Defining function of wild-type and three patient-specific TP53 mutations in a zebrafish model of embryonal rhabdomyosarcoma

In embryonal rhabdomyosarcoma (ERMS) and generally in sarcomas, the role of wild-type and loss-or gain-of-function TP53 mutations remains largely undefined. Eliminating mutant or restoring wild-type p53 is challenging; nevertheless, understanding p53 variant effects on tumorigenesis remains central to realizing better treatment outcomes. In ERMS, >70% of patients retain wild-type TP53, yet mutations when present are associated with worse prognosis. Employing a kRAS^G12D-driven ERMS tumor model and tp53 null (tp53^-/-) zebrafish, we define wild-type and patient-specific TP53 mutant effects on tumorigenesis. We demonstrate that tp53 is a major suppressor of tumorigenesis, where tp53 loss expands tumor initiation from <35% to >97% of animals. Characterizing three patient-specific alleles reveals that TP53^C176F partially retains wild-type p53 apoptotic activity that can be exploited, whereas TP53^P153Δ and TP53^Y220C encode two structurally related proteins with gain-of-function effects that predispose to head musculature ERMS. TP53^P153Δ unexpectedly also predisposes to hedgehog-expressing medulloblastomas in the kRAS^G12D-driven ERMS-model.