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Targeting PRMT1-mediated SRSF1 Methylation to Suppress Exon Inclusion within Oncogenic Transcripts and Breast Tumorigenesis

ABSTRACT: PRMT1 is highly expressed in breast tumors, and has been suggested to play a vital role in breast tumorigenesis, but the underlying molecular mechanisms remain to be fully characterized. Here, we reveal that PRMT1 exhibits a wide-spreading role in RNA alternative splicing based on transcriptome analysis, with a preference for exon inclusion in a large cohort of oncogenic genes. Profiling PRMT1 methylome reveals that the arginine/serine-rich splicing factor SRSF1 is heavily arginine-methylated by PRMT1, which is critical for SRSF1 phosphorylation, SRSF1 binding with RNA, and PRMT1-induced exon inclusion. In breast tumors, the overexpression of PRMT1 is associated with high levels of SRSF1 arginine methylation and aberrant exon inclusion in those oncogenic genes. Accordingly, PRMT1-mediated SRSF1 methylation and exon inclusion events are found to be critical for the malignant behaviors of breast cancer cells. Furthermore, we identified and characterized a selective PRMT1 inhibitor iPRMT1, which is potent in inhibiting PRMT1-mediated SRSF1 methylation and exon inclusion events, and breast cancer cell growth both in vitro and in vivo. Combination treatment with iPRMT1 and inhibitor targeting SRSF1 phosphorylation, SPHINX31 or SRPIN340, exhibits synergistic effects on suppressing breast cancer cell growth, strengthening the cross-talk between arginine methylation and phosphorylation in SRSF1. In conclusion, our data uncover a key mechanism underlying PRMT1-mediated gene alternative splicing, demonstrating targeting PRMT1 has great potential to treat breast cancer in clinic.

ORGANISM(S): Homo sapiens

PROVIDER: GSE212049 | GEO | 2023/10/02

REPOSITORIES: GEO

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Project description:Protein methylation has been implicated in many important biological contexts including signaling, metabolism, and transcriptional control. Despite the importance of this post- translational modification, the global analysis of protein methylation by mass spectrometry-based proteomics has not been extensively studied due to the lack of robust, well-characterized techniques for methyl-peptidemethyl peptide enrichment. Here, to better investigate protein methylation, we optimized and compared two methods for methyl-peptidemethyl peptide enrichment: immunoaffinity purification (IAP) and high pH strong cation exchange (SCX). Comparison of these methods revealed that they are largely orthogonal for monomethyl arginine (MMA), suggesting that the usage of both techniques is required to provide a global view of protein methylation. Using both IAP and SCX, we investigated changes in protein methylation downstream of protein arginine methyltransferase 1 (PRMT1). Together, these techniques allowed us to quantify over ~1,000 arginine methylation sites on 407 proteins. Of these methylation sites, PRMT1 knockdown resulted in significant changes to 110 arginine methylation sites on 59 proteins. In contrast, zero lysine methylation sites were significantly changed upon PRMT1 knockdown. In PRMT1 knockdown cells, 24 MMA sites exhibited both significant downregulation (ie, putative PRMT1-mediated MMA targets) and 63 significant upregulation (ie, putative PRMT1-mediated ADMA targets). PRMT1 knockdown induced significant changes in asymmetric dimethyl arginine (ADMA), consistent with being PRMT1 targets. Additionally, We also observed that PRMT1 knockdown induced significant increases in symmetric dimethyl arginine (SDMA) methylation, suggesting that loss of PRMT1 activity allows scavenging of PRMT1 substrates by Type II PRMTs. Analysis of the subcellular localization and protein function of the significantly changing methyl-proteins revealed that the majority of PRMT1 substrates are localized to the nucleus and involved in RNA and DNA binding. Taken together, our results suggest that deep protein methylation profiling by mass spectrometry requires orthogonal enrichment techniques, identify novel PRMT1 methylation targets, and highlight in order to understand the dynamic interplay between methyltransferases in mammalian cells.

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Targeting PRMT1-mediated SRSF1 Methylation to Suppress Exon Inclusion within Oncogenic Transcripts and Breast Tumorigenesis

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