Glycogen synthase kinase 3 (GSK-3) is a constitutively active, proline-directed serine (Ser)/threonine (Thr) protein kinase encoded by two isoforms and GSK-3b (approx. 47 kDa)], which possess similar biochemical characteristics and substrate specificities.1-3) GSK-3 has been originally identified as a protein kinase that phosphorylates the rate-limiting enzyme, glycogen synthase (GS), in glycogen synthesis. 4,5) Further detail characterization revealed that (i) GSK-3b has a wide array of substrates, including cytoplasmic enzymes, nuclear transcriptional factors and signal-mediating molecules; and (ii) this kinase plays an important physiological role in the regulation of numerous signalling pathways involved in cell differentiation and morphological development of neurons. 5,6) In the present study, we used two basic brain proteins [bovine myelin basic protein (bMBP, pIϭ11.3) and human tau protein (hTP, pIϭ8.2)] and two acidic proteins [human vimentin (hVM, pIϭ5.1) and rat collapsing response mediator protein-2 (rCRMP-2, pIϭ6.0)] as effective substrates for GSK-3b in vitro, because (i) these proteins, containing multiple potent phosphorylation sites for GSK-3b, function as effective phosphate acceptors for the kinase in vitro; (ii) GSK3b is identified as a key protein kinase responsible for their functional regulation in brain [7][8][9][10] ; and (iii) phosphatidylinositol (PI) and two sulfated lipids [sulfatide and heparin (SH)] function as effective stimulators for autophosphorylation of GSK-3b and the GSK-3b-mediated high phosphorylation of SH-binding proteins, such as MBP and TP, in the highly accumulated levels of these acidic and sulfated modulators in the brain.
11)A number of epidemiological studies have shown that the consumption of green tea may account for the anti-oxdant, anti-inflammatory, anti-carcinogenic, and neuropotective effects.12) The chemical structures of four major catechins [(Ϫ)-epigallocatechin gallate (EGCG), (Ϫ)-epigallocatechin, (Ϫ)-epicatechin gallate and (Ϫ)-epicatechin] in green tea have been determined and EGCG is a major polyphenol in green tea and accounts for 50-80% of the total catechins in the tea.12,13) Several EGCG-binding proteins, such as plasma proteins (fibronectin, fibrinogen and histidine-rich glycoprotein), 14) fatty acid synthase (Fas), 15) 67 kDa laminin receptor (67-LR), 16) platelet derived growth factor (PDGF), 17) and vimentin (type III intermediate filament protein) 18) have been identified. The N-terminal head (50-63: SLYSSSPG-GAYVTR) of VM is identified as a target for EGCG, which inhibits dose-dependently the A-kinase-mediated phosphorylation of the head fragment, containing two phosphorylation sites at Ser-50 for A-kinase and Ser-55 for Cdc2-kinase, in vitro.18) Furthermore, early studies concerning the biological effects of EGCG in vivo revealed that (i) green tea polyphenols exhibit potentially anti-amyloidgenic effect and induce to protect neuron-like cells against amyloid b-mediated toxicity 19) ; (ii) EGCG can induce apoptosis preferentially in can...