TDP1 serine 81 promotes interaction with DNA ligase IIIα and facilitates cell survival following DNA damage

Tyrosyl DNA phosphodiesterase (TDP1) is a DNA 3'-end processing enzyme that preferentially hydrolyses the bond between the 3'-end of DNA and stalled DNA topoisomerase 1. The importance of TDP1 is highlighted by its association with the human genetic disease spinocerebellar ataxia with axonal neuropathy. TDP1 comprises of a highly conserved C-terminus phosphodiesterase domain and a less conserved N-terminus tail. The importance of the N-terminus domain was suggested by its interaction with Lig3 alpha. Here we show that this interaction is promoted by serine 81 that is located within a putative S/TQ site in the N-terminus domain of TDP1. Although mutation of serine 81 to alanine had no impact on TDP1 activity in vitro and had little impact on the ability of TDP1 to mediate the rapid repair of CPT- or IR-induced DNA breaks in vivo, it led to marked reduction of protein stability. Moreover, it reduced the ability of TDP1 to promote cell survival following genotoxic stress. Together, our findings highlight a novel mechanism for regulating TDP1 function in mammalian cells that is not directly related to its enzymatic activity.