Saturday, May 31, 2025
5/31/2025
Resolving cellular functions of arginine methylation - Summary PRMT5 is an essential enzyme and the cell’s primary enzyme capable of symmetric dimethylation of arginine residues. PRMT5 is a therapeutic target in cancer and neurodegenerative diseases. PRMT5 methylation of multiple protein substrates regulates a host of important cellular pathways and processes including transcription, chromatin dynamics, mRNA splicing, and translation. While PRMT5 activity is required for cell and tissue survival, which function(s) or substrate(s) of PRMT5 are required for general cell maintenance or involved in cancer and neurodegenerative diseases has not been elucidated. Further, while PRMT5 substrate proteins are strongly enriched for RNA binding and RNA regulatory pathways, the biochemical effects of arginine dimethylation have not been resolved. Specifically, methyl-Arg increases the size, hydrophobicity, and charge distribution, and decreases the H-bonding potential of substrate arginines but the mechanics of how the Arg-methyl groups affect PRMT5 substrates’ structure/function and subsequent cell survival are not known. In this project, I will explore how PRMT5 methylation of substrate proteins affect their ability to (1) bind to mRNA, (2) bind to other proteins/form higher order protein complexes and (3) affect substrate-dependent processes such as mRNA splicing. We will identify how substrates are recruited for methylation by PRMTs and what the downstream biochemical function is in order to better understand PRMT5 essential functions in normal cells and disease. Achieving a therapeutic window where select PRMT5 activities can be blocked without disrupting normal cell function is critical for targeting this essential enzyme. Thus, understanding the mechanisms of PRMT5 biology has the potential to inform our understanding of an important posttranslational modification on multiple intracellular targets and to guide future efforts in developing modulators of PRMT activity in disease settings. The discovery of novel sites on PRMT5 or on substrates may provide new therapeutic targets that would allow for targeting select PRMT5 function in disease while preserving the normal healthy cells and overcoming issues of toxicity observed with broad, catalytic PRMT5 inhibitors. We have previously defined the first mechanism of substrate recruitment to PRMT5 through the conserved, colinear PRMT5 binding motif using a computational tool to discover enriched protein motifs. We have predicted a new binding site for several additional PRMT5 substrates including ZNF326 – a substrate that is consistently methylated in all cells tested and that regulates mRNA splicing. We will determine how substrates get recruited to PRMT5 (and other PRMT family enzymes) for methylation and their cellular and biochemical outcomes as we establish a comprehensive research program devoted to understanding how enzymes select their substrates and performing early validation of their therapeutic potential. Overall, this project will dissect the cellular consequence of substrate arginine methylation by PRMT5 and from this we can uncover how therapeutic PRMT5 inhibitors will affect disease and normal tissue.
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