| Co-Investigator(Kenkyū-buntansha) |
AKIMOTO Kazunori Yohohama City University School of Medicine, Department of Molecular Biology, Assistant Professor, 医学部, 助手 (70285104)
SUZUKI Atsushi Yohohama City University School of Medicine, Department of Molecular Biology, Lecturer, 医学部, 講師 (00264606)
HIRAI Syu-ichi Yohohama City University School of Medicine, Department of Molecular Biology, Associate Professor, 医学部, 助教授 (80228759)
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| Research Abstract |
We as well as other people working on C.elegans and Drosophia revealed that aPKC, PAR-3 and PAR-6 are polarity proteins that co-operate in the establishment of cell polarity in C.elegans and Drosophila embryos. These three proteins co-localize asymjmetrically in C.elegans one-cell ambryo and in Drosophial epithelial cells and neuroblasts. Here we have shown that, in mammalian elitheial cells, these three proteins co-localize to the apical end of the junctional complex, tight junctions. Furthermore, we have shown that aPKC is required for the formation of the epithelia-specific cell-cell junctional structure, and thus plays an indispensable role in the establishment of mammalian epithelial cell polarity. The formation of a ternary complex with aPKC, as well as co-localization at the most apical end of the junctional complex, also suggest the involvement of a mammalian homologue of PAR-6 and PAR-3, ASIP, in this aPKC function in epithelial cell polarization. We also show that the pre-existing ternary complex translocates to the cell-cell contact region in response to cell adhesion. Furthermore, overexpression of PAR-6 mutant lacking the aPKC-binding region in MDCK cells disturbs the cell-cell contact-induced junctional localization of tight junction proteins, as well as inhibiting TER development. These results not only indicate the involvement of the ternary complex in aPKC function. Consistent with this, the binding of Cdc42 : GTP to the CRIB/PDZ domain of PAR-6 enhances the kinase activity of PAR-6-bound aPKC.Detailed analyses suggest that the binding of PAR-6 to the N-terminal region of aPKC has the intrinsic potential to activate aPKC, which is released only when Cdc42 : GTP binds to the CRIB/PDZ domain. Taken together, the results suggest not only a novel mode of aPKC activation, but also the possible involvement of this regulation in the early phase of epithelial cell polarization.
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