The protein disulfide isomerase P4HB/PDIA1 modulates cellular and misfolded forms of the prion protein

Prions are misfolded, self-propagating versions of cellular proteins. In humans and animals, misfolding of the cellular prion protein (PrP C ) causes invariably fatal transmissible neurodegenerative diseases. Little is known about how mammalian prions replicate in the brain, including whether other proteins participate in prion replication in vivo . Several members of the protein disulfide isomerase family have been shown to reside in close spatial proximity to PrP C in cells and mice, implying that they could be involved in prion biogenesis. Here, we show that stable knock-down of the protein disulfide isomerase P4HB (also called PDIA1) in prion-susceptible CAD5 cells reduces PrP C levels and hinders the generation of protease-resistant PrP (PrP res ) following infection with two different prion strains. Moreover, transient knock-down of P4HB decreases PrP res levels in cells with established prion infection. Partial reduction of P4HB activity using the P4HB-selective inhibitor KSC-34 also decreases PrP C levels in uninfected CAD5 cells whereas treatment of prion-infected CAD5 cells with KSC-34 results in higher levels of PrP res . A proportion of P4HB reaches the cell surface where PrP C is located, and a secreted P4HB variant increases PrP res levels in cells. Collectively, these results suggest that P4HB influences PrP C homeostasis and modulates the conversion of PrP C into misfolded species. Thus, targeting P4HB during prion disease may have therapeutic benefit.