Involvement of Brca1 in S-phase and G(2)-phase checkpoints after ionizing irradiation

TIPIN is essential for chromosome stability and cell viability in BRCA1-deficient cells

The mutations of breast cancer type 1 susceptibility gene (BRCA1) cause hereditary breast cancer. One of the medical revolutions of cancer therapy for BRCA1-mutated breast cancer is the drug approval of Poly (ADP-ribose) polymerase (PARP) inhibitors because of the synthetic lethal interaction between BRCA1 mutation and PARP inhibition. Here, we report another synthetic lethal interaction between BRCA1 and TIMELESS interacting protein (TIPIN), the latter of which encodes a protein involved in DNA replication, DNA damage checkpoint and sister chromatid cohesion. Cells deficient for both BRCA1 and TIPIN die due to elevated chromosomal aberrations including chromosomal breaks and radial chromosomes. The synthetic lethality of TIPIN/BRCA1-deficient cells is restored by the depletion of Tumor protein p53 binding protein 1 (53BP1), which prevents homologous recombination (HR) by its restricting DNA processing. Thus, spontaneous DNA lesions in TIPIN deficient cells could be preferentially repaired by BRCA1-mediated HR pathway. The viability of TIPIN/53BP1/BRCA1 triple mutant is lost by the depletion of Ring finger protein 8 (RNF8) E3-ubiquitin ligase, implicating that RNF8-mediated sub-HR pathway may work in a complementary manner of BRCA1 and 53BP1 pathway.

Thirty Years of BRCA1: Mechanistic Insights and Their Impact on Mutation Carriers

SIGNIFICANCE

Here, we explore the impact of three decades of BRCA1 research on the lives of mutation carriers and propose strategies to improve the prevention and treatment of BRCA1-associated cancer.

BRCA1 and BRCA2: from cancer susceptibility to synthetic lethality

The discovery of BRCA1 and BRCA2 as tumor susceptibility genes and their role in genome maintenance has transformed our understanding of hereditary breast and ovarian cancer. This review traces the evolution of BRCA1/2 research over the past 30 years, highlighting key discoveries in the field and their contributions to tumor development. Additionally, we discuss current preventive measures for BRCA1/2 mutation carriers and targeted treatment options based on the concept of synthetic lethality. Finally, we explore the challenges of acquired therapy resistance and discuss potential alternative avenues for targeting BRCA1/2 mutant tumors.

Whole‑exome sequencing insights into synchronous bilateral breast cancer with discordant molecular subtypes

The incidence of synchronous bilateral breast cancer (SBBC) is very low, and SBBC with discordant molecular subtypes is even more uncommon. As such, little is known about the pathogenesis of SBBC with discordant molecular subtypes, and reports about this entity are scarce. In the present study, the case of a 72-year-old female patient who presented with SBBC with discordant molecular subtypes is reported, with a stage IA hormone receptor negative {human epidermal growth factor receptor-2 [HER2(+)]} tumor in the left breast and a stage IIIA hormone sensitive tumor [HER2(-)] in the right breast. Whole-exome sequencing was performed to identify the differential genetic variations in the BBC tissues. A total of 8 key mutated cancer susceptibility genes (ALK, BRCA1, FAT1, HNF1A, KDR, PTCH1, SDHA and SETBP1) were screened, and mutations were found in 10 vital cancer driver genes, including BRCA1, EBF1, MET, NF2, NUMA1 RALGAPA1, ROBO2, SMYD4, UBR5 and ZNF844. The high-frequency mutated genes mainly contained missense mutations, among which single nucleotide variants were the most common mutations, with C > T and C > A as the main forms. The pathways associated with the high frequency mutated genes were further elucidated by functional category and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. Heterogeneity in the hormone receptor and HER2 status of SBBC poses unique therapeutic challenges. Future studies should aim to identify the optimal management strategy for this disease.

Monoubiquitinated H2B, a Main Chromatin Target of Formaldehyde, Is Important for S-Phase Checkpoint Signaling and Genome Stability

Formaldehyde (FA) is a human carcinogen with ubiquitous environmental exposures and significant endogenous formation. Genotoxic activity of FA stems from its reactivity with DNA-NH2 groups. Histone lysines are another source of aldehyde-reactive amino groups in chromatin, however, chromatin/histone damage responses to FA and their biological significance are poorly understood. We examined histone posttranslational modifications in FA-treated human lung cells and found that the majority of the most prominent small lysine modifications associated with active or inactive chromatin were unchanged. FA moderately decreased H3K9 and H3K27 acetylation and H2A-K119 monoubiquitination but caused surprisingly severe losses of H2B-K120 monoubiquitination, especially in primary and stem-like cells. H2Aub1 decreases reflected its slower ubiquitination linked to a lower ubiquitin availability due to K48-polyubiquitination of FA-damaged proteins. Depletion of H2Bub1 resulted from its rapid deubiquitination in part by ATXN7L3-associated deubiquitinases and was independent on DNA damage signaling, indicating a direct chromatin damage response. Manipulations of H2Bub1 abundance showed that it was important for robust ATM and ATR signaling, efficient S-phase checkpoint, and suppression of mitotic transmission of unreplicated DNA and formation of micronuclei. Our findings identified H2B deubiquitination as a major FA-induced chromatin damage response that regulates S-phase checkpoint signaling and genome stability.

Homologous Recombination Repair Gene Mutations in Prostate Cancer: Prevalence and Clinical Value

Despite advances in our understanding of the molecular landscape of prostate cancer and the development of novel biomarker-driven therapies, the prognosis of patients with metastatic prostate cancer that is resistant to conventional hormonal therapy remains poor. Data suggest that a significant proportion of patients with metastatic castration-resistant prostate cancer (mCRPC) have mutations in homologous recombination repair (HRR) genes and may benefit from poly(ADP-ribose) polymerase (PARP) inhibitors. However, the adoption of HRR gene mutation testing in prostate cancer remains low, meaning there is a missed opportunity to identify patients who may benefit from targeted therapy with PARP inhibition, with or without novel hormonal agents. Here, we review the current knowledge regarding the clinical significance of HRR gene mutations in prostate cancer and discuss the efficacy of PARP inhibition in patients with mCRPC. This comprehensive overview aims to increase the clinical implementation of HRR gene mutation testing and inform future efforts in personalized treatment of prostate cancer.

Brca1 Mouse Models: Functional Insights and Therapeutic Opportunities

Brca1 mouse models were first reported in the mid-1990's shortly after cloning the human gene. Since then, many mouse models with a range of mutations have been generated, some mimic patient mutations, others are designed to probe specific protein domains and functions. In this review, we discuss early and recent studies using engineered Brca1 mouse alleles, and their implications for understanding Brca1 protein function in the context of DNA repair, tumorigenesis, and anti-cancer therapeutics.

