[Molecular and pharmacological studies on signal transduction in the brain]

Many of the extracellular signals such as neurotransmitters and hormones regulate the intracellular concentration of second messengers such as cAMP, cGMP, and calcium ion (Ca2+), diacylglycerol and IP3. Accumulating evidence indicates that protein phosphorylation-dephosphorylation is an important mechanism by which second messengers act to regulate a variety of cellular processes. Ca2+/calmodulin-dependent protein kinase II, cAMP-dependent protein kinase and protein kinase C are three major classes of protein kinases in the central nervous system. In an attempt to elucidate the physiological roles of the protein kinases, I have been studying the substrate proteins and functional significance of the enzymes and phosphorylated proteins. For these purposes, I investigated the phosphorylation-dephosphorylation of cytoskeletal proteins such as microtubule-associated protein 2 and tau, which are involved in the assembly-disassembly of microtubules and the production of abnormally phosphorylated forms of tau in neurofibrillary tangles in Alzheimer's disease brain. As the natural consequence, studying the protein phosphatases is significant for elucidating the switch-off mechanism of protein phosphorylation. Thus, I have been investigating the functional significance of protein phosphorylation-dephosphorylation for the elucidation of signal transduction in the brain, which is widely involved in the regulation of brain functions.