XRCC1 protects transcription from toxic PARP1 activity during DNA base excision repair

Marek Adamowicz,Keith W Caldecott,Emilia Komulainen,Amit Gautam,Jan Brazina,Richard Hailstone,Hana Hanzlikova,Annie A Demin,Sophie E Wells

doi:10.1038/s41556-021-00792-w

Abstract

Genetic defects in the repair of DNA single-strand breaks (SSBs) can result in neurological disease triggered by toxic activity of the single-strand-break sensor protein PARP1. However, the mechanism(s) by which this toxic PARP1 activity triggers cellular dysfunction are unclear. Here we show that human cells lacking XRCC1 fail to rapidly recover transcription following DNA base damage, a phenotype also observed in patient-derived fibroblasts with XRCC1 mutations and Xrcc1−/− mouse neurons. This defect is caused by excessive/aberrant PARP1 activity during DNA base excision repair, resulting from the loss of PARP1 regulation by XRCC1. We show that aberrant PARP1 activity suppresses transcriptional recovery during base excision repair by promoting excessive recruitment and activity of the ubiquitin protease USP3, which as a result reduces the level of monoubiquitinated histones important for normal transcriptional regulation. Importantly, inhibition and/or deletion of PARP1 or USP3 restores transcriptional recovery in XRCC1−/− cells, highlighting PARP1 and USP3 as possible therapeutic targets in neurological disease.

Highlights

Genetic defects in the repair of DNA single-strand breaks (SSBs) can result in neurological disease triggered by toxic activity of the single-strand-break sensor protein poly-ADP-ribose polymerase 1 (PARP1)
The lack of transcription recovery in XRCC1−/− cells was accompanied by a progressive loss of RNA polymerase I (RNAPI) foci (RPA194; Fig. 1a,c)
Given that we did not detect a reduction in the global levels of RPA194 in the XRCC1−/− cells, this most probably reflected the dissociation of RNAPI from nucleolar sites of ribosomal RNA transcription rather than degradation of the RNAP (Extended Data Fig. 1a)

Summary

Introduction

Genetic defects in the repair of DNA single-strand breaks (SSBs) can result in neurological disease triggered by toxic activity of the single-strand-break sensor protein PARP1. We show that human cells lacking XRCC1 fail to rapidly recover transcription following DNA base damage, a phenotype observed in patient-derived fibroblasts with XRCC1 mutations and Xrcc1−/− mouse neurons This defect is caused by excessive/aberrant PARP1 activity during DNA base excision repair, resulting from the loss of PARP1 regulation by XRCC1. We show that aberrant PARP1 activity suppresses transcriptional recovery during base excision repair by promoting excessive recruitment and activity of the ubiquitin protease USP3, which as a result reduces the level of monoubiquitinated histones important for normal transcriptional regulation. Either PARP1 or USP3 inhibition/depletion rescue normal levels of histone monoubiquitination and transcription recovery following DNA base damage, highlighting these enzymes as possible therapeutic targets in the treatment of base excision repair (BER)-defective neurological disease

Methods

Results

Conclusion