Chemical Inhibition of RPA by HAMNO Alters Cell Cycle Dynamics by Impeding DNA Replication and G2-to-M Transition but Has Little Effect on the Radiation-Induced DNA Damage Response

Replication protein A (RPA) is the major single-stranded DNA (ssDNA) binding protein that is essential for DNA replication and processing of DNA double-strand breaks (DSBs) by homology-directed repair pathways. Recently, small molecule inhibitors have been developed targeting the RPA70 subunit and preventing RPA interactions with ssDNA and various DNA repair proteins. The rationale of this development is the potential utility of such compounds as cancer therapeutics, owing to their ability to inhibit DNA replication that sustains tumor growth. Among these compounds, (1Z)-1-[(2-hydroxyanilino) methylidene] naphthalen-2-one (HAMNO) has been more extensively studied and its efficacy against tumor growth was shown to arise from the associated DNA replication stress. Here, we study the effects of HAMNO on cells exposed to ionizing radiation (IR), focusing on the effects on the DNA damage response and the processing of DSBs and explore its potential as a radiosensitizer. We show that HAMNO by itself slows down the progression of cells through the cell cycle by dramatically decreasing DNA synthesis. Notably, HAMNO also attenuates the progression of G2-phase cells into mitosis by a mechanism that remains to be elucidated. Furthermore, HAMNO increases the fraction of chromatin-bound RPA in S-phase but not in G2-phase cells and suppresses DSB repair by homologous recombination. Despite these marked effects on the cell cycle and the DNA damage response, radiosensitization could neither be detected in exponentially growing cultures, nor in cultures enriched in G2-phase cells. Our results complement existing data on RPA inhibitors, specifically HAMNO, and suggest that their antitumor activity by replication stress induction may not extend to radiosensitization. However, it may render cells more vulnerable to other forms of DNA damaging agents through synthetically lethal interactions, which requires further investigation.

Conservation of transcriptional regulation by BRCA1 and BARD1 in Caenorhabditis elegans

The tumor-suppressor proteins BRCA1 and BARD1 function as an E3 ubiquitin ligase to facilitate transcriptional repression and DNA damage repair. This is mediated in-part through its ability to mono-ubiquitylate histone H2A in nucleosomes. Studies in Caenorhabditis elegans have been used to elucidate numerous functions of BRCA1 and BARD1; however, it has not been established that the C. elegans orthologs, BRC-1 and BRD-1, retain all the functions of their human counterparts. Here we explore the conservation of enzymatic activity toward nucleosomes which leads to repression of estrogen-metabolizing cytochrome P450 (cyp) genes in humans. Biochemical assays establish that BRC-1 and BRD-1 contribute to ubiquitylation of histone H2A in the nucleosome. Mutational analysis shows that while BRC-1 likely binds the nucleosome using a conserved interface, BRD-1 and BARD1 have evolved different modes of binding, resulting in a difference in the placement of ubiquitin on H2A. Gene expression analysis reveals that in spite of this difference, BRC-1 and BRD-1 also contribute to cyp gene repression in C. elegans. Establishing conservation of these functions in C. elegans allows for use of this powerful model organism to address remaining questions regarding regulation of gene expression by BRCA1 and BARD1.

PARylation of BRCA1 limits DNA break resection through BRCA2 and EXO1

The nucleolytic processing (resection) of a DNA double-strand break (DSB) is a critical step to repair the lesion by homologous recombination (HR). PARylation, which is the attachment of poly(ADP-ribose) (PAR) units to specific targets by PAR polymerases (PARPs), regulates many steps of HR, including resection. Here, we show that preventing PARylation of the oncosuppressor BRCA1 induces hyper-resection of DSBs through BRCA2 and the EXO1 nuclease. Upon expression of the unPARylatable variant of BRCA1, we observe a reduced 53BP1-RIF1 barrier for resection accompanied by an increase in the recruitment of the RAD51 recombinase. Similar results are observed when cells are treated with the clinically approved PARP inhibitor olaparib. We propose that PARylation of BRCA1 is important to limit the formation of excessively extended DNA filaments, thereby reducing illegitimate chromosome rearrangements. Our results shed light on molecular aspects of HR and on the mechanisms of PARP inhibitor treatment.

BRCA1 deficiency in triple-negative breast cancer: Protein stability as a basis for therapy

Mutations in breast cancer-associated 1 (BRCA1) increase the lifetime risk of developing breast cancer by up to 51% over the risk of the general population. Many aspects of this multifunctional protein have been revealed, including its essential role in homologous recombination repair, E3 ubiquitin ligase activity, transcriptional regulation, and apoptosis. Although most studies have focused on BRCA1 deficiency due to mutations, only a minority of patients carry BRCA1 mutations. A recent study has suggested an expanded definition of BRCA1 deficiency with reduced BRCA1 levels, which accounts for almost half of all triple-negative breast cancer (TNBC) patients. Reduced BRCA1 levels can result from epigenetic modifications or increased proteasomal degradation. In this review, we discuss how this knowledge of BRCA1 function and regulation of BRCA1 protein stability can help overcome the challenges encountered in the clinic and advance current treatment strategies for BRCA1-related breast cancer patients, especially focusing on TNBC.

Identification of Novel Regulators of Radiosensitivity Using High-Throughput Genetic Screening

The biological impact of ionizing radiation (IR) on humans depends not only on the physical properties and absorbed dose of radiation but also on the unique susceptibility of the exposed individual. A critical target of IR is DNA, and the DNA damage response is a safeguard mechanism for maintaining genomic integrity in response to the induced cellular stress. Unrepaired DNA lesions lead to various mutations, contributing to adverse health effects. Cellular sensitivity to IR is highly correlated with the ability of cells to repair DNA lesions, in particular coding sequences of genes that affect that process and of others that contribute to preserving genomic integrity. However, accurate profiling of the molecular events underlying individual sensitivity requires techniques with sensitive readouts. Here we summarize recent studies that have used whole-genome analysis and identified genes that impact individual radiosensitivity. Whereas microarray and RNA-seq provide a snapshot of the transcriptome, RNA interference (RNAi) and CRISPR-Cas9 techniques are powerful tools that enable modulation of gene expression and characterizing the function of specific genes involved in radiosensitivity or radioresistance. Notably, CRISPR-Cas9 has altered the landscape of genome-editing technology with its increased readiness, precision, and sensitivity. Identifying critical regulators of cellular radiosensitivity would help tailor regimens that enhance the efficacy of therapeutic treatments and fast-track prediction of clinical outcomes. It would also contribute to occupational protection based on average individual sensitivity, as well as the formulation of countermeasures to the harmful effects of radiation.

Synergistic Effect of Quercetin Magnetite Nanoparticles and Targeted Radiotherapy in Treatment of Breast Cancer

Quercetin is a potent cancer therapeutic agent present in fruits and vegetables. The pharmaceutical uses of quercetin are limited due to many problems associated with low solubility, bioavailability, permeability, and instability. In addition, the high doses of quercetin show toxic effects in clinical and experimental studies. Therefore, a new strategy is warranted to overcome these problems without the use of toxic doses. The iron oxide nanoparticles can be used as a drug delivery system. This study aimed to prepare quercetin-conjugated magnetite nanoparticles (QMNPs) using biological simple nanoprecipitation and mediated by fungus Aspergillus oryzae. Also, we initiated in vitro and in vivo studies to determine whether QMNPs might sensitize breast cancer to radiotherapy treatment. The structural, morphological, and magnetic properties of the prepared nanoparticles were studied. The results indicated that QMNPs were spherical in shape and 40 nm in diameter. The in vitro studies showed that the incubation of MCF-7, HePG-2, and A459 cancer cells with QMNPs for 24 h effectively inhibited the growth of cancer cell lines in a concentration-dependent manner with IC50 values of 11, 77.5, and104 nmol/mL, respectively. The combination of QMNPs with irradiation (IR) potently blocked MCF-7 cancer cell proliferation and showed significant changes in the morphology of these cells as observed by bright-field inverted light microscopy. Focusing on the long-term toxicity of QMNPs (20 ml/kg), the assessment of hematological, hepatic, and renal markers indicated no toxic effect. Besides, QMNPs inhibited tumor growth and potently enhanced the lateral radiotherapy treatment in N-methyl-N-nitrosourea (MNU)-induced breast cancer in female white albino rats. These anticancer and radiosensitizing activities were ascribed to cytotoxicity, cell cycle arrest, immunomodulation, and efficiency through induction of apoptosis. In a conclusion, these observations suggest that the QMNPs combined with LRT could act as a potential targeted therapy in breast cancer.

