Deep Protein Arginine Asymmetric Di-Methylation Profiling of Breast Cancer Patient-derived Xenografts

Arginine methylation catalyzed by protein arginine methyltransferases (PRMTs) is a prevalent posttranslational modification that regulates diverse cellular processes. Aberrant expression of type I PRMTs that catalyze asymmetric arginine demethylation (ADMA) is often found in cancer; however, little is known about the ADMA status of substrate proteins in tumors. Using LC-MS/MS along with pan-specific ADMA antibodies, we performed global mapping of ADMA in five patient-derived xenograft (PDX) tumors representing different subtypes of human breast cancer and identified 415 methylated peptides from 213 proteins. Approximately 70% of the putative substrates were validated using peptide arrays in vitro methylated by PRMT1, PRMT4, and PRMT6, among which 48% of substrates varied from estrogen receptor (ER) positive and negative tumors. Comparing with our previously identified ADMA sites from breast cancer cell lines, 75 ADMA sites overlapped between cell lines and PDX tumors. Collectively, this study provides a useful resource to PRMT and breast cancer communities to exploit the functions of PRMT dysregulation during breast cancer progression.