Characterization of Puma-Dependent and Puma-Independent Neuronal Cell Death Pathways following Prolonged Proteasomal Inhibition

Abstract

Proteasomal stress and the accumulation of polyubiquitinated proteins are key features of numerous neurodegenerative disorders. Previously we demonstrated that stabilization of p53 and activation of its target gene, puma (p53-upregulated mediator of apoptosis), mediated proteasome inhibitor-induced apoptosis in cancer cells. Here we demonstrated that Puma also contributed to proteasome inhibitor-induced apoptosis in mouse neocortical neurons. Although protection afforded by puma gene deletion was incomplete, we found little evidence indicating contributions from other proapoptotic BH3-only proteins. Attenuation of bax expression did not further reduce Puma-independent apoptosis, suggesting that pathways other than the mitochondrial apoptosis pathway were activated. Real-time imaging experiments in wild-type and puma-deficient neurons using a fluorescence resonance energy transfer (FRET)-based caspase sensor confirmed the involvement of a second cell death pathway characterized by caspase activation prior to mitochondrial permeabilization and, more prominently, a third, caspase-independent and Puma-independent pathway characterized by rapid cell shrinkage and nuclear condensation. This pathway involved lysosomal permeabilization in the absence of autophagy activation and was sensitive to cathepsin but not autophagy inhibition. Our data demonstrate that proteasomal stress activates distinct cell death pathways in neurons, leading to both caspase-dependent and caspase-independent apoptosis, and demonstrate independent roles for Puma and lysosomal permeabilization in this model.

Loss of nuclear factor E2-related factor 1 in the brain leads to dysregulation of proteasome gene expression and neurodegeneration

“…Instead, the knockout of Nrf1 in both mouse brains and cells produces defects in proteasome function and alterations in proteasome gene expression, and cell-based studies indicate that this defect is directly associated with Nrf1 deficiency and not secondary to a systemic process in the knockout animals. Because lowered proteasome function induces toxicity and apoptosis in neurons and other cells (19,20), this suggests that proteasomal impairment is a major causative factor by which Nrf1 deficiency promotes neuronal degeneration. Our results also indicate that Nrf1 is an important effector of proteasome gene expression in the nervous system.…”

Nuclear Clusterin Is Associated with Neuronal Apoptosis in the Developing Rat Brain upon Ethanol Exposure

“…On the other hand, deficiency of Noxa, Bim, or Hrk showed no effect on ethanol‐induced brain cell death in mice (Ghosh et al., 2009). Bid does not contribute to mouse neuronal cell death by proteasomal inhibition (Tuffy et al., 2010). Activated Bax triggers mitochondrial permeabilization, which could be measured by cytochrome C release, and activation of caspase‐3 (Han et al., 2005; Olney et al., 2002; Young et al., 2003).…”

Tumor suppression by resistant maltodextrin, Fibersol-2

“…37 Our results indicating Puma-independent Fibersol-2's activity are consistent with the recent study showing stress-induced cell death by Puma-independent pathway characterized by rapid cell shrinkage and nuclear condensation. 38 It has been well illustrated that Akt/ mTOR signaling is involved in cell proliferation and anti-apoptosis. [26][27][28] However, recent reports described that single or combination treatment of anti-cancer drugs induces apoptosis through ROS/ Akt signaling in colorectal cancer cells.…”