GDF15 activity is dependent on AKT and SOX2. (A) Western blot detection of phosphorylated AKT, BMI-1, and SOX2 expression by NCI-H929 cells after treatment with GDF (100 ng/mL). (B) Serial colony formation after treatment with GDF15 and the Akti 124018 for 3 days. *P < .05 compared with 0 ng/mL GDF15. (C) Western blot analysis of SOX2 after treatment with GDF15 and AKT inhibitor. (D) Serial colony formation of NCI-H929 cells after transfection of SOX2 or control short interfering RNA (siRNA) and treatment with GDF15 for 3 days. *P < .05 compared with scramble control and 0 ng/mL GDF15. The inset shows SOX2 expression by qRT-PCR 3 days after transfection.