Apolipoprotein E (ApoE) peptide regulates tau phosphorylation via two different signaling pathways.
Previous studies have shown that treating rat cortical neurons in primary culture with apolipoprotein E (apoE) peptide increased cytoplasmic Ca2+ by 2 mechanisms: 1) an influx of extracellular Ca2+ resulting from the activation of a cell surface Ca2+ channel; and 2) release of Ca2+ from internal Ca2+ stores via a G-protein-coupled pathway (Wang and Gruenstein, 1997). These studies employed a biologically active apoE synthetic peptide (apoEdp) derived from the receptor binding domain of apoE. In the present study we examined whether activation of these 2 signal transduction pathways affects phosphorylation of microtubule-associated protein tau. The levels of tau phosphorylation at thr231, ser235, and ser396 were quantified by ELISA employing monoclonal antibodies PHF-6, SMI33, and PHF-1. ApoEdp treatment resulted in a concentration- and time-dependent dephosphorylation of tau at all 3 phosphorylation sites. The apoEdp-induced dephosphorylation of tau at thr231, and ser235 was dependent on the influx of extracellular Ca2+, while dephosphorylation at ser396 was mediated by a pertusis toxin-sensitive G-protein pathway. The involvement of protein phosphatases in mediating the apoEdp-induced dephosphorylation of tau was examined. Pretreatment with the protein phosphatase 2B inhibitor cyclosporin A blocked the apoEdp-induced dephosphorylation of tau at thr231 and ser235 but not at ser396. Pretreatment with the protein phosophatase 2A/1 inhibitor okadaic acid blocked the apoEdp-induced dephosphorylation of tau at all 3 sites, while pretreatment with the protein phosphates 1 inhibitor tautomycin was without effect. The present study suggests that apoE may affect several Ca2+-associated signal transduction pathways that increase the activity of protein phosphatases 2A and 2B, which in turn dephosphorylate tau.
Wang
X
X
Neuroscience Graduate Program, University of Cincinnati College of Medicine, Ohio 45267-0559, USA.
Luebbe
P
P
Gruenstein
E
E
Zemlan
F
F
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000935:Antifungal Agents / Q000494:pharmacology; D001057:Apolipoproteins E / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008969:Molecular Sequence Data; D009474:Neurons / Q000737:chemistry / Q000201:enzymology*; D019319:Okadaic Acid / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011714:Pyrans; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013141:Spiro Compounds; D013997:Time Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D016875:tau Proteins / Q000276:immunology / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D000935:Antifungal Agents; D001057:Apolipoproteins E; D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D010446:Peptide Fragments; D011714:Pyrans; D013141:Spiro Compounds; D010566:Virulence Factors, Bordetella; D016875:tau Proteins; C053079:tautomycin; D019319:Okadaic Acid; D016572:Cyclosporine; D010744:Phosphoric Monoester Hydrolases; D002118:Calcium