ABCG2 and neoplasm: Compared with the respective control cells infected with empty lentivirus, overexpression of SIRT4 in α2δ1- cells resulted in elevated expression of stem cell-related genes such as ABCG2, BMI1, and NANOG (Figure 2F), along with significantly enhanced abilities to initiate spheroid formation in serum-free medium (Figure 2G and H), and increased tumor-formation capacities in NOD/SCID mice (Figure 2I, Table 1).