The sequence containing T619 is well-conserved across mammalian species, and interestingly, it is replaced by a negatively charged residue (T619D) that mimics phosphorylation and possibly increases de novo purine synthesis in a subset of cancers. and oncogenic ERK signaling activation leads to acute metabolic flux stimulation through the de novo purine synthesis pathway, thereby increasing building block availability for RNA and DNA synthesis, which is required for cell growth and proliferation. We demonstrate that ERK2, but not ERK1, phosphorylates the purine synthesis enzyme PFAS (phosphoribosylformylglycinamidine synthase) at T619 in cells to stimulate de novo purine synthesis. The expression of nonphosphorylatable PFAS (T619A) decreases purine synthesis, RAS-dependent cancer cell colony formation, and tumor growth. Thus, ERK2-mediated PFAS phosphorylation facilitates the increase in nucleic acid synthesis required for anabolic cell growth and proliferation. Graphical Abstract eTOC Blurp: Ali and Sahu et al. demonstrate that ERK signaling acutely stimulates de novo purine synthesis through direct phosphorylation of the purine enzyme PFAS in response to physiological growth signals or oncogenic activation of RAS or RAF. The ERK-dependent phosphorylation of PFAS is required for cell and tumor growth. INTRODUCTION Cells and organisms must synchronize their metabolic activity with changes in their nutrient and hormonal environments. This synchronization is coordinated by the signaling networks that integrate local and systemic nutrient and hormonal signals to convey the metabolic status of the cell (Erez and DeBerardinis, 2015; Ward and Thompson, 2012). The extracellular signal-regulated kinase-mitogen-activated protein kinase (ERK-MAPK) cascade, often hyperactive in cancer cells (Ryan et al., 2015), is a central signaling network that regulates a wide variety of stimulated cellular processes, including proliferation, differentiation, survival, apoptosis and stress responses (Brunet et al., 1999; Cargnello and Roux, 2011; Plotnikov Rabbit polyclonal to CD146 et al., 2011; Shaul and Seger, 2007; Zhang and Liu, 2002). Briefly, the integration of signals by the RAS-ERK cascade involves the binding of an extracellular ligand to a receptor tyrosine kinase (RTK) in the plasma membrane to cause receptor dimerization and tyrosine residue autophosphorylation in the intracellular domains (Lemmon and Schlessinger, 2010). The small G protein RAS is recruited and becomes GTP-loaded, leading to the activation of the serine/threonine protein kinase RAF, which promotes the subsequent activation of MAPK/ERK kinase (MEK) and then ERK. Activated ERK phosphorylates numerous substrates and regulates the activity of different transcription factors, leading to alterations in gene expression (Whitmarsh, 2007). The importance of closely linking ERK signaling to metabolism control is highlighted by the fact that aberrant regulation of Betanin this signaling pathway and cellular metabolism have been implicated in the pathophysiology of a diverse set of human diseases, including cancer and metabolic disorders (DeBerardinis and Chandel, 2016; Haigis et al., 2008; Humpton et al., Betanin 2019; Shaw and Cantley, 2006). This evidence supports our efforts to identify key metabolic targets downstream of ERK that contribute to cancer cell growth. Previously, in two separate studies, we demonstrated that the mechanistic target of rapamycin complex 1 (mTORC1) stimulates de novo pyrimidine and purine synthesis (Ben-Sahra et al., Betanin 2013; Ben-Sahra et al., 2016) to support an increased demand for RNA and DNA, which is required for anabolic growth and proliferation. The synthesis of both purines and pyrimidines requires ribose 5-phosphate from glucose-derived pentose phosphate. Purines and pyrimidines (e.g., ATP, GTP, dATP, dGTP, UTP, CTP, dTTP and dCTP) are essential for growing cells, not only as RNA and DNA building blocks but also for cellular homeostasis maintenance. Cells can acquire purines and pyrimidines through either the salvage pathways, requiring exogenous nucleoside availability and uptake, or de novo synthesis from small molecule precursors such as glutamine, aspartate, glycine, formate, and bicarbonate (Lane and Fan, 2015). Although it is generally accepted that the salvage pathways are sufficient to sustain the demands of quiescent terminally differentiated cells, growing and proliferating cells require activation of de novo synthesis Betanin (Villa et al., 2019). With a few remarkable exceptions (Ben-Sahra et al., 2013; Graves et al., 2000; Hoxhaj et al., 2019), most established links between growth factor signaling and cellular metabolism involve the regulation of transcription factors that control the expression of genes encoding metabolic enzymes (Barbie et al., 2009; Stine et al., 2015). ERK signaling is physiologically activated by growth factors in normal settings (Lange-Carter and Johnson, 1994) Betanin and pathologically activated by oncogenic RAS and RAF proteins in various cancer types (Downward, 2003; Halilovic and Solit, 2008; Murugan et al., 2019). The ERK signaling network, when activated, promotes anabolic metabolism typically through long-term changes mediated by the transcription factor c-MYC (Davis, 1995; Kerkhoff et al., 1998). The ERK-MYC axis controls various metabolic processes, including glucose and nucleotide metabolism, through transcriptional mechanisms (Dang, 2013; Grassian et al., 2011; Kimmelman, 2015; Liu et al., 2008; Santana-Codina et al., 2018). However, examples of acute and direct regulation of cellular metabolism by ERK signaling remain largely unknown, with one exception of ERK corroborating the immediate regulation of de novo.
The sequence containing T619 is well-conserved across mammalian species, and interestingly, it is replaced by a negatively charged residue (T619D) that mimics phosphorylation and possibly increases de novo purine synthesis in a subset of cancers