A novel proteomics approach to uncover Rho GTPases effector pathways

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OVERVIEW OF THE PROBLEMATIC Cellular processes including cell migration and adhesion rely on cytoskeletal dynamics, i.e. the ability of the cells to remodel its shape in a dynamic manner in response to signals in the external environment. Aberrant cell migration, for example, can cause the spreading of cancers (known as metastasis). We are studying the 22 Rho GTPases as they are believed to be the central molecules to regulate the cytoskeleton. Rho GTPases are, in appearance, simple small on/off molecular switches that regulate cell shape. However, there are at least 150 regulatory proteins that control how and when Rho proteins become active but only a handful of them are well characterized. Which positive and negative regulate Rho proteins is not defined. In addition, once a Rho protein is turned “on”, it interacts with effectors that promote specific signals inside the cell (for example to tell to the cell to migrate). Again, this simple molecular system becomes highly complex when we think that each Rho protein can interact with up to 40 effectors and which remain to be fully identified. In reality, we already know that the activators of the Rho proteins, known as GEFs, do not activate all possible effectors. We predict that the GEFs provide a logistic signal that allows for the activation of only the required effectors. This interplay between GEFs and Rho proteins has never been explored carefully because of technical limitations. OBJECTIVES Recently, a novel technique, termed BioID, is emerging as a powerful approach to uncover how proteins interact (i.e. are in physical contact) inside the cell. We adapted this technology to study Rho protein signaling organization in cells. We have 3 major objectives for this project: 1) We want to systematically map, at high-resolution, all the interacting proteins of the 20 Rho GTPases. 2) We will develop a new technique to identify the specific effectors for individual Rho GTPase/GEF pairs. 3) We will characterize the biological function of the novel effectors and effectors signaling identified Aim 1-2. NOVELTY and EXPECTED SIGNIFICANCE OF THE WORK Globally, completion of these interaction screens will systematically define, for the first time, Rho GTPases interactions with GEFs and with effector proteins. It will be the first time that such a large-scale analysis of the Rho GTPase signaling is conducted and it may transform the study of Rho GTPase signaling. These methods will be applicable to analyze signaling from all 150 Ras-family GTPases. This project will provide an outstanding platform for training graduate students toward the next generation of scientists that can understand highly complex signaling inside the cells. In the future, such a deep understanding of the molecular organization of signaling pathways is needed to rationally design powerful drugs to cure human diseases.