title: Loss of Cellular Sialidases Does Not Affect the Sialylation Status of the Prion Protein but Increases the Amounts of Its Proteolytic Fragment C1.
abstract: The central molecular event underlying prion diseases involves conformational change of the cellular form of the prion protein (PrPC), which is a sialoglycoprotein, into the disease-associated, transmissible form denoted PrPSc. Recent studies revealed a correlation between the sialylation status of PrPSc and incubation time to disease and introduced a new hypothesis that progression of prion diseases could be controlled or reversed by altering the sialylation level of PrPC. Of the four known mammalian sialidases, the enzymes that cleave off sialic acid residues, only NEU1, NEU3 and NEU4 are expressed in the brain. To test whether cellular sialidases control the steady-state sialylation level of PrPC and to identify the putative sialidase responsible for desialylating PrPC, we analyzed brain-derived PrPC from knockout mice deficient in Neu1, Neu3, Neu4, or from Neu3/Neu4 double knockouts. Surprisingly, no differences in the sialylation of PrPC or its proteolytic product C1 were noticed in any of the knockout mice tested as compared to the age-matched controls. However, significantly higher amounts of the C1 fragment relative to full-length PrPC were detected in the brains of Neu1 knockout mice as compared to WT mice or to the other knockout mice. Additional experiments revealed that in neuroblastoma cell line the sialylation pattern of C1 could be changed by an inhibitor of sialylatransferases. In summary, this study suggests that targeting cellular sialidases is apparently not the correct strategy for altering the sialylation levels of PrPC, whereas modulating the activity of sialylatransferases might offer a more promising approach. Our findings also suggest that catabolism of PrPC involves its α-cleavage followed by desialylation of the resulting C1 fragments by NEU1 and consequent fast degradation of the desialylated products.
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.|Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Elizaveta
authors.initials: E
authors.lastname: Katorcha
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.|Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Nina
authors.initials: N
authors.lastname: Klimova
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.|Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Natallia
authors.initials: N
authors.lastname: Makarava
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.|Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Regina
authors.initials: R
authors.lastname: Savtchenko
authors.affiliation: Division of Medical Genetics, Sainte-Justine University Hospital Research Center, University of Montreal, Montreal, QC, Canada.
authors.forename: Xuefang
authors.initials: X
authors.lastname: Pan
authors.affiliation: Department of Genetics, St Jude Children's Research Hospital, Memphis, Tennessee, United States of America.
authors.forename: Ida
authors.initials: I
authors.lastname: Annunziata
authors.affiliation: Institute of Molecular Biomembrane and Glycobiology, Tohoku Pharmaceutical University, Sendai, Miyagi, Japan.
authors.forename: Kohta
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Institute of Molecular Biomembrane and Glycobiology, Tohoku Pharmaceutical University, Sendai, Miyagi, Japan.
authors.forename: Taeko
authors.initials: T
authors.lastname: Miyagi
authors.affiliation: Division of Medical Genetics, Sainte-Justine University Hospital Research Center, University of Montreal, Montreal, QC, Canada.
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Pshezhetsky
authors.affiliation: Department of Genetics, St Jude Children's Research Hospital, Memphis, Tennessee, United States of America.
authors.forename: Alessandra
authors.initials: A
authors.lastname: d'Azzo
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.|Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland, United States of America.
authors.forename: Ilia V
authors.initials: IV
authors.lastname: Baskakov
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D009439:Neuraminidase / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011328:Prions / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D010446:Peptide Fragments; D011328:Prions; D020033:Protein Isoforms; D012333:RNA, Messenger; C110128:Neu1 protein, mouse; C511796:Neu3 protein, mouse; C481539:Neu4 protein, mouse; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid