Department of Molecular and Cellular Oncology, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Biochem Biophys Res Commun. 2011 Sep 16;413(1):46-52. doi: 10.1016/j.bbrc.2011.08.034. Epub 2011 Aug 16.
The Akt kinase is a critical effector in growth factor signaling. Activation of Akt driven by the growth factor dependent PI3K (phosphatidylinositol-3-OH kinase) is coupled to the plasma membrane translocation and phosphorylation of Akt on two sites by PDK1 (phosphoinositide-dependent protein kinase-1) on Thr-308 and by mTORC2 (mammalian Target of Rapamycin Complex 2) on Ser-473. In our study we examined the sub-cellular localization of mTORC2 and identified that this kinase complex predominantly resides on endoplasmic reticulum (ER). Our immunostaining analysis did not show a substantial co-localization of the mTORC2 component rictor with Golgi, lysosome, clathrin-coated vesicles, early endosomes, or plasma membrane but indicated a strong co-localization of rictor with ribosomal protein S6 and ER marker. Our biochemical study also identified the mTORC2 components rictor, SIN1, and mTOR as the highly abundant proteins in the ER fraction, whereas only small amount of these proteins are detected in the plasma membrane and cytosolic fractions. We found that growth factor signaling does not alter the ER localization of mTORC2 and also does not induce its translocation to the plasma membrane. Based on our study we suggest that the mTORC2-dependent phosphorylation of Akt on Ser-473 takes place on the surface of ER.
Akt 激酶是生长因子信号传导中的关键效应物。由生长因子依赖性 PI3K（磷脂酰肌醇-3-激酶）驱动的 Akt 激活与 Akt 在 Thr-308 处由 PDK1（磷酸肌醇依赖性蛋白激酶-1）和在 Ser-473 处由 mTORC2（雷帕霉素靶蛋白复合物 2）进行的质膜易位和磷酸化相关。在我们的研究中，我们检查了 mTORC2 的亚细胞定位，并确定该激酶复合物主要位于内质网 (ER) 上。我们的免疫染色分析并未显示 mTORC2 成分rictor 与高尔基体、溶酶体、网格蛋白包被小泡、早期内体或质膜有大量共定位，但表明 rictor 与核糖体蛋白 S6 和 ER 标记物有强烈的共定位。我们的生化研究还确定了 mTORC2 成分 rictor、SIN1 和 mTOR 是 ER 部分中含量丰富的蛋白质，而这些蛋白质在质膜和胞质部分中仅检测到少量。我们发现生长因子信号不会改变 mTORC2 的 ER 定位，也不会诱导其向质膜易位。基于我们的研究，我们认为 mTORC2 依赖性 Akt 在 Ser-473 上的磷酸化发生在 ER 的表面。
