Structural Aspects of Raf-1:Rok-alpha Interaction

In order to survive, cells must translate and integrate the signals they receive from their environment. Many intracellular enzyme cascades are activated concomitantly in the cell, and they must potentiate or antagonize each other to implement physiologically relevant outcomes. Kinases, for example, can inhibit each other by direct phosphorylation of negative regulatory residues. We have recently discovered a new paradigm of kinase regulation and pathway cross-talk mediated by protein:protein interaction, in which the regulatory domain of a modular kinase (the Ras effector Raf-1) binds to and inhibits the catalytic domain of another kinase (the RhoA effector Rok-a). Importantly, this interaction is crucial for the developments of Ras-driven epidermal tumors. We now propose to obtain detailed structural information on this interaction, with the aim of informing the design of inhibitors that would disrupt it.

In order to survive, cells must translate and integrate the signals they receive from their environment. Several intracellular enzyme cascades are activated concomitantly in the cell, and they must potentiate or antagonize each other to implement physiologically relevant outcomes. Kinases, for example, can inhibit each other by direct phosphorylation of negative regulatory residues. Many studies have implicated the Ras and Rho pathway in the control of cell proliferation, migration, and tumorigenesis. As a consequence, major efforts are being made to target the druggable nodes, that is, the kinases, using inhibitors to block pathway activation. A better understanding of kinase regulation is crucial to reach this goal. We have recently discovered a new paradigm of kinase regulation and pathway cross-talk mediated by protein:protein interaction, in which a kinase (the Ras effector Raf-1) binds to and inhibits the another kinase (the RhoA effector Rok-?). Importantly, the latter interaction is crucial for the development of Ras-driven epidermal tumors. The results of this project show that the ability of Raf-1 to phosphorylate itself is a decisive step to maintain signal flux through the Ras pathway, at the expense of the cross-talk with Rho/Rok-?.