Figure 6.

Polyploidy promotes cellular transformation and tumor formation. (A) MEF cells were left untreated or treated with 0.5 mM H₂O₂ (15 min). H₂O₂-treated cells were incubated in DMEM containing 1 μg/ml Chk1 inhibitor SB218078 (5 h), washed and replaced with fresh DMEM. All cells were incubated for an additional 24 h. MEF cells were trypsinized and seeded onto a new dish (10⁵ cells per dish) for the colony-focus formation assay. Upper panels, colony-focus formation assays. Each focus (blue) was scored as a transformed cell, which was normalized to the total number of cells plated; mean ± SD is summarized in the lower panel, n = 3 independent experiments. (B) Representative graphs showing the DNA contents of transformed WT/FFAA cells as analyzed with flow cytometry (lower two panels) and compared to the diploid control (upper panel). (C) Anatomic and histological analysis of tumors in NOD/SCID mice injected with transformed WT/FFAA cells. Histological examination indicated that the tumor was a subcutaneous sarcoma. Scale bar: 200 μm.