Compartmentalized signalling of Ras in cancer cells

Ras原癌基因(s)编码转化gtpase， gtpase在高尔基体和内质网（统称：内膜）被翻译后修饰，然后到达质膜（PM）。最近的过表达研究揭示了生长因子激活的、gtp负载的Ras存在于分泌途径的不同细胞器中，包括高尔基体。然而，Ras的高尔基活化仅在Ras工程过表达的细胞中检测到，这表明Ras的膜活化可能是Ras过表达的结果，反过来又对膜活化Ras的生理作用提出了质疑。有趣的是，高Ras- gtp水平也是Ras依赖性肿瘤的主要特征，这导致了Ras可能在癌细胞的细胞膜上活跃的假设。根据这一概念，我们在n -Ras转化白血病细胞系的高尔基体中检测到活性Ras。在此，我们建议对Ras活性在癌细胞中的亚细胞定位进行全面的研究。由于Ras- gtp的异常水平也会由于激活Ras突变以外的病变而发生，包括Ras基因扩增或Ras上游的超形态病变，我们将研究所有这些情况下模型细胞系统中活性Ras的空间分布。此外，我们将讨论Ras-GTP在细胞膜上的信号传导是否对每种情况下的致癌转化都很重要。总之，我们建议确定Ras信号在癌细胞中的空间动力学，并填补我们对Ras病理生物化学理解的重要空白。

Ras proto-oncogene(s) code for transforming GTPases that become post-translationally modified at the Golgi and endoplasmic reticulum (collectively: endomembranes) on their way to the plasma membrane (PM). Recent overexpression studies have disclosed the existence of growth-factor-activated, GTP-loaded Ras in distinct organelles of the secretory pathway, including the Golgi. However, Golgi-activation of Ras is exclusively detected in cells engineered to overexpress Ras, indicating that endomembrane activation of Ras may be a consequence of Ras overexpression, in turn raising doubts on the physiological role of endomembrane-activated Ras. Interestingly, high Ras-GTP levels are also the main attribute of Ras-dependent tumors, which leads to the hypothesis that Ras might be active at endomembranes in cancer cells. In line with this concept, we have detected active Ras at the Golgi of a N-Ras-transformed leukaemia cell line. We propose here a comprehensive study on the sub-cellular localization of Ras activity in cancer cells. Since aberrant levels of Ras-GTP also occur as a result of lesions other than activating Ras mutations, including Ras gene amplification or hypermorphic lesions upstream of Ras, we will investigate the spatial distribution of active Ras in model cell systems for all those scenarios. Moreover we will address whether signalling by Ras-GTP at endomembranes is important for oncogenic transformation in each case. In sum, we propose to determine the spatial dynamics of Ras signalling in cancer cells and close an important gap in our understanding of the pathobiochemistry of Ras.