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Interaction between DNA Polymerase β and BRCA1.

ABSTRACT: The breast cancer 1 (BRCA1) protein is a tumor suppressor playing roles in DNA repair and cell cycle regulation. Studies of DNA repair functions of BRCA1 have focused on double-strand break (DSB) repair pathways and have recently included base excision repair (BER). However, the function of BRCA1 in BER is not well defined. Here, we examined a BRCA1 role in BER, first in relation to alkylating agent (MMS) treatment of cells and the BER enzyme DNA polymerase β (pol β). MMS treatment of BRCA1 negative human ovarian and chicken DT40 cells revealed hypersensitivity, and the combined gene deletion of BRCA1 and pol β in DT40 cells was consistent with these factors acting in the same repair pathway, possibly BER. Using cell extracts and purified proteins, BRCA1 and pol β were found to interact in immunoprecipitation assays, yet in vivo and in vitro assays for a BER role of BRCA1 were negative. An alternate approach with the human cells of immunofluorescence imaging and laser-induced DNA damage revealed negligible BRCA1 recruitment during the first 60 s after irradiation, the period typical of recruitment of pol β and other BER factors. Instead, 15 min after irradiation, BRCA1 recruitment was strong and there was γ-H2AX co-localization, consistent with DSBs and repair. The rapid recruitment of pol β was similar in BRCA1 positive and negative cells. However, a fraction of pol β initially recruited remained associated with damage sites much longer in BRCA1 positive than negative cells. Interestingly, pol β expression was required for BRCA1 recruitment, suggesting a partnership between these repair factors in DSB repair.

SUBMITTER: Masaoka A

PROVIDER: S-EPMC3694962 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:XRCC1 (X-ray cross-complementing group 1) is a DNA repair protein that forms complexes with DNA polymerase beta (beta-Pol), DNA ligase III and poly-ADP-ribose polymerase in the repair of DNA single strand breaks. The domains in XRCC1 have been determined, and characterization of the domain-domain interaction in the XRCC1-beta-Pol complex has provided information on the specificity and mechanism of binding. The domain structure of XRCC1, determined using limited proteolysis, was found to include an N-terminal domain (NTD), a central BRCT-I (breast cancer susceptibility protein-1) domain and a C-terminal BRCT-II domain. The BRCT-I-linker-BRCT-II C-terminal fragment and the linker-BRCT-II C-terminal fragment were relatively stable to proteolysis suggestive of a non-random conformation of the linker. A predicted inner domain was found not to be stable to proteolysis. Using cross-linking experiments, XRCC1 was found to bind intact beta-Pol and the beta-Pol 31 kDa domain. The XRCC1-NTD(1-183)(residues 1-183) was found to bind beta-Pol, the beta-Pol 31 kDa domain and the beta-Pol C-terminal palm-thumb (residues 140-335), and the interaction was further localized to XRCC1-NTD(1-157)(residues 1-157). The XRCC1-NTD(1-183)-beta-Pol 31 kDa domain complex was stable at high salt (1 M NaCl) indicative of a hydrophobic contribution. Using a yeast two-hybrid screen, polypeptides expressed from two XRCC1 constructs, which included residues 36-355 and residues 1-159, were found to interact with beta-Pol, the beta-Pol 31 kDa domain, and the beta-Pol C-terminal thumb-only domain polypeptides expressed from the respective beta-Pol constructs. Neither the XRCC1-NTD(1-159), nor the XRCC1(36-355)polypeptide was found to interact with a beta-Pol thumbless polypeptide. A third XRCC1 polypeptide (residues 75-212) showed no interaction with beta-Pol. In quantitative gel filtration and analytical ultracentrifugation experiments, the XRCC1-NTD(1-183)was found to bind beta-Pol and its 31 kDa domain in a 1:1 complex with high affinity (K(d) of 0.4-2.4 microM). The combined results indicate a thumb-domain specific 1:1 interaction between the XRCC1-NTD(1-159)and beta-Pol that is of an affinity comparable to other binding interactions involving beta-Pol.

Project description:In this study, loss of expression of the fragile site-encoded Wwox protein was found to contribute to radiation and cisplatin resistance of cells, responses that could be associated with cancer recurrence and poor outcome. WWOX gene deletions occur in a variety of human cancer types, and reduced Wwox protein expression can be detected early during cancer development. We found that Wwox loss is followed by mild chromosome instability in genomes of mouse embryo fibroblast cells from Wwox-knockout mice. Human and mouse cells deficient for Wwox also exhibit significantly enhanced survival of ionizing radiation and bleomycin treatment, agents that induce double-strand breaks (DSBs). Cancer cells that survive radiation recur more rapidly in a xenograft model of irradiated breast cancer cells; Wwox-deficient cells exhibited significantly shorter tumor latencies vs Wwox-expressing cells. This Wwox effect has important consequences in human disease: in a cohort of cancer patients treated with radiation, Wwox deficiency significantly correlated with shorter overall survival times. In examining mechanisms underlying Wwox-dependent survival differences, we found that Wwox-deficient cells exhibit enhanced homology directed repair (HDR) and decreased non-homologous end-joining (NHEJ) repair, suggesting that Wwox contributes to DNA DSB repair pathway choice. Upon silencing of Rad51, a protein critical for HDR, Wwox-deficient cells were resensitized to radiation. We also demonstrated interaction of Wwox with Brca1, a driver of HDR, and show via immunofluorescent detection of repair proteins at ionizing radiation-induced DNA damage foci that Wwox expression suppresses DSB repair at the end-resection step of HDR. We propose a genome caretaker function for WWOX, in which Brca1-Wwox interaction supports NHEJ as the dominant DSB repair pathway in Wwox-sufficient cells. Taken together, the experimental results suggest that reduced Wwox expression, a common occurrence in cancers, dysregulates DSB repair, enhancing efficiency of likely mutagenic repair, and enabling radiation and cisplatin treatment resistance.

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Interaction between DNA Polymerase β and BRCA1.

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