Trypanosoma brucei PRMT1 Is a Nucleic Acid Binding Protein with a Role in Energy Metabolism and the Starvation Stress Response

In Trypanosoma brucei and related kinetoplastid parasites, transcription of protein coding genes is largely unregulated. Rather, mRNA binding proteins, which impact processes such as transcript stability and translation efficiency, are the predominant regulators of gene expression. Arginine methylation is a posttranslational modification that preferentially targets RNA binding proteins and is, therefore, likely to have a substantial impact on T. brucei biology. The data presented here demonstrate that cells depleted of T. brucei PRMT1 (TbPRMT1), a major type I protein arginine methyltransferase, exhibit decreased virulence in an animal model. To understand the basis of this phenotype, quantitative global proteomics was employed to measure protein steady-state levels in cells lacking TbPRMT1. The approach revealed striking changes in proteins involved in energy metabolism. Most prominent were a decrease in glycolytic enzyme abundance and an increase in proline degradation pathway components, changes that resemble the metabolic remodeling that occurs during T. brucei life cycle progression. The work describes several RNA binding proteins whose association with mRNA was altered in TbPRMT1depleted cells, and a large number of TbPRMT1-interacting proteins, thereby highlighting potential TbPRMT1 substrates. Many proteins involved in the T. brucei starvation stress response were found to interact with TbPRMT1, prompting analysis of the response of TbPRMT1-depleted cells to nutrient deprivation. Indeed, depletion of TbPRMT1 strongly hinders the ability of T. brucei to form cytoplasmic mRNA granules under starvation conditions. Finally, this work shows that TbPRMT1 itself binds nucleic acids in vitro and in vivo, a feature completely novel to protein arginine methyltransferases. IMPORTANCE Trypanosoma brucei infection causes human African trypanosomiasis, also known as sleeping sickness, a disease with a nearly 100% fatality rate when untreated. Current drugs are expensive, toxic, and highly impractical to administer, prompting the community to explore various unique aspects of T. brucei biology in search of better treatments. In this study, we identified the protein arginine methyltransferase (PRMT), TbPRMT1, as a factor that modulates numerous aspects of T. brucei biology. These include glycolysis and life cycle progression signaling, both of which are being intensely researched toward identification of potential drug targets. Our data will aid research in those fields. Furthermore, we demonstrate for the first time a direct association of a PRMT with nucleic acids, a finding we believe could translate to other organisms, including humans, thereby impacting research in fields as distant as human cancer biology and immune response modulation.