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: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:In Saccharomyces cerevisiae, the Silent Information Regulator (SIR) proteins Sir2/3/4 form a complex suppressing transcription of genes at subtelomeric regions and the homothallic mating type (HM) loci. Here we identify a non-canonical BRCA1 C-terminal domain (H-BRCT) in Sir4 which is responsible for tethering telomeres to the nuclear periphery. We show that Sir4 H-BRCT and the closely related Dbf4 H-BRCT serve as selective phospho-epitope recognition domains that bind to a variety of phosphorylated target peptides. We present detailed structural information about the binding mode of established Sir4 interactors (Esc1, Ty5, Ubp10) and identify several novel interactors of Sir4 H-BRCT, including the E3 ubiquitin ligase Tom1. Based on these findings, we propose a phospho-peptide consensus motif for interaction with Sir4 H-BRCT and Dbf4 H-BRCT. Ablation of the Sir4 H-BRCT phospho-peptide interaction disrupts SIR-mediated repression and perinuclear localization. In conclusion, the Sir4 H-BRCT domain serves as a hub for recruitment of phosphorylated target proteins to heterochromatin to properly regulate silencing and nuclear order.
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: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:BRCA1 exerts transcriptional repression through interaction with CtIP in the C-terminal BRCT domain and ZBRK1 in the central domain. A dozen genes, including angiopoietin-1 (ANG1), a secreted angiogenic factor, are corepressed by BRCA1 and CtIP based on microarray analysis of mammary epithelial cells in 3D culture. BRCA1, CtIP, and ZBRK1 form a complex that coordinately represses ANG1 expression via a ZBRK1 recognition site in the ANG1 promoter. Impairment of this complex upregulates ANG1, which stabilizes endothelial cells that form a capillary-like network structure. Consistently, Brca1-deficient mouse mammary tumors exhibit accelerated growth, pronounced vascularization, and overexpressed ANG1. These results suggest that, besides its role in maintaining genomic stability, BRCA1 directly regulates the expression of angiogenic factors to modulate the tumor microenvironment.
Project description:BRCA1 exerts transcriptional repression through interaction with CtIP in the C-terminal BRCT domain and ZBRK1 in the central domain. A dozen of genes including angiopoietin-1 (ANG1), a secreted angiogenic factor, are co-repressed by BRCA1 and CtIP based on microarray analysis of mammary epithelial cells in 3-D culture. BRCA1, CtIP and ZBRK1 form a complex that coordinately represses ANG1 expression via a ZBRK1 recognition site in ANG1 promoter. Impairment of this complex upregulates ANG1, which stabilizes endothelial cells forming capillary-like network structure. Consistently, Brca1-deficient mouse mammary tumors exhibit accelerated growth, pronounced vascularization and overexpressed ANG1. These results suggest, besides its role in maintaining genomic stability, BRCA1 directly regulates the expression of angiogenic factors to modulate the tumor microenvironment. Keywords: MCF10A, human mammary epithelial cells, 3-D Matrigel, 15 h, BRCA1-RNAi
Project description:BRCA1 exerts transcriptional repression through interaction with CtIP in the C-terminal BRCT domain and ZBRK1 in the central domain. A dozen of genes including angiopoietin-1 (ANG1), a secreted angiogenic factor, are co-repressed by BRCA1 and CtIP based on microarray analysis of mammary epithelial cells in 3-D culture. BRCA1, CtIP and ZBRK1 form a complex that coordinately represses ANG1 expression via a ZBRK1 recognition site in ANG1 promoter. Impairment of this complex upregulates ANG1, which stabilizes endothelial cells forming capillary-like network structure. Consistently, Brca1-deficient mouse mammary tumors exhibit accelerated growth, pronounced vascularization and overexpressed ANG1. These results suggest, besides its role in maintaining genomic stability, BRCA1 directly regulates the expression of angiogenic factors to modulate the tumor microenvironment. Keywords: MCF10A, human mammary epithelial cells, 3-D Matrigel, 15 h, CtIP-RNAi
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.