BRCA1 and neoplasm: In addition, overexpression of cyclin B1 in Brca1-mutant tumor cells increased the levels of apoptosis-promoting proteins, including p53, caspase-3, caspase-7, and PARP (Fig. 4g), indicating that overexpression of cyclin B1 in BRCA1-mutant tumor cells reduces cell survival in association with induction of apoptosis.