BRCA1, a breast and ovarian tumor suppressor, maintains genome stability through its functions in DNA
repair, cell-cycle checkpoints, heterochromatin formation and centrosome amplification. BRCA1 interacts with BARD1 to
constitute a RING heterodimer-type E3 ubiquitin ligase. BRCA1-associated protein 1 (BAP1) is a deubiquitinating
enzyme that also regulates similar cellular events, including cell-cycle control, transcription, chromatin modification and
DNA damage response. Germline mutations in BRCA1 predispose individuals to breast, ovarian, fallopian tube,
peritoneal, pancreatic and prostate cancers, whereas BAP1 mutations combined with certain types of DNA damage
provoke malignant mesothelioma, uveal and cutaneous melanoma, lung adenocarcinoma and renal cell carcinoma.
Although BAP1 was initially discovered as a BRCA1-associated protein, recent mass-spectrometric screens of BAP1
interactors failed to detect BRCA1, raising questions about their presumed endogenous interaction. However, in addition
to physical interaction, new evidence indicates a functional correlation between the two proteins. This review summarizes
BAP1 function in histone modification and the DNA damage response, focusing on BAP1’s relevance to BRCA1
function. An understanding of the cooperative functions between BRCA1 and BAP1 may uncover opportunities for new
drug targets in a variety of related cancers.