Biochemical Characterization of Novel Lignans Isolated from the Wood of Taxus yunnanensis as Effective Stimulators for Glycogen Synthase Kinase-3β and the Phosphorylation of Basic Brain Proteins by the Kinase in Vitro

Abstract

The stimulatory and inhibitory effects of several compounds and lignans isolated from the water extract of Taxus yunnanensis on the phosphorylation of three functional brain proteins (bovine myelin basic protein (bMBP), recombinant human tau protein (rhTP) and rat collapsin response mediator protein-2 (rCRMP-2)) by glycogen synthase kinase-3β (GSK-3β) were quantitatively compared in vitro, using (−)-epigallocatechin-3-gallate [(−)EGCG] as a positive control. We found that (i) three selected Taxus lignans [(3S,4R)-4′-hydroxy-6,3′-dimethoxyisoflavan-4-ol,(7R)-7-hydroxytaxiresinol and tanegool] highly stimulated the autophosphorylation of GSK-3β and the GSK-3β-mediated phosphorylation of two basic brain proteins [bMBP (pI=11.3) and rhTP (pI=8.2)], but inhibited dose-dependently the phosphorylation of an acidic protein (rCRMP-2, pI=6.0) by the kinase; (ii) these three Taxus lignans showed binding-affinities with bMBP as well as rhTP, but had low affinities with rCRMP-2; (iii) the binding of tanegool and (7R)-7-hydroxytaxiresinol to these two basic proteins induced their novel potent phosphorylation sites for GSK-3β; and (iv) these three Taxus lignans, but not EGCG, induced Tyr-phosphorylation of GSK-3β in vitro. These results provided here suggest that (i) these three Taxus lignans act as novel effective activators for GSK-3β and the GSK-3β-mediated phosphorylation of their binding basic proteins (rhTP and bMBP); and (ii) tanegool (IC₅₀=1 μM) is an effective inhibitor for the phosphorylation of rCRMP-2 by the kinase in vitro.