The Protein Disulfide Isomerase P4HB/PDIA1 Modulates PrPC Levels and Prion Replication

Prions are misfolded, self-propagating versions of the cellular prion protein (PrPC) that cause invariably fatal transmissible neurodegenerative diseases in humans and animals. Little is known about how 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 results in lower levels of protease-resistant PrP (PrPres), a marker of infectious prions, following infection with two different prion strains. 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 facilitates prion replication in cells by stabilizing PrPC and potentially acting as a chaperone that directly modulates prion conversion. Thus, targeting P4HB during prion disease may have therapeutic benefit.