Interaction of prion protein mRNA with CBP35 and other cellular proteins Possible implications for prion replication and age-dependent changes

A study of the intracellular distribution of prion protein (PrP) in N2a neuroblastoma cells which had been infected with prions (ScN2a cells) revealed that most PrP is present in the cytoplasm. However, a significant amount of PrP is also present in the nucleus (predominantly in the nucleoli) of these cells, as analyzed by confocal laser scanning microscopy. By contrast, no PrP could be detected in the nucleus of uninfected N2a cells. The steady-state level of PrP mRNA did not markedly differ between the two cell strains. Likewise, no changes were found in the rate of transcription and in the half-life of PrP mRNA. A number of cellular proteins, among them the nuclear lectin CBP35, was identified that bound to the predicted RNA stem-loop structure of PrP RNA. CBP35 could also be detected in purified infections prions, suggesting a possible role in prion replication. Age-dependent studies revealed that the content of normal cellular PrP (PrPC) in brain extracts of rats did not change significantly during ageing, while the level of certain proteins that associate with PrPC mRNA decreases with age. In addition, we show that rat cortical cells when challenged with infectious PrP (PrPSc) undergo cell death (apoptosis) in vitro. This deleterious effect was prevented by memantine (1-amino-3,5-dimethyladamantane) and other blockers of N-methyl-d-aspartate (NMDA) receptor channels.