RPS6KB1 and hepatoblastoma: Phosphorylated mTOR and P70S6K (a serine/threonine kinase that is directly downstream of mTOR) expression was much higher in hepatoblastoma cells (HuH-6) than that in nonmalignant QSG-7701 and L02 cells, indicating that mTOR signaling was activated in hepatoblastoma cells (Figure 4A).