BRCA1: Beyond double-strand break repair

Effects of Aqueous Dispersions of C60, C70, and Gd@C82 Fullerenes on DNA Oxidative Damage/Repair and Apoptosis in Human Embryonic Lung Fibroblasts

Fullerenes and metallofullerenes play an active role in homeostasis of reactive oxygen species and may cause oxidative damage to cells. As pristine fullerenes are a basis for derivatization, studying oxidative DNA damage/repair and apoptosis is important in terms of genotoxicity and cytotoxicity for their biomedical application. Aqueous dispersions of C₆₀, C₇₀, and Gd@C₈₂ (5 nM and 1.5 μM) were cultured with human fetal lung fibroblasts for 1, 3, 24, and 72 h. Oxidative DNA damage/repair was assessed through concentration of 8-oxodG, double-strand breaks, and activation of BRCA1. Activity of apoptosis was assessed through the BCL2/BAX ratio. All three fullerenes caused oxidative modification of DNA at the early stages; C₆₀ caused the most long-term damage, Gd@C₈₂ caused the most short-term damage, and C₇₀ caused "wave-like" dynamics. The dynamics of DNA repair correlated with the dynamics of oxidative damage, but Gd@C₈₂ caused more prolonged activation of the repair system than C₆₀ or C₇₀. The oxidative toxicity of Gd@C₈₂, is minor and the oxidative toxicity of C₆₀ is mild and short-term, in contrast to C₇₀. In relation to the studied effects, the fullerenes can be arranged in a safety row of Gd@C₈₂ > C₆₀ > C₇₀.

Single-cell analysis of somatic mutation burden in mammary epithelial cells of pathogenic BRCA1/2 mutation carriers

Inherited germline mutations in the breast cancer gene 1 (BRCA1) or BRCA2 genes (herein BRCA1/2) greatly increase the risk of breast and ovarian cancer, presumably by elevating somatic mutational errors as a consequence of deficient DNA repair. However, this has never been directly demonstrated by a comprehensive analysis of the somatic mutational landscape of primary, noncancer, mammary epithelial cells of women diagnosed with pathogenic BRCA1/2 germline mutations. Here, we used an accurate, single-cell whole-genome sequencing approach to first show that telomerized primary mammary epithelial cells heterozygous for a highly penetrant BRCA1 variant displayed a robustly elevated mutation frequency as compared with their isogenic control cells. We then demonstrated a small but statistically significant increase in mutation frequency in mammary epithelial cells isolated from the breast of BRCA1/2 mutation carriers as compared with those obtained from age-matched controls with no genetically increased risk for breast cancer.

Transcriptional dysregulation of base excision repair proteins in breast cancer

Base excision repair (BER) addresses the numerous base lesions and strand breaks induced by exogenous and endogenous stressors daily. The complexity and importance of BER requires careful regulation of basal levels of these proteins and inducible responses following DNA damage. Several reports have noted the dysregulation of BER proteins and defects in BER capacity in cancer. Modulated gene and protein expression of several BER proteins, including APE1, PARP1, POL β, and XRCC1, have been observed in breast cancer. Overexpression of these factors has been associated with chemoresistance and cancer aggressiveness, but the regulatory mechanisms that drive overexpression have not been defined. Here, we review the known transcriptional regulators of these key BER proteins and examine potential mechanisms that may drive overexpression in breast cancer.

DNA/Lysozyme-binding affinity study of novel peptides from TAT (47-57) and BRCA1 (782-786) in vitro by spectroscopic analysis

SISLL-TAT and TAT-SISLL were synthesized by modifying the N- or C-termini of cell-penetrating peptides as transacting activator of transcription TAT (47-57) by attaching BRCA1 (782-786) (SISLL). The novel peptides were synthesized through Fmoc solid-phase synthesis procedures and characterized by LCQ Fleet MS, ¹H NMR and ¹³C NMR. SISLL-TAT and TAT-SISLL displayed forceful antibacterial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella typhimurium with low hemolysis. SISLL-TAT showed better antibacterial activity than TAT-SISLL, with the minimum inhibitory concentration (MIC) values of 10-33 μg·mL^-1. The results of the DNA-binding activities showed that both SISLL-TAT and TAT-SISLL could interact with DNA via the minor groove mode, and the binding constants were 4.97 × 10⁵ L·mol^-1 and 4.42 × 10⁵ L·mol^-1 at 310 K, respectively. Circular dichroism analysis showed slight transformation of the lysozyme secondary structure caused by SISLL-TAT and TAT-SISLL. We also found that the novel peptides SISLL-TAT and TAT-SISLL targeted bacterial DNA resulting in cell death. This explains the antibacterial mechanism of SISLL-TAT and TAT-SISLL, and is a solid theoretical basis for further designing novel and highly effective antibiotics for clinical application.

