Tau 6D and 6P isoforms inhibit polymerization of full-length tau in vitro.

Alzheimer's disease and other tauopathies are characterized by the intracellular accumulation of insoluble filaments of the microtubule-associated protein tau. The six canonical tau isoforms in the adult brain consist of an N-terminal "projection" domain followed by a proline-rich region, a microtubule-binding repeat region, and a C-terminal tail. However, alternative splicing in exon 6 produces an additional set of tau isoforms, termed 6D and 6P, which contain only the N-terminus and part of the proline-rich region. We have previously shown that constructs representing N-terminal fragments of tau, which resemble the naturally occurring 6P and 6D isoforms, inhibit polymerization of the full-length protein in an in vitro filament formation assay and traced the inhibitory activity to amino acids 18-42. Here we report that 6P and 6D tau isoforms inhibit polymerization of full-length tau (hTau40) in a similar manner, likely by stabilizing full-length tau in a soluble conformation. The absence of exons 2 and 3 decreased the effectiveness of the 6D isoforms but not the 6P variants or the N-terminal tau fragments from our previous study, indicating that the 18-42 region is not the sole determinant of inhibitory ability. Finally, this paper demonstrates that inhibition is blocked by pseudophosphorylation of tyrosines 18 and 29, providing a potential link between tyrosine phosphorylation and disease progression. Taken together, these results indicate that the 6P/6D isoforms are potential endogenous inhibitors of tau filament formation and suggest a mechanism by which this ability may be disrupted in disease.

Citation

Nichole E Lapointe, Peleg M Horowitz, Angela L Guillozet-Bongaarts, Andres Silva, Athena Andreadis, Lester I Binder. Tau 6D and 6P isoforms inhibit polymerization of full-length tau in vitro. Biochemistry. 2009 Dec 29;48(51):12290-7

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PMID: 19919107

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