The DNA repair function of BCL11A suppresses senescence and promotes continued proliferation of triple-negative breast cancer cells.

We identified the BCL11A protein in a proximity-dependent biotinylation screen performed with the DNA glycosylase NTHL1. In vitro, DNA repair assays demonstrate that both BCL11A and a small recombinant BCL11A^160-520 protein that is devoid of DNA binding and transcription regulatory domains can stimulate the enzymatic activities of two base excision repair enzymes: NTHL1 and DNA Pol β. Increased DNA repair efficiency, in particular of the base excision repair pathway, is essential for many cancer cells to proliferate in the presence of elevated reactive oxygen species (ROS) produced by cancer-associated metabolic changes. BCL11A is highly expressed in triple-negative breast cancers (TNBC) where its knockdown was reported to reduce clonogenicity and cause tumour regression. We show that BCL11A knockdown in TNBC cells delays repair of oxidative DNA damage, increases the number of oxidized bases and abasic sites in genomic DNA, slows down proliferation and induces cellular senescence. These phenotypes are rescued by ectopic expression of the short BCL11A^160-520 protein. We further show that the BCL11A^160-520 protein accelerates the repair of oxidative DNA damage and cooperates with RAS in cell transformation assays, thereby enabling cells to avoid senescence and continue to proliferate in the presence of high ROS levels.