Arginine methylation of hnRNPK negatively modulates apoptosis upon DNA damage through local regulation of phosphorylation

Abstract

Heterogeneous nuclear ribonucleoprotein K (hn- RNPK) is an RNA/DNA-binding protein involved in chromatin remodeling, RNA processing and the DNA damage response. In addition, increased hnRNPK expression has been associated with tumor development and progression. A variety of post-translational modifications of hnRNPK have been identified and shown to regulate hnRNPK function, including phosphorylation, ubiquitination, sumoylation and methylation. However, the functional significance of hn- RNPK arginine methylation remains unclear. In the present study, we demonstrated that the methylation of two essential arginines, Arg296 and Arg299, on hnRNPK inhibited a nearby Ser302 phosphorylation that was mediated through the pro-apoptotic kinase PKCδ. Notably, the engineered U2OS cells carrying an Arg296/Arg299 methylation-defective hn- RNPK mutant exhibited increased apoptosis upon DNA damage. While such elevated apoptosis can be diminished through addition with wild-type hn- RNPK, we further demonstrated that this increased apoptosis occurred through both intrinsic and extrinsic pathways and was p53 independent, at least in part. Here, we provide the first evidence that the arginine methylation of hnRNPK negatively regulates cell apoptosis through PKCδ-mediated signaling during DNA damage, which is essential for the antiapoptotic role of hnRNPK in apoptosis and the evasion of apoptosis in cancer cells.