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Neuropathological hallmarks of Alzheimer’s disease are extracellular senile plaques and intracellular neurofibrillary lesions. The neurofibrillary lesions mainly consist of the hyperphosphorylated microtubule-associated protein Tau predominantly expressed in the axon of CNS neurons. Hyperphosphorylation of Tau negatively affects its binding to tubulin and decreases the capacity to promote microtubule assembly. Among a number of proline-directed kinases capable of phosphorylating paired helical filament-Tau, glycogen synthase kinase 3β (GSK3β) was first identified as a Tau protein kinase I and has been demonstrated to phosphorylate Tau both in vivo and in vitro. However, the phosphorylation mechanism of Tau by GSK3β remained unclear. In this study, we show that the T231 is the primary phosphorylation site for GSK3β and the Tau227–237 (AVVRTPPKSPS) derived from Tau containing T231P232 motif is identified as the GSK3β binding site with high affinity of a Kd value 0.82 ± 0.16 μmol/L. Our results suggest that direct binding and phosphorylation of T231P232 motif by GSK3β induces conformational change of Tau and consequentially alters the inhibitory activity of its N-terminus that allows the phosphorylation of C-terminus of Tau by GSK3β. Furthermore, hyperphosphorylation reduces Tau’s ability to promote tubulin assembly and to form bundles in N18 cells. T231A mutant completely abolishes Tau phosphorylation by GSK3β and retains the ability to promote tubulin polymerization and bundle formation. Taken together, these results suggest that phosphorylation of T231 by GSK3β may play an important role in Tau’s hyperphosphorylation and functional regulation. [ABSTRACT FROM AUTHOR]

1. The effect of maprotiline, an antidepressant, on human prostate cells is unclear. In the present study, the effect of maprotiline on [Ca2+]i and growth in PC3 human prostate cancer cells was measured using the fluorescent dyes fura-2 and tetrazolium, respectively. 2. Maprotiline caused a rapid, concentration-dependent increase in [Ca2+]i (EC50 = 200 µmol/L). The maprotiline-induced [Ca2+]i increase was reduced by removal of extracellular Ca2+ or pretreatment with nicardipine. 3. The maprotiline–induced Mn2+ influx-associated fura-2 fluorescence quench directly suggests that maprotiline caused Ca2+ influx. 4. In Ca2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, caused a monophasic [Ca2+]i increase, after which the effects of maprotiline of increasing [Ca2+]i were abolished. In addition, pretreatment with maprotiline reduced a major portion of the thapsigargin-induced increase in [Ca2+]i. 5. U73122, an inhibitor of phospholipase C, abolished the ATP (but not maprotiline)-induced increase in [Ca2+]i. 6. Overnight incubation with 1–10 µmol/L maprotiline did not alter cell proliferation, although incubation with 30–50 µmol/L maprotiline decreased cell proliferation. 7, These findings suggest that maprotiline rapidly increases [Ca2+]i in human prostate cancer cells by stimulating both extracellular Ca2+ influx and intracellular Ca2+ release and that it may modulate cell proliferation in a concentration-dependent manner. [ABSTRACT FROM AUTHOR]