BRCA1-Associated Protein 1 Interferes with BRCA1/BARD1 RING Heterodimer Activity

Abstract

The breast and ovarian tumor suppressor BRCA1 constitutes a RING heterodimer E3 ligase with BARD1. BRCA1-associated protein 1 (BAP1) is a ubiquitin COOH-terminal hydrolase that was initially identified as a protein that bound to the RING finger domain of BRCA1. However, how BAP1 contributes to the E3 activity of BRCA1/BARD1 is unclear. Here, we report that BAP1 interacts with BARD1 to inhibit the E3 ligase activity of BRCA1/BARD1. Domains comprised by residues 182-365 of BAP1 interact with the RING finger domain of BARD1, and surface plasmon resonance spectroscopy (BIAcore) analyses showed that BAP1 interferes with the BRCA1/ BARD1 association. The perturbation resulted in inhibition of BRCA1 autoubiquitination and NPM1/B23 ubiquitination by BRCA1/BARD1. Although BAP1 was capable of deubiquitinating the polyubiquitin chains mediated by BRCA1/BARD1 in vitro, a catalytically inactive mutant of BAP1, C91S, still inhibited the ubiquitination in vitro and in vivo, implicating a second mechanism of action. Importantly, inhibition of BAP1 expression by short hairpin RNA resulted in hypersensitivity of the cells to ionizing irradiation and in retardation of S-phase progression. Together, these results suggest that BAP1 and BRCA1/BARD1 coordinately regulate ubiquitination during the DNA damage response and the cell cycle. [Cancer Res 2009;69(1):111-9]

Tumor suppressor and deubiquitinase BAP1 promotes DNA double-strand break repair

“…Thus, it is plausible that BAP1 depletion affects the expression of genes involved in BRCA1 recruitment on chromatin. It is also possible that the effects of BAP1 on the recruitment of HR proteins might be directly linked to its previously reported interaction with BRCA1/BARD1 (31,32). Although our studies failed to reveal BRCA1/BARD1 as stable components of the BAP1 complexes (13) and BAP1 exerts BRCA1-independent effects on cell proliferation (25), it is possible that BRCA1 interaction with BAP1 is transient and associated with DNA damage-dependent and -independent events.…”

Stabilization and targeting of INO80 to replication forks by BAP1 during normal DNA synthesis

“…Although BAP1 can promote cell proliferation by accelerating G1/S progression via host cell factor-1 activation 52,53 , our results suggest that BAP1 can also contribute to cell proliferation by promoting replication fork progression. Indeed, BAP1 depletion results in an accumulation of cells in S phase; conversely, BAP1 re-expression in BAP1-null cells reduces cells in S phase 18,53,54 . Thus, the impact of BAP1 on cell proliferation appears to manifest as the combined effects on DNA replication and other cellular pathways that control cell cycle progression.…”

The BAP1/ASXL2 Histone H2A Deubiquitinase Complex Regulates Cell Proliferation and Is Disrupted in Cancer

“…Because BAP1 knockdown delays cell proliferation in multiple cell types (22,23,57), we sought to determine whether ASXL1/2 and BAP1 interactions influence cell cycle progression. We generated U2OS cells stably expressing comparable levels of siRNA-resistant BAP1, BAP1 C91S or BAP1 R666-H669 (Fig.…”