Updated publication reference for PubMed record(s): 30940768. Protein arginine methyltransferases (PRMTs) catalyze arginine methylation, an abundant post-translational modification occurring on both chromatin-bound and cytoplasmic proteins. Growing evidence supports the involvement of PRMT5, the major Type II PRMT, in pro-survival and differentiation pathways, important during development and to promote tumorigenesis. Thus, PRMT5 emerges as an attractive drug target and inhibitors are currently in clinical trials for cancer therapy. However, the knowledge of PRMT5 non-histone substrates is still limited, as are the dynamic changes in methylation levels upon its inhibition. Here, we employed a newly established pipeline coupling SILAC with methyl-peptides immuno-enrichment to globally profile arginine methylation following PRMT5 inhibition by GSK591 and adopted the heavy-methyl SILAC as orthogonal validation method to reduce false discovery rate. Then, in vitro methylation assays on a set of PRMT5 targets provided novel mechanistic insights into its strict preference to methylate arginine sandwiched between two neighbouring glycines (GRG). In conclusion, we identified novel PRMT5 substrates, thus providing the first proof of concept of the in vivo efficacy of PRMT5 inhibitor that impacts on arginine methylation beyond histones.