Abstract A vast majority of the 25,000 genes identified in the human genome are subjected to alternative splicing, and their protein products are often heavily modified with posttranslational modifications including but not limited to ubiquitination, phosphorylation, methylation, and acetylation, thereby vastly increasing the functional diversity of the human proteome. However, aberrant cell signaling events caused by dysregulation of protein modifications often lead to altered protein homeostasis and cellular function to facilitate the development of human diseases including cancer. In keeping with a critical role for these modifications to governing tumorigenesis, inhibitors targeting enzymes regulating these post-translational modifications have attracted extensive attention as biomarkers and anti-cancer drug targets. To this end, the heart of my laboratory has been focused on studying the regulatory mechanisms and physiological functions of two major multi-component protein enzyme complexes: Cullin-based E3 ubiquitin ligase complexes and the Mammalian Target of Rapamycin Complex (mTOR), as well as their interplay with other cell signaling pathways to govern cell cycle regulation and tumorigenesis. The long-term goal of my research program is to understand how aberrant cell signaling pathways including phosphorylation and ubiquitination influence tumorigenesis, which guides the identification of novel drug targets for treating human cancers. Over the past thirteen years of independence, my laboratory has established an outstanding track record of original, cutting-edge, research in the cell cycle and cancer signaling fields. In this proposal, I have expanded our research by further deciphering the role of ubiquitination in regulating the mTORC1 signaling pathway, as well as the interplay between ubiquitination and phosphorylation signaling pathways to govern tumorigenesis, thereby providing mechanistic insights and the rationale to develop inhibitors targeting key modules of cell signaling pathways including E3 ligases and kinases to enhance our capability of creating highly targeted cancer therapies. To achieve these goals, one major theme is to use both biochemical and genetic approaches to understand the oncogenic role of Skp2 and the tumor suppressive role of Fbw7 in part via modulating cell metabolism through ubiquitination-mediated pathways. The second major theme of this proposal aims to investigate the physiological and pathological impacts of GATOR2-mediated ubiquitination of GATOR1 signaling events during cancer development in vivo, which will guide us to uncover novel therapeutic opportunities targeting these signaling pathways. This prestigious award would therefore provide us the necessary resources to use highly innovative approaches to tackle challenging questions such as understanding the molecular and cellular mechanisms governing tumorigenesis to shed light on novel pathways to target cancer more effectively. Receiving this p...