Nonalcoholic fatty liver disease (NAFLD)-associated hepatocellular carcinoma (HCC) is the fastest growing cause of HCC and predicted to become the leading indication for liver transplantation. As liver transplantation remains a scarce resource, chemoprevention and early treatment are imperative. NAFLD patients represent a distinct high-risk population due to the challenges of HCC screening related to obesity, potential absence of elevated tumor markers, and the observation that 20-30% of cases occur in the absence of cirrhosis, who are not targeted for screening. Given that early detection is key in improved survival and receipt of curative treatment, understanding the mechanisms leading to NAFLD-related HCC have important clinical consequences. Although lipophilic statins have been associated with decreased HCC incidence, their chemo-preventative mechanism(s) remains elusive. Over the years, the YAP/TAZ cascade emerged as an important signal transduction pathway in the pathogenesis of HCC, and has been shown to be modulated by changes in intracellular lipids. Stearoyl- CoA desaturate (SCD), the rate limiting enzyme of monounsaturated fatty acids (MUFAs), is a key enzyme in the Hippo pathway that links YAP/TAZ to sterol regulatory element binding protein 1 (SREBP1) and mTORC1 in hepatocarcinogenesis. Using human liver bulk RNA sequencing studies of a prospective cohort of NAFLD/NASH patients undergoing bariatric surgery, we discovered a novel regulatory role of SCD by a long non-coding enhancer RNA. After characterizing the intracellular lipid pool with an SCD inhibitor, we next investigated the role of SCD on the YAP/TAZ pathway using an in vitro cell culture model and demonstrate SCD-dependent decrease on YAP protein and its target genes. Our preliminary data led us to hypothesize that SCD and monounsaturated to saturated fatty acid ratios regulate and are a point of convergence in the YAP/TAZ, mTORC1 and mevalonic acid pathways. In this proposal, we aim to delineate the mechanisms underpinning the role of lipids in HCC through the YAP/TAZ pathway. In Aim 1, we will study cellular sub-types in HCC and adjacent non-HCC human samples to identify how the YAP/TAZ pathway relates to lipid gene expression. Gene- environment interactions with statin use will also be investigated using the Million Veteran Program, to identify the sub-group of patients who would benefit from statin chemoprevention. In Aim 2, we test the hypothesize that statins and the mevalonic acid pathway regulate YAP/TAZ function through Rho in hepatocytes and patient- derived tumoroids. The effects of statin on cellular localization and phosphorylation of YAP/TAZ and the YAP/TEAD-regulated genes will be examined. We will determine if these effects are dependent on Rho or intracellular cholesterol/lipid metabolites. In Aim 3, the role of SCD on the regulation of YAP/TAZ, cell proliferation and migration in a panel of hepatocytes and cancer cells will be examined. These studies will ...