The role of ZNRF3 and TP53 inactivation in adrenocortical tumorigenesis Authors list: 1- James Wilmouth Jr, 1- Julie Olabe, 2- Kaitlin J. Basham, 1- Laly Pucheu, 1- Florence Roucher-Boulez, 1- Cecily Lucas-Rodrigues, 1- Antoine Martinez, 2- Gary Hammer, & 1- Pierre Val Affiliations: 1- Génétique Reproduction et Développement, UMR 6293, Clermont-Ferrand Cedex, France 63000, 2- Endocrine Oncology Program, University of Michigan Rogel Cancer Center, Ann Arbor, MI 48109. Abstract: Adrenocortical carcinoma (ACC) is an infrequent and aggressive cancer that originates from steroidogenic cells within the adrenal cortex. Half of patients present with metastatic spread at initial diagnosis, resulting in a low 5-year survival rate. Recent genomic analysis identified the most common alteration in ACC as inactivation of the transmembrane E3 ubiquitin-ligase Zinc and Ring Finger 3 (Znrf3), a potent tumor suppressor responsible for regulating the WNT/beta-catenin pathway. In order to study the role of Znrf3 inactivation in the adrenal cortex, we generated a steroidogenic factor-1 (Sf-1) Cre mediated Znrf3 knockout mouse model. The resulting mice developed hyperplasia associated with moderate increase in WNT/beta-catenin signaling by 6 weeks; however, this was followed by regression characterized by the induction of senescence and immune recruitment. In an attempt to surpass this senescent phenotype, we developed a mouse model derived from the most aggressive subgroup of ACC, composed of p53 & Znrf3 inactivation. TP53 is involved in p21-induced senescence, therefore we hypothesize that p53 ablation in the context of Znrf3 inactivation will surpass the senescent phenotype and allow tumorigenesis to proceed. We show that inactivation of p53 & Znrf3 in the mouse adrenal cortex does not completely surpass the immune recruitment and senescent phenotype caused by Znrf3 inactivation alone; however, these double KOs eventually form aggressive carcinomas that metastasize to the lungs, liver, and peritoneal. Interestingly, these aggressive tumors are associated with immune cell exclusion at primary and potentially secondary locations. Our current aim is to use this ACC mouse model to further investigate whether immune exclusion is required for tumor progression, and whether steroid secretion plays a role in this process.