The Mechanism Of Gene Transcriptional Activation By Arginine Methyltransferase CARM1

Protein Argine Methyltransferase4PRMT4(also called Coactivitor-Associated Arginine Methyltransferase1CARM1), which transfers the methyl group from S-adenosylmethionine (AdoMet) to the terminal guanidino nitrogens of arginine residues generating asymmetric ω-NG,N’G-dimethylarginine, is classified into the type I arginine methyltransferases. CARM1methylates arginines2/17/26at N-terminus and arginines128/129/131/134at C-terminus of histone H3, and histone H2A. Of note, arginines17and26at N-terminus of histone H3are the major target sites for CARM1, which plays a role in gene activation.The mechanism by which CARM1mediates transcriptional activation after methylating H3R17/R26remains to be elucidated, and our paper is aiming at the molecular mechanism.First, we found that histone H3peptide dramatically reduces its ability to bind some nucleoproteins in Hela NE pull-down assay when it is both acetylated and arginine-methylated on R17and R26of H3(Ac/mR-H3). The reduced nucleoproteins include some subunits of NuRD complex and members of TIF1family. Our hypothesis is that CARM1mediates transcriptional activation by reducing the recruitment of these transcriptional corepressors to histones. Then, we found that the level of corepressors which associated with chromatin increased in the CARM1knock out (KO) MEF cells compare to wide type (WT) MEF cells; When CARM1was knocking down (KD) in Hela cells, the level of corepressors which associated with chromatin increased compare to control cells. Moreover, the level of acetylated H3is lower in the KO and KD cells. Finally, we found that overexpression of CARM1dramatically stimulates the expression of PREP7-MMTV-luciferase reportor gene in the luciferase reportor assay. Moreover, using CHIP assay, we proved that the binding of these corepressors with gene promoter are lower in the CARM1overexpression cells compared to the control cells. So, we suggested that one of the mechanisms that CARM1mediates transcriptional activation is by reducing the recruitment of the corepressors to the transcriptional machinary.