Squalene epoxidase drives NAFLD-induced hepatocellular carcinoma and is a pharmaceutical target

Abstract

Nonalcoholic fatty liver disease (NAFLD)-induced hepatocellular carcinoma (HCC) is an emerging malignancy in the developed world; however, mechanisms that contribute to its formation are largely unknown, and targeted therapy is currently not available. Our RNA sequencing analysis of NAFLD-HCC samples revealed squalene epoxidase (<i>SQLE</i>) as the top outlier metabolic gene overexpressed in NAFLD-HCC patients. Hepatocyte-specific <i>Sqle</i> transgenic expression in mice accelerated the development of high-fat, high-cholesterol diet-induced HCC. <i>SQLE</i> exerts its oncogenic effect via its metabolites, cholesteryl ester and nicotinamide adenine dinucleotide phosphate (NADP⁺). Increased <i>SQLE</i> expression promotes the biosynthesis of cholesteryl ester, which induces NAFLD-HCC cell growth. <i>SQLE</i> increased the NADP⁺/NADPH (reduced form of NADP⁺) ratio, which triggered a cascade of events involving oxidative stress-induced DNA methyltransferase 3A (DNMT3A) expression, DNMT3A-mediated epigenetic silencing of PTEN, and activation of AKT-mTOR (mammalian target of rapamycin). In human NAFLD-HCC and HCC, <i>SQLE</i> is overexpressed and its expression is associated with poor patient outcomes. Terbinafine, a U.S. Food and Drug Administration-approved antifungal drug targeting <i>SQLE</i>, markedly inhibited <i>SQLE</i>-induced NAFLD-HCC cell growth in NAFLD-HCC and HCC cells and attenuated tumor development in xenograft models and in <i>Sqle</i> transgenic mice. Suppression of tumor growth by terbinafine is associated with decreased cholesteryl ester concentrations, restoration of PTEN expression, and inhibition of AKT-mTOR, consistent with blockade of SQLE function. Collectively, we established <i>SQLE</i> as an oncogene in NAFLD-HCC and propose that repurposing SQLE inhibitors may be a promising approach for the prevention and treatment of NAFLD-HCC.