SIRT1 is required for the SIRT4 deficiency-induced BCSC phenotype. (A) Sphere formation efficiency of MDA-MB-468 (left) and MCF-7 cells (right panel) transfected with different combinations of control vector, sh-SIRT4, and sh-SIRT1. (B) Quantification of CD44+/CD24- subpopulations (C) SIRT4, SIRT1, H4K16ac, BRCA1, SOX2, Oct4, and Nanog in MDA-MB-468 (left) and MCF-7 cells (right panel) described above. (D) Immunofluorescence images of cells described in (A) stained with antibodies against BRCA1/DAPI. (E) Representative ventral view images of bioluminescence from mice described above. (F) Tumor volume. (G) Quantification of E. Data are means ±SEM. **p < 0.01; t-test. Scale bars, 100 µm (A) and 20 µm (D).