BRCT phosphoprotein recognition, but not E3 ligase activity, is essential for BRCA1 tumor suppression
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ABSTRACT: It has been recognized that BRCA1, in the form of the BRCA1/BARD1 heterodimer, acting as an ubiquitin E3 ligase offered a possible mechanism to explain its pleiotrophic nature of BRCA1 activity. Our observation that mice lacking BRCA1 enzymatic activity are viable apart from male sterility was unexpected. Our results suggest that the E3 ligase activity of BRCA1 is largely dispensable for normal development and is not essential for all BRCA1 functions. Thus, many of the known and unknown functions of BRCA1 are likely to be mediated independent of its ability to catalyze ubiquitination. The genome copy number patterns were studied on the mice tumors that lacks E3 ubiqitin ligase activity of BRCA1 and were compared to copy number profile of mice lacking p53 and both brca1 and p53.
Project description:It has been recognized that BRCA1, in the form of the BRCA1/BARD1 heterodimer, acting as an ubiquitin E3 ligase offered a possible mechanism to explain its pleiotrophic nature of BRCA1 activity. Our observation that mice lacking BRCA1 enzymatic activity are viable apart from male sterility was unexpected. Our results suggest that the E3 ligase activity of BRCA1 is largely dispensable for normal development and is not essential for all BRCA1 functions. Thus, many of the known and unknown functions of BRCA1 are likely to be mediated independent of its ability to catalyze ubiquitination. The genome copy number patterns were studied on the mice tumors that lacks E3 ubiqitin ligase activity of BRCA1 and were compared to copy number profile of mice lacking p53 and both brca1 and p53. Array CGH was performed using Agilent mouse CGH microarray 244K kit. Genomic DNA isolated from tumor tissue and its corresponding mouse tail were labelled with two different dyes and hybridized simultaneously on to microarray slides to perform comparitive genomic hybridization.
Project description:Deficiencies in the BRCA1 tumor suppressor gene are the main cause of hereditary breast and ovarian cancer. BRCA1 is involved in the Homologous Recombination DNA repair pathway, and, together with BARD1, forms a heterodimer with ubiquitin E3 activity. The relevance of the BRCA1/BARD1 ubiquitin E3 activity for tumor suppression and DNA repair remains controversial and most efforts aimed to identify BRCA1/BARD1 ubiquitination substrates rely on indirect evidence. Here, we observed that the BRCA1/BARD1 ubiquitin E3 activity was not required for Homologous Recombination or resistance to Olaparib. Using TULIP2 methodology, which enables the direct identification of E3-specific ubiquitination substrates, we identified substrates for BRCA1/BARD1. We found that PCNA is ubiquitinated by BRCA1/BARD1 in unperturbed conditions independently of RAD18. PCNA ubiquitination by BRCA1/BARD1 avoids the formation of ssDNA gaps during DNA replication and promotes continuous DNA synthesis. These results address the controversy about the function of BRCA1/BARD1 E3 activity in Homologous Recombination.
Project description:Deficiencies in the BRCA1 tumor suppressor gene are the main cause of hereditary breast and ovarian cancer. BRCA1 is involved in the Homologous Recombination DNA repair pathway, and, together with BARD1, forms a heterodimer with ubiquitin E3 activity. The relevance of the BRCA1/BARD1 ubiquitin E3 activity for tumor suppression and DNA repair remains controversial and most efforts aimed to identify BRCA1/BARD1 ubiquitination substrates rely on indirect evidence. Here, we observed that the BRCA1/BARD1 ubiquitin E3 activity was not required for Homologous Recombination or resistance to Olaparib. Using TULIP2 methodology, which enables the direct identification of E3-specific ubiquitination substrates, we identified substrates for BRCA1/BARD1. PCNA is ubiquitinated by BRCA1/BARD1 in unperturbed conditions independently of RAD18, avoiding the formation of ssDNA gaps during DNA replication and promoting replication fork stability upon replication stress, solving the controversy about the function of BRCA1/BARD1 E3 activity in Homologous Recombination.
Project description:BRCA1/BARD1 is a tumor suppressor E3 ubiquitin (Ub) ligase with roles in DNA damage repair and in transcriptional regulation. BRCA1/BARD1 RING domains interact with nucleosomes to facilitate mono-ubiquitylation of distinct residues on the C-terminal tail of histone H2A. These enzymatic domains constitute a small fraction of the heterodimer, raising the possibility of functional chromatin interactions involving other regions such as the BARD1 C-terminal domains that bind nucleosomes containing the DNA damage signal H2A K15-Ub and H4 K20me0, or portions of the expansive intrinsically disordered regions found in both subunits. Herein, we reveal novel interactions that support robust H2A ubiquitylation activity mediated through a high-affinity, intrinsically disordered DNA-binding region of BARD1. These interactions support BRCA1/BARD1 recruitment to chromatin and sites of DNA damage in cells and contribute to their survival. We also reveal distinct BRCA1/BARD1 complexes that depend on the presence of H2A K15-Ub, including a complex where a single BARD1 subunit spans adjacent nucleosome units. Our findings identify an extensive network of multivalent BARD1-nucleosome interactions that serve as a platform for BRCA1/BARD1-associated functions on chromatin.
