Modulation of tau phosphorylation within its microtubule-binding domain bycellular thiols

Tau is a microtubule-stabilizing protein that is functionally modulated by alterations in its phosphorylation state. Because phosphorylation regulates both normal and pathological tau functioning, it is of importance to ident ify the signaling pathways that regulate tau phosphorylation in vivo. The p resent study examined changes in tau phosphorylation and function in respon se to modulation of cellular thiol content. Treatment of cells with phenyla rsine oxide, which reacts with vicinal thiols, selectively increased tau ph osphorylation within its microtubule-binding domain, at the non-Ser/Thr-Pro sites Ser(262/356), while decreasing tau phosphorylation at Ser/ Thr-Pro s ites outside this region. This increase in tau phosphorylation correlated w ith a decrease in the amount of tau associated with the cytoskeleton and de creased microtubule stability. Phenylarsine oxide-induced tau phosphorylati on was inhibited by oxidants and by the protein kinase inhibitor staurospor ine. Although staurosporine completely eliminated the increase in tau phosp horylation at Ser262/356, as detected by immunostaining with 12E8, it had a comparatively minor effect on the changes in tau localization induced by p henylarsine oxide. The results suggest that regulation of cellular thiols i s important for modulating tau phosphorylation and function in situ. Additi onally, although phosphorylation of Ser262/356 decreases tau's interaction with the cytoskeleton, phosphorylation of these residues alone is not suffi cient for the phenylarsine oxide-induced changes in tau localization.