Paper : THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 279, No. 47, Issue of November 19, pp. 49420–49429, 2004 Critical Role of Endogenous Akt/IAPs and MEK1/ERK Pathways in Counteracting Endoplasmic Reticulum Stress-induced Cell Death* Ping Hu侩, Zhang Han, Anthony D. Couvillon, and John H. Exton 闺teracting Endoplasmic Reticulum Stress-induced Cell Death 我妹妹看这篇 paper ，有一段看不太懂意思，麻烦大家帮忙翻译一下要义： 黄色部份...先谢谢各位 To elucidate whether activation of the PI3K/Akt pathway is required to protect cells from ER stress-induced cell death, we first assessed the effect of the PI3K inhibitor LY294002. As shown by phase-contrast microscopy and a cell viability assay (MTT assay) in Fig. 2 (C and D), co-incubation with LY294002 significantly sensitized MCF-7 cells to thapsigargin- or tunicamycin- induced cell death. LY294002 treatment alone had no effect on cell viability. Similar results were obtained when the same experiments were performed with H1299 cells (Fig. 2D). To further confirm that Akt signaling is protective of cell survival during ER stress, we established MCF-7 cell pools stably expressing HA-tagged dominant-negative (DN) Akt in which a point mutation (K197M) was introduced at a site required for kinase activity. Control cells were transfected with empty vector. Stable transfectants were identified by Western blotting with an HA-specific monoclonal antibody. A cell viability assay showed that ectopic expression of DN-Akt significantly increased thapsigargin- and tunicamycin-induced cell death (Fig. 2E). Similar results were obtained in H1299 cell expressing DN-Akt (data not shown). These results provide evidence that activation of the PI3K/Akt pathway is a critical cell survival response to ER stress. Akt-dependent Activation of mTOR Is Not Required for Aktmediated Survival Signaling in ER Stress—Recent research has shown that mTOR, an established Akt effector, is essential for Akt-mediated survival signaling . There is also much evidence that mitogens and growth factors stimulate phosphorylation of mTOR at Ser2448 . It was therefore interesting to investigate the role of mTOR in regulation of ER stress considering its critical controlling role in protein synthesis. Acute phosphorylation of mTOR at Ser2448 was found in MCF-7 cells treated with thapsigargin or tunicamycin, which was blocked by either LY249002 or expression of DN-Akt (Fig. 3A). Next, we tested whether activated mTOR contributes to cell survival during ER stress. As shown in Fig. 3B, co-incubation of MCF-7 cells with rapamycin, an inhibitor of mTOR, did not increase ER stress-induced cell death. Our data indicate that ER stress induces phosphorylation of mTOR in an Akt-dependent manner; however, this is not involved in cell survival. --

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