Mammogram-induced DNA damage response in early and late PD HMECs.

<p><b>A.</b> Mean incidence of 53BP1 foci per cell 120 min after mammogram X-ray exposures: weakened low-dose radiation response of late PD HMECs. The foci were counted in 2000 cells per group (donor 1). Error bars signify standard error. Asterisk denotes statistically significant difference in a group of irradiated HMECs compared to the shamirradiated controls of each subpopulation. <b>B.</b> Diagram showing the kinetics of 53BP1 foci formation. Late PD HMECs show a 100-minute delay in their peak of 53BP1 foci per cell as compared to early PD HMECs. The 53BP1 foci for kinetics analyses were counted in 1000 cells per time-point and cell subpopulation (donor 1). Cells were exposed to 10 automatic X-ray shots under a mammogram device. <b>A & B.</b> Error bars signify standard error. Simple asterisk (*) refers to statistically significant difference p<0.05 and double asterisk (**) refers to highly significant difference p<0.0001. Mann Whitney test was performed in all samples. <b>C.</b> Histogram showing the fraction of cells with full colocalitzation of γH2AX and 53BP1 for both early and late PD in time (donor 1). Late PD samples do not reach full colocalitzation even after 2 h post-irradiation, revealing a slower mobilization of repair proteins to the damaged site than early PD HMECs. <b>D.</b> Representative images of early and late PD HMECs immunostained for γH2AX and 53BP1 at various times post-IR. Cells were irradiated with 1Gy of γ-rays. Red (γH2AX) and green (53BP1) fluorochromes appear yellow where they coincide in the merged images. Post-IR mobilization of 53BP1 to the γH2AX nuclear foci follows different kinetics in early and late PD HMECs.