Cytosolic prion protein is the predominant anti-Bax prion protein form: Exclusion of transmembrane and secreted prion protein forms in the anti-Bax function

Abstract

Prion protein (PrP) prevents Bax-mediated cell death by inhibiting the initial Bax conformational change that converts cytosolic Bax into a pro-apoptotic protein. PrP is mostly a glycophosphatidylinositol-anchored cell surface protein but it is also retrotranslocated into cytosolic PrP (CyPrP) or can become a type 1 or type 2 transmembrane protein. To determine the form and subcellular location of the PrP that has anti-Bax function, we co-expressed various Syrian hamster PrP (SHaPrP) mutants that favour specific PrP topologies and subcellular localization with N-terminally green fluorescent protein tagged pro-apoptotic Bax (EGFP-Bax) in MCF-7 cells and primary human neurons. Mutants that generate both CyPrP and secreted PrP ((Sec)PrP) or only CyPrP have anti-Bax activity. Mutants that produce (Ctm)PrP or (Ntm)PrP lose the anti-Bax activity, despite their ability to also make (Sec)PrP. Transmembrane-generating mutants do not produce CyPrP and both normal and cognate mutant forms of CyPrP rescue against the loss of anti-Bax activity. (Sec)PrP-generating constructs also produce non-membrane attached (Sec)PrP. However, this form of PrP has minimal anti-Bax activity. We conclude that CyPrP is the predominant form of PrP with anti-Bax function. These results imply that the retrotranslocation of PrP encompasses a survival function and is not merely a pathway for the proteasomal degradation of misfolded protein.

Loss of Anti-Bax Function in Gerstmann-Sträussler-Scheinker Syndrome-Associated Prion Protein Mutants

“…Consistent with our observations, a portion of PrP Q217R V accumulates in the cytosol [43]. Because we have previously demonstrated that CyPrP is the main form of PrP with the anti-Bax function [26], we conclude that the mutant CyPrP generated from these three mutants are less efficient at inhibiting the Bax activation pathway than the WT PrP. Previously, we have shown that the helix 3 is necessary and sufficient to inhibit Bax-mediated cell death [30].…”

Enhanced Neural Progenitor/Stem Cells Self‐Renewal via the Interaction of Stress‐Inducible Protein 1 with the Prion Protein

“…Indeed, LT‐HSCs from Prnp 0/0 bone marrow exhibits impaired self‐renewal in serial transplantation of lethally irradiated mouse recipients, which is a hallmark of LT‐HSCs with respect to their capacity for reconstituting bone marrow [31]. One proposed mechanism that has been advanced to explain how PrP C could sustain self‐renewal refers its property of having the ability to protect cells from apoptosis‐related signals, such as oxidative stress [55], bax‐mediated cell death [56–58], staurosporine‐induced cell death [27, 29, 30, 59, 60], and hypoxic‐ischemic insults [61–63]. Remarkably, we have demonstrated that PrP C ‐STI1 engagement protects postmitotic neuroblastic cells in retina explants and dissociated hippocampal neurons subjected to induced cell death [27, 29].…”

The relationship between the 20S proteasomes and prion-mediated neurodegenerations: potential therapeutic opportunities

“…This suggests the widespread biological role of the prion protein, which nevertheless assumes particular relevance in neuronal cells. The function of PrP C is not yet completely understood, however, an involvement in synaptic transmission [64,65], neuroprotection [66][67][68], angiogenesis [69] and copper homeostasis [70,71], was experimentally documented. Interestingly, PrP knock-out mice do not develop manifestations of neurodegeneration or any changes in phenotype or life span, suggesting that PrP C function is not crucial for the pathogenesis of prion disorders [72][73][74].…”