Functional impact of oncogene mutants on the Ras and Rho signaling pathways

Coordinator:		PD Dr. Reza  Ahmadian
Institution:		Institut für Biochemie und Molekularbiologie II
Homepage:		www.uniklinik-duesseldorf.de

Members of the Ras and Rho families are small GTPases, which usually cycle between an inactive GDP-bound and an active GTP-bound state. The GDP/GTP cycle is highly regulated by GEFs that induce the release of the bound GDP to be replaced by the more abundant GTP and by GAPs that terminate signaling by inducing GTP hydrolysis. Given the significant contributions that dysregulated Ras and Rho signalling make to tumor growth and progression, targeting these signalling pathways has become a major endeavour in the fight against cancer. We know from our studies in the last 15 years that in the case of Ras, the GTP hydrolysis reaction of the Ras oncogene mutants is, for several reasons, a valuable small molecule drug target: (i) oncogene mutations in RAS genes, found in 25% of human tumors, abolish GAP induced GTP-hydrolysis of the protein products, which, consequently, become locked in the ‘ON’ state; (ii) ERBB2/Her2 mutations provides sustained activation of Ras; (iii) due to mutations in the NF1 tumor suppressor gene encoding a Ras-specific GAP active Ras•GTP also accumulates abnormally high levels. Based on our structural and functional data we generated compounds that exhibit GAP-like function (chemical GAPettes) by selectively promoting GTP hydrolysis of Ras oncogene mutants in vitro. In context of this interdisciplinary initiative we will both further improve the concept an anti-Ras compounds and systematically analyze their bioactivity on different cancer cell types including those containing oncogene mutants using established methods in our laboratories. For Rho GTPases, there are no known examples of oncogene mutations so far; however, it is generally accepted that patient mutations in the genes of their regulators (GEFs/GAPs) is the major reason for their involvement of Rho GTPases (e.g. Rho/ROCK signaling pathways) in tumor growth, invasion and mestastasis. This and the fact that Rho GTPases are downstream of Ras and PI3K promote the notion of investigating comprehensively the role of these pathways in the activation of the Rho GTPase regulators in various cell lines transfected with oncogene mutants in a combination of the use of available pharmacological compounds and RNAi technology. Expected results along with parallel structure-function studies of tumor-relevant regulators of the Rho GTPases will advance our knowledge of the underlying regulatory mechanisms and will help identifying novel therapeutic Targets. Together, results from these experime