title: LST8 level controls basal p70 S6 kinase and Akt phosphorylations, and mTORC1 and mTORC2 negatively regulate each other by competing for association with LST8.
abstract: LST8 is a component of both mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Herein, to examine the role of LST8, a common component of mTOR complexes, in the regulation of mTORC1 and mTORC2, first, we showed over-expression of LST8 in HepG2 to markedly enhance basal phosphorylation levels of not only p70 S6 kinase but also Akt. In contrast, LST8 knockdown by siRNA in HepG2 decreased phosphorylation levels of both p70 S6 kinase and Akt. These results indicate the LST8 expression level to determine basal mTORC1 and mTORC2 activities, since LST8 appears to be the component present at the lowest level in both mTORC1 and mTORC2 complexes. Previously, we reported S6 kinase phosphorylation to be reduced by over-expression of the Cterminally deleted Raptor mutant (Raptor-ΔCT) not binding to mTOR or LST8, while phosphorylation levels of Akt were markedly enhanced with no alteration in IRS-1 phosphorylation or PI 3-kinase activity. Using Raptor-ΔCT, we investigated the competition for association with LST8 between mTORC1 and mTORC2. Over-expression of Raptor-ΔCT abolished formation of the Raptor, S6 kinase, mTOR and LST8 complex, while the amount of LST8 in the Rictor-mTOR complex was increased. Therefore, it is likely that Raptor-mTOR and Rictor-mTOR complexes compete for association with LST8, and this mechanism may contribute to the reciprocal negative regulations of mTORC1 and mTORC2 activities, in terms of their LST8 components.:
authors: The Institute for Adult Diseases, Asahi Life Foundation, 2-2-6 Nihonbashi Bakurocho, Chuo-ku, Tokyo, 103-0002, Japan.
authors: Takako
authors: T
authors: Kikuchi
authors: Department of Medical Science, Graduate School of Medicine, University of Hiroshima, 1-2-3 Kasumi, Minami-ku, Hiroshima City 734-8553, Hiroshima, Japan.
authors: Jun
authors: J
authors: Zhang
authors: Department of Internal Medicine, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
authors: Hideyuki
authors: H
authors: Sakoda
authors: Department of Internal Medicine, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
authors: Yuko
authors: Y
authors: Koketsu
authors: Department of Internal Medicine, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
authors: Midori
authors: M
authors: Fujishiro
authors: The Institute for Adult Diseases, Asahi Life Foundation, 2-2-6 Nihonbashi Bakurocho, Chuo-ku, Tokyo, 103-0002, Japan.
authors: Akifumi
authors: A
authors: Kushiyama
authors: Department of Medical Science, Graduate School of Medicine, University of Hiroshima, 1-2-3 Kasumi, Minami-ku, Hiroshima City 734-8553, Hiroshima, Japan.
authors: Yusuke
authors: Y
authors: Nakatsu
authors: Department of Medical Science, Graduate School of Medicine, University of Hiroshima, 1-2-3 Kasumi, Minami-ku, Hiroshima City 734-8553, Hiroshima, Japan.
authors: Hideaki
authors: H
authors: Kamata
authors: Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
authors: Ken
authors: K
authors: Inoki
authors: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.
authors: Shin-Ichiro
authors: S
authors: Takahashi
authors: Department of Physiological Chemistry and Metabolism, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.
authors: Hiroki
authors: H
authors: Kurihara
authors: Division of Molecular Metabolism and Diabetes, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Japan.
authors: Katagiri
authors: K
authors: Hideki
authors: Division of Molecular Metabolism and Diabetes, Tohoku University Graduate School of Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Japan.
authors: Yoshitomo
authors: Y
authors: Oka
authors: Department of Medical Science, Graduate School of Medicine, University of Hiroshima, 1-2-3 Kasumi, Minami-ku, Hiroshima City 734-8553, Hiroshima, Japan. Electronic address:asano-tky@umin.ac.jp.
authors: Tomoichiro
authors: T
authors: Asano