Role of BRCA gene dysfunction in breast and ovarian cancer predisposition

"There should be one spot that you can go:" BRCA mutation carriers' perspectives on cancer risk management and a hereditary cancer registry

Individuals who carry BRCA1 or BRCA2 pathogenic variants are recommended to have extensive cancer prevention screening and risk-reducing surgeries. Uptake of these recommendations is variable, and there remains room for improvement in the risk management of BRCA carriers. This paper explores female BRCA carriers' experiences with the current model of care and their perspectives on (and interest in) an inherited cancer registry. Findings can inform the development of a dedicated high-risk screening and management program for these patients. Quantitative and qualitative data were gathered through a provincial descriptive survey and semi-structured qualitative interviews to assess BRCA carriers' opinions toward risk management services in the province of Newfoundland and Labrador (NL), Canada. Survey (n = 69) and interview data (n = 15) revealed continuity and coordination challenges with the current system of care of high-risk individuals. Respondents suggested an inherited cancer registry would help identify high-risk individuals and provide a centralized system of risk management for identified carriers. Respondents identified concerns about the privacy of their registry data, including who could access it. Findings suggest BRCA carriers see great value in an inherited cancer registry. Specifically, participants noted it could provide a centralized system to help improve the coordination of burdensome, life-long risk management. Important patient concerns about protecting their privacy and their health data confidentiality must be addressed in patient and public information and informed consent documents about a registry.

BRCA1/2 variants of unknown significance in hereditary breast and ovarian cancer (HBOC) syndrome: looking for the hidden meaning

Hereditary breast and ovarian cancer syndrome is caused by germline mutations in BRCA1/2 genes. These genes are very large and their mutations are heterogeneous and scattered throughout the coding sequence. In addition to the above-mentioned mutations, variants of uncertain/unknown significance (VUSs) have been identified in BRCA genes, which make more difficult the clinical management of the patient and risk assessment. In the last decades, several laboratories have developed different databases that contain more than 2000 variants for the two genes and integrated strategies which include multifactorial prediction models based on direct and indirect genetic evidence, to classify the VUS and attribute them a clinical significance associated with a deleterious, high-low or neutral risk. This review provides a comprehensive overview of literature studies concerning the VUSs, in order to assess their impact on the population and provide new insight for the appropriate patient management in clinical practice.

Feasibility of targeted cascade genetic testing in the family members of BRCA1/2 gene pathogenic variant/likely pathogenic variant carriers

The pathogenic variant (PV) or likely pathogenic variant (LPV) BRCA1/2 gene is strongly associated with hereditary breast or ovarian cancer. Therefore, it is important to screen blood relatives to establish preventive modalities and surveillance. This study evaluated the feasibility of targeted cascade genetic testing for family members of BRCA1/2 gene PV or LPV carriers. We screened 18 families for BRCA1/2 gene status via the conventional cascade genetic test (n = 9) and targeted cascade genetic test (n = 9), which targeted the exon region wherein the index patient showed PV or LPV. The pedigree and clinicopathologic characteristics were reviewed and analyzed. All index patients were diagnosed with breast cancer, while the third family members were all healthy. In the conventional cascade test group, 3 index patients and 3 family members had the BRCA1/2 gene PV or LPV. In the targeted cascade test group, 5 family members had same type of BRCA1/2 gene PV or LPV as their index patients. Two families had an identical string of BRCA1/2 gene PV or LPV. Although the targeted cascade genetic test cannot completely characterize the BRCA1/2 gene, it is sufficient for determining its PV or LPV status. This limited genetic test can be used for family members of PV or LPV carriers.

YouTube as an information source on BRCA mutations: implications for patients and professionals

Genetic testing for BRCA1/2 mutations in early breast cancer has been shown to be beneficial, and an increase in surveillance using these genetic markers is recommended. Given this recommendation, it is likely that individuals gather information about such testing. Social media is increasingly becoming a common source of health information