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The interrelationship between selective tau phosphorylation and microtubule association
H Xie1, J M Litersky, J A Hartigan
1Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1720 Seventh Avenue S., SC1061, Birmingham, AL 35294-0017, USA.
Brain Research
|July 17, 1998
Summary
Glycogen synthase kinase and protein kinase A regulate tau phosphorylation at specific sites, influencing tau-microtubule interactions. Phosphorylation at Ser262/356 by protein kinase A disrupts tau binding to microtubules.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Tau protein phosphorylation is crucial for microtubule stability.
- Dysregulation of tau phosphorylation is implicated in neurodegenerative diseases.
- Specific kinases, such as glycogen synthase kinase (GSK) and protein kinase A (PKA), play roles in tau phosphorylation.
Purpose of the Study:
- To investigate how PKA and GSK modulate tau phosphorylation.
- To determine the effects of altered tau phosphorylation on tau-microtubule association.
- To examine these processes in differentiated human SH-SY5Y neuroblastoma cells.
Main Methods:
- Utilized differentiated human SH-SY5Y neuroblastoma cells.
- Employed forskolin and rolipram to activate PKA.
- Used okadaic acid (inhibitor of protein phosphatase 2A/1) and cyclosporin A (inhibitor of protein phosphatase 2B).
- Inhibited GSK with lithium.
- Perturbed microtubules using nocodazole or taxol.
- Assessed tau phosphorylation at specific sites (Ser262/356, Thr181, Ser396/404, Tau-1 epitope).
- Performed Triton X-100 extraction assays to analyze tau-microtubule association and microtubule stability (acetylated alpha-tubulin levels).
Main Results:
- PKA activation increased tau phosphorylation at Ser262/356 only with okadaic acid, suggesting rapid turnover.
- GSK inhibition by lithium reduced tau phosphorylation at Thr181 and Ser396/404.
- Lithium treatment decreased tau and tyrosinated alpha-tubulin levels.
- Microtubule disruption (nocodazole/taxol) induced tau dephosphorylation at Tau-1 sites (Thr181, Ser396/404), blocked by okadaic acid but not cyclosporin A.
- Osmotic stress (NaCl) increased tau phosphorylation at the Tau-1 epitope.
- PKA activation (with okadaic acid) increased soluble tau and decreased microtubule stability.
- Phosphorylation at Ser262/356 correlated with reduced tau-microtubule association.
Conclusions:
- Tau phosphorylation is regulated by GSK, microtubule dynamics, and osmotic stress at overlapping sites, with minimal impact on tau-microtubule association.
- Phosphorylation at Ser262/356, partly mediated by PKA, prevents tau association with microtubules in situ.
- These findings highlight distinct regulatory mechanisms for tau phosphorylation and its impact on microtubule binding.