The 3'-5' Exonuclease, TREX1, Interacts with Poly(ADP-ribose) Polymerase-1 (PARP1) in Response to DNA Damage

Recognition of nucleic acids plays a key role in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE). The major 3'-5' DNA exonuclease, TREX1, degrades single- and double-stranded DNA to minimize potential immune activation by persistent self or retroelement DNA. Mutations in the human TREX1gene have been linked to four diseases: SLE; Aicardi-Goutières syndrome (AGS); retinal vasculopathy and cerebral leukodystrophy (RVCL); and familial chilblain lupus (CBL). SLE, AGS and CBL have overlapping features characterized by expression of interferon-alpha and autoantibody production, but are distinct clinical conditions. RVCL is a non-inflammatory endotheliopathy.

As part of our efforts to determine the molecular mechanisms underlying TREX1 involvement in the pathogenesis of these diseases, we identified a novel TREX1-binding partner protein by Mass Spectrometry and Co-Immunoprecipitation (Co-IP) assays. We examined the interaction domains and the effects of mutations in TREX1 associated with these diseases.

We found that TREX1 interacted with poly(ADP-ribose) polymerase-1 (PARP1), a nuclear DNA repair enzyme involved in the DNA damage response. The interaction domain of PARP1 was mapped to the amino-terminal zinc finger domains. Subcellular localization analysis showed that TREX1 normally localized to the cytoplasm and cytomembranes, but translocated to the nucleus (with some bound to chromatin) in response to sublethal DNA damage. Co-IP assays revealed that the interaction was increased following DNA damage in concert with the post-translational PARlation of PARP1. Functional studies showed that TREX1 induced the PARlation of PARP1 in a TREX1 dose-dependent manner. Furthermore, siRNA knockdown of TREX1 promoted PARP1 cleavage and loss of PARP1 enzymatic activity, resulting in the induction of apoptosis. We further analyzed the effects of TREX1-PARP1 interaction in relation to the pathogenesis of AGS or RVCL. Co-IP assays revealed that the RVCL-related TREX1-mutant protein, V235fs, bound to PARP1 as well as wild-type TREX1, whereas the AGS-related R114H mutant protein did not bind PARP1.

These findings demonstrate that TREX1 contributes to the regulation of PARP1 in the DNA damage response and that mutation-induced alterations in the function of TREX1 may be a factor in the development or progression of these autoimmune diseases by affecting PARP1 activity.

No relevant conflicts of interest to declare.