Direct Evidence of Generation and Accumulation of β-Sheet-rich Prion Protein in Scrapie-infected Neuroblastoma Cells with Human IgG1 Antibody Specific for β-Form Prion Protein

We prepared beta-sheet-rich recombinant full-length prion protein (beta-form PrP) (Jackson, G. S., Hosszu, L. L., Power, A., Hill, A. F., Kenney, J., Saibil, H., Craven, C. J., Waltho, J. P., Clarke, A. R., and Collinge, J. (1999) Science 283, 1935-1937). Using this beta-form PrP and a human single chain Fv-displaying phage library, we have established a human IgG1 antibody specific to beta-form but not alpha-form PrP, PRB7 IgG. When prion-infected ScN2a cells were cultured with PRB7 IgG, they generated and accumulated PRB7-binding granules in the cytoplasm with time, consequently becoming apoptotic cells bearing very large PRB7-bound aggregates. The SAF32 antibody recognizing the N-terminal octarepeat region of full-length PrP stained distinct granules in these cells as determined by confocal laser microscopy observation. When the accumulation of proteinase K-resistant PrP was examined in prion-infected ScN2a cells cultured in the presence of PRB7 IgG or SAF32, it was strongly inhibited by SAF32 but not at all by PRB7 IgG. Thus, we demonstrated direct evidence of the generation and accumulation of beta-sheet-rich PrP in ScN2a cells de novo. These results suggest first that PRB7-bound PrP is not responsible for the accumulation of beta-form PrP aggregates, which are rather an end product resulting in the triggering of apoptotic cell death, and second that SAF32-bound PrP lacking the PRB7-recognizing beta-form may represent so-called PrPSc with prion propagation activity. PRB7 is the first human antibody specific to beta-form PrP and has become a powerful tool for the characterization of the biochemical nature of prion and its pathology.