PROJECT SUMMARY Cells and organisms must coordinate their metabolic activity with changes in their nutrient environment. This coordination is achieved via the signaling networks that integrate local and systemic nutrient inputs and relay nutrient status to the control of cellular anabolic and catabolic processes. This task can be carried out by the RAS-RAF-MEK-ERK cascade, a signaling system that is commonly activated by various growth factors and oncogenic events. In response to a mitogen factor such as the epithelial growth factor (EGF), ERK is activated and promotes cell proliferation and differentiation by regulating activity of transcription factors involved in cell cycle progression and proliferation. However, much less is understood about how ERK signaling directly controls metabolic processes. Targeting the kinases RAF, MEK or ERK is currently a strategy employed to treat several diseases including cancer, type 2 diabetes, metabolic disorders and neurodegeneration, however mechanisms of resistance often occur. Therefore, elucidating the downstream targets of ERK and more specifically the molecular mechanisms by which ERK signaling drives metabolism is of great interest in order to identify new therapeutic strategies against ERK driven disease. Recently we discovered that the mechanistic target of rapamycin complex 1 (mTORC1) stimulates synthesis of purines and pyrimidines de novo through different molecular mechanisms. Nucleotides play a central role in metabolism at a fundamental and cellular level. Purine and pyrimidine bases can be synthesized de novo or recycled through the salvage pathways. Nucleotides carry packets of chemical energy (e.g. ATP, GTP) throughout the cell to the many cellular functions that demand energy, which include: synthesizing nucleic acids, proteins and cell membranes. Under this proposal, we propose to study the influence of ERK signaling on nucleotide synthesis. We have identified that ERK signaling stimulates de novo purine synthesis in various settings through posttranslational modification of the enzyme PFAS (phosphoformylglycinamidine synthase) which belongs to the de novo purine synthesis pathway. We propose to dissect the molecular mechanisms underlying this regulation (Specific Aim1). We will determine the role of the ERK-PFAS axis in the control of cell growth (Specific Aim 2). Furthermore, we will determine the implication of this regulation in ERK-mediated biology and disease (Specific Aim3). Thus, the overall goal of this proposal is to decipher the molecular mechanisms by which ERK controls de novo nucleotide synthesis in normal and pathological settings. We anticipate that the proposed studies will yield new insights into how nucleotide synthesis is regulated by ERK and ...