Impact of Etoposide on BRCA1 Expression in Various Breast Cancer Cell Lines

Breast cancer 1 (BRCA1), as a tumor suppressor, exerts an effective influence on protecting DNA integrity to suppress the development of breast cancer (BC). BRCA1 expression is induced in response to DNA-damaging agents such as etoposide. Germline BRCA1 gene mutations are associated with development of hereditary BC. However, besides BRCA-mutated BCs, some sporadic cancers may also exhibit a BRCA-like phenotype, displaying so-called ‘BRCAness’. This common phenotype may respond to similar therapeutic approaches as BRCA-mutated tumors and may thus have important implications for the clinical management of these cancers. In order to determine whether and how etoposide regulates the protein levels of BRCA1 in BC cells, we exposed a panel of five selected cell lines to etoposide, compared the results to untreated control cells, and then stained the cells with the specific, reliable, and reproducible MS110 antibody directed against phosphorylated Ser1423 BRCA1. By evaluating cytoplasmic BRCA1 protein levels, we were able to distinguish three aggressive BC subtypes with BRCAness characteristics. In addition, determination of early and late apoptosis helped to complete the analysis of BRCA1 functions in the DNA damage pathway of aggressive BC. In conclusion, our study suggested that high cytoplasmic BRCA1 protein levels could be considered as a potential predictive marker for response to chemotherapy in both sporadic and hereditary BC. Tumors with either BRCAness phenotype or germline BRCA1 mutation are both aggressive BCs associated with poor prognosis and could both be subjected to targeted therapies against BRCA1-mutated BC in future clinical management strategies.

Structural analysis of BRCA1 reveals modification hotspot

Cancer cells afflicted with mutations in the breast cancer susceptibility protein (BRCA1) often suffer from increased DNA damage and genomic instability. The precise manner in which physical changes to BRCA1 influence its role in DNA maintenance remains unclear. We used single-particle electron microscopy to study the three-dimensional properties of BRCA1 naturally produced in breast cancer cells. Structural studies revealed new information for full-length BRCA1, engaging its nuclear binding partner, the BRCA1-associated RING domain protein (BARD1). Equally important, we identified a region in mutated BRCA1 that was highly susceptible to ubiquitination. We refer to this site as a modification "hotspot." Ubiquitin adducts in the hotspot region proved to be biochemically reversible. Collectively, we show how key changes to BRCA1 affect its structure-function relationship, and present new insights to potentially modulate mutated BRCA1 in human cancer cells.

Molecular Analysis of BRCA1 in Human Breast Cancer Cells Under Oxidative Stress

The precise manner in which physical changes to the breast cancer susceptibility protein (BRCA1) affect its role in DNA repair events remain unclear. Indeed, cancer cells harboring mutations in BRCA1 suffer from genomic instability and increased DNA lesions. Here, we used a combination of molecular imaging and biochemical tools to study the properties of the BRCA1 in human cancer cells. Our results reveal new information for the manner in which full-length BRCA1 engages its binding partner, the BRCA1-associated Ring Domain protein (BARD1) under oxidative stress conditions. We also show how physical differences between wild type and mutated BRCA1^5382insC impact the cell's response to oxidative damage. Overall, we demonstrate how clinically relevant changes to BRCA1 affect its structure-function relationship in hereditary breast cancer.

Differences in the expression of cell cycle genes in osteoblasts and endothelial cells cultured on the surfaces of Ti6Al4V and Ti6Al7Nb alloys

Three medically used alloys (Ti6Al4V, Ti6Al7Nb, and AISI 316 L) are compared due to proliferative potential and metabolic response of human cells (osteoblasts line Saos-2 and endothelial cells line EA.hy-926) seeded on the surfaces of these alloys. Although no statistically significant difference in the proliferative potential of the cells cultured on the surfaces of examined biomaterials was observed, it does not exclude relevant differences in metabolic response of these cells assessed as changes in genes' expression. As a result of our studies it was demonstrated that the changes in the expression of examined genes were very common. Our observation suggests the presence of the process of selective recognition of the contacted biomaterials by the cells seeded on their surfaces. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1607-1617, 2017.

DNA repair prognostic index modelling reveals an essential role for base excision repair in influencing clinical outcomes in ER negative and triple negative breast cancers

Stratification of oestrogen receptor (ER) negative and triple negative breast cancers (TNBCs) is urgently needed. In the current study, a cohort of 880 ER- (including 635 TNBCs) was immuno-profiled for a panel of DNA repair proteins including: Pol β, FEN1, APE1, XRCC1, SMUG1, PARP1, BRCA1, ATR, ATM, DNA-PKcs, Chk1, Chk2, p53, and TOPO2. Multivariate Cox proportional hazards models (with backward stepwise exclusion of these factors, using a criterion of p < 0.05 for retention of factors in the model) were used to identify factors that were independently associated with clinical outcomes. XRCC1 (p = 0.002), pol β (p = 0.032) FEN1 (p = 0.001) and BRCA1 (p = 0.040) levels were independently associated with poor BCSS. Subsequently, DNA repair index prognostic (DRPI) scores for breast cancer specific survival (BCSS) were calculated and two prognostic groups (DRPI-PGs) were identified. Patients in prognostic group 2 (DRPI-PG2) have higher risk of death (p < 0.001). Furthermore, in DRPI-PG2 patients, exposure to anthracycline reduced the risk of death [(HR (95% CI) = 0.79 (0.64–0.98), p = 0.032) by 21–26%. In addition, DRPI-PG2 patients have adverse clinicopathological features including higher grade, lympho-vascular invasion, Her-2 positive phenotype, compared to those in DRPI-PG1 (p < 0.01). Receiver operating characteristic (ROC) curves indicated that the DRPI outperformed the currently used prognostic factors and adding DRPI to lymph node stage significantly improved their performance as a predictor for BCSS [p < 0.00001, area under curve (AUC) = 0.70]. BER strongly influences pathogenesis of ER- and TNBCs. The DRPI accurately predicts BCSS and can also serve as a valuable prognostic and predictive tool for TNBCs.