The interplay between arginine dimethylation and ubiquitylation coordinates TDP1 proteostasis for the repair of topoisomerase I covalent complexes. Bhattacharjee et al

SUMMARY Tyrosyl-DNA phosphodiesterase (TDP1) hydrolyzes the phosphodiester bond between a DNA 3'-end and a tyrosyl moiety and is implicated in the repair of trapped topoisomerase I (Top1)-DNA covalent complexes (Top1cc). Protein arginine methyltransferase 5 (PRMT5) catalyzes methylation of TDP1 at residues R361 and R586. Here we establish mechanistic crosstalk between TDP1 arginine methylation and ubiquitylation, which is critical for TDP1 homeostasis and cellular responses to Top1 poisons. Using PRMT5 knockout cells, we show that loss of TDP1 arginine methylation results in an imbalance in TDP1 degradation with marked elevation of Top1cc-induced DNA breaks and cell death. We identify that R586 methylation promotes TDP1 ubiquitylation that facilitates ubiquitin/proteasome-dependent TDP1 turnover by impeding the binding of UCHL3 (deubiquitylase enzyme) with TDP1. Intriguingly, R586 dimethylation also enhances TDP1-XRCC1 binding and propagation of the DNA damage response through the recruitment of XRCC1 foci at Top1cc-damage sites. We further show R361 dimethylation enhances the 3'-phosphodiesterase activity of TDP1 in real-time fluorescence-based cleavage assays and this was rationalized using structural modeling. Together, our findings establish arginine methylation as a coregulator of TDP1 proteostasis and activity, which modulates the repair of trapped Top1cc.