title: Proteasomal degradation of tau protein.
abstract: Filamentous inclusions composed of the microtubule-associated protein tau are a defining characteristic of a large number of neurodegenerative diseases. Here we show that tau degradation in stably transfected and non-transfected SH-SY5Y cells is blocked by the irreversible proteasome inhibitor lactacystin. Further, we find that in vitro, natively unfolded tau can be directly processed by the 20S proteasome without a requirement for ubiquitylation, and that a highly reproducible pattern of degradation intermediates is readily detectable during this process. Analysis of these intermediates shows that 20S proteasomal processing of tau is bi-directional, proceeding from both N- and C-termini, and that populations of relatively stable intermediates arise probably because of less efficient digestion of the C-terminal repeat region. Our results are consistent with an in vivo role for the proteasome in tau degradation and support the existence of ubiquitin-independent pathways for the proteasomal degradation of unfolded proteins.
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015153:Blotting, Western; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006801:Humans; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D009447:Neuroblastoma / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism; D016875:tau Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D009097:Multienzyme Complexes; D020033:Protein Isoforms; D025801:Ubiquitin; D016875:tau Proteins; C067713:lactacystin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine