Loss of Pten, a tumor suppressor, causes the strong inhibition of autophagy without affecting LC3 lipidation
Loss of Pten, a tumor suppressor, causes the strong inhibition of autophagy without affecting LC3 lipidation
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DOI：
10.4161/auto.6085
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发表时间：
2008-05
期刊：
影响因子：
13.3
通讯作者：
T. Ueno;Wataru Sato;Y. Horie;M. Komatsu;I. Tanida;Mitsutaka Yoshida;Shigetoshi Ohshima;T. Mak;Sumio Watanabe;E. Kominami
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文献类型：
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作者：
T. Ueno;Wataru Sato;Y. Horie;M. Komatsu;I. Tanida;Mitsutaka Yoshida;Shigetoshi Ohshima;T. Mak;Sumio Watanabe;E. Kominami
1 Pten（phosphatase and tensin homolog deleted on chromosome ten）是一种具有多种底物特异性的磷酸酶，是一种肿瘤抑制因子。其作为I类磷脂酰肌醇3-激酶/Akt途径的负调节剂的功能拮抗胰岛素依赖性细胞信号传导。小鼠肝脏中Pten的靶向缺失导致胰岛素超敏反应和磷脂酰肌醇3-激酶/Akt信号通路的上调。在这项研究中，我们研究了Pten缺乏对自噬的影响，自噬是一种主要的细胞降解系统，负责细胞成分的周转。与对照肝细胞相比，从Pten缺乏的肝脏中分离的肝细胞的[14 C]-亮氨酸标记的蛋白质的自噬降解被强烈抑制。然而，在对照组和Pten缺乏组之间，Atg 12-Atg 5缀合物和LC 3-II（LC 3的脂化形式，一种内在自噬体膜标记物）的水平没有发现显著差异。电子显微镜分析表明，许多自噬空泡（自噬体加自溶酶体）存在于对照小鼠的肝脏已经饥饿48小时，而它们显着减少在Pten缺乏的肝脏在相同的条件下。亮抑酶肽对对照肝脏的体内给药引起自噬蛋白水解的抑制，导致自溶体的积累。通过Percoll密度梯度离心，这些自溶酶体可以作为更致密的自溶酶体部分与其他细胞膜分离。然而，在亮抑酶肽给药的突变体肝脏中，致密的自溶酶体的积累大幅减少。总的来说，我们得出结论，在Pten缺乏症中增强的胰岛素信号传导在自噬体的形成和成熟步骤中抑制自噬，而不抑制ATG缀合反应。
1Pten (phosphatase and tensin homolog deleted on chromosome ten), a tumor suppressor, is a phosphatase with a variety of substrate specificities. Its function as a negative regulator of the class I phosphatidyl-inositol 3-kinase/Akt pathway antagonizes insulin-dependent cell signaling. The targeted deletion of Pten in mouse liver leads to insulin hypersensitivity and the upregulation of the phosphatidyl-inositol 3-kinase/Akt signaling pathway. In this study, we investigated the effects of Pten deficiency on autophagy, a major cellular degradative system responsible for the turnover of cell constituents. The autophagic degradation of [14C]-leucine-labeled proteins of hepatocytes isolated from Pten-deficient livers was strongly inhibited, compared with that of control hepatocytes. However, no significant difference was found in the levels of the Atg12-Atg5 conjugate and LC3-II, the lipidated form of LC3, an intrinsic autophagosomal membrane marker, between control and Pten-deficient livers. Electron microsopic analyses showed that numerous autophagic vacuoles (autophagosomes plus autolysosomes) were present in the livers of control mice that had been starved for 48 hours, whereas they were markedly reduced in Pten-deficient livers under the same conditions. In vivo administration of leupeptin to control livers caused the inhibition of autophagic proteolysis, resulting in the accumulation of autolysosomes. These autolysosomes could be separated as a denser autolysosomal fraction from other cell membranes by Percoll density gradient centrifugation. In leupeptin-administered mutant livers, however, the accumulation of denser autolysosomes was reduced substantially. Collectively, we conclude that enhanced insulin signaling in Pten deficiency suppresses autophagy at the formation and maturation steps of autophagosomes, without inhibiting ATG conjugation reactions.