Submitted to: Keystone Symposia
Publication Type: Abstract only
Publication Acceptance Date: 11/21/2004
Publication Date: 1/11/2005
Citation: Anantharam, V., Vorberg, I., Choi, C., Kanthasamy, A., Richt, J., Priola, S.A., Kanthasamy, A.G. 2005. Differential role of prion protein in oxidative stress- and ER stress-induced apoptotic signaling in neural cells [abstract]. Molecular Mechanisms of TSEs (Prion Diseases), Keystone Symposia. p. 39. Interpretive Summary:
Technical Abstract: Although prion protein is abundantly expressed in the CNS, its biological function has not yet been established. To determine the role of prion protein in oxidative stress and protein processing, we compared the effects of H2O2 and the endoplasmic reticulum (ER) stress-inducers brefeldin A and tunicamycin on apoptotic cell signaling in a neural cell line derived from PrP knockout mice engineered to stably express non-pathogenic mouse prion protein (PrPsen) and empty vector-expressing prion knockout cells (PrPko). Treatment with H2O2 (10-100 uM), brefeldin A (3-30 uM), and tunicamycin (0.6-6 uM) resulted in dose- and time-dependent increases in cytotoxic cell death, cytochrome c release, caspase-3 and -9 activation, and DNA fragmentation over a 24 hr period in both PrPsen and PrPko cells. However, ER stress-induced caspase-3 activation, DNA fragmentation, and cytotoxic cell death were significantly higher in PrPsen than PrPko. Alternatively, H2O2 stress-induced caspase-3 activation, DNA fragmentation, and cytotoxic cell death were significantly reduced in PrPsen as compared to PrPko, suggesting that prion protein may be neuroprotective against oxidative damage. Pretreatment with 2 uM MnTBAP (SOD mimetic, ROS inhibitor) suppressed H2O2 stress but not ER stress-induced apoptotic cell death. Additionally, caspase-12 and -8 were activated only in cells treated with brefeldin A and tunicamycin but not with H2O2. Interestingly, PKC-delta, an oxidative stress sensitive kinase, was proteolytically cleaved and activated by caspase-3 during both oxidative stress and ER stress. Comparative analysis of PKC' proteolytic activation in PrPsen and PrPko revealed that prion expressing cells were protected from oxidative stress-induced PKC-delta activation; however, exacerbated ER stress induced PKC-delta activation. Overexpression of the kinase inactive PKC' dominant negative mutant (PKC-deltaK376R) or the caspase-3 cleavage site-resistant PKC-delta mutant (PKC-deltaD327A) significantly attenuated both ER- and oxidative stress-induced apoptotic cell death. Together, these results suggest that prion protein enhances the susceptibility of neural cells to impairment in protein processing and trafficking but decreases the vulnerability to oxidative insults, and that PKC-delta is a key downstream mediator of cellular stress-induced neuronal apoptosis. (supported by ILHAC).