Aggregation properties of the small nuclear ribonucleoprotein U1-70K in Alzheimer disease.

Abstract

Recent evidence indicates that U1-70K and other U1 small nuclear ribonucleoproteins are Sarkosyl-insoluble and associate with Tau neurofibrillary tangles selectively in Alzheimer disease (AD). Currently, the mechanisms underlying the conversion of soluble nuclear U1 small nuclear ribonucleoproteins into insoluble cytoplasmic aggregates remain elusive. Based on the biochemical and subcellular distribution properties of U1-70K in AD, we hypothesized that aggregated U1-70K itself or other biopolymers (e.g. proteins or nucleic acids) interact with and sequester natively folded soluble U1-70K into insoluble aggregates. Here, we demonstrate that total homogenates from AD brain induce soluble U1-70K from control brain or recombinant U1-70K to become Sarkosyl-insoluble. This effect was not dependent on RNA and did not correlate with detergent-insoluble Tau levels as AD homogenates with reduced levels of these components were still capable of inducing U1-70K aggregation. In contrast, proteinase K-treated AD homogenates and Sarkosyl-soluble AD fractions were unable to induce U1-70K aggregation, indicating that aggregated proteins in AD brain are responsible for inducing soluble U1-70K aggregation. It was determined that the C terminus of U1-70K, which harbors two disordered low complexity (LC) domains, is necessary for U1-70K aggregation. Moreover, both LC1 and LC2 domains were sufficient for aggregation. Finally, protein cross-linking and mass spectrometry studies demonstrated that a U1-70K fragment harboring the LC1 domain directly interacts with aggregated U1-70K in AD brain. Our results support a hypothesis that aberrant forms of U1-70K in AD can directly sequester soluble forms of U1-70K into insoluble aggregates.

• Authors: Ian Diner, Chadwick M Hales, Isaac Bishof, Lake Rabenold, Duc M Duong, Hong Yi, Oskar Laur, Marla Gearing, Juan Troncoso, Madhav Thambisetty, James J Lah, Allan I Levey, Nicholas T Seyfried
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 289 Issue 51 Pg. 35296-313 (Dec 19 2014) ISSN: 1083-351X [Electronic] United States
• PMID: 25355317 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)
• Copyright: © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

Chemical References

• Peptide Fragments
• Recombinant Proteins
• Ribonucleoprotein, U1 Small Nuclear
• SNRNP70 protein, human
• sarkosyl
• Sarcosine

Topics

• Aged
• Aged, 80 and over
• Alzheimer Disease (metabolism)
• Autopsy
• Blotting, Western
• Brain (metabolism, pathology, ultrastructure)
• Female
• HEK293 Cells
• Humans
• Male
• Mass Spectrometry
• Microscopy, Immunoelectron
• Middle Aged
• Peptide Fragments (chemistry, genetics, metabolism)
• Protein Conformation
• Protein Structure, Tertiary
• Recombinant Proteins (chemistry, metabolism)
• Ribonucleoprotein, U1 Small Nuclear (chemistry, genetics, metabolism)
• Sarcosine (analogs & derivatives, chemistry)
• Solubility