Cooperation of breast cancer proteins PALB2 and piccolo BRCA2 in stimulating homologous recombination

Genome Stability Laboratory, Laval University Cancer Research Center, Hôtel-Dieu de Québec, Quebec City, Quebec, Canada.
Nature Structural & Molecular Biology (Impact Factor: 13.31). 10/2010; 17(10):1247-54. DOI: 10.1038/nsmb.1915
Source: PubMed


Inherited mutations in human PALB2 are associated with a predisposition to breast and pancreatic cancers. PALB2's tumor-suppressing effect is thought to be based on its ability to facilitate BRCA2's function in homologous recombination. However, the biochemical properties of PALB2 are unknown. Here we show that human PALB2 binds DNA, preferentially D-loop structures, and directly interacts with the RAD51 recombinase to stimulate strand invasion, a vital step of homologous recombination. This stimulation occurs through reinforcing biochemical mechanisms, as PALB2 alleviates inhibition by RPA and stabilizes the RAD51 filament. Moreover, PALB2 can function synergistically with a BRCA2 chimera (termed piccolo, or piBRCA2) to further promote strand invasion. Finally, we show that PALB2-deficient cells are sensitive to PARP inhibitors. Our studies provide the first biochemical insights into PALB2's function with piBRCA2 as a mediator of homologous recombination in DNA double-strand break repair.

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Available from: Yan Coulombe, Jul 02, 2014
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    • "Given the promising response of BRCA-mutated breast and ovarian cancers to PARP inhibitors [4] [16], it is of interest to identify additional determinants of PARP inhibitor sensitivity, thereby extending their utility in cancer therapy. Recently, PALB2-, RAD51C-and SLX4-deficiency have been coupled to PARP inhibitor sensitivity [17] [18] [19]. Bi-allelic germ-line mutations in BRCA2, PALB2 or SLX4 cause Fanconi anemia (FA), a genomic instability syndrome characterized by congenital abnormalities, bone marrow failure and a high risk to develop cancer, whereas mutations in RAD51C lead to an FA-like syndrome [20] [21] [22] [23] [24] [25]. "
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    ABSTRACT: The encouraging response rates of BRCA1- and BRCA2-mutated cancers toward PARP inhibitors make it worthwhile to identify other potential determinants of PARP inhibitor responsiveness. Since the Fanconi anemia (FA) pathway coordinates several DNA repair pathways, including homologous recombination in which BRCA1 and BRCA2 play important roles, we investigated whether this pathway harbors other predictors of PARP inhibitor sensitivity. Lymphoblastoid cell lines derived from individuals with FA or clinically related syndromes, such as Warsaw breakage syndrome, were tested for PARP inhibitor sensitivity. Remarkably, we found a strong variability in PARP inhibitor sensitivity among different FANCD1/BRCA2-deficient lymphoblasts, suggesting that PARP inhibitor response depends on the type of FANCD1/BRCA2 mutation. We identified the DNA helicases FANCM and DDX11 as determinants of PARP inhibitor response. These results may extend the utility of PARP inhibition as effective anticancer treatment. Copyright © 2014 Elsevier B.V. All rights reserved.
    DNA Repair 12/2014; 26. DOI:10.1016/j.dnarep.2014.12.003 · 3.11 Impact Factor
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    • "Determining PALB2 mutation status is important, however, as it may allow female relatives of mutation positive patients the opportunity to make informed decisions about options to mitigate their elevated risk for disease. Also, new effective targeted therapeutic options are becoming available (PARP inhibitors) that have shown promising results in in vitro studies with PALB2 deficient cells exhibiting a defect in homologous repair [11]. "
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    ABSTRACT: Background PALB2 has emerged as a breast cancer susceptibility gene. Mutations in PALB2 have been identified in almost all breast cancer populations studied to date, but the rarity of these mutations and lack of information regarding their penetrance makes genetic counseling for these families challenging. We studied BRCA1/2 -negative breast and/or ovarian cancer families to a) assess the contribution of PALB2 mutations in this series and b) identify clinical, pathological and family history characteristics that might make PALB2 screening more efficient. Methods The coding region of the PALB2 gene was analyzed in 175 probands with family histories of breast and/or ovarian cancer ascertained from a single Canadian institution in Eastern Ontario. Results We identified 2 probands with PALB2 mutations that are known or strongly considered to be pathogenic and 3 probands with missense mutations that are possibly pathogenic. One of the identified truncating mutations [c.3113G > A (p.Gly1000_Trp1038del – major product)], has been previously described while the other four mutations [c.3507_3508delTC (p.H1170Ffs*19), c.1846G > C (p.D616H), c.3418 T > G (p.W1140G), c.3287A > G (p.N1096S)] have not been previously reported. Loss of heterozygosity was detected in two breast tumors from one c.3507_3508delTC mutation carrier but not in other available tumors from that family or in tumors from carriers of other mutations. Conclusions PALB2 mutation screening identifies a small, but significant number of mutations in BRCA1/2 -negative breast and/or ovarian cancer families. We show that mutations are more likely to be found in families with three or more breast cancers as well as other BRCA2-related cancers. In our cohort, both clearly pathogenic mutations were identified in premenopausal breast cancer cases (2/77, 2.6%). Testing should be preferentially offered to affected women from such families.
    Hereditary Cancer in Clinical Practice 08/2014; 12(1):19. DOI:10.1186/1897-4287-12-19 · 1.47 Impact Factor
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    • "A third domain, named ChAM (chromatin-association motif), is located at the center of the protein (395–446 amino acids) and is required for PALB2 chromatin localization (Bleuyard et al., 2012). Recently, we showed that purified PALB2 binds D loops preferentially and interacts directly with RAD51 to stimulate strand invasion (Buisson et al., 2010; Dray et al., 2010). At the same time, Jensen et al. (2010), Liu et al. (2010), and Thorslund et al. (2010) reported the purification of full-length BRCA2 and showed that human BRCA2 promotes RAD51 filament assembly on single-strand DNA (ssDNA), which stimulates RAD51-mediated DNA strand exchange. "
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    ABSTRACT: One envisioned function of homologous recombination (HR) is to find a template for DNA synthesis from the resected 3'-OH molecules that occur during double-strand break (DSB) repair at collapsed replication forks. However, the interplay between DNA synthesis and HR remains poorly understood in higher eukaryotic cells. Here, we reveal functions for the breast cancer proteins BRCA2 and PALB2 at blocked replication forks and show a role for these proteins in stimulating polymerase η (Polη) to initiate DNA synthesis. PALB2, BRCA2, and Polη colocalize at stalled or collapsed replication forks after hydroxyurea treatment. Moreover, PALB2 and BRCA2 interact with Polη and are required to sustain the recruitment of Polη at blocked replication forks. PALB2 and BRCA2 stimulate Polη-dependent DNA synthesis on D loop substrates. We conclude that PALB2 and BRCA2, in addition to their functions in D loop formation, play crucial roles in the initiation of recombination-associated DNA synthesis by Polη-mediated DNA repair.
    Cell Reports 01/2014; 6(3). DOI:10.1016/j.celrep.2014.01.009 · 8.36 Impact Factor
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