Regulation of the Rac activator Tiam1 by ubiquitylation

RAS蛋白是细胞从正常向癌症转化过程中涉及的生化途径的主要调节者。它们的功能在大多数人类肿瘤中都是异常的。对RAS蛋白激活的通路的研究已经确定了可以被药物靶向抑制肿瘤生长和扩散的分子。Rac是一种结构上与RAS相似的蛋白质，它确实介导了RAS的致癌特性。RAC激活广泛的过程，如细胞迁移和侵袭。RAC在两种不同的“开”或“关”状态之间循环，分别由两个蛋白质家族控制，分别称为鸟嘌呤核苷酸交换因子(Egf)和GTPase激活蛋白(GAP)。T细胞淋巴瘤侵袭和转移蛋白1(TIAM1)是一种激活RAC的全球环境基金，其本身也是肿瘤形成所必需的。然而，TIAM1通过RAC也可以刺激细胞的黏附，并有可能减缓癌症的扩散。来自我们实验室的未发表的数据现在表明，TIAM1的水平可以通过它与另一种标记TIAM1进行降解的蛋白质-HUWE1的相互作用来降低。我们假设HUWE1可能会在癌细胞中积聚，以便将TIAM1减少到仍然允许肿瘤发展但不能抑制癌症扩散的量。这项提议有三个主要目标。首先，我们将定义这两种蛋白质中允许物理相互作用的部分。其次，利用这些信息，我们将制造不能降解的突变的TIAM1蛋白，通过用突变的TIAM1取代正常的TIAM1，我们将从功能上评估TIAM1降解在癌症生长和扩散过程中的重要性。第三，我们计划使用两种不同的小鼠模型，其中TIAM1和HUWE1的表达可以被遗传改变，以研究TIAM1和HUWE1调控在肿瘤发生中的作用。最后，为了确认上述发现对癌症研究领域的重要性，我们计划分析TIAM1和HUWE1在人类肿瘤样本中的表达。我们预计，我们从这些研究中学到的知识将增加我们对RAS功能异常如何导致癌症的理解，并改进治疗癌症的药物设计。

RAS proteins are master regulators of biochemical pathways involved in the transformation of cells from normal to cancer. Their function is abnormal in most human tumours. Investigation of the pathways activated by RAS proteins has identified molecules which can be targeted by drugs to inhibit tumour growth and spread. RAC is a protein structurally similar to RAS which indeed mediates the cancer-inducing properties of RAS. RAC activates a wide range of processes such as cell migration and invasion. RAC cycles between two different states 'on' or 'off' controlled by two families of proteins known as Guanine nucleotide Exchange Factors (GEF) and the GTPase activating proteins (GAPs) respectively. In its active or switched 'on' state RAC is able to bind various other proteins to elicit consequent responses in the cell.The T-cell lymphoma invasion and metastasis 1 (TIAM1) protein is a GEF specific for the activation of RAC and is itself required for tumour formation. However, TIAM1 through RAC can also stimulate the adhesion of cells and potentially slow down the spread of cancer. Unpublished data from our lab now indicates that TIAM1 levels can be reduced via its interaction with another protein- HUWE1- which labels TIAM1 for degradation. We hypothesize that HUWE1 may accumulate in cancer cells in order to reduce TIAM1 to an amount that still allows tumours to develop but can not inhibit cancer spreading.There are three main objectives to this proposal. Firstly we will define the parts of these two proteins that allow physical interaction. Secondly, using this information we will then make 'mutant' TIAM1 proteins which cannot be degraded and by replacing normal TIAM1 with mutant TIAM1, we will functionally assess the importance of TIAM1 degradation during processes involved in cancer growth and spreading. Thirdly, we plan to use two different mouse models where the expression of TIAM1 and HUWE1 can be genetically altered, to investigate the effect of TIAM1 and HUWE1 modulation on tumourigenesis. Finally, to confirm the importance of the above findings to the field of cancer research we plan to analyse the expression of TIAM1 and HUWE1 in human tumour samples. We envisage that the knowledge we learn from these studies will increase our understanding of how abnormal RAS function results in cancer and improve the design of drugs to treat cancer.