| Co-Investigator(Kenkyū-buntansha) |
ENDO Sachiko Dept. Biophys. Biochem., Fac. Sci. Univ. Tokyo Instructor, 理学部, 教務職員
MAEKAWA Shohei Dept. Biophys. Biochem., Fac. Sci. Univ. Tokyo Assistant Professor, 理学部, 助手 (40173695)
NISHIDA Eisuke Dept. Biophys. Biochem., Fac. Sci. Univ. Tokyo Assistant Professor, 理学部, 助手 (60143369)
MUROFUSHI Hiromu Dept. Biophys. Biochem., Fac. Sci. Univ. Tokyo Associate Professor, 理学部, 助教授 (70101128)
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| Research Abstract |
[Mechanism of signal transduction for call proliferatrion] : We demonstrated phosphorylation of high molecular weight microtubule-associated proteins (MAPS) as well as activation of a MAP-2 kinase after stimulation of cultured mammalian cells by growth factor or phorbol ester (promoter of carcinogenesis) and further identified a protein kinase which does not phosphorylate histone or casein but only MAP-2 and myelin basic-protein, proved to be a protein kinase newly identified. We further demonstrated that disassembly of microtubules produced by microtubule-disrupting drugs directly signals cell proliferation without stimulation by growth factor or pharbol ester. These results strongly suggest that MAP-2 kinase is involved in the cascade of phosphorylation in signal transduction for cell proliferation and demonstrate that microtubule cytoskeleton is directly relevant to the signal transduction, raising a now concept in the mechanism.
[Mechanism of the formation of the mitotic apparatus]
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: We identified the major protein component of the centrasons, 51-kD protein, and demonstrated its aster forming ability in the presence of some minor components of the contrasome and tubulin. The protein, which has an isoelectric point of 9.8 as basic protein, has an ability to bind guanine nucleotide, GTP and GDP, and proved to be a G protein. Furthermore, we demonstrated interconversion between GTP and GDP bound to the 51-kD protein, and the GTP-form protein is competent to be a signal protein for microtubule assembly. This provided a new standpoint in the mechanism of the formation of the mitotic apparatus, that is, the GTP<double arrow>GDP interconversion in the 51-kD protein sites governs the ability of the contrasome to initiate microtubules to build up the aster and the spindle. In fact, we demonstrated that isolated centrosomal fragments saturated with GTP (with the 51-kD protein saturated with GTP) can initiate astral microtubules much more efficiently than those saturated with GDP.
[Mechanism of transduction of cleavage signal] : We purified kinesin, which is most likely concerned with the trainduction of cleavage signal as a translocation motor, and characterized its enzymatic properties. We further isolated and purified a 260-kD protein which localizes underneath the cell membrane Just co-localized with actin bundles in the contractile ring. The 260-kD protein was shown to form curled thick actin bundles in vitro. Furthermore, an important finding is that a transmembrane glycoprotein labeled with WGA assembles as a precursor structure along the predicted contractile ring through the action of the cleavage signal which was shown to be dependent on microtubules, possibly astral microtubules. Less
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