PRMT2 Links Histone H3R8 Asymmetric Dimethylation To Oncogenic Activation And Tumorigenesis Of Glioblastoma

BackgroundGlioblastoma multiforme(GBM)is the most common and aggressive form of malignant astrocytoma(grade IV),with a median survival time of 15 months following diagnosis.Transcriptional deregulation plays a vital role in Glioblastoma multiforme(GBM).Thus,identification of epigenetic modifiers essential for oncogenic transcriptional programs is a key to designing effective therapeutic strategies for this deadly disease.In the past decades,lysine methylations on histones and the lysine methytransferases(KMTs)have been intensively studied.In contrast,the roles of protein arginine methyltransferases(PRMTs)as epigenetic regulators in cancers are poorly understood.Methods1.We first take advantage of TCGA and CGGA datasets to get insight into the expression profilings of catalytically active PRMTs in glioma samples and their values in prognosis.By means of immunohistochemistry staining and cell proliferation assays,we focus our following investigations on PRMT2 in GBM pathogenesis.2.We take advantage of cell proliferation assays and Limiting Dilution assay to elucidate the role of PRMT2 in proliferation of GBM and the self-renewal of GSCs.We established orthotopic models,PRMT2 downregulation results in tumor volumes and the survival as detected by the bioluminescence imaging.3.Performe RNA sequencing(RNA-seq)to identify transcripts differentially expressed upon PRMT2 knockdown.The expression of several representative genes are validated by qRT-PCR analysis and WB assays.4.We next explored the distribution of H3R8me2 a in the genome through an optimized ChIP protocol.Than we combine ChIP-seq and RNA-seq analysis to examine how the loss of PRMT2-mediated H3R8me2 a correlates with changes of the target gene capture a clearer picture of this not well-characterized histone mark,we compared the H3R8me2 a enrichment profile with the genomic distributions of well-known histone modificationsResultHere we show that PRMT2 is highly expressed in GBM,which is correlated with poor prognosis.The silencing of PRMT2 inhibits GBM cell growth and glioblastoma stem cell self-renewal in vitro and suppreses orthotopic tumor growth.Transcriptome analysis demonstrated that PRMT2 depletion leads to significant deregulation of genes mainly associated with cell cycle progression and pathways in cancer.In agreement with previously published results,we show that PRMT2 is responsible for H3R8 asymmetric methylation(H3R8me2a)and that H3R8me2 a enrichment at promoters and enhancers is closely correlated with known active histone marks.Furthermore,we show that PRMT2-mediated H3R8me2 a is required for the maintenance of target gene expression and that the catalytic activity of PRMT2 is required for its protumorigenic functions.ConclusionThis study demonstrates that the elevated expression level of PRMT2 is an indicator of the GBM aggressiveness and PRMT2 acts as a transcriptional co-activator for oncogenic gene expression programs in GBM pathogenesis and provides a rationale for PRMT2 targeting in aggressive gliomas.