Neuronal Apoptosis Induced by Endoplasmic Reticulum Stress Is Regulated by ATF4–CHOP-Mediated Induction of the Bcl-2 Homology 3-Only Member PUMA

Abstract

An increasing body of evidence points to a key role of endoplasmic reticulum (ER) stress in acute and chronic neurodegenerative conditions. Extensive ER stress can trigger neuronal apoptosis, but the signaling pathways that regulate this cell death remain unclear. In the present study, we demonstrate that PUMA, a Bcl-2 homology 3 (BH3)-only member of the Bcl-2 family, is transcriptionally activated in cortical neurons by ER stress and is essential for ER-stress-induced cell death. PUMA is known to be a key transcriptional target of p53, but we have found that ER stress triggers PUMA induction and cell death through a p53-independent mechanism mediated by the ER-stress-inducible transcription factor ATF4 (activating transcription factor 4). Specifically, we demonstrate that ectopic expression of ATF4 sensitizes mouse cortical neurons to ER-stress-induced apoptosis and that ATF4-deficient neurons exhibit markedly reduced levels of PUMA expression and cell death. However, chromatin immunoprecipitation experiments suggest that ATF4 does not directly regulate the PUMA promoter. Rather, we found that ATF4 induces expression of the transcription factor CHOP (C/EBP homologous protein) and that CHOP in turn activates PUMA induction. Specifically, we demonstrate that CHOP binds to the PUMA promoter during ER stress and that CHOP knockdown attenuates PUMA induction and neuronal apoptosis. In summary, we have identified a key signaling pathway in ER-stress-induced neuronal death involving ATF4 -CHOP-mediated transactivation of the proapoptotic Bcl-2 family member PUMA. We propose that this pathway may be an important therapeutic target relevant to a number of neurodegenerative conditions.

Triptolide Protects Neurons from Endoplasmic Reticulum Stress-Mediated Apoptosis in Cerebral Ischemic Injury Rats

“…We found that the expression of FADD, caspase-8 and CHOP was not detected in the ischemic core but were obvious in the peri-infarct area, which may be due to the rapid initiation of necrosis in the ischemic core. Moreover, we observed that the ER stressassociated factors were predominantly expressed in the ischemic penumbra, which is in agreement with previous reports that under severe ER stress, apoptotic pathways can be activated inducing the expression of downstream effectors [36][37][38]. Our findings further revealed that T10 significantly down-regulated the expression levels of FADD, caspase-8, and CHOP in the peri-infarct area.…”

Imaging of single cell responses to ER stress indicates that the relative dynamics of IRE1/XBP1 and PERK/ATF4 signalling rather than a switch between signalling branches determine cell survival

“…[19][20][21] CHOP can trigger the downregulation of pro-survival BCL2 and upregulation of pro-apoptotic BH3-only proteins BIM 22,23 or PUMA. 20 Additionally, a recent study proposed that increased protein synthesis driven by ATF4/CHOP after re-initiation of general translation increases the amount of reactive oxygen species, thus leading to apoptosis. 13 Therefore, a slower increase in ATF4 levels could be protective.…”

Mutations in Cx30 that are linked to skin disease and non-syndromic hearing loss exhibit several distinct cellular pathologies

“…Although the expression of the V37E Cx30 mutant did not induce the upregulation of GRP78, which might occur upon the activation of the activating transcription factor 6 (ATF6) pathway (Berridge, 2002), the V37E mutant only moderately induced the expression of ATF4. ATF4 activates cell-deathinitiating caspases, including caspase 3, through the mitochondria-dependent intrinsic cell death pathway (Galehdar et al, 2010;Groenendyk and Michalak, 2005;Malhotra and Kaufman, 2007). By contrast, the ER-stress-induced splicing of XBP1 through activation of IRE1 did not occur in cells that expressed the V37E mutant, suggesting that the mechanism of cell death might be independent of the UPR.…”