Structural basis for nuclear import defects of mutant p53 in cancer

TP53 is a tumour suppressor gene commonly mutated in cancer. As a transcription factor, the activity of p53 depends on its localisation into the nucleus. Previously, efforts have been made to characterise the nuclear localisation sequence (NLS) that enables translocation of p53 from the cytosol into the nucleus upon its activation. Surprisingly, to date there is still debate around the exact mechanism for the nuclear import of p53, including for its preference of nuclear import shuttle protein. Here, we describe a high-resolution protein crystal structure of the p53 NLS bound to Importin-alpha (IMPA), confirming that p53 exhibits a bona-fide bipartite NLS. Importantly, using p53 tumour databases we identified clinically relevant mutations in the NLS of p53 in a variety of cancers, potentially interfering with the binding of mutant p53 to IMPA. Confirming this, we performed biochemical binding assays in vitro and show that mutations in the NLS of p53 block binding to IMPA in both, the minor and major IMPA NLS-binding pocket. Since the majority of p53 mutations occur in the DNA-binding domain of the protein, targeting the nuclear entry of mutant p53 utilising structure-guided gene editing approaches represents a potential novel therapeutic strategy.