MAMMALIAN RASGAP RELATED GENES

本项目拟探索两种新的 发现了Ras GTP酶激活蛋白（RasGAP）相关的人类蛋白质， 称为IQGAP 1&2，可能在人类疾病中发挥作用， 为治疗提供了新的靶点。 这两种新型蛋白质具有广泛的 在它们的C-末端半部分与sar 1/gap 1假定的RasGAP相似 来自粟酒裂殖酵母，可能是这种裂殖酵母的同系物 Ras调节器。 进一步暗示IQGAP作为Ras监管机构，其中之一 蛋白质类似于神经纤维蛋白，其抑制生长的能力， 人H=Ras依赖性酵母菌株。 此外，令人惊讶的是， 发现这两种蛋白质都含有IQ基序，并与 钙调素 由于IQGAP 2仅在肝脏和肝细胞中表达， 细胞系，而IQGAP 1 mRNA水平在胎盘中特别高， 肺、肾和外周血白细胞，这些蛋白质因此可能 作为可能的上皮细胞特异性整合剂， Ras和Ca 2 +/钙调素介导的信号通路。 然而，虽然在 体外实验表明Ras结合，在初步研究中， 刺激Ras或其直系亲属的GTdR， 检测到，这表明IQGAP 1&2的活动紧密地 由Ca 2 +/钙调素调节，或者这些蛋白质是Ras相互作用物 没有明显的GAP活性。 由于拉斯的中心作用及其 在促有丝分裂信号转导中的调节子由高水平的 致癌Ras途径突变的频率，组合生化， 表达，细胞生物学和遗传学研究，建议进一步 探索的生物学特性和潜在的肿瘤抑制作用， 这些有趣的新蛋白质 具体而言，该项目包括 生物化学研究，以确定潜在的钙调素调节的GT3 IQGAP 1和2的调节活性，表达研究以确定 这些蛋白质在其中执行其功能的确切组织和细胞类型。 功能，细胞生物学分析，以测试IQGAP 1和2是否形成瞬时 蛋白质复合物的刺激细胞，这是由意想不到的建议， 观察到钙离子载体依赖性核转位，以及 基因研究，以探索潜在的肿瘤抑制作用。 超出 事实上，NF 1和p120 GAP在特定的癌症中都发生了突变，后者 由于IQGAP 1和IQGAP 2是异质的， 在肺癌和肝癌细胞系中表达，因为 已经用IQGAP 1探针在肺肿瘤中检测到杂合性， 因为IQGAP 1基因映射到一个与复发性肺部疾病有关的区域， 腺癌染色体易位 除了提供线索， 这些有趣的新蛋白质的生物学功能，这些研究可能 也有助于更好地了解其他RasGAP，并提供 Ras和钙调蛋白之间经常被怀疑的联系的结构基础- 介导的信号转导。

This project proposes to explore the biological functions of two newly discovered Ras GTPase activating protein (RasGAP)-related human proteins, called IQGAP1&2, which may play roles in human disease and which may present novel targets for therapy. Both novel proteins share extensive similarity in their C-terminal halves with the sar1/gap1 putative RasGAP from Schizosaccharomyces pombe and may be homologs of this fission yeast Ras regulator. Further implicating IQGAPs as Ras regulators, one of these proteins resembled neurofibromin in its ability to suppress the growth of a human H=Ras dependent yeast strain. In addition, it was surprising to find that both proteins harbor IQ motifs and form stable complexes with calmodulin. Since IQGAP2 is uniquely expressed in liver and hepatocyte cell line, whereas IQGAP1 mRNA levels are especially high in placenta, lung, kidney, and peripheral blood leukocytes, these proteins may thus perform novel roles as perhaps epthelial cell specific integrators of the signaling pathways mediated by Ras and Ca2+/calmodulin. However, while in vitro experiments have suggested Ras binding, in preliminary studies to stimulation of the GTPase of Ras or its immediate relatives has yet been detected, indicating either that the activities of IQGAP1&2 are tightly regulated by Ca2+/calmodulin, or that these proteins are Ras interactors without prominent GAP activity. Since the central role of Ras and its regulators in mitogenic signal transduction is reflected by a high frequency of oncogenic Ras pathway mutations, a combination biochemical, expression, cell biological and genetic studies is proposed to further explore the biological properties and potential tumor suppressor roles of these intriguing new proteins. Specifically, this project includes biochemical studies to define the potentially calimodulin-regulated GTPase modulating activities of IQGAP1&2, expression studies to determine the exact tissues and cell types in which these proteins perform their function, cell biological analyses to test whether IQGAP1&2 form transient protein complexes in stimulated cells, as is suggested by the unexpected observation of a calcium ionophore-dependent nuclear translocation, and genetic studies to explore potential tumor suppressor roles. Beyond the fact that NF1 and p120GAP are both mutated in specific cancers, the latter studies are also proposed because IQGAP1 and IQGAP2 are heterogenously expressed in lung and liver cancer cell lines, because loss-of- heterozygosity has been detected with IQGAP1 probes in lung tumors, and because the IQGAP1 gene maps to a region involved in a recurring lung adenocarcinoma chromosome translocation. In addition to providing clues to the biological functions of these intriguing new protein, these studies may also contribute to a better understanding of other RasGAPs and provide a structural basis for often suspected links between Ras and calmodulin- mediated signal transduction.