Guijarro Maria V, Link Wolfgang, Rosado Aránzazu, Leal Juan F M, Carnero Amancio
Experimental Therapeutics Programme, Centro Nacional de Investigaciones Oncológicas, Madrid 28029, Spain.
Carcinogenesis. 2007 Dec;28(12):2443-50. doi: 10.1093/carcin/bgm154. Epub 2007 Aug 3.
MAP17 is a non-glycosylated membrane-associated protein that has been shown to be over-expressed in human carcinomas, suggesting a possible role of this protein in tumorigenesis. However, very little is known about the molecular mechanism mediating the possible tumor promoting properties of MAP17. To analyze the effect of MAP17 on cell survival, we used Rat1 fibroblasts model where Myc over-expression promotes apoptosis in low serum conditions. In the present work, we report that over-expression of MAP17 protects Rat1a fibroblasts from Myc-induced apoptosis through reactive oxygen species (ROS)-mediated activation of the PI3K/AKT signaling pathway. MAP17-mediated survival was associated with absence of Bax translocation to the mitochondria and reduced caspase-3 activation. We show that a fraction of PTEN undergoes oxidation in MAP17-over-expressing cells. Furthermore, activation of AKT by MAP17 as measured by Thr308 phosphorylation was independent of PI3K activity. Importantly, modulation of ROS by antioxidant treatment prevented activation of AKT, restoring the level of apoptosis in serum-starved Rat1/c-Myc fibroblasts. Finally, over-expression of a dominant-negative mutant of AKT in MAP17-expressing clones makes them sensitive to serum depletion. Our data indicate that MAP17 protein activates AKT through ROS and this is determinant to confer resistance to Myc-induced apoptosis in the absence of serum.
微管相关蛋白17（MAP17）是一种非糖基化的膜相关蛋白，已证实在人类癌症中过度表达，提示该蛋白在肿瘤发生中可能发挥作用。然而，关于介导MAP17可能的肿瘤促进特性的分子机制却知之甚少。为了分析MAP17对细胞存活的影响，我们使用了大鼠1型成纤维细胞模型，其中Myc的过度表达在低血清条件下促进细胞凋亡。在本研究中，我们报告MAP17的过度表达通过活性氧（ROS）介导的PI3K/AKT信号通路激活，保护大鼠1a型成纤维细胞免受Myc诱导的细胞凋亡。MAP17介导的细胞存活与Bax转位至线粒体的缺失以及caspase-3激活的减少有关。我们发现，在MAP17过度表达的细胞中，一部分磷酸酶及张力蛋白同源物（PTEN）发生氧化。此外，通过苏氨酸308磷酸化检测，MAP17对AKT的激活独立于PI3K活性。重要的是，抗氧化剂处理对ROS的调节可阻止AKT的激活，恢复血清饥饿的大鼠1/c-Myc成纤维细胞中的细胞凋亡水平。最后，在表达MAP17的克隆中过表达AKT的显性负性突变体，使其对血清耗竭敏感。我们的数据表明，MAP17蛋白通过ROS激活AKT，这是在无血清条件下赋予对Myc诱导的细胞凋亡抗性的决定因素。
