Fig. 2

APOBEC3 activity and replication stress in breast cancer cell lines. a APOBEC3B (black), APOBEC3G (grey) and APOBEC3A (white) mRNA expression in 15 breast cancer cell lines as determined by quantitative PCR. HER2+ cell lines (red), basal cell lines (black), luminal cell lines (green). SKBR3 cells have a null mutation for APOBEC3B. Error bars represent standard deviation. b APOBEC3 activity in the 15 breast cancer cell lines used in a. Cells were lysed and subjected to oligonucleotide-based cytidine deamination assay followed by electrophoresis on 15 % TBE-urea gels. c Cells were grown for two population doublings on glass coverslips followed by fixation and staining with 53BP1 and cyclin A antibodies. The fractions of cyclin A-negative cells displaying more than five 53BP1 nuclear foci were scored. APOBEC3B mRNA expression was determined by quantitative PCR from parallel cell lysates. A Spearman’s rank correlation test was performed to correlate the fraction of 53BP1 nuclear bodies in cell lines with the level of APOBEC3B (r = 0.62, p = 0.0284). Error bars represent standard deviation. d BT474 cells were treated with 12.5–300 μM nucleosides for 72 h prior to lysis. Western blots were probed with the indicated antibodies. e BT474 cells were treated as in d followed by lysis and an APOBEC3 cytidine deamination assay