Protein Engineering vol.2 no.l pp.69-76, 1988 Prion protein gene expression in cultured cells

A single copy gene encodes both the scrapie (PrP80) and cellular (PrP-) isoforms of the prion protein (PrP). Cultured cell lines were found to express the endogenous PrP mRNA at levels comparable to those observed in the brains of adult rodents; however, these cells were invariably found to express greatly reduced levels of PrP. In all the cell lines examined, PrP was undetectable by Western immunoblot analysis. These cells were also poor recipients for expression constructs link-ing the hamster PrP gene open reading frame to several strong eukaryotic promoters; stable clones derived by transfection of these expression vectors failed to show elevated expression of PrP. When extremely high levels of PrP mRNA were pro-duced using either an insect baculovirus or a mammalian SV40 based vector, significant quantities of PrP were pro-duced, although in both cases the proteins were apparently processed differently from the PrP0 observed in brains. In an expression system using an SV40 late promoter vector in monkey COS-7 cells, a significant fraction of PrP was trans-ported to the cell surface where PrPc is found in vivo. PrP synthesized by the baculovirus vector failed to induce scrapie in hamsters and did not possess the characteristics of the PrP * isoform associated with infectivity. The SV40 late pro-moter vector system may permit experiments designed to elucidate the role of PrP * during scrapie infection as well as the function of PrP0 in normal metabolism. Key words: prioo/scrapie/expression vectors/PrP gene/cultured cell