Sialylation of glycosylphosphatidylinositol (GPI) Anchors of mammalian prions is regulated in a Host-, Tissue-, and Cell-specific manner

Abstract

Prions or PrPSc are proteinaceous infectious agents that consist of misfolded, self-replicating states of the prion protein or PrPC . PrPC is posttranslationally modified with N-linked glycans and a sialylated glycosylphosphatidylinositol (GPI) anchor. Conformational conversion of PrPC gives rise to glycosylated and GPI-anchored PrPSc . The question of the sialylation status of GPIs within PrPSc has been controversial. Previous studies that examined scrapie brains reported that both sialo- and asialo-GPIs were present in PrPSc , with the majority being asialo-GPIs. In contrast, recent work that employed cultured cells claimed that only PrPC with sialylo-GPIs could be recruited into PrPSc , whereas PrPC with asialo-GPIs inhibited conversion. To resolve this controversy, we analyzed the sialylation status of GPIs within PrPSc generated in the brain, spleen, or cultured N2a or C2C12 myotube cells. We found that recruiting PrPC with both sialo- and asialo-GPIs is a common feature of PrPSc . The mixtures of sialo- and asialo-GPIs were observed in PrPSc universally regardless of prion strain as well as host, tissue, or type of cells that produced PrPSc . Remarkably, the proportion of sialo- versus asialo-GPIs was found to be controlled by host, tissue, and cell type but not prion strain. In summary, this study found no strain-specific preferences for selecting PrPC with sialo- versus asialo-GPIs. Instead, this work suggests that the sialylation status of GPIs within PrPSc is regulated in a cell-, tissue-, or host-specific manner and is likely to be determined by the specifics of GPI biosynthesis.