ras oncogenes are frequently associated with human cancer and activated forms of ras are powerfully transforming in experimental systems. Ras proteins control multiple signaling pathways via multiple effectors. The mechanisms by which those effectors are activated by Ras remain unclear. We are investigating the molecular mechanism by which the Ras proteins activate the Raf kinase class of effectors, as well as a novel Ras effector molecule, designated Nore1. The ultimate aim of these studies is to allow the design of highly specific small molecule inhibitors of Ras mediated transformation. we have found that Ras activates Raf by binding to two distinct sites on Raf. Both binding interactions are crtitical in generating a fully activated Raf molecule. we have identified specific residues within the second Ras binding domain which are essential for Ras interaction. Moreover, we have characterized the interplay of 14-3-3 and Phosphatidylserine as co-factors in the Ras mediated activation of Raf. We are currently investigating the possibility that Ras serves to release the c-terminal kinase domain of Raf from inhibitory, intramolecular binding contacts in the n-terminal, regulatory domain of Raf, and whether 14-3-3 may serve as a bridge in such an interaction. We have extrapolated the Lesons learned from the activation of raf by ras to the Ras effector Nore1. Unlike Raf, this effector mediates a powerful growth inhibitory effect. However, the mechanism of regulation of Nore1 appears to be similar to that of Raf-1 with the Ras binding domain serving to regulate the biological activity of the non-Ras binding region. The mechanism of growth inhibition by Nore1 is being investigated. - Ras, oncogene, Raf,
