La Completa inibizione della via di segnale mTORC1 è necessaria per la soppressione dell’epatocancerogenesi indotta dall’iperespressione dei protooncogeni AKT e N-Ras nel topo

Aim:Concomitant expression of activated forms of AKT and Ras protooncogenes in the mouse liver leads to rapid tumor development via strong activity of the mTORC1 pathway. In mouse hepatocytes, mTORC1 functions by regulating the p70S6K/RPS6 and 4E-BP1/eIF4E cascades. We investigated the effect of mTORC1 inhibition on hepatocarcinogenesis driven by AKT and Ras co-expression.Methods:Activated forms of AKT and Ras genes were injected together withRaptorfl/fl(conditional knockout) and Cre recombinase via hydrodynamic injection in mice to allow the expression of AKT and Ras in mTORC1 deleted hepatocytes. AKT/Ras mice were treated with Rapamycin, which inhibits p-RPS6 without affecting p-4E-BP1, for 7 weeks (starting immediately after hydrodynamic injection). 4E-BP1A4, an unphophorylable mutant of 4E-BP1, was co-injected with AKT and Ras into the mouse liver.Results:Disruption of mTORC1 byRaptorablation completely inhibited AKT/Ras induced hepatocarcinogenesisin vivo. Blocking of RPS6 pathway via Rapamycin effectively inhibited AKT/Ras induced hepatocarcinogenesis. Liver tissues from Rapamycin treated mice showed small clusters of lipid-rich preneoplastic cells with few proliferating cells. Inhibition of 4E-BP1/eIF4E cascade by injection of 4E-BP1A4 significantly delayed AKT/Ras induced liver tumor progression. However, over long term, large liver tumors eventually developed in AKT/Ras/4EBP1A4 mice. Combined treatment with Rapamycin and 4E-BP1A4 completely suppressed AKT/Ras hepatocarcinogenesis.Conclusion:Complete inhibition of mTORC1 is required to suppress liver cancer development induced by AKT and Ras protooncogenes in mice. The two major downstream effectors of mTORC1, RPS6 and 4E-BP1/eIF4E, are both required for AKT/Ras-driven hepatocarcinogenesis.