SIRT4 and neoplasm: Overexpression of SIRT4 in the α2δ1- PLC/PRF/5 cells enhanced the tumorigenicity of these cells, which was consistent with our above conclusion that SIRT4 was an oncogene (Figure 6I and J, Figure S2C), whereas forced expression of SIRT4 in α2δ1+ ones resulted in remarkable suppression of the tumorigenicity of the cells (Figure 6K and L, Figure S2 D), supporting its tumor suppressor role in α2δ1+ HCC cells.