| BAP1 (BRCA1-Associated Protein 1) was originally identified as a BRCA1 associated, nuclear localized ubiquitin hydrolase that suppresses cell growth (1). The protein belongs to the UCH family of deubiquitinases, with a UCH domain in its N-terminal segment and a BRCA1 interaction domain as well as a nuclear localization signal in its C-terminal segment (1). Frequent gene locus rearrangement, deletion and null mutation of BAP1 have been found in lung and breast cancers (1,2). Mutation analysis in vivo in cancer cell line survival and in animal tumorigenesis indicate that both the deubiquitinase activity and the nuclear localization signal are required for BAP1 function as a tumor suppressor (3). BAP1 does not have direct deubiquitination activity towards the autoubiquitinyled BRCA1/BARD1 E3 complex (4), but its interaction with BARD1 inhibits BRCA1/BARD1 E3 activity by interfering with the compex dimerization process (5). In addition to its interaction with BRCA1/BARD1, BAP1 has also been shown to interact with and deubiquitinylate HCF-1, thereby controlling its stability (6). |
