Page 18 - T. Protein modification and regulation
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[T. Protein modification and regulation-9]
Phosphorylated tau induces hyperubiquitylation, which
promotes the formation of insoluble tau aggregates
Seoyoung Park¹, Seohyeung Park¹, Min Jae Lee¹
¹Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine, Seoul 03080,
Republic of Korea
The tau protein is an intrinsically disordered and highly soluble protein. Under physiological condition, tau binds to
microtubules in axons and contributes to stability. However, under pathological conditions, tau undergoes multiple
post-translational modifications and conformational changes to form insoluble filaments, which are the
proteinaceous signatures of tauopathies. To dissect the crosstalk between post-translational modifications during
tau aggregation, we phosphorylated and ubiquitylated recombinant tau in vitro using GSK3β and CHIP, respectively.
The phosphorylated tau was polyubiquitylated through lysine 48 linkages, sufficient for proteasomal degradation,
whereas unphosphorylated ub-tau species retained only two–three ubiquitin moieties. Mass-spectrometric analysis
of in vitro reconstituted phospho-ub-tau revealed seven additional ubiquitylation sites. When the ubiquitylation
reaction was prolonged, phospho-ub-tau transformed into a less soluble hyperubiquitylated tau species. We
developed small-molecule inhibitors of CHIP through biophysical screening; these effectively suppressed tau
ubiquitylation in vitro and delayed its aggregation in cultured cells. These data indicate that tau hyperubiquitylation
is a key driver in the pro-fibrillation process of tau.
