Identification of Aurora kinases as RasGAP Src homology 3 domain-binding proteins

The GTPase-activating protein RasGAP functions as both a negative regulator and an effector of Ras proteins. In tumor cells, RasGAP is no longer able to deactivate oncogenic Ras proteins, and its effector function becomes predominant. As RasGAP itself has no obvious enzymatic function that may explain this effector function, we looked for downstream RasGAP effectors that could fulfill this role. We looked for the existence of RasGAP Src homology 3 (SH3) domain partners as this domain is involved in the regulation of cell proliferation and has an anti-apoptotic effect. We report here the identification of a new RasGAP SH3 domain-binding protein, named Aurora. This Drosophila melanogaster Ser/Thr kinase has three human orthologs called Aurora/Ipl1-related kinase or HsAIRK-1, -2, and -3. Coimmunoprecipitation experiments in COS cells confirmed that HsAIRK-1 and HsAIRK-2 both interact with RasGAP. RasGAP pull-down experiments showed that it interacts with HsAIRK-1 in G(2)/M HeLa cells. We also demonstrated that RasGAP binds to the kinase domain of Aurora and that this interaction inhibits the kinase activity of HsAIRK-1 and HsAIRK-2. Finally we showed that RasGAP forms a ternary complex with HsAIRK and survivin. This complex may be involved in the regulation of the balance between cell division and apoptosis.