MAMMALIAN RASGAP RELATED GENES

该项目计划探索两个新的生物功能 发现了与Ras GTP酶激活蛋白(RasGAP)相关的人类蛋白质， 称为IQGAP1&2，它可能在人类疾病中发挥作用，并可能 提出治疗的新靶点。这两种新蛋白质具有广泛的共同点 它们的C末端半部分与推测的RasGAP的Sar1/Gap1相似 从裂殖酵母中分离出来，可能是这种分裂酵母的同源物 RAS调节器。进一步牵连IQGAP作为RAS监管机构，其中之一 蛋白质类似于神经纤维蛋白，其抑制肿瘤生长的能力 一株依赖H=RAS的人酵母菌株。此外，令人惊讶的是 发现这两种蛋白质都含有IQ基序并与之形成稳定的络合物 钙调素。由于IQGAP2在肝脏和肝细胞中唯一表达 而IQGAP1基因在胎盘中的表达水平特别高， 肺、肾和外周血白细胞，这些蛋白质可能因此 发挥新的作用，可能是上皮细胞特异性的整合子 RAS和钙/钙调蛋白介导的信号转导通路。然而，当在 体外实验表明RAS结合，在初步研究中 对RAS或其直系亲属GTP酶的刺激尚未被 检测到，表明IQGAP1和IQGAP2的活动紧密 受钙离子/钙调蛋白调节，或这些蛋白是RAS相互作用因子 没有明显的空隙活动。由于RAS及其核心作用 调节剂在有丝分裂信号转导中的高水平反映 致癌RAS途径突变的频率，一种组合的生化， 建议进行表达、细胞生物学和遗传学研究，以进一步 探讨其生物学特性及潜在的肿瘤抑制作用 这些引人入胜的新蛋白质。具体地说，这个项目包括 可能受钙调蛋白调节的GTP酶的生化研究 调控IQGAP1和IQGAP2活性的表达研究 这些蛋白质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IQGAP1&2是否形成瞬变 刺激细胞中的蛋白质复合体，如意想不到的暗示 观察到钙离子载体依赖的核转位，以及 基因研究，以探索潜在的肿瘤抑制作用。超越了 NF1和p120GAP在特定癌症中都发生突变的事实，后者 还提出了研究，因为IQGAP1和IQGAP2是异质性的 在肺癌和肝癌细胞系中表达，因为- 已经用IQGAP1探针在肺癌中检测到杂合性，并且 因为IQGAP1基因映射到与复发肺相关的区域 腺癌染色体易位。除了提供线索之外 这些耐人寻味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可疑联系的结构基础- 中介信号转导。

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.