Asymmetric arginine dimethylation of heterogeneous nuclear ribonucleoprotein K by protein-arginine methyltransferase 1 inhibits its interaction with c-Src

Arginine methylation is a post-translational modification found in many RNA-binding proteins. Heterogeneous nuclear ribonucleoprotein K (hnRNP K) from HeLa cells was shown, by mass spectrometry and Edman degradation, to contain asymmetric N(G),N(G)-dimethylarginine at five positions in its amino acid sequence (Arg256, Arg258, Arg268, Arg296, and Arg299). Whereas these five residues were quantitatively modified, Arg303 was asymmetrically dimethylated in <33% of hnRNP K and Arg287 was monomethylated in <10% of the protein. All other arginine residues were unmethylated. Protein-arginine methyltransferase 1 was identified as the only enzyme methylating hnRNP K in vitro and in vivo. An hnRNP K variant in which the five quantitatively modified arginine residues had been substituted was not methylated. Methylation of arginine residues by protein-arginine methyltransferase 1 did not influence the RNA-binding activity, the translation inhibitory function, or the cellular localization of hnRNP K but reduced the interaction of hnRNP K with the tyrosine kinase c-Src. This led to an inhibition of c-Src activation and hnRNP K phosphorylation. These findings support the role of arginine methylation in the regulation of protein-protein interactions.