Figure 2.

Triple-negative breast cancers (TNBCs) with low molecular weight cyclin E (LMWE) expression are sensitive to poly (ADP-ribose) polymerase (PARP) inhibition. (A) The IC₅₀ of the PARP inhibitor (MK-4827) in 9 TNBC cells as a function of BRCA1/2 mutation status and LMWE expression. (B) Western blots of 9 TNBC cells with indicated antibodies. Actin was used as loading control. (C,D) the comparison of IC₅₀ of PARP inhibitor in 9 TNBC cells (from A) as a function of (C) BRCA1/2 mutational status or (D) LMWE status. A two-tailed unpaired t-test was used to compare the two groups in each panel. (E) HCC1806-shRNA cyclin E cells were subjected to high through put survival analysis with increasing concentrations of PARPi (MK-4827) for 48 h as shown in Figure S2A and were immunoblotted (inset) with the indicated antibodies. A two-tailed paired t-test was used to compare two groups. (F) Representative images (top) and quantification of foci-positive cell (>5 foci per cell, bottom) population of RPA and RAD51 in MDA231 cells treated with 5 μM MK-4827 (PARPi) for 48 h. RPA+RAD51 indicates cells with both RPA and RAD51 foci. Scale bar, 10 μm. n = 3. A two-tailed unpaired t-test was used to compare two groups. Error bars represent standard error of the mean. **, p < 0.01. (G) MDA231 and BT549 cells were treated with 10 μM MK-4827 (PARPi) for 48 h and subjected to Western blots with the indicated antibodies. CNL, control. Vinculin was used as loading control. Densitometry was performed on all western blots and the relative expression of each band to its loading control is noted on the bottom of each panel for each antibody used. n.a. densitometry is not available because the western blot band cannot be detected.