Geranylgeranyl Diphosphate Synthase(GGPPS)Regulates Hepatocellular Carcinogenesis By Targeting Glucose Metabolism

Liver cancer is the second leading cause of cancer mortality worldwide and hepatocellular carcinoma(HCC),the predominant form of liver cancer,arises from complex interplay of risk factors,including environmental carcinogens,hepatitis virus,alcohol and obesity,etc.Though great advances in developing targeted therapies have led to continuously increasing cancer survivors,long-term prognosis after current treatments remains poor due to the instability and heterogeneity of tumor cells.Thus illuminating the mechanisms underlying hepatocellular carcinogenesis will benefit the exploration of preventive therapies.Emerging evidence suggests that cellular metabolism reprogramming is the driving force of tumorigenesis.In the 1920s,Otto Warburg found that tumor cells preferred to metabolize glucose by glycolysis instead of oxidative phosphorylation.Altered hepatic glycolysis can lead to complicated disorders,including non-alcoholic fatty liver disease(NAFLD),fibrosis and HCC.Altered mevalonate pathway has received less attention but are increasingly being recognized.The mevalonate pathway is a highly conserved metabolic cascade,which converts mevalonate into sterol isoprenoids,such as cholesterol and steroid hormones,and non-sterol isoprenoids,such as farnesyl pyrophosphate(FPP)and geranylgeranylpyrophosphate(GGPP),serving as substrates for protein prenylation.Geranylgeranyl diphosphate(GGPPS)is a branch point enzyme in the downstream of the mevalonate pathway that catalyzes the synthesis of GGPP from FPP.Our previous work have revealed it as central insulin regulator in skeletal muscle and β-cell.Additionally,we also reported that GGPPS predicted the biological character of HCC in patients with cirrhosis and participated in the regulation of CCl4-induced liver fibrosis.However,the exact function of GGPPS in HCC development is still unknown.In this study,we use diethylnitrosamine(DEN)and high-fat-diet to mimic DNA damage-and NAFLD-associated hepatocellular carcinogenesis,respectively and analyze role of GGPPS in hepatic metabolism reprogramming during tumorigenesis induced by different challenges.Here we show that carcinogen induces expression of GGPPS through DNA-damage-inducible transcript 3(DDIT3).The reduction of GGPPS predicts poor survival of HCC patients.Besides,under carcinogenic stress,liver-specific deletion of Ggpps accelerates hepatocellular carcinogenesis via rerouting glucose toward the pentose phosphate pathway(PPP).Dietary supplement with DHEA,an inhibitor of glucose-6-phosphate dehydrogenase(G6PD),suppresses tumor incidence induced by Ggpps knockout.Notably,GGPPS inhibits activity of G6PD through direct binding and decreasing its active dimer.Taken together,our results reveal that GGPPS reduction accelerates HCC development via rerouting glucose toward PPP through directly interaction with G6PD,providing a novel non-prenylation way of GGPPS in tumor metabolic interplay.Clinic data implies that reduced GGPPS expression predicts advanced stage of NAFLD and recurrence of NAFLD-associated HCC.Based on above role of GGPPS in metabolism reprogramming under DNA damage-associated HCC development,we use HFD and CCl4 to mimic NAFLD/fibrosis/HCC process and help to investigate role of GGPPS in NAFLD progression.Long-term HFD overloading decreases GGPPS expression in mice.Seahorse extracellular flux analysis indicates that Ggpps knockdown impairs mitochondrial respiration of hepatocytes,whereas increases glycolysis.Proteomic profiles of wild type(WT)and liver-specific Ggpps knockout(KO)primary hepatocytes further reveal mitochondria dysfunction and metabolic reprogramming.Ggpps deficiency increases LKB1 farnesylation and subsequent AMPK activation,thus promoting catabolism.However,considering the impairment of mitochondria function,Ggpps deletion eventually drives the catabolism of glucose but not lipid in hepatocytes.Under fat overloading,such fuel preference toward glycolysis further elevates hepatic inflammation.Though NAFLD patients without fibrosis may develop HCC,advanced fibrosis has been shown to increase the risk of HCC 25-fold.Notably,Ggpps deletion drives NAFLD-associated fibrosis.When we treat the mice with 2-deoxyglucose(2-DG),an inhibitor of glycolysis,liver injury,inflammation and fibrosis are dramatically decreased initiated by Ggpps deletion.Taken together,liver-specific Gpps defiency drives Warburg effect by impairing mitochondria function and enhancing the farnesylation of LKB1,collectively promoting hepatic inflammation and fibrosis under fat overloading.Our study interprets that reduced GGPPS promotes HCC development by improving glucose utilization.Under carcinogenic stress,metabolic adaptation toward PPP drives HCC development through binding with G6PD.Under NAFLD condition,impaired mitochondria function and active LKB1/AMPK collectively increase glycolysis and subsequent inflammation,exacerbating fibrosis progression.Thus our study extends the understanding of the mevalonate pathway in tumorigenic metabolism and contributes aid in personalized medicine according to metabolic hallmarks.