Crosstalk to Histone Arginine Methylation

ABSTRACT Eukaryotic gene expression requires both transcription factor binding to DNA and histone post-translational modifications (PTMs). In many cases, how these PTMs are mechanistically connected to transcription are still unclear. Transcription factor binding to chromatin–such as by growth factors like TGF or by the hormone-in- ducible glucocorticoid receptor (GR)–initiates transcription. Histone acetylation is transiently deposited on chro- matin during transcriptional activation and during ongoing transcription. In contrast, histone arginine methyla- tion–lasting for days–is a stable PTM. The two major protein arginine methyltransferases, PRMT1 and 5, are regulated by substrate acetylation and phosphorylation. Studying this PTM crosstalk will illuminate how chro- matin environments are transformed to establish and maintain gene expression. We can now transform our understanding of how inducible transcription factor binding works together with both dynamic and long-lasting PTMs to encode transcriptional programs. We hypothesize that PRMT1 and PRMT5 link inducible transcrip- tional activation to a persistent chromatin environment. This hypothesis is compatible with a feed-forward model of chromatin state maintenance, transferring gene activation through multiple histone PTMs. We will test this hypothesis in the following specific aims: 1) How is stable histone arginine methylation regulated by transi- ent PTMs? We will determine biochemical, enzymatic and structural mechanisms of PRMT1 and PRMT5 regu- lation by histone substrate PTMs, like acetylation and phosphorylation. 2) How do transient histone PTMs co- operate with PRMTs to regulate transcription? We will determine how PRMT1 or PRMT5 activity coupled with histone phosphorylation or acetylation affects inducible transcription. 3) Does inducible transcription establish a persistent chromatin environment? We will determine if inducible transcription is persistent past removal of the initial stimulus. The ultimate goal and overall impact of this proposed project is to determine how transcriptional and chromatin-based memory is established and maintained by combinatorial histone modifications. This study will provide mechanistic insight for the clinically critical glucocorticoid signaling pathways, and it will build new understanding of the understudied, but druggable, arginine methyltransferase family. This project will move the field forward in the following ways: 1) it will establish a new paradigm reconciling the long-standing debates over the role of histone PTMs in relationship to transcription factors in transcriptional regulation; 2) we will un- derstand the biochemical mechanisms and biological implications of crosstalk between transient histone PTMs and stable histone arginine methylation; 3) we will understand how hormone-inducible chromatin environments are both established and maintained.