Poster Presentation 32nd Lorne Cancer 2020

Yap reprograms de novo lipogenesis to fuel liver cancer (#342)

Talhah M Salmi 1 2 3 , Srimayee Vaidyanathan 1 2 , Malcolm J McConville 3 4 , Kristin K Brown 1 2 3 , Andrew G Cox 1 2 3
  1. Peter MacCallum Cancer Centre, Parkville, VIC, Australia
  2. Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC, Australia
  3. Department of Biochemistry and Molecular Biology, Bio21 Institute, University of Melbourne, Parkville, VIC, Australia
  4. Metabolomics Australia, Bio21 Institute, The University of Melbourne, Melbourne, VIC, Australia

Hepatocellular carcinoma (HCC) is the most common form of liver cancer, originating from liver cells known as hepatocytes. At the molecular level, HCC is driven by transcription factors which are able to reprogram metabolism to support tumorigenesis that are still poorly understood. The Yes-associated protein (Yap) is the nuclear effector of the Hippo pathway, responsible in regulating organ size control and metabolism. Metabolic reprogramming has recently emerged as a fundamental hallmark of cancer. In our previous studies, we found that Yap integrates the anabolic demands of tumour growth by reprogramming glutamine and glucose metabolism to support nucleotide biosynthesis. The central aim of this study was to determine the role that Yap plays in regulating lipid metabolism in the context of liver cancer. We took advantage of a larval zebrafish model in which a hyperactivated form of Yap is specifically expressed in hepatocytes (lf:YapS87A;lf:NLS-mcherry). We found that the expression of Yap was sufficient to stimulate de novo lipogenesis (DNL) and induce lipid droplet formation in hepatocytes (steatosis). To determine whether the stimulation of DNL was required for oncogenic growth, we exposed larvae to pharmacological inhibitors of DNL  and examined the impact on growth at the cellular level by multiphoton microscopy. Strikingly, we identified that fatty acid synthase (FAS) and steroyl-CoA desaturase (SCD) inhibitors suppressed Yap-driven growth. To complement these studies, we took a genetic approach using CRISPR to generate fas and scd KO zebrafish larvae and we found that Yap-driven growth required both FAS and SCD. Importantly both chemical and genetic suppression of FAS and SCD activity had no effect on normal liver growth. Together, these findings suggest that oncogenic Yap-driven growth is conditionally dependent upon the stimulation of DNL. Consequently, these studies provide a rationale for examining the clinical efficacy of DNL inhibitors to combat liver cancer.