| Co-Investigator(Kenkyū-buntansha) |
NAKATA Motomi Sumitomo Electric industry, Biomedical division, Chief Researcher, バイオメディカル研究部, 主査(研究職)
ASAHARA Toshimasa Faculty of Medicine, HIROSHIMA UNIVERSITY, Professor, 医学部, 教授 (70175850)
KIKUCHI Akira Faculty of Medicine, HIROSHIMA UNIVERSITY, Professor, 医学部, 教授 (10204827)
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| Research Abstract |
In colorectal cancers, most patients carry APC (Adenomatous Polyposis Coli) mutations and colorectal carcinoma cells with mutant APC contains a large amount of β-catenin. The mechanism by which the stability of β-catenin is regulated by APC was not clear. When Wnt acts on Frizzled, Dvl is activated and antagonizes the action of GSK-3β, and β-catenin is stabilized. In this study we identified Axin and Axil (Axin like) as GSK-3β-binding proteins. They enhanced GSK-3β-dependent phosphorylation of β-catenin, resulting in the ubiquitination and degradation of the β-catenin. Axin prevented the Wnt-induced TCF activation. Axin may be a scaffold protein that selectively transmits the signal from Wnt to β-catenin, in that it binds to several Wnt signaling molecules including GSK-3β, APC, β-catenin, Dvl, protein phosphatase 2A.We showed that phosphorylation of β-catenin and APC by GSK-3β is enhanced in the Axin complex and that APC promotes the GSK-3β-dependent phosphorylation of β-catenin by interacting with Axin. Recently some mutations of Axin or Axil in cancer cells were reported. Taken together, Axin and Axil can be candidates for clinical gene diagnosis of cancer.
Furthermore, we identified three novel Wnt-signaling molecules that bind to β-catenin, Axin, Dvl, respectively and analyzed the their functions in the Wnt signaling pathway. Duplin, a novel nuclear protein, interacted with β-catenin, inhibited the complex formation of β-catenin and TCF and suppressed Wnt-induced TCF activation. Axam, a novel Axin-binding protein, inhibited the complex formation of Axin and Dvl, and induced the degradation of β-catenin in the SW480 cells. Idax, a novel Dvl-binding protein, inhibited the complex formation of Dvl and Axin and suppressed Wnt-induced accumulation of β-catenin and TCF activation. It is suggested that these three molecules which we identified in this study may function as tumor suppressor gene products in that they suppressed Wnt signaling.
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