SHOC2 plays an oncogenic or tumor-suppressive role by differentially targeting the MAPK and mTORC1 signals in liver cancer

SHOC2 is a scaffold protein that activates the RAS-MAPK signal. Our recent study showed that SHOC2 is also a negative regulator of the mTORC1 signal in lung cancer cells. Whether and how SHOC2 differentially regulates the RAS-MAPK vs. the mTORC1 signals in liver cancer remains unknown. Here, we showed that SHOC2 is overexpressed in human liver cancer tissues, and SHOC2 overexpression promotes the growth and survival of liver cancer cells via activation of the RAS-MAPK signal, although the mTORC1 signal is inactivated. SHOC2 knockdown suppresses the growth of liver cancer cells mainly through inactivating the RAS-MAPK signal. Thus, in the cell culture models, SHOC2 regulation of growth is dependent of the RAS-MAPK but not the mTORC1 signal. Interestingly, in a mouse liver cancer model induced by diethylnitrosamine (DEN)-high-fat diet (HFD), hepatocyte-specific Shoc2 deletion inactivates the Ras-Mapk signal but has no effect in liver tumorigenesis. However, in the Pten loss-induced liver cancer model, Shoc2 deletion further activates mTorc1 without affecting the Ras-Mapk signal and promotes liver tumorigenesis. Collectively, it appears that SHOC2 could act as either an oncogene (via activating the MAPK signal) or a tumor suppressor (via inactivating the mTORC1 signal) in the manner dependent of the dominancy of the MAPK vs. mTORC1 signals.