Characterization of growth factor-coupled signaling

描述（由申请人提供）：EGF受体（EGFR）家族的成员与许多人类癌症有关，包括肺癌、乳腺癌和脑癌。我们的研究得到了GM 40654的支持，集中于鉴定通过EGF（EGFR的主要配体/生长因子）和调蛋白（HRG）（EGFR家族成员ErbB 3和ErbB 4的配体和ErbB 2/Neu酪氨酸激酶的激活剂）的作用进行调节的新型信号传导终点。这些努力使我们发现了两个信号通路，在建立生长调节蛋白的合成和降解之间的平衡中发挥重要作用。一种涉及通过调节EGFR-Cbl相互作用和EGFR降解的小GTdR Cdc 42的EGFR信号传导，而第二种途径通过小GTdR Rac将HRG信号传导连接到mTOR/p70 S6激酶和核GTdR Ran，导致加帽mRNA的加工。最近，我们发现了第三个信号机制的重要生长调节蛋白的稳态。这涉及Rho GTP酶和mTOR激活线粒体酶谷氨酰胺酶的能力，所述线粒体酶谷氨酰胺酶催化谷氨酰胺水解为谷氨酸，并导致产生细胞增殖和致癌转化所必需的生物合成中间体。我们建议以这些发现为基础，通过以下研究路线更好地理解生长因子信号传导途径如何调节细胞生长所必需的RNA加工和细胞代谢事件，以及当去调节时导致癌症的发展：1）理解小GTdR an在细胞生长调节和细胞转化中的作用。我们将继续研究我们的发现，即Ran的过度激活诱导细胞转化，并观察这是否需要向RNA加工机制和刺激有丝分裂活动的蛋白质合成发出信号。2)了解生长因子调节RNA加工和细胞代谢活动之间的联系。我们将确定生长因子（例如HRG）如何调节线粒体转氨酶，以及这是否涉及该酶的特定亚型。3)了解Rho GTPases和小GTPs Rheb在控制生长调节蛋白稳态的生长因子信号通路中的关系。我们将使用新设计的活化Rheb突变体来确定Rac如何与Rheb一起介导mTOR的HRG依赖性活化和加帽RNA转录物的加工，并确定Rheb是否通过mTOR信号影响线粒体中的谷氨酰胺代谢。期望这些研究将揭示EGFR家族成员如何通过调节RNA加工和细胞代谢来控制细胞生长，以及确定干预癌症的新靶点。 公共卫生相关性：EGF受体及其密切相关的家族成员Neu/ErbB 2酪氨酸激酶与许多类型的人类癌症有关。通过了解这些受体酪氨酸激酶如何发送调节细胞生长的信号，以及当去调节改变细胞代谢和细胞中促生长蛋白的稳态时，我们希望获得将为恶性肿瘤的发展提供新的信息。期望这些信息将突出治疗干预的新靶点和策略。

DESCRIPTION (provided by applicant): Members of the EGF receptor (EGFR) family have been implicated in a number of human cancers including those of the lung, breast, and brain. Our studies supported by GM40654 have centered on identifying novel signaling endpoints that are regulated through the actions of EGF, a primary ligand/growth factor for the EGFR, and Heregulin (HRG), a ligand for EGFR family members ErbB3 and ErbB4 and an activator of the ErbB2/Neu tyrosine kinase. These efforts have led us to discover two signaling pathways that play important roles in establishing the balance between the synthesis and degradation of growth regulatory proteins. One involves EGFR-signaling through the small GTPase Cdc42 that regulates EGFR-Cbl interactions and EGFR degradation, whereas the second pathway links HRG-signaling through the small GTPase Rac to mTOR/p70 S6 kinase and the nuclear GTPase Ran, resulting in the processing of capped mRNAs. Recently, we discovered a third signaling mechanism important for growth regulatory protein homeostasis. This involves the ability of Rho GTPases and mTOR to activate the mitochondrial enzyme glutaminase that catalyzes the hydrolysis of glutamine to glutamate and leads to the generation of biosynthetic intermediates essential for cellular proliferation and oncogenic transformation. We propose to build on these findings to better understand how growth factor-signaling pathways regulate RNA-processing and cellular metabolic events necessary for cell growth, and when de- regulated lead to the development of cancer, through the following lines of study: 1) Understanding the role of the small GTPase Ran in cell growth regulation and cellular transformation. We will follow-up on our discovery that excessive activation of Ran induces cellular transformation and see whether this requires signaling to the RNA-processing machinery and the synthesis of proteins that stimulate mitogenic activities. 2) Understanding the connection between the growth factor-regulation of RNA-processing and cellular metabolic activities. We will determine how growth factors (e.g. HRG) regulate mitochondrial glutaminase and whether this involves a specific isoform of the enzyme. 3) Understanding the relationship between Rho GTPases and the small GTPase Rheb in the growth factor-signaling pathways that control the homeostasis of growth regulatory proteins. We will use newly designed activated Rheb mutants to establish how Rac works together with Rheb to mediate the HRG-dependent activation of mTOR and the processing of capped RNA-transcripts, and to determine whether Rheb signals through mTOR to influence glutamine metabolism in the mitochondria. The expectation is that these studies will shed light on how EGFR family members, through their regulation of RNA-processing and cellular metabolism, control cell growth, as well as identify new targets for intervention against cancer. PUBLIC HEALTH RELEVANCE: The EGF receptor and its closely related family member, the Neu/ErbB2 tyrosine kinase, have been linked to a number of types of human cancers. By understanding how these receptor tyrosine kinases send signals that regulate cell growth, and when de-regulated alter cellular metabolism and the homeostasis of growth-promoting proteins in cells, we hope to obtain information that will shed new light on the development of malignant cancers. The expectation is that this information will highlight novel targets and strategies for therapeutic intervention.