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PRMT5 interacting partners and substrates in oligodendrocyte lineage cells

ABSTRACT: The protein arginine methyl transferase PRMT5 is an enzyme expressed in oligodendrocyte lineage cells and responsible for the symmetric methylation of arginine residues on histone tails. Previous work from our laboratory identified PRMT5 as critical for myelination, due to its transcriptional regulation of survival and early stages of differentiation. However, besides its nuclear localization, PRMT5 is found at high levels in the cytoplasm of oligodendrocyte progenitor cells (OPCs) and yet, its interacting partners and non-histone substrates in this lineage, remain elusive. By using mass spectrometry on protein eluates from extracts generated from OPC and immunoprecipitated with PRMT5 antibodies, we identified 1116 proteins as PRMT5 interacting partners. These proteins are related to molecular functions such as RNA binding, ribosomal structure, nucleotide binding, cadherin and actin binding, GTP and GTPase activity. We then investigated PRMT5 substrates using iTRAQ-based proteomics on protein samples isolated from CRISPR-PRMT5 knockdown immortalized oligodendrocyte progenitors compared to CRISPR-EGFP controls. This analysis identified 169 peptides with statistically different symmetric methylation of arginine residues in the two groups. Those peptides led to 30 unique non-histone substrates of PRMT5. The majority of these proteins were consistent with PRMT5 substrates, previously identified in distinct cancer cell lines (e.g. the transcription factor ZN326), and were functionally related to RNA processing and transport, splicing, regulation of mRNA stability and transcription. In addition, we detected three substrates as unique to the oligodendrocyte lineage and not identified in cancer cells. They included the proline-rich protein PRC2C, involved in methyl-RNA binding, the RNA binding protein KHDR2, regulating splicing events and the heterogeneous nuclear RNA binding protein HNRPD, involved in regulation of RNA stability. Together, these results highlight a cell-specific role of PRMT5 in regulating, not only transcription, but RNA processing and translation in OPCs. (287 WORDS)

INSTRUMENT(S): LTQ Orbitrap Velos Pro

ORGANISM(S): Mus Musculus (ncbitaxon:10090)

SUBMITTER: Patrizia Casaccia

PROVIDER: MSV000088396 | MassIVE | Tue Nov 16 12:23:00 GMT 2021

REPOSITORIES: MassIVE

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Project description:Protein arginine methylation, catalyzed by the protein arginine methyltransferase (PRMT) family, is recognized as a widespread post-translational modification (PTM) with implications in a plethora of biological processes in eukaryotes. PRMT proteins were classified into three types, type I, II and III, according to the final methyl-arginine products generated. Despite that thousands of substrates have been identified for Type I and II PRMTs, a full scope of arginine methylation catalyzed by the only type III PRMT, PRMT7, as well as its connection with that of type I and II PRMTs remain unknown, limiting our understanding of the network of arginine methylation and its functions in cells. In this study, global profiling of PRMT4 (type I), PRMT5 (type II) and PRMT7 (type III) substrates (also referred as methylome) revealed that PRMT7 methylated a GAR (glycine and arginine) motif similar as PRMT5, while PRMT4 uniquely methylated a motif in which proline was highly enriched. PRMT4, 5 and 7-methylome were all enriched with proteins functioning in mRNA splicing, and knockdown of PRMT4, 5 or 7 led to a global change of alternative splicing events, among which a cohort with implications in cancer development was co-regulated by all three PRMTs. PRMT4, 5 and 7-mediated arginine methylation on splicing factors such as hnRNPA1, though at different status, were shown to enhance RNA binding in general and participate in the regulation of PRMT4, 5 and 7 co-regulated alternative splicing events.The clinical significance of PRMT4, 5 and 7-mediated arginine methylation was underscored by the fact that these three PRMTs as well as hnRNPA1 arginine methylation were over-represented in multiple types of cancers, which were associated with aberrant gene alternative splicing. Consistently, silencing or pharmacological inhibition of PRMT4, 5 and 7 altered gene alternative splicing and suppressed cancer cell growth, and co-treatment exhibited synergistic effects. Taken together, our study provided an integrative view of substrates for the three types of PRMTs, revealing the important function of arginine methylation in RNA splicing and cancer.

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PRMT5 interacting partners and substrates in oligodendrocyte lineage cells

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