BRCA1: An Endocrine and Metabolic Regulator

The breast and ovarian cancer susceptibility gene (BRCA1) is a tumor suppressor whose mutation has been associated with the development of breast, ovarian and, probably, other malignancies at young ages. The BRCA1 gene product participates in multiple biological pathways including the DNA damage response, transcriptional control, cell growth and apoptosis. Inactivating germline mutations of the BRCA1 gene can be detected in a substantial portion of families with inherited breast and/or ovarian cancer. While the genomic and cancer-related actions of BRCA1 have been extensively investigated, not much information exists regarding the cellular and circulating factors involved in regulation of BRCA1 expression and action. The present review article dissects the emerging role of BRCA1 as an important regulator of various endocrine and metabolic axes. Experimental and clinical evidence links BRCA1 with a number of peptide and steroid hormones. Furthermore, comprehensive analyses identified complex interactions between the insulin/insulin-like growth factor-1 (IGF1) signaling axis and BRCA1. The correlation between metabolic disorders, including diabetes and the metabolic syndrome, and BRCA1 mutations, are discussed in this article.

iTRAQ-based proteomic analysis reveals potential osteogenesis-promoted role of ATM in strontium-incorporated titanium implant

The present study aims to reveal the osteogenic roles played by DNA damage response biomarkers through implementing isobaric tags for relative and absolute quantitation (iTRAQ) technique. First, sandblasted large-grit double acid-etched (SLA) titanium implant and strontium-incorporated (SLA-Sr) titanium implant were used for inserting in the tibiae of rats. iTRAQ technique was used to detect protein expression changes and identify differentially expressed proteins (DEPs). In total, 19,343 peptides and 4280 proteins were screened out. Among them, 91 and 138 DEPs were identified in the SLA-Sr group after implantation for 3 and 7 days, respectively. Ataxia-telangiectasia mutated (ATM) protein up-regulated on the 3rd day showed a trend of further up-regulation on the 7th day. Moreover, functional enrichment analyses were also conducted to explore the biological function of DEPs during the initial stage of osseointegration in vivo, which revealed that the biological functions of the DEPs on the 7th day were mainly related to "mismatch repair" and "mitotic G1 DNA damage checkpoint." Analysis of the Reactome signaling pathway showed that ATM was associated with TP53's regulation and activation. Finally, DNA damage repair related genes were selected for validation at mRNA and protein expression levels. Real-time reverse transcription-polymerase chain reaction and immunohistochemistry validation results demonstrated that mRNA expression level of ATM was higher in SLA-Sr group. In conclusion, SLA-Sr titanium implant could initiate DNA damage repair by activating expression levels of ATM. This study was striving to reveal new faces of better osseointegration and shedding light on the biological function and underlying mechanisms of this important procedure.

ATM Kinase Dead: From Ataxia Telangiectasia Syndrome to Cancer

ATM is one of the principal players of the DNA damage response. This protein exerts its role in DNA repair during cell cycle replication, oxidative stress, and DNA damage from endogenous events or exogenous agents. When is activated, ATM phosphorylates multiple substrates that participate in DNA repair, through its phosphoinositide 3-kinase like domain at the 3'end of the protein. The absence of ATM is the cause of a rare autosomal recessive disorder called Ataxia Telangiectasia characterized by cerebellar degeneration, telangiectasia, immunodeficiency, cancer susceptibility, and radiation sensitivity. There is a correlation between the severity of the phenotype and the mutations, depending on the residual activity of the protein. The analysis of patient mutations and mouse models revealed that the presence of inactive ATM, named ATM kinase-dead, is more cancer prone and lethal than its absence. ATM mutations fall into the whole gene sequence, and it is very difficult to predict the resulting effects, except for some frequent mutations. In this regard, is necessary to characterize the mutated protein to assess if it is stable and maintains some residual kinase activity. Moreover, the whole-genome sequencing of cancer patients with somatic or germline mutations has highlighted a high percentage of ATM mutations in the phosphoinositide 3-kinase domain, mostly in cancer cells resistant to classical therapy. The relevant differences between the complete absence of ATM and the presence of the inactive form in in vitro and in vivo models need to be explored in more detail to predict cancer predisposition of A-T patients and to discover new therapies for ATM-associated cancer cells. In this review, we summarize the multiple discoveries from humans and mouse models on ATM mutations, focusing into the inactive versus null ATM.

The fellowship of the RING: BRCA1, its partner BARD1 and their liaison in DNA repair and cancer

The breast cancer type 1 susceptibility protein (BRCA1) and its partner - the BRCA1-associated RING domain protein 1 (BARD1) - are key players in a plethora of fundamental biological functions including, among others, DNA repair, replication fork protection, cell cycle progression, telomere maintenance, chromatin remodeling, apoptosis and tumor suppression. However, mutations in their encoding genes transform them into dangerous threats, and substantially increase the risk of developing cancer and other malignancies during the lifetime of the affected individuals. Understanding how BRCA1 and BARD1 perform their biological activities therefore not only provides a powerful mean to prevent such fatal occurrences but can also pave the way to the development of new targeted therapeutics. Thus, through this review work we aim at presenting the major efforts focused on the functional characterization and structural insights of BRCA1 and BARD1, per se and in combination with all their principal mediators and regulators, and on the multifaceted roles these proteins play in the maintenance of human genome integrity.

Functions and Molecular Mechanisms of Deltex Family Ubiquitin E3 Ligases in Development and Disease

Ubiquitination is a posttranslational modification of proteins that significantly affects protein stability and function. The specificity of substrate recognition is determined by ubiquitin E3 ligase during ubiquitination. Human Deltex (DTX) protein family, which functions as ubiquitin E3 ligases, comprises five members, namely, DTX1, DTX2, DTX3, DTX3L, and DTX4. The characteristics and functional diversity of the DTX family proteins have attracted significant attention over the last decade. DTX proteins have several physiological and pathological roles and are closely associated with cell signal transduction, growth, differentiation, and apoptosis, as well as the occurrence and development of various tumors. Although they have been extensively studied in various species, data on structural features, biological functions, and potential mechanisms of action of the DTX family proteins remain limited. In this review, recent research progress on each member of the DTX family is summarized, providing insights into future research directions and potential strategies in disease diagnosis and therapy.

ATR/ATM-mediated phosphorylation of BRCA1 T1394 promotes homologous recombinational repair and G2/M checkpoint maintenance

BRCA1 maintains genome integrity and suppresses tumorigenesis by promoting homologous recombination (HR)-mediated repair of DNA double strand breaks (DSB) and DNA damage-induced cell cycle checkpoints. Phosphorylation of BRCA1 by ATM, ATR, CHK2, CDK, and PLK1 kinases has been reported to regulate its functions. Here we show that ATR and ATM-mediated phosphorylation of BRCA1 on T1394, a highly conserved but functionally uncharacterized site, is a key modification for its function in the DNA damage response. Following DNA damage, T1394 phosphorylation ensured faithful repair of DSBs by promoting HR and preventing single strand annealing, a deletion-generating repair process. BRCA1 T1394 phosphorylation further safeguarded chromosomal integrity by maintaining the G2/M checkpoint. Moreover, multiple patient-derived BRCA1 variants of unknown significance were shown to affect T1394 phosphorylation. These results establish an important regulatory mechanism of BRCA1 function in the DNA damage response and may have implications in the development or prognosis of BRCA1-associated cancers.