Project description:The tumor suppressor BRCA1 regulates DNA damage responses and multiple other processes. Among these, BRCA1 heterodimerizes with BARD1 to ubiquitylate targets via its N-terminal RING domain. Here we show that BRCA1 promotes oxidative metabolism via degradation of Oct1, a transcription factor with pro-glycolytic/tumorigenic effects. BRCA1 E3 ubiquitin ligase mutation skews cells towards a glycolytic metabolic profile while elevating Oct1 protein. CRISPR-mediated Oct1 deletion reverts the glycolytic phenotype. RNAseq confirms the deregulation of metabolic genes. BRCA1 mediates direct Oct1 ubiquitylation and degradation, and mutation of two ubiquitylated Oct1 lysines insulates the protein against BRCA1-mediated destabilization. Oct1 deletion in MCF-7 breast cancer cells does not perturb growth in standard culture, but inhibits growth in soft agar and xenografts. Oct1 protein levels correlate positively with tumor aggressiveness, and inversely with BRCA1, in primary breast cancer samples. These results identify BRCA1 as an Oct1 ubiquitin ligase that catalyzes Oct1 degradation to promote oxidative metabolism.
Project description:The E3 ligase MDM2 promotes tumor growth and progression by inducing ubiquitin-mediated degradation of P53 and other tumor suppressing proteins. Here, we identified an MDM2-interacting lncRNA NRON, which promotes tumor formation by suppressing both P53-dependent and independent pathways. NRON binds to MDM2 and MDMX (MDM4) via two different stem-loops respectively and induces their heterogenous dimerization, thereby enhancing the E3 ligase activity of MDM2 towards its tumor suppressing substrates, including P53, RBI and NFATI, etc.
Project description:For a long time, the BARD1 (BRCA1-associated RING domain 1) protein has been considered as a BRCA1 (BReast Cancer susceptibility gene 1, early onset) interactor, and tumor suppressor mutated in breast and ovarian cancers. Despite its functions in a stable heterodimer with BRCA1, there is increasing evidence for BRCA1-independent functions of BARD1. Here, we investigated BARD1 expression and function in human acute myeloid leukemias and their modulation by epigenetic mechanisms and microRNA. We show that the HDACi (histone deacetylase inhibitor) Vorinostat reduces BARD1 mRNA levels by increasing miR-19a and miR-19b expression levels. Moreover, we identify specific BARD1 isoforms that might act as tumor diagnostic and prognostic markers.
Project description:For a long time, the BARD1 (BRCA1-associated RING domain 1) protein has been considered as a BRCA1 (BReast Cancer susceptibility gene 1, early onset) interactor, and tumor suppressor mutated in breast and ovarian cancers. Despite its functions in a stable heterodimer with BRCA1, there is increasing evidence for BRCA1-independent functions of BARD1. Here, we investigated BARD1 expression and function in human acute myeloid leukemias and their modulation by epigenetic mechanisms and microRNA. We show that the HDACi (histone deacetylase inhibitor) Vorinostat reduces BARD1 mRNA levels by increasing miR-19a and miR-19b expression levels. Moreover, we identify specific BARD1 isoforms that might act as tumor diagnostic and prognostic markers. Two-condition experiment: untreated NB4 cells (control) vs. NB4 cells treated with 5M-BM-5M SAHA (Vorinostat) for 6h. Biological replicates: 3 control, 3 treated, independently grown and harvested at 6 hours. One replicate per array.
Project description:Tamoxifen resistance has been a major clinical problem and is accountable for relapse in about one third of ER positive breast cancer patients. Most of the recurrent patients will eventually receive chemotherapy. However, the chemosensitivity of these tamoxifen-resistant breast cancer patients has never been explored. In this study, we demonstrate that tamoxifen-resistant breast cancer cells express significantly more BARD1 and BRCA1, which results in the resistance to DNA-damaging chemotherapy including cisplatin and adriamycin , but not to paclitaxel. Silencing BARD1 or BRCA1 expression or inhibition of BRCA1 phosphorylation by Dinaciclib restored the sensitivity to cisplatin in tamoxifen-resistant cells. In addition, we identified that activated PI3K/AKT pathway in tamoxifen-resistant cells was responsible for the upregulation of BARD1 and BRCA1. PI3K inhibitors, BKM120 and BYL719, decreased the expression of BARD1 and BRCA1 in tamoxifen-resistant cells and re-sensitized them to cisplatin both in vitro and in xenografted mice. Higher BARD1 and BRCA1 expression was associated with poor prognosis of early breast cancer patients, especially the ones received radiotherapy, indicating the potential use of PI3K inhibitors to reverse chemoresistance and radioresistance in ER positive breast cancer patients.