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Abstract

The cellular prion protein (PrPc), tissue-type plasminogen activator (t-PA) and plasminogen are expressed in synaptic membranes in vivo. In the central nervous system the fibrinolytic system is associated with excitotoxin-mediated neurotoxicity and Alzheimer's disease. Recently binding of the disease associated isoform of the prion protein (PrPSc) to plasminogen and stimulation of t-PA activity have been reported. In this study the interaction of PrPc and plasminogen was investigated using chromogenic assays in vitro.We found that plasmin is able to cleave recombinant PrPc at lysine residue 110 generating an NH2-terminal truncated molecule that has previously been described as a major product of PrPc metabolism.We further characterized the proteolytic fragments with respect to their ability to stimulate plasminogen activation in vitro. Our results show that the NH2-terminal part of PrPc spanning amino acids 23-110 (PrP23-110) together with low molecular weight heparin stimulates t-PA mediated plasminogen activation in vitro. The apparent rate constant was increased 57 fold in the presence of 800 nM PrP23-110. Furthermore,we compared the stimulation of t-PA activity by PrPc and beta-amyloid peptide (1-42).While the activity of the beta-amyloid was independent of low molecular weight heparin, PrP23-110 was approximately 4- and 37 fold more active than beta-amyloid in the absence or presence of low molecular weight heparin. In summary, plasmin cleaves PrPc in vitro and the liberated NH2-terminal fragment accelerates plasminogen activation. Cleavage of PrPc has previously been reported.Thus cleavage of PrPcenhancing plasminogen activation at the cell surface could constitute a regulatory mechanism of pericellular proteolysis.