FIGURE 7.

TopBP1 knockdown induces cellular senescence in human primary cells. A, the indicated human cell lines were transfected five times with control siRNA (GL3) or TopBP1-specific siRNA as previously described (12). B, 3 days after first siRNA transfection, HS68 and IMR90 cells were immunostained with anti-TopBP1, anti-γH2AX, and anti-p-Chk2 antibodies (supplemental Fig. S6), then the immunostained cells were scored. To detect BrdU incorporation, the cells were incubated with 10 μm BrdU for 30 min followed by detection with anti-BrdU antibody. C, 3–7 days after the first transfection, the cells were stained with SA-β-gal stain and viewed under a phase contrast microscope.