An overview on breast cancer genetics and recent innovations: Literature survey

Breast cancer is one of the leading cancers nowadays. The genetical mechanism behind breast cancer development is an intricate one. In this review, the genetical background of breast cancer, particularly BRCA 1 and BRCA 2 had been included. Moreover, to summarize the genetics of breast cancer, the recent and ongoing preclinical and clinical studies on the treatment of BRCA-associated breast cancer had also been included. A prime knowledge is that the BRCA gene is the basis of breast cancer risk. How it mediates cell proliferation and associated mechanisms are reviewed here. BRCA 1 gene can influence all phases of the cell cycle and regulate cell cycle progression. BRCA 1 gene can also respond to DNA damages and induce responsive mechanisms. The action of the BRCA gene on associated protein has a wide consideration in breast cancer development. Heterogeneity in breast cancer makes them a fascinating and challenging stream to diagnose and treat. Several clinical therapies are available for breast cancer treatments. Chemotherapy, endocrine therapy, radiation therapy and immunotherapy are the milestones in the cancer treatments. Ral binding protein 1 is a promising target for breast cancer treatment and the platinum-based chemotherapies are the other remarkable fields. In immunotherapy, the usage of anti-programmed death (PD)-1 antibody is a new class of cancer immunotherapy that hinders immune effecter inhibition and potentially expanding preexisting anticancer immune responses. Breast cancer genetics and treatment strategies are crucial in escalating survival rates.

Requirements for Designing an Effective Metallic Nanoparticle (NP)-Boosted Radiation Therapy (RT)

Simple Summary

Recent advances in nanotechnology gave rise to trials with various types of metallic nanoparticles (NPs) to enhance the radiosensitization of cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy. This work reviews the physical and chemical mechanisms leading to the enhancement of ionizing radiation’s detrimental effects on cells and tissues, as well as the plethora of experimental procedures to study these effects of the so-called “NPs’ radiosensitization”. The paper presents the need to a better understanding of all the phases of actions before applying metallic-based NPs in clinical practice to improve the effect of IR therapy. More physical and biological experiments especially in vivo must be performed and simulation Monte Carlo or mathematical codes based on more accurate models for all phases must be developed.

Abstract

Many different tumor-targeted strategies are under development worldwide to limit the side effects and improve the effectiveness of cancer therapies. One promising method is to enhance the radiosensitization of the cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy using metallic nanoparticles (NPs). Radiotherapy with MV photons is more commonly available and applied in cancer clinics than high LET particle radiotherapy, so the addition of high-Z NPs has the potential to further increase the efficacy of photon radiotherapy in terms of NP radiosensitization. Generally, when using X-rays, mainly the inner electron shells are ionized, which creates cascades of both low and high energy Auger electrons. When using high LET particles, mainly the outer shells are ionized, which give electrons with lower energies than when using X-rays. The amount of the produced low energy electrons is higher when exposing NPs to heavy charged particles than when exposing them to X-rays. Since ions traverse the material along tracks, and therefore give rise to a much more inhomogeneous dose distributions than X-rays, there might be a need to introduce a higher number of NPs when using ions compared to when using X-rays to create enough primary and secondary electrons to get the desired dose escalations. This raises the questions of toxicity. This paper provides a review of the fundamental processes controlling the outcome of metallic NP-boosted photon beam and ion beam radiation therapy and presents some experimental procedures to study the biological effects of NPs’ radiosensitization. The overview shows the need for more systematic studies of the behavior of NPs when exposed to different kinds of ionizing radiation before applying metallic-based NPs in clinical practice to improve the effect of IR therapy.

Breast cancer type 1 and neurodegeneration: consequences of deficient DNA repair

Numerous cellular processes, including toxic protein aggregation and oxidative stress, have been studied extensively as potential mechanisms underlying neurodegeneration. However, limited therapeutic efficacy targeting these processes has prompted other mechanisms to be explored. Previous research has emphasized a link between cellular senescence and neurodegeneration, where senescence induced by excess DNA damage and deficient DNA repair results in structural and functional changes that ultimately contribute to brain dysfunction and increased vulnerability for neurodegeneration. Specific DNA repair proteins, such as breast cancer type 1, have been associated with both stress-induced senescence and neurodegenerative diseases, however, specific mechanisms remain unclear. Therefore, this review explores DNA damage-induced senescence in the brain as a driver of neurodegeneration, with particular focus on breast cancer type 1, and its potential contribution to sex-specific differences associated with neurodegenerative disease.

Expanding roles of cell cycle checkpoint inhibitors in radiation oncology

PURPOSE

Radiation-induced activation of cell cycle checkpoints have been of long-standing interest. The WEE1, CHK1 and ATR kinases are key factors in cell cycle checkpoint regulation and are essential for the S and G2 checkpoints. Here, we review the rationale for why inhibitors of WEE1, CHK1 and ATR could be beneficial in combination with radiation.

CONCLUSIONS

Combined treatment with radiation and inhibitors of these kinases results in checkpoint abrogation and subsequent mitotic catastrophe. This might selectively radiosensitize tumor cells, as they often lack the p53-dependent G1 checkpoint and therefore rely more on the G2 checkpoint to repair DNA damage. Further affecting the repair of radiation damage, inhibition of WEE1, CHK1 or ATR also specifically suppresses the homologous recombination repair pathway. Moreover, inhibition of these kinases can induce massive replication stress during S phase of the cell cycle, likely contributing to eliminate radioresistant S phase cells. Intriguingly, recent findings suggest that cell cycle checkpoint inhibitors in combination with radiation can also enhance anti-tumor immune effects. Altogether, the expanding knowledge about the functional roles of WEE1, CHK1 and ATR inhibitors support that they are promising candidates for use in combination with radiation treatment.

PARP-1 overexpression does not protect HaCaT cells from DNA damage induced by SiO2 nanoparticles

Nano-SiO₂ is increasingly used in diagnostic and biomedical research because of its ease of production and relatively low cost and which is generally regarded as safe and has been approved for use as a food or animal feed ingredient. Although recent literature reveals that nano-SiO₂ may present toxicity and DNA damage, however, the underlying mechanism remains poorly understood. Since in previous studies, we found that nano-SiO₂ treatment down-regulated the expression of the poly(ADP-ribose) polymerases-1 (PARP-1), a pivotal DNA repair gene, in human HaCaT cells and PAPR-1 knockdown can aggravate DNA damage induced by nano-SiO₂. Therefore, we speculate whether PARP-1 overexpression can protect DNA from damage induced by nano-SiO₂. However, our data demonstrated that overexpression of PARP-1 in HaCaT cells slightly enhanced the cellular proliferation of undamaged cells, when compared with both empty vector control cells and parental cells, but had drastic consequences for cells treated with nano-SiO₂. The PARP-1 overtransfected cells were sensitized to the cytotoxic effects and DNA damage of nano-SiO₂ compared with control parental cells. Meanwhile, flow cytometric analysis of nano-SiO₂ stimulated poly(ADP-ribose) synthesis revealed consistently larger fractions of cells positive for this polymer in the PARP-1 overexpression cells than in control clones. Combining our previous research on PARP-1 knockdown HaCaT cells, we hypothesize that an optimal level of cellular poly(ADP-ribose) accumulation exists for the cellular recovery from DNA damage.

Excision of mutagenic replication-blocking lesions suppresses cancer but promotes cytotoxicity and lethality in nitrosamine-exposed mice

N-Nitrosodimethylamine (NDMA) is a DNA-methylating agent that has been discovered to contaminate water, food, and drugs. The alkyladenine DNA glycosylase (AAG) removes methylated bases to initiate the base excision repair (BER) pathway. To understand how gene-environment interactions impact disease susceptibility, we study Aag-knockout (Aag-/-) and Aag-overexpressing mice that harbor increased levels of either replication-blocking lesions (3-methyladenine [3MeA]) or strand breaks (BER intermediates), respectively. Remarkably, the disease outcome switches from cancer to lethality simply by changing AAG levels. To understand the underlying basis for this observation, we integrate a suite of molecular, cellular, and physiological analyses. We find that unrepaired 3MeA is somewhat toxic, but highly mutagenic (promoting cancer), whereas excess strand breaks are poorly mutagenic and highly toxic (suppressing cancer and promoting lethality). We demonstrate that the levels of a single DNA repair protein tip the balance between blocks and breaks and thus dictate the disease consequences of DNA damage.

