitochondrial transmembrane potential (ΔΨm). Mouse embryonic fibroblasts (MEFs) from caspase-9, -2 and, -3 knock-out mice were resistant to ER stress-induced apoptosis which correlated with decreased processing of pro-caspase-3 and -9. Furthermore, pretreatment of cells with caspase inhibitors (Boc-D.fmk and DEVD.fmk) attenuated ER stress-induced loss of ΔΨm. However, only deficiency of caspase-9 and -2 could prevent ER stress-mediated loss of ΔΨm. Bcl-2 overexpression or pretreatment of cells with the cell permeable BH4 domain (BH4-Tat) or the mitochondrial permeability transition pore inhibitors, bongkrekic acid or cyclosporine A, attenuated the ER stress-induced loss of ΔΨm. These data suggest a role for caspase-9 and -2, Bcl-2 family members and the mitochondrial permeability transition pore in loss of mitochondrial membrane potential during ER stress-induced apoptosis.

Highlights

The endoplasmic reticulum (ER) is a cytosolic membrane bound network connected to the nucleus, mitochondria, and the plasma membrane
Our results show that ER stress-induced apoptosis involves loss of ΔΨm that is dependent on caspases and regulated by Bcl-2 family members and the mitochondrial permeability transition pore (PTP)
We examined protein levels by Western blot analysis for a subset of these genes and found them to reflect the changes observed in mRNA expression with Grp78, Grp90, and the proapoptotic transcription factor CHOP/GADD153 being significantly upregulated after treating cells with Tg (Figure 1(b))

Summary

Introduction

The endoplasmic reticulum (ER) is a cytosolic membrane bound network connected to the nucleus, mitochondria, and the plasma membrane. Release of cytochrome c from mitochondria during ER stress-induced apoptosis has been suggested to be mediated by mitochondrial permeability transition (MPT) [17, 18]. Bcl-2 family members are known to localize both to the ER and the mitochondria, where they may act to regulate the signaling pathways that promote the opening of the PTP [19, 24]. The cytochrome c-dependent apoptotic pathway activated by ER-mitochondria crosstalk seems to play an essential role in the ER stress-mediated cell death [26]. We have determined the role of caspases, Bcl-2 family members, and PTP on the mitochondrial changes associated with ER-induced apoptosis. Our results show that ER stress-induced apoptosis involves loss of ΔΨm that is dependent on caspases and regulated by Bcl-2 family members and the mitochondrial PTP

Materials and Methods

Results and Discussion

48 Cytosol