Characterising the molecular mode of Ras-mediated Cdc42 activation from a mechanical viewpoint

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Ras belongs to a conserved group of small GTPases involved in cell proliferation, differentiation and survival. Physiological importance of Ras proteins is underlined by the fact that approximately 30% of all cancers have oncogenic Ras mutations. As a molecule Ras is small and its "smooth" surface is often not readily compatible with conventional drug design approaches. Therefore the focus in recent years has fallen onto specifically targeting the downstream effectors of Ras - molecules such as PI3K and MAPK. However inhibiting these proteins have not yielded the success that had been hoped - inhibition of one effector brings about minimal effect and simultaneous inhibition of PI3K and MAPK have resulted in deleterious side effects. Furthermore, in an oncogenic Kras.G12D mouse model, although tumor susceptibility was observed, attenuation of PI3K and ERK (MAPK) pathways occurs upon growth factor stimulation in the isolated mouse embryonic fibroblasts (MEFs), in a similar way as in the wildtype MEFs. Therefore, in physiological conditions, PI3K or MAPK pathway may not be the major causal signaling pathway.Therefore the focus needs to move onto another pathway. Our focus is set on a pathway which leads to Cdc42 activation (a small GTPase integral in actin cytoskeleton reassembly), which appears to also be a requirement for oncogenic Ras-mediated transformation of tissue culture cells and tumor development in the nude mouse system. Our aim is to characterise and reveal the molecular and mechanical mode of Ras-mediated Cdc42 activation. To this end, the project consists of three parts: (1) identification of Ras residues responsible for Cdc42 activation, (2) examination of the mechanism how these Ras residues facilitate Cdc42 activation and (3) development of small molecules that bind and mask these key Ras residues in order to block the Cdc42 activation.By revealing the interaction surface between Ras and Cdc42 activators and further understanding how Cdc42 is activated (by precisely identifying the critical residues required), the basis of potentially novel anti-cancer drugs for the future can be formed.