Identification Of Methylation Network Regulated By PRMT Family Proteins And Its Function And Molecular Mechanisms In Gene Alternative Splicing And Cancer Development

Although numerous substrates have been identified for Type Ⅰ and Ⅱ arginine methyltransferases(protein arginine methyltransferases,PRMTs),a full scope of substrates for the only type Ⅲ PRMT,PRMT7,and its connection with that of type Ⅰand Ⅱ PRMTs remains unknown.This study investigates the landscape of PRMT4-,PRMT5-,and PRMT7-mediated arginine methylation(methylome)using highresolution mass spectrometry.PRMT7-regulated mono-methylation at 297 arginine sites in 174 proteins revealed several features:PRMT7 predominantly methylates a consensus glycine and arginine motif,and multiple arginine methylation sites are found in a given protein,with phosphorylation sites in proximity.In addition,PRMT7regulated methylation sites and proximal sequences are vulnerable to cancer mutations.Moreover,PRMT7 regulates the methylation of biological pathways associated with spliceosome,RNA transport,mRNA surveillance pathway,and herpes simplex infection.We further revealed that PRMT4-,PRMT5-,and PRMT7-methylome shared a group of proteins implicated in mRNA splicing and co-regulated a cohort of alternative splicing events as evidenced by RNA-seq analysis.Arginine methylation by PRMT4,5 and 7 regulates the binding of the splicing factor hnRNPA1 with RNA directly,and therefore alternative splicing.In breast,colorectal,and prostate cancers,PRMT4,5,and 7 were upregulated and associated with high levels of hnRNPA1 arginine methylation and aberrant gene alternative splicing,thereby potentially driving cancer cell growth.Our findings demonstrate that the pharmacological inhibition of PRMT4,5,and 7 effectively suppressed the growth of breast,colon,and prostate cancer cells and that their co-treatment exhibited synergistic killing effects,thereby providing a new direction for cancer therapy.