Variation at the R181 residue of p53 confer loss of p53 DNA binding cooperativity with the retention of mitochondrial-associated apoptosis

The p53 tumor suppressor binds DNA cooperatively as a tetramer, mediated by salt-bridge interactions between p53 residues E180 and R181. Variants at the R181 residue are one of the most commonly identified TP53 pathogenic variants by germline genetic testing. We show that families with TP53 p.R181H and p.R181C variants show an attenuated cancer risk phenotype compared to patients with classic Li Fraumeni Syndrome due to hotspot loss of function variants. Despite this phenotype, we find that p53 R181H and R181C variants have reduced ability to bind to p53 promotor target sequences and transactivate p53 target genes. We further show that p53 R181H and R181C retain wild-type p53 structure and tetramerization. In addition, R181-mutant cells undergo apoptosis through wild-type p53 activity at the mitochondria. These results indicate that retention of transcription-independent p53 tumor suppressor function may result in a reduced penetrance cancer risk syndrome in humans. RNA-sequencing of cancer cell lines (HCT116 colorectal and MCF7 breast cancer lines) CRISPR-engineered at the TP53 locus for the genotypes: TP53 +/-, TP53 R181H/-, and TP53 R181C/-. Triplicates of each cell type were cultured in a Nutlin-3a drug timecourse (Nutlin-3a activates TP53 pathways) for 0 hours (DMSO-treated), 8 hours, and 24 hours. RNA-seq was performed on each replicate for each sample to observe if the mutant p53 cell lines were able to induce p53 target genes after Nutlin-3a treatment.