Possible involvement of calpain-like activity in normal processing of cellular prion protein

Abstract

Time-lapse imaging analysis was previously used to show that spontaneous proteolysis of PrP C, which is fluorescence-labeled at both NH 2- and COOH-termini, occurred in mouse neuroblastoma neuro2a (N2a) cells susceptible to PrP Sc. We demonstrated that, unlike other protease inhibitors, a calpain inhibitor, calpastatin, drastically inhibited endoproteolysis of PrP C, as observed with time-lapse imaging in living cells, suggesting calpain-like activity. Calpastatin also inhibited cleavage of endogenous PrP C, and unprocessed molecules and the double-labeled PrP C accumulated around the perinuclear region. The molecular weight of PrP C fragments generated by spontaneous proteolysis was identical to those produced when PrP C synthesized in vitro was exposed to exogenous calpain. These results suggest that a calpain-like activity mediates normal processing of PrP C in N2a cells.