Molecular basis for substrate recruitment to the PRMT5 methylosome

PRMT5 is an essential arginine methyltransferase and a therapeutic target in MTAP null cancers. PRMT5 utilizes adaptor proteins for substrate recruitment through a previously undefined mechanism. Here, we identify an evolutionarily conserved peptide sequence shared among the three known substrate adaptors (CLNS1A, RIOK1 and COPR5) and show it is necessary and sufficient for interaction with PRMT5. We demonstrate that PRMT5 uses modular adaptor proteins containing a common binding motif for substrate recruitment, comparable to other enzyme classes such as kinases and E3 ligases. We structurally resolve the interface with PRMT5 and show via genetic perturbation that it is required for methylation of adaptor-recruited substrates including the spliceosome, histones, and ribosome assembly complexes. Further, disruption of this site affects Sm spliceosome stability and activity, leading to intron retention. Genetic disruption of the PRMT5-substrate adaptor interface leads to a hypomorphic decrease in growth of MTAP null tumor cells in vitro and in vivo, and is thus a novel site for development of therapeutic inhibitors of PRMT5. 2 experimental conditions (WT or ADA treatment), in triplicate, of human HCT116 tumor cells. Please note that the published GSM2462895-GSM2462900 (in GSE93813) data has been re-analyzed as below and the re-analyzed 'prev_publish_*txt' data (is linked as Series supplementary files: The fastq files from the above mentioned previously published data was processed using rMATS turbo v4.1.1 with read length as 75 and gencode.v19.chr_patch_hapl_scaff.annotation.gtf gtf file to create tab delimited files recording events observed for each of the different alternate splicing events among the replicates and comparing them across the DMSO and EPZ015666 scenarios. The generated JC files for the 5 splicing events were used for further analysis.