DTX3L and USP28 fine-tune DNA double strand repair through mutual regulation of their protein levels

The DNA damage response involves a complex protein network with members mediating different post-translational modifications such as ubiquitination and deubiquitination. Thereby the E3 ubiquitin ligase DTX3L as well as the deubiquitinase USP28 are recruited especially to DNA double strand breaks (DSBs) suggesting mutual functional interactions. Here we present evidence for the existence of such crosstalk. Mechanistically we show that DTX3L interacts directly with USP28 and ubiquitinates it, which leads to its proteasomal degradation. Vice versa, USP28 can remove those polyubiquitin chains from itself as well as from autoubiquitinated DTX3L. Consequently, these mutual regulatory interactions between DTX3L and USP28 affected DSB repair activities. Analysis of distinct DSB repair pathways reveals synthetic dysfunction of canonical non-homologues end joining (NHEJ) and homologous recombination (HR), upon USP28 and DTX3L double knockdown, suggesting cooperation between these proteins. Conversely, error-prone microhomology-mediated end joining (MMEJ) requires USP28 to counterbalance the antagonistic DTX3L effect. Together, the present data indicate that DTX3L and USP28 are under mutual control to fine-tune the capacity and quality of the cellular responses to stresses such as DNA damage.