SIRT2 promotes BRCA1-BARD1 heterodimerization through deacetylation

The breast cancer type I susceptibility protein (BRCA1) and BRCA1-associated RING domain protein I (BARD1) heterodimer promote genome integrity through pleiotropic functions, including DNA double-strand break (DSB) repair by homologous recombination (HR). BRCA1-BARD1 heterodimerization is required for their mutual stability, HR function, and role in tumor suppression; however, the upstream signaling events governing BRCA1-BARD1 heterodimerization are unclear. Here, we show that SIRT2, a sirtuin deacetylase and breast tumor suppressor, promotes BRCA1-BARD1 heterodimerization through deacetylation. SIRT2 complexes with BRCA1-BARD1 and deacetylates conserved lysines in the BARD1 RING domain, interfacing BRCA1, which promotes BRCA1-BARD1 heterodimerization and consequently BRCA1-BARD1 stability, nuclear retention, and localization to DNA damage sites, thus contributing to efficient HR. Our findings define a mechanism for regulation of BRCA1-BARD1 heterodimerization through SIRT2 deacetylation, elucidating a critical upstream signaling event directing BRCA1-BARD1 heterodimerization, which facilitates HR and tumor suppression, and delineating a role for SIRT2 in directing DSB repair by HR.

Minten et al. show that SIRT2, a sirtuin deacetylase and tumor suppressor protein, promotes BRCA1-BARD1 heterodimerization through deacetylation of BARD1 at conserved lysines within its RING domain. These findings elucidate a critical upstream signaling event directing BRCA1-BARD1 heterodimerization, which facilitates HR and tumor suppression.

Transcriptomic profiling and genomic mutational analysis of Human coronavirus (HCoV)-229E -infected human cells

Human coronaviruses (HCoVs) cause mild to severe respiratory infection. Most of the common cold illnesses are caused by one of four HCoVs, namely HCoV-229E, HCoV-NL63, HCoV-HKU1 and HCoV-OC43. Several studies have applied global transcriptomic methods to understand host responses to HCoV infection, with most studies focusing on the pandemic severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome CoV (MERS-CoV) and the newly emerging SARS-CoV-2. In this study, Next Generation Sequencing was used to gain new insights into cellular transcriptomic changes elicited by alphacoronavirus HCoV-229E. HCoV-229E-infected MRC-5 cells showed marked downregulation of superpathway of cholesterol biosynthesis and eIF2 signaling pathways. Moreover, upregulation of cyclins, cell cycle control of chromosomal replication, and the role of BRCA1 in DNA damage response, alongside downregulation of the cell cycle G1/S checkpoint, suggest that HCoV-229E may favors S phase for viral infection. Intriguingly, a significant portion of key factors of cell innate immunity, interferon-stimulated genes (ISGs) and other transcripts of early antiviral response genes were downregulated early in HCoV-229E infection. On the other hand, early upregulation of the antiviral response factor Apolipoprotein B mRNA editing enzyme catalytic subunit 3B (APOBEC3B) was observed. APOBEC3B cytidine deaminase signature (C-to-T) was previously observed in genomic analysis of SARS-CoV-2 but not HCoV-229E. Higher levels of C-to-T mutations were found in countries with high mortality rates caused by SARS-CoV-2. APOBEC activity could be a marker for new emerging CoVs. This study will enhance our understanding of commonly circulating HCoVs and hopefully provide critical information about still-emerging coronaviruses.

FANCJ compensates for RAP80 deficiency and suppresses genomic instability induced by interstrand cross-links

FANCJ, a DNA helicase and interacting partner of the tumor suppressor BRCA1, is crucial for the repair of DNA interstrand crosslinks (ICL), a highly toxic lesion that leads to chromosomal instability and perturbs normal transcription. In diploid cells, FANCJ is believed to operate in homologous recombination (HR) repair of DNA double-strand breaks (DSB); however, its precise role and molecular mechanism is poorly understood. Moreover, compensatory mechanisms of ICL resistance when FANCJ is deficient have not been explored. In this work, we conducted a siRNA screen to identify genes of the DNA damage response/DNA repair regime that when acutely depleted sensitize FANCJ CRISPR knockout cells to a low concentration of the DNA cross-linking agent mitomycin C (MMC). One of the top hits from the screen was RAP80, a protein that recruits repair machinery to broken DNA ends and regulates DNA end-processing. Concomitant loss of FANCJ and RAP80 not only accentuates DNA damage levels in human cells but also adversely affects the cell cycle checkpoint, resulting in profound chromosomal instability. Genetic complementation experiments demonstrated that both FANCJ's catalytic activity and interaction with BRCA1 are important for ICL resistance when RAP80 is deficient. The elevated RPA and RAD51 foci in cells co-deficient of FANCJ and RAP80 exposed to MMC are attributed to single-stranded DNA created by Mre11 and CtIP nucleases. Altogether, our cell-based findings together with biochemical studies suggest a critical function of FANCJ to suppress incompletely processed and toxic joint DNA molecules during repair of ICL-induced DNA damage.

Molecular contribution of BRCA1 and BRCA2 to genome instability in breast cancer patients: review of radiosensitivity assays

BACKGROUND

DNA repair pathways, cell cycle arrest checkpoints, and cell death induction are present in cells to process DNA damage and prevent genomic instability caused by various extrinsic and intrinsic ionizing factors. Mutations in the genes involved in these pathways enhances the ionizing radiation sensitivity, reduces the individual's capacity to repair DNA damages, and subsequently increases susceptibility to tumorigenesis.

BODY

BRCA1 and BRCA2 are two highly penetrant genes involved in the inherited breast cancer and contribute to different DNA damage pathways and cell cycle and apoptosis cascades. Mutations in these genes have been associated with hypersensitivity and genetic instability as well as manifesting severe radiotherapy complications in breast cancer patients. The genomic instability and DNA repair capacity of breast cancer patients with BRCA1/2 mutations have been analyzed in different studies using a variety of assays, including micronucleus assay, comet assay, chromosomal assay, colony-forming assay, γ -H2AX and 53BP1 biomarkers, and fluorescence in situ hybridization. The majority of studies confirmed the enhanced spontaneous & radiation-induced radiosensitivity of breast cancer patients compared to healthy controls. Using G2 micronucleus assay and G2 chromosomal assay, most studies have reported the lymphocyte of healthy carriers with BRCA1 mutation are hypersensitive to invitro ionizing radiation compared to non-carriers without a history of breast cancer. However, it seems this approach is not likely to be useful to distinguish the BRCA carriers from non-carrier with familial history of breast cancer.

CONCLUSION

In overall, breast cancer patients are more radiosensitive compared to healthy control; however, inconsistent results exist about the ability of current radiosensitive techniques in screening BRCA1/2 carriers or those susceptible to radiotherapy complications. Therefore, developing further radiosensitivity assay is still warranted to evaluate the DNA repair capacity of individuals with BRCA1/2 mutations and serve as a predictive factor for increased risk of cancer mainly in the relatives of breast cancer patients. Moreover, it can provide more evidence about who is susceptible to manifest severe complication after radiotherapy.

