FY27 Determining Antimorphic Activity of T253I p53 Variant

Determining antimorphic activity of the T253I p53 variant Abstract: We identified a germline T253I mutation in the TP53 gene in an eight-month-old patient who presented with adrenocortical carcinoma. Our lab has been studying this mutation and its impact on the p53 protein, the tumor suppressor encoded by TP53. To date, we have documented that T253I p53 exhibits attenuated p53- mediated activity (https://doi.org/10.1101/2025.02.26.25322616). Molecular profiling of the patient’s tumor documented mixed expression of wild type (wt) and T253I p53, raising the possibility that T253I p53 may have inhibited wt p53 during oncogenesis. We are now interested to determine whether the T253I p53 mutant is antimorphic (dominant negative) to wt p53 in order to more fully understand its capacity to promote oncogenesis and tumor suppression in the germline state as occurred in our patient. Accordingly, we propose a series of experiments to determine if the T253I variant interferes with the function of wt p53. We developed an epitope- tagged p53 system (Myc-T253I p53, FLAG-wt p53) in which to test T253I’s capacity to bind wt p53 and key p53 binding partners such as MDM2 and to determine whether T253I reduces wt activity. We will also include Myc- tagged controls of known antimorphic p53 (R175H, R248W) and non-antimorphic (R337H) mutants to put the T253I mutation’s impact on p53 responses in context of other well-studied variants. These studies will determine whether the T253I mutation merely reduces the amount of functional p53 tumor suppressor protein in the cell (haploinsufficiency) or whether it produces a variant p53 protein capable of inhibiting the remaining wt allele’s function (antimorphic effect) to favor oncogenesis. Determining this will help clarify risk for cancer in the setting of heterozygous T253I p53 for this patient, her family and others harboring this germline variant. Lay summary of the proposal: We are interested in helping children who have inherited a gene that gives them a higher cancer risk. Our clinic provides medical care to several patients with “Li-Fraumeni Syndrome” (LFS), a genetic cancer syndrome associated with high lifetime cancer risk. We found a mutation in a gene called TP53, the gene associated with Li-Fraumeni syndrome, in one of our cancer patients and want to understand how and why this specific mutation, along with other mutations from our patients, causes cancer. We are doing this in order to understand why some Li-Fraumeni Syndrome patients get more cancers than others. Our hope is that through understanding the impact that specific TP53 mutations have on cells, we can better predict which patients will get cancer and allow us to be smarter in our cancer preventive care. This work may also lead to new ways to treat cancers that have specific TP53 mutations.