A majority of cellular proteins undergo post-translational modifications. The purpose of these modifications is to serve as cellular molecular switches and to increase proteomic repertoire of a cell. Recently, protein arginine methylation has emerged as a major regulator of protein function. This modification is catalyzed by a family of evolutionarily conserved enzyme called protein arginine methyltransferase (PRMT). In the metazoans, protein arginine methylation has been shown to play a role in the differentiation and development as well as etiology of human diseases such as multiple sclerosis, spinal muscular atrophy, and cancer. Using both yeast and mammalian cells as model organisms, my lab is focused on understanding the biological functions of protein arginine methylation at the molecular level using cell biological, biochemistry, proteomics, and genomics approaches.
The Role of Protein Arginine Methylation in pre-mRNA Splicing
In eukaryotes, pre-mRNA splicing is a process by which intronic sequences are precisely removed from pre-mRNAs. This process is critical to ensure proper gene expression. Pre-mRNA splicing is carried out by the spliceosome, a large molecular machine composed of five small nuclear ribonucleoprotein complexes (snRNPs) and scores of associated factors. Many spliceosomal and associated proteins are subject to regulation via post-translational modifications such as methylation and phosphorylation. Although the role of phosphorylation has been widely examined, far less is known about mechanisms by which methylation impacts pre-mRNA splicing, despite of our ever-increasing awareness of the importance of this post-translational modification in other facets of biology such as chromatin function. As such, elucidating how methylation affects the molecular interactions that are key to the creation of a properly functioning spliceosome will significantly advance our understanding of splicing regulation. Previous work from my lab has established a critical role for protein arginine methylation in pre-mRNA splicing, wherein it functions by an as yet poorly understood mechanism to control co-transcriptional recruitment of spliceosomal and associated proteins to nascent pre-mRNA molecules. Building upon these findings, my lab is interested in defining the molecular basis by which this critical regulatory step is manifested.
Modulation of RNA Pol III Transcription by Protein Arginine Methylation
Within the cell, RNA polymerase III (Pol III) is responsible for the production of small, untranslated structural RNAs for protein synthesis. These include the 5S rRNA and tRNA, which are highly abundant and account for approximately 15% of total cellular RNA by weight. Regulating the biogenesis of these small RNAs is important, as the availability of components of the protein synthesis apparatus is a determinant of a cell’s biosynthesis capacity and must be produced in high quantity to fulfill the cell’s biosynthetic demand during growth. Recently, we defined a role for PRMT1 in controlling transcription by RNA Pol III. In budding yeast, we used a genomic approach to uncover an enrichment of yeast PRMT1 (termed Hmt1) occupancy at tRNA genes and physical association of Hmt1 with RNA Pol III transcription factors. A change in the level of precursor tRNAs is also observed in Hmt1 loss-of-function mutants, suggesting a role for this enzyme in facilitating the biogenesis of tRNAs. Our lab is interested in dissecting the molecular basis by which Hmt1 modulates RNA Pol III transcription and in the process, learning how this post-translational modification impacts the biology of tRNA biogenesis.
Control of GPCR Signaling by Protein Arginine Methylation
In eukaryotes, G protein-coupled receptors (GPCRs) are the largest and most diverse group of membrane receptors and these receptors play an important role in mediating a variety of physiological responses such as responses to hormones, neurotransmitters, and environmental stimulants. Individual GPCRs have unique combination of signal-transduction activities and understanding the mechanisms that regulate these activities is crucial for designing potential therapeutic strategies. In collaboration with Drs. Denise Ferkey and Stewart Clark here at UB, we have identified arginine methylation as a post-translational modification that contributes to human D2 dopamine receptor function. Currently, we are interested in elucidating the molecular mechanism by which this modification regulates receptor signaling.