The tumour suppression TP53 is mutated in over half of all cancers, resulting in mutant p53 protein accumulation and poor patient survival. Our recent study demonstrated that mutant p53 accumulation suppresses the expression of SLC7A11, the functional subunit of the cystine/glutamate antiporter, system xc-, through binding to the master antioxidant transcription factor NRF2. This diminishes glutathione synthesis, rendering mutant p53 tumour sensitive to further redox perturbations through system xc- inhibition. Whilst we attributed the capacity of mutant p53 to suppress SLC7A11 to a gain-of-function mechanism, this was complicated by studies suggesting that wild type p53 represses SLC7A11 via direct binding to the SLC7A11 promoter.
The aim of this study was to determine the mechanisms by which wild type p53 and mutant p53 regulate SLC7A11 expression in order to inform rationales for targeting mutant p53 cancers. To this end, we demonstrate by SLC7A11 promoter-reporter and chromatin immunoprecipitation studies that wild type p53 suppression of SLC7A11 is not mediated through direct transcriptional repression, and instead propose an indirect mechanism involving the prototypical oncogene, c-Myc. Furthermore, we refine the mechanism through which mutant p53 disrupts NRF2 function to transrepressses SLC7A11. We perform cellular subfractionation experiments to demonstrate that mutant p53 does not sequester NRF2 cytoplasmically, and chromatin immunoprecipitation studies following NRF2 knockdown, which demonstrate the requirement for NRF2 expression for mutant p53 recruitment to the SLC7A11 promoter. Given that wild type and mutant p53 to inhibit SLC7A11 transcription through differing molecular mechanisms, this study contributes valuable insight into the complexity of targeting mutant p53 cancers.