Fig. 5

Involvement of NuRD complex in the regulation of breast cancer cell senescence and suppression mediated by SALL1. a and b Transfection of mutated SALL1 (mSALL1, deleted the NuRD binding peptide motif of conserved 12-amino) in MCF-7 and E0771 cancer cells did not induce SA-β-Gal⁺ cell populations (in a) and promote cancer cell cycle arrest in S phase (in b). In contrast, transfection of full-length SALL1 into MCF-7 and E0771 breast cancer cells significantly induced tumor cell senescence (around 40%) and promoted cell cycle arrest in S phase. Breast cancer cells were transfected with the indicated constructs and cultured for additional 72 h. Senescent cells were analyzed using the SA-β-Gal activity assay and the cell cycle distribution in tumor cells was analyzed after incubation with propidium iodide. Data shown in (a) are mean ± SD from three independent experiments with similar results. **p < 0.01 compared with the mSALL1 and vector control groups. c and d Transfection of SALL1-S2E into MCF-7 and E0771 breast cancer cells lost the ability to induce tumor cell senescence. However, transfection of SALL1-S2A into breast cancer cells significantly augmented senescence induction in both cell lines compared with that of in wild type SALL1-transfected tumor cells. Cell transfection procedure and SA-β-Gal⁺ cell determination were identical to (a). SALL1-S2E: substitution of the serine with a glutamic acid in SALL1. SALL1-S2A: mutating the serine to an alanine in SALL1. SA-β-Gal⁺ tumor cells were identified with dark blue granules as indicated by the arrows (in c). Data shown in (d) are mean ± SD from three independent experiments with similar results. **p < 0.01, compared with the vector control group. #p < 0.01, compared with the wild type SALL1 group. e Transfection of wild type SALL1 and SALL1-S2A into MCF-7 tumor cells recruited NuRD complex components determined with GST pulldown analyses. In contrast, transfection of SALL1-S2E markedly disrupted recruitment of NuRD components. MCF-7 cells were transfected with or without plasmids pEBG-SALL1, pEBG-SALL1-S2A, and pEBG-SALL1-S2E, and cultured for 3 days. Total protein lysates precipitated with Protein G-Sepharose beads. Pulldowns were analyzed by western blotting with antibodies against SALL1, HDAC1, MTA2, MBD3 and RbAp46/48