Arginine Methyltransferase PRMT7’s Regulation On Stemness Transcription Factors And Effect On Embryonic Stem Cells

Arginine Methyltransferases 7 (PRMT7) is a member of the arginine methyltransferases family which catalyzed the reaction of transferring a methyl group from S-Adenosyl Methionine to the arginine group of the substrate proteins. This post-translational modification is very important and has many biological functions, including transcriptional regulation, RNA synthesis, DNA repair, and signal transduction. Although a lot of studies are done on the substrates and functions of PRMT1, PRMT4, PRMT5 and PRMT6, relatively little is known about the other members in the PRMT family. This thesis is focused on PRMT7, which is highly expressed in ES cells but still lack of the knowledge on its physiological function.Embryonic stem cells (ESCs) are derived from the inner cell mass of early embryos. They have the ability of self-renewal and pluripotency. ESCs can differentiate into all types of cells upon induction. The core transcription factors SOX2, OCT4, C-MYC and KLF4 play indispensable roles on the maintenance of ESCs pluripotency. Thus, the protein levels and transcriptional activities of these factors must be accurately regulated. Our goal is to study the effect of PRMT7 on these core factors in order to better understand its role in ESCs pluripotency.We first check the endogenous protein level of PRMT7 in different cell lines, and find that PRMT7 is highly expressed in ESCs. The level of PRMT7 is decreased after ESCs is induced for differentiation. To further investigate the effect of PRMT7 on ESCs pluripotency, we perform siRNA knockdown experiments. We observe increased level of ESCs differentiation upon PRMT7 knockdown. Thus, PRMT7 maybe involve in ESCs pluripotency maintenance. Next we check the effect of PRMT7 on transcriptional activity and posttranslational modification on the core factor OCT4 in order to reveal the potential role of PRMT7. We observe that PRMT7 can interact with OCT4 both in vitro and in vivo as well as some other core factors. Luciferase Reporter assays show that PRMT7 could specifically activate the transcriptional activity of OCT4 but not SOX2 or KLF4. In addition, we purified GST-PRMT7 proteins and detect the automethylation of PRMT7 in an in vitro methylation assay. In general, this thesis reveals that PRMT7 regulates OCT4 and is involved in ES cell pluripotency maintenance.