Endoplasmic Reticulum Stress-induced Cysteine Protease Activation in Cortical Neurons

Abstract

Endoplasmic reticulum (ER) stress elicits protective responses of chaperone induction and translational suppression and, when unimpeded, leads to caspase-mediated apoptosis. Alzheimer's disease-linked mutations in presenilin-1 (PS-1) reportedly impair ER stress-mediated protective responses and enhance vulnerability to degeneration. We used cleavage site-specific antibodies to characterize the cysteine protease activation responses of primary mouse cortical neurons to ER stress and evaluate the influence of a PS-1 knock-in mutation on these and other stress responses. Two different ER stressors lead to processing of the ER-resident protease procaspase-12, activation of calpain, caspase-3, and caspase-6, and degradation of ER and non-ER protein substrates. Immunocytochemical localization of activated caspase-3 and a cleaved substrate of caspase-6 confirms that caspase activation extends into the cytosol and nucleus. ER stress-induced proteolysis is unchanged in cortical neurons derived from the PS-1 P264L knock-in mouse. Furthermore, the PS-1 genotype does not influence stress-induced increases in chaperones Grp78/BiP and Grp94 or apoptotic neurodegeneration. A similar lack of effect of the PS-1 P264L mutation on the activation of caspases and induction of chaperones is observed in fibroblasts. Finally, the PS-1 knock-in mutation does not alter activation of the protein kinase PKR-like ER kinase (PERK), a trigger for stress-induced translational suppression. These data demonstrate that ER stress in cortical neurons leads to activation of several cysteine proteases within diverse neuronal compartments and indicate that Alzheimer's disease-linked PS-1 mutations do not invariably alter the proteolytic, chaperone induction, translational suppression, and apoptotic responses to ER stress.

Multiple death pathways in retina-derived 661W cells following growth factor deprivation: crosstalk between caspases and calpains

“…35 We detected an early upregulation of caspase-12 (48 kDa) and cleavage to an approximately 35-kDa peptide (Figure 2c), which has also been reported to be consequence of calpain-mediated proteolysis. 24,36 Together, these results indicate that caspase-dependent pathways are implicated in apoptosis of 661W cone photoreceptors.…”

Caspase-12: an overview

“…7 During the mitochondrial apoptotic pathway, caspase-12 is processed in serumdeprived AKR-2B fibrosarcoma cells, in staurosporine-treated www.nature.com/cdd murine cortical neurons and MEF cells, and in etoposidetreated PC12 cells. 8,13,14 Is caspase-12 implicated in ER-stress induced apoptosis?…”

“…[15][16][17] Caspase-12 has been localized on the cytoplasmic side of the ER using immunofluorescence and subcellular fractionation techniques. 10,11,13 ER stress can be induced by chemicals such as brefeldin A, tunicamycin, thapsigargin and the calcium ionophore A23187. Brefeldin A induces ER stress by blocking the transport of proteins from the ER to the Golgi complex.…”

Differential behavioral state-dependence in the burst properties of CA3 and CA1 neurons

“…Misfolded proteins that accumulate in the ER lumen stimulate expression of molecular chaperones, such as BiP, and transcription factors, such as CHOP (39 -41). Some studies claim that this ER stress response is significantly diminished by ADlinked presenilin mutations (23,42), while others demonstrate that up-regulation of the ER stress-induced signaling pathway and chaperones are independent of presenilin expression (25) and are not altered by knock-in presenilin-1 mutations (43). In addition to these discrepancies, the potential impact of alterations in the stress response caused by presenilin mutations has not been assessed at the synaptic level.…”