Basal p53 activity is differentially impacted by individual mutations, defining the immediate response to genotoxicity

Abstract

Genotoxicity induces p53 to coordinate a cellular response, however basal p53 activity preserves genome integrity by maintaining low expression of its target genes that scan the DNA and quickly repair damage. Acquired p53 mutations disrupt this regulation and the cellular capacity to respond effectively to environmental insults. Three breast cancer cell lines with different p53 status: wild type (MCF-7) and mutated in the DNA binding domain (R280K, MDA-MB231) and (L194F, T47D) are used to identify an unbiased high-confidence subset of direct p53-target-genes. Expression of these genes is differentially impacted by the mutations in resting conditions, with a strongly reduced overall p53 activity in MDA-MB231 and mildly in T47D. Short exposure to 4NQO is used to induce DNA adducts without p53 activation as confirmed by limited changes in p53-target-gene expression. MDA-MB231 show dysfunctional DNA repair and G1 checkpoint while T47D maintain some DNA repair capacity. Both mutant lines have increased survival to genotoxicity, particularly T47D, compared to MCF-7, consistent with a different effect on p53 function and cell homeostasis. Clinical data for mutations in these residues suggests that in the balance of tumour progression impaired DNA repair is more important than proliferation and these pathways are differentially affected by specific mutations.