Combination of CHEK1/2 inhibition and ionizing radiation results in abscopal tumor response through increased micronuclei formation

We explore a novel strategy of activating immune signaling through increased micronuclei formation utilizing a cell cycle checkpoint inhibitor to drive cell cycle progression following ionizing radiation. The Chk1/2 inhibitor AZD7762 is used to abrogate radiation therapy (RT)-induced G2/M cell cycle arrest in multiple cell lines and, we find that this therapeutic combination promotes increased micronuclei formation in vitro and subsequently drives increased type I interferon signaling and cytotoxic T-cell activation. In vivo studies using B16-F10 melanoma cancer cells implanted in C57/BL6 mice demonstrate improved rates of tumor control at the abscopal (unirradiated) site, located outside of the radiation field, only in the AZD7762+RT group, with a corresponding reduction in mean tumor volume, increase in the CD8 T-cell population, and immune activated gene signaling. Our results demonstrate that targeted inhibition of cell cycle checkpoint activation following ionizing radiation drives increased production of immunogenic micronuclei, leading to systemic tumor response with potential future clinical benefit.

The Homologous Recombination Repair Pathway is Associated with Resistance to Radiotherapy in Nasopharyngeal Carcinoma

Radiotherapy plays a major role in the management of nasopharyngeal carcinoma (NPC). However, the radioresistant cells limit its efficiency and drive recurrence inside the irradiated tumor volume leading to poor outcome for patients. To illuminate the signal pathway involved in the radioresistance and evaluate the potential for predicting NPC response to radiotherapy, we established the radioresistant NPC cell line (CNE2-RR) derived from NPC cell line CNE2 by gradually increased the radiation dose (total 60 Gy), and the radioresistance of CNE2-RR cells was evaluated by the colony formation, FCM and comet assays. Furthermore, comparison of established CNE2-RR cell line to parental cell line found the homologous recombination repair (HRR) proteins differences involved in NPC radioresistance. In addition, the differentially expressed proteins were further validated by western blotting, immunofluorescence and IHC in tumor xenografs and radioresistant NPC tissues. Furthermore, the correlation of HRR proteins expression levels with NPC radioresistance were evaluated. The results showed that the upregulation of HRR proteins were significantly correlated with NPC radioresistance. In addition, using the Youden Index cutoff value, a panel of the HRR proteins analyses revealed a sensitivity of 70%, specificity of 72%. Furthermore, silencing NFBD1 enhanced the radiosensitivity of CNE2-RR cells by impairing IR-inducing γ-H2AX and HR proteins foci formation. These results suggest that controlling the HRR signaling pathway may hold promise to overcome NPC radioresistance.

Assembly of a parts list of the human mitotic cell cycle machinery

The set of proteins required for mitotic division remains poorly characterized. Here, an extensive series of correlation analyses of human and mouse transcriptomics data were performed to identify genes strongly and reproducibly associated with cells undergoing S/G2-M phases of the cell cycle. In so doing, 701 cell cycle-associated genes were defined and while it was shown that many are only expressed during these phases, the expression of others is also driven by alternative promoters. Of this list, 496 genes have known cell cycle functions, whereas 205 were assigned as putative cell cycle genes, 53 of which are functionally uncharacterized. Among these, 27 were screened for subcellular localization revealing many to be nuclear localized and at least three to be novel centrosomal proteins. Furthermore, 10 others inhibited cell proliferation upon siRNA knockdown. This study presents the first comprehensive list of human cell cycle proteins, identifying many new candidate proteins.

The Cajal Body Protein WRAP53β Prepares the Scene for Repair of DNA Double-Strand Breaks by Regulating Local Ubiquitination

Proper repair of DNA double-strand breaks is critical for maintaining genome integrity and avoiding disease. Modification of damaged chromatin has profound consequences for the initial signaling and regulation of repair. One such modification involves ubiquitination by E3 ligases RNF8 and RNF168 within minutes after DNA double-strand break formation, altering chromatin structure and recruiting factors such as 53BP1 and BRCA1 for repair via non-homologous end-joining (NHEJ) and homologous recombination (HR), respectively. The WD40 protein WRAP53β plays an essential role in localizing RNF8 to DNA breaks by scaffolding its interaction with the upstream factor MDC1. Loss of WRAP53β impairs ubiquitination at DNA lesions and reduces downstream repair by both NHEJ and HR. Intriguingly, WRAP53β depletion attenuates repair of DNA double-strand breaks more than depletion of RNF8, indicating functions other than RNF8-mediated ubiquitination. WRAP53β plays key roles with respect to the nuclear organelles Cajal bodies, including organizing the genome to promote associated transcription and collecting factors involved in maturation of the spliceosome and telomere elongation within these organelles. It is possible that similar functions may aid also in DNA repair. Here we describe the involvement of WRAP53β in Cajal bodies and DNA double-strand break repair in detail and explore whether and how these processes may be linked. We also discuss the possibility that the overexpression of WRAP53β detected in several cancer types may reflect its normal participation in the DNA damage response rather than oncogenic properties.

Two synchronous malignancies: nodular melanoma and renal cell carcinoma in a patient with an underlying germline BRCA2 mutation

Modernised genetic testing among patients with cancer has led to an increasing wealth of knowledge regarding cancer biology and aetiology. Furthermore, some germline mutations have the potential to direct therapeutic approaches as well. While BRCA1/2 mutations are well-established risk factors for breast and ovarian cancers, their impact on other cancers is less understood. We describe a patient with a germline BRCA2 mutation who developed synchronous melanoma and renal cell carcinoma, but responded well to treatment and is now cancer free.

Homologous recombination deficiency in triple negative breast cancer

Triple negative breast cancer (TNBC) represents a heterogeneous subtype of breast cancer characterized by an unfavorable prognosis due to its aggressive biology. The median overall survival (OS) for patients with metastatic TNBC is around 9-12 months with conventional cytotoxic agents. Considering this suboptimal outcome, which is induced despite of medical treatment, new therapeutic strategies would be urgently needed. The ultimate goal of precision medicine is to identify specific molecular alterations that permit considering effective targeted drug(s). Germline BRCA mutations occur in 10-20% of TNBC patients while somatic mutations occur in 3-5% of them. Alterations in the homologous recombination (HR) system are typical of BRCA mutant tumors, but can also be identified in tumors that do not carry this mutation, defining a subgroup of patients referred to as BRCAness. In this review, we focus on the role of homologous recombination deficiency (HRD) as both predictive and prognostic factor in different settings of TNBC patients treated with DNA damaging drugs and poly ADP ribose polymerase (PARP) inhibitors.

PALB2 connects BRCA1 and BRCA2 in the G2/M checkpoint response

The G2/M checkpoint inhibits mitotic entry upon DNA damage thereby preventing segregation of broken chromosomes and preserving genome stability. The tumor suppressor proteins BRCA1, PALB2 and BRCA2 constitute a BRCA1-PALB2-BRCA2 axis that is essential for homologous recombination (HR)-based DNA double strand break repair. Besides HR, BRCA1 has been implicated in both the initial activation and the maintenance of the G2/M checkpoint, while BRCA2 and PALB2 have been shown to be critical for its maintenance. Here we show that all 3 proteins can play a significant role in both checkpoint activation and checkpoint maintenance, depending on cell type and context, and that PALB2 links BRCA1 and BRCA2 in checkpoint response. The BRCA1-PALB2 interaction can be important for checkpoint activation, whereas the PALB2-BRCA2 complex formation appears to be more critical for checkpoint maintenance. Interestingly, the function of PALB2 in checkpoint response appears to be independent of CHK1 and CHK2 phosphorylation. Following ionizing radiation, cells with disengaged BRCA1-PALB2 interaction show greatly increased chromosomal abnormalities due apparently to combined defects in HR and checkpoint control. These findings provide new insights into DNA damage checkpoint control and further underscore the critical importance of the proper cooperation of the BRCA and PALB2 proteins in genome maintenance.

