Prion proteins (PrPs) are cellular polypeptides of unknown function, modified forms of which have been implicated in the pathogenesis of several degenerative diseases of the central nervous system, including Creutzfeldt-Jakob disease and Gerstmann-Straussler syndrome in man, and scrapie in animals. We have recently identified a cDNA that encodes a chicken prion-like protein (ch-PLP), the first non-mammalian example to be described. The objective of the present application is to carry out further studies of ch-PLP using molecular and cell biological techniques. These studies are likely to provide important information about the structure, function and metabolism of PrPs that is relevant to understanding their role in neurological disease. Only a single PrP gene and protein have been described in each of several mammalian species examined, and this fact has played an prominent role in hypotheses about the pathogenesis of prion diseases. Several considerations suggest that ch-PLP may not be the only prion-related protein encoded in the chicken genome. We propose here to characterize the gene that encodes chPLP; and to search for cDNAs that encode other prion-like proteins in chicken, as well as mouse and man, by low-stringency screening of libraries, and by use of the polymerase chain reaction. Preliminary studies indicate that ch-PLP undergoes several kinds of posttranslational processing, including a novel proteolytic cleavage near its N-terminus that has not been previously observed for mammalian PrP. We propose to further characterize the posttranslational processing of ch-PLP using antibody mapping and pulse-chase labeling. We will also define critical processing sites in the molecule by expression in transfected cells of deleted and chimeric proteins, as well as proteins harboring mutations that have been linked to prion diseases in man. Ch-PLP was originally identified as the major sequenceable protein in purified preparations of an acetylcholine receptor-inducing activity (ARIA) from chick brain that is postulated to play a role in neuromuscular synaptogenesis. Indirect evidence suggests that ch-PLP and ARIA are identical or closely related molecules. We propose to determine which posttranslationally processed forms of ch-PLP are present in preparations of ARIA, and to raise antisera against these molecules that can be used to immunoprecipitate AChR-inducing activity. We will also create N- and C-terminally deleted forms of ch-PLP that mimic the molecules present in ARIA preparations, and assay the receptor-inducing activity of these recombinant proteins.
