Variation at the R181 residue of p53 confers 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 identified TP53 pathogenic variants by germline genetic testing. We show that families with TP53 p.R181H and p.R181C variants have an attenuated cancer risk phenotype compared to patients with hotspot dominant negative loss of function TP53 variants. Despite this phenotype, we find that p53 R181H and R181C variants have significantly reduced ability to bind to p53 promoter/enhancer target sequences and transactivate p53 target genes, similar to null variants. However, 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 results in a reduced penetrance cancer risk syndrome in humans. Statement of SignificanceInherited TP53 variants cause Li-Fraumeni Syndrome (LFS), which has significant phenotypic heterogeneity in lifetime cancer risk. Our study shows that retention of transcription-independent p53 functions, despite loss of p53 transactivation activity, results in a reduced penetrance phenotype. Classification of TP53 variants should incorporate assays of transcriptional and non-transcriptional functions.