Yin Yang 1 facilitates hepatocellular carcinoma cell lipid metabolism and tumor progression by inhibiting PGC-1β-induced fatty acid oxidation

Lipid accumulation is a driving force in tumor development, as it provides tumor cells with both energy and the building blocks of phospholipids for construction of cell membranes. Aberrant homeostasis of lipid metabolism has been observed in various tumors; however, the molecular mechanism has not been fully elucidated. Methods: Yin yang 1 (YY1) expression in hepatocellular carcinoma (HCC) was analyzed using clinical specimens, and its roles in HCC in lipid metabolism were examined using gain- and loss-of function experiments. The mechanism of YY1 regulation on peroxisome proliferator-activated receptor gamma coactivator-1 beta (PGC-1 beta) and its downstream genes medium-chain acyl-CoA dehydrogenase (MCAD) and long-chain acyl-CoA dehydrogenase (LCAD) were investigated using molecular biology and biochemical methods. The role of YY1/ PGC-1 beta axis in hepatocarcinogenesis was studied using xenograft experiment. Results: This study showed that YY1 suppresses fatty acid beta-oxidation, leading to increase of cellular triglyceride level and lipid accumulation in HCC cells, and subsequently induction of the tumorigenesis potential of HCC cells. Molecular mechanistic study revealed that YY1 blocks the expression of PGC-1 beta an activator of fatty acid beta-oxidation, by directly binding to its promoter; and thus downregulates PGC-1 beta/MCAD and PGC1-beta/LCAD axis. Importantly, we revealed that YY1 inhibition on PGC-1 beta occurs irrespective of the expression of hypoxia-inducible factor-1 alpha(HIF1-alpha), enabling it to promote lipid accumulation under both normoxic and hypoxic conditions. Conclusion: Our study reveals the critical role of YY1/PGC-1 beta axis in HCC cell lipid metabolism, providing novel insight into the molecular mechanisms associated with tumor cell lipid metabolism, and a new perspective regarding the function of YY1 in tumor progression. Thus, our study provides evidences regarding the potential of YY1 as a target for lipid metabolism-based anti-tumor therapy.