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 (PrPC) 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 PrPC 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 PrPC levels and hinders the generation of protease-resistant PrP (PrPres) following infection with two different prion strains. Moreover, transient knock-down of P4HB decreases PrPres levels in cells with established prion infection. Partial reduction of P4HB activity using the P4HB-selective inhibitor KSC-34 also decreases PrPC levels in uninfected CAD5 cells whereas treatment of prion-infected CAD5 cells with KSC-34 results in higher levels of PrPres. A proportion of P4HB reaches the cell surface where PrPC is located, and a secreted P4HB variant increases PrPres levels in cells. Collectively, these results suggest that P4HB influences PrPC homeostasis and modulates the conversion of PrPC into misfolded species. Thus, targeting P4HB during prion disease may have therapeutic benefit.