Cyclin B1 stability is increased by interaction with BRCA1, and its overexpression suppresses the progression of BRCA1-associated mammary tumors

Germline BRCA1 mutations predispose women to breast and ovarian cancer. BRCA1, a large protein with multiple functional domains, interacts with numerous proteins involved in many important biological processes and pathways. However, to date, the role of BRCA1 interactions at specific stages in the progression of mammary tumors, particularly in relation to cell cycle regulation, remains elusive. Here, we demonstrate that BRCA1 interacts with cyclin B1, a crucial cell cycle regulator, and that their interaction is modulated by DNA damage and cell cycle phase. In DNA-damaged mitotic cells, BRCA1 inhibits cytoplasmic transportation of cyclin B1, which prevents cyclin B1 degradation. Moreover, restoration of cyclin B1 in BRCA1-deficient cells reduced cell survival in association with induction of apoptosis. We further demonstrate that treatment of Brca1-mutant mammary tumors with vinblastine, which induces cyclin B1, significantly reduced tumor progression. In addition, a correlation analysis of vinblastine responses and gene expression profiles in tumors at baseline revealed 113 genes that were differentially expressed between tumors that did and did not respond to vinblastine treatment. Further analyses of protein–protein interaction networks revealed gene clusters related to vinblastine resistance, including nucleotide excision repair, epigenetic regulation, and the messenger RNA surveillance pathway. These findings enhance our understanding of how loss of BRCA1 disrupts mitosis regulation through dysregulation of cyclin B1 and provide evidence suggesting that targeting cyclin B1 may be useful in BRCA1-associated breast cancer therapy.

The role of disrupted activity of the protein BRCA1 in the progression of breast cancer has been clarified, suggesting that targeting another protein with which it interacts could offer a new route to treatment. Mutations of BRCA1 are known to predispose women to both breast and ovarian cancers. Researchers led by Sang Soo Kim (National Cancer Center, South Korea) and Rui-Hong Wang (University of Macau, China) studied the interaction with a protein called cyclin B1 that controls cell growth and division. They found that, in mitosis, BRCA1 interacts with and stabilizes cyclin B1, explaining why the loss of BRCA1 can disrupt the G2/M cell cycle control and accumulate the genetic instability. Treatment of Brca1-mutant mammary tumors with vinblastine, which alters cyclin B1 level, significantly reduced tumor progression with reduction of survival and induction of apoptosis.

Identification of a novel cell cycle-related gene signature predicting survival in patients with gastric cancer

Gastric cancer (GC) is one of the most fatal cancers in the world. Thousands of biomarkers have been explored that might be related to survival and prognosis via database mining. However, the prediction effect of single gene biomarkers is not specific enough. Increasing evidence suggests that gene signatures are emerging as a possible better alternative. We aimed to develop a novel gene signature to improve the prognosis prediction of GC. Using the messenger RNA (mRNA)-mining approach, we performed mRNA expression profiling in a large GC cohort (n = 375) from The Cancer Genome Atlas (TCGA) database. Gene Set Enrichment Analysis (GSEA) was performed, and we recovered genes related to the G2/M checkpoint, which we identified with a Cox proportional regression model. We identified a set of five genes (MARCKS, CCNF, MAPK14, INCENP, and CHAF1A), which were significantly associated with overall survival (OS) in the test series. Based on this five-gene signature, the test series patients could be classified into high-risk or low-risk subgroups. Multivariate Cox regression analysis indicated that the prognostic power of this five-gene signature was independent of clinical features. In conclusion, we developed a five-gene signature related to the cell cycle that can predict survival for GC. Our findings provide novel insight that is useful for understanding cell cycle mechanisms and for identifying patients with GC with poor prognoses.

Nucleoporin 54 contributes to homologous recombination repair and post-replicative DNA integrity

The nuclear pore complex (NPC) machinery is emerging as an important determinant in the maintenance of genome integrity and sensitivity to DNA double-strand break (DSB)-inducing agents, such as ionising radiation (IR). In this study, using a high-throughput siRNA screen, we identified the central channel NPC protein Nup54, and concomitantly its molecular partners Nup62 and Nup58, as novel factors implicated in radiosensitivity. Nup54 depletion caused an increase in cell death by mitotic catastrophe after IR, and specifically enhanced both the duration of the G2 arrest and the radiosensitivity of cells that contained replicated DNA at the time of IR exposure. Nup54-depleted cells also exhibited increased formation of chromosome aberrations arisen from replicated DNA. Interestingly, we found that Nup54 is epistatic with the homologous recombination (HR) factor Rad51. Moreover, using specific DNA damage repair reporters, we observed a decreased HR repair activity upon Nup54 knockdown. In agreement with a role in HR repair, we also demonstrated a decreased formation of HR-linked DNA synthesis foci and sister chromatid exchanges after IR in cells depleted of Nup54. Our study reveals a novel role for Nup54 in the response to IR and the maintenance of HR-mediated genome integrity.

NEK1 loss-of-function mutation induces DNA damage accumulation in ALS patient-derived motoneurons

Mutations in genes coding for proteins involved in DNA damage response (DDR) and repair, such as C9orf72 and FUS (Fused in Sarcoma), are associated with neurodegenerative diseases and lead to amyotrophic lateral sclerosis (ALS). Heterozygous loss-of-function mutations in NEK1 (NIMA-related kinase 1) have also been recently found to cause ALS. NEK1 codes for a multifunctional protein, crucially involved in mitotic checkpoint control and DDR. To resolve pathological alterations associated with NEK1 mutation, we compared hiPSC-derived motoneurons carrying a NEK1 mutation with mutant C9orf72 and wild type neurons at basal level and after DNA damage induction. Motoneurons carrying a C9orf72 mutation exhibited cell specific signs of increased DNA damage. This phenotype was even more severe in NEK1^c.2434A>T neurons that showed significantly increased DNA damage at basal level and impaired DDR after induction of DNA damage in an maturation-dependent manner. Our results provide first mechanistic insight in pathophysiological alterations induced by NEK1 mutations and point to a converging pathomechanism of different gene mutations causative for ALS. Therefore, our study contributes to the development of novel therapeutic strategies to reduce DNA damage accumulation in neurodegenerative diseases and ALS.

DNA repair and cell cycle checkpoint defects in a mouse model of 'BRCAness' are partially rescued by 53BP1 deletion

'BRCAness' is a term used to describe cancer cells that behave similarly to tumors with BRCA1 or BRCA2 mutations. The BRCAness phenotype is associated with hypersensitivity to chemotherapy agents including PARP inhibitors, which are a promising class of recently-licensed anti-cancer treatments. This hypersensitivity arises because of a deficiency in the homologous recombination (HR) pathway for DNA double-strand break repair. To gain further insight into how genetic modifiers of HR contribute to the BRCAness phenotype, we created a new mouse model of BRCAness by generating mice that are deficient in BLM helicase and the Exo1 exonuclease, which are involved in the early stages of HR. We find that cells lacking BLM and Exo1 exhibit a BRCAness phenotype, with diminished HR, and hypersensitivity to PARP inhibitors. We further tested how 53BP1, an important regulator of HR, affects repair efficiency in our BRCAness model. We find that deletion of 53BP1 can relieve several of the repair deficiencies observed in cells lacking BLM and Exo1, just as it does in cells lacking BRCA1. These results substantiate the importance of BRCAness as a concept for classification of cancer cases, and further clarify the role of 53BP1 in regulation of DNA repair pathway choice in mammalian cells.

RAP80 is an independent prognosis biomarker for the outcome of patients with esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is the most popular pathology of esophageal cancer (EC) in China, especially in Henan province, mid-east of China. Presently, targeting DNA damage repair (DDR) factors is a promising approach for cancer therapy. Our group has been focusing on exploring the DDR factors overexpressed in ESCC tissues to provide potential targets for therapies for many years. RAP80/UIMC1 (ubiquitin interaction motif containing 1), one of those DDR factors we tested, was highly overexpressed in ESCC tissues compared with adjacent normal tissues. Moreover, the RAP80 mRNA level was validated to be an independent prognosis biomarker for the overall survival time of ESCC patients. The following biological assays revealed that it promoted cell proliferation both in vitro and in vivo, inhibited cell apoptosis at both early and late stages, and participated in G2/M checkpoint regulation. Even though studies have reported that ATM phosphorylates RAP80 at different serine sites upon DNA damage, the reversal regulation of RAP80 on the activity of ATM has never been investigated. In the study, mechanism explorations revealed that RAP80 positively regulated the ATM activity via proteasome–ubiquitination pathway to promote the transition of G2/M phase in cell cycle. By examining a number of E3 ubiquitination ligases (Ub) and deubiquitination (DUb) enzymes, we found that RAP80 positively regulated the stability of USP13 to promote cell proliferation of EC cells. Moreover, inhibition of RAP80 greatly sensitized EC cells to ATM inhibitor KU-55933, triggering a potential combination of RAP80 inhibitors and ATM inhibitors to enhance the therapeutic efficiency of ESCC patients for the clinicians.

Low concentrations of antimony impair DNA damage signaling and the repair of radiation-induced DSB in HeLa S3 cells

Antimony is utilized in a large variety of industrial applications, leading to significant environmental and occupational exposure. Mainly based on animal experiments, the IARC and MAK Commission have classified antimony and its inorganic compounds as Group 2B or 2 carcinogens, respectively. However, the underlying mode(s) of action are still largely unknown. In the present study, we investigated the impact of non-cytotoxic up to cytotoxic concentrations of SbCl₃ on DNA DSB repair and cell cycle control in HeLa S3 cells. We induced DSB by γ-irradiation and analyzed inhibitory actions of antimony on potential molecular targets of the DSB repair machinery. Antimony disturbed cell cycle control, affecting phosphorylation of Chk1. Furthermore, the repair of DSB was impaired in the presence of antimony, as monitored by pulsed-field gel electrophoresis and γH2AX foci formation of cells in G1 and G2 phase. Specifically, BRCA1 and RAD51 were identified as molecular targets. Our results point towards an interference with both non-homologous end-joining (NHEJ) and homologous recombination (HR), and inhibitory effects may be explained by interactions with critical cysteine groups; this needs to be further investigated. Altogether, the results provide further evidence for the impairment of DNA repair processes as one underlying mechanism in antimony-induced carcinogenicity.

Effect of TPA and HTLV-1 Tax on BRCA1 and ERE controlled genes expression

Interference with the expression and/or functions of the multifunctional tumor suppressor BRCA1 leads to a high risk of breast and ovarian cancers. BRCA1 expression is usually activated by the estrogen (E2) liganded ERα receptor. Activated ERα is considered as a potent transcription factor which activates various genes expression by 2 pathways. A classical pathway, ERα binds directly to E2-responsive elements (EREs) in the promoters of the responsive genes and a non-classical pathway where ERα indirectly binds with the appropriate gene promoter. In our previous study, HTLV-1Tax was found to strongly inhibit ERα induced BRCA1 expression while stimulating ERα induced ERE dependent genes. TPA is a strong PKC activator which found to induce the expression of HTLV-1. Here we examined the effect of TPA on the expression of BRCA1 and genes controlled by ERE region in MCF-7 cells and on Tax activity on these genes. Our results showed strong stimulatory effect of TPA on both BRCA1 and ERE expression without treatment with E2. Tax did not show any significant effect on these TPA activities. It seems that TPA activation of BRCA1 and ERE expression is dependent on PKC activity but not through the NFκB pathway. However, 53BP1 may be involved in this TPA activity because its overexpression significantly reduced the TPA stimulatory effect on BRCA1 and ERE expression. Additionally, our Chip assay results probably exclude possible involvement of ERα pathway in this TPA activity because TPA did not interfere with the binding of ERα to both BRCA1 promoter and ERE region.

Identification of direct target genes of miR-7, miR-9, miR-96, and miR-182 in the human breast cancer cell lines MCF-7 and MDA-MB-231

Some microRNAs have carcinogenic or tumor suppressive effects in breast cancer, which is the most common cancer in women worldwide. MiR-7 and miR-9 are tumor suppressor microRNAs, which induce apoptosis and inhibit proliferation in breast cancer cells. Moreover, miR-96 and miR-182 are onco-microRNAs that increase proliferation, migration, and tumorigenesis in breast cancer cells. This study aimed to identify the direct target genes of these four microRNAs in the human breast cancer cell lines MCF-7 and MDA-MB-231. Initially, bioinformatics tools were used to identify the target genes that have binding sites for miR-7, MiR-9, MiR-96, and miR-182 and are also associated with breast cancer. Subsequently, the findings of the bioinformatics analysis relating to the effects of these four microRNAs on the 3'-UTR activity of the potential target genes were confirmed using the dual luciferase assay in MCF-7 and MDA-MB-231 cells co-transfected with the vectors containing 3'-UTR segments of the target genes downstream of a luciferase coding gene and each of the microRNAs. Finally, the effects of microRNAs on the endogenous expression of potential target genes were assessed by the overexpression of each of the four microRNAs in MCF-7 and MDA-MB-231 cells. Respectively, three, three, three, and seven genes were found to have binding sites for miR-7, miR-9, miR-96, and miR-182 and were associated with breast cancer. The results of empirical studies including dual luciferase assays and real-time PCR confirmed that miR-7 regulates the expression of BRCA1 and LASP1; MiR-9 regulates the expression of AR; miR-96 regulates the expression of ABCA1; and miR-182 regulates the expression of NBN, TOX3, and LASP1. Taken together, our results suggest that the tumor suppressive effects of miR-7 may be mediated partly by regulating the expression of BRCA1 as a tumor suppressor gene in breast cancer. In addition, this microRNA and miR-182 may have effects on the nodal-positivity and tumor size of breast carcinoma through the regulation of LASP1. The tumor suppressive functions of miR-9 may be mediated partly by suppressing the expression of AR-an oncogene in breast cancer. Moreover, miR-96 may play an oncogenic role in breast cancer by suppressing the apoptosis through the regulation of ABCA1.

Distinct implications of different BRCA mutations: efficacy of cytotoxic chemotherapy, PARP inhibition and clinical outcome in ovarian cancer

Approximately a fifth of ovarian carcinoma (OC) is associated with inherited germline mutations, most commonly in the DNA repair genes BRCA1 or BRCA2 (BRCA). BRCA1- and BRCA2-associated OCs have historically been described as a single subgroup of OC that displays a distinct set of characteristics termed the "BRCAness" phenotype. The hallmarks of this phenotype are superior clinical outcome and hypersensitivity to platinum-based chemotherapy and poly-(ADP-ribose) polymerase (PARP) inhibitors. However, growing evidence suggests that BRCA1- and BRCA2-associated OCs display distinct characteristics, most notably in long-term patient survival. Furthermore, recent data indicate that the site of BRCA1 mutation is important with regard to platinum and PARP inhibitor sensitivity. Here, we summarize the body of research describing the BRCAness phenotype and highlight the differential implications of different BRCA mutations with regard to clinicopathologic features, therapy sensitivity and clinical outcome in OC.