Project Summary/Abstract Obesity is a prevalent global health problem, and it increases the overall risks of many types of chronic diseases and cancers. Nonalcoholic steatohepatitis (NASH) is a major liver complication of obesity, and importantly, the fastest growing etiology of hepatocellular carcinoma (HCC) with alarming future projections. However, how obesity and NASH contribute to the development of NASH-driven HCC is ill- defined, hindering the comprehensive understanding of the disease and the development of effective therapeutics. While p53 is a well-defined tumor suppressor, its involvement in NASH and associated HCC is poorly understood. In a dietary mouse model of NASH, p53 protein is initially stabilized in early stages of NASH but lost prior to tumorigenesis, while p53 loss is sufficient to promote HCC in mice with NASH. In human patients, NASH-driven HCCs from obese subjects display a lower frequency of genomic TP53 inactivation compared to lean ones, raising the idea that p53 functions are impaired by NASH that facilitates the progression to HCC without necessitating genomic p53 loss. The preliminary data suggest that obesity and NASH profoundly shape the cancer genotypes. The objective of this proposal is to understand how obesity and NASH influence the activity of p53, as well as the selective pressure against p53 to drive HCC. The central hypothesis is that p53 inhibition by NASH- associated cholesterol accumulation is an early and critical event linking NASH to tumorigenesis. The following specific aims are proposed to test the hypothesis: 1) to dissect the functions of p53 and senescence, and to identify p53 downstream effectors in suppressing NASH-driven HCC; 2) to determine the effects of cholesterol and cholesterol-lowering drug statin on p53 activity during NASH-to-HCC transition to elucidate a mechanism by which p53 is inhibited. These studies will apply a dietary mouse model of NASH and HCC along with the state-of-art tools of molecular biology and genetics. Findings from the studies will discover a potentially critical mechanism linking obesity and NASH to liver malignancy, as well as the novel biology of p53 and NASH. The results will also reveal new therapeutic possibilities to combat NASH-driven HCC, such as repurposing cholesterol-lowering drug and/or exploring new tractable targets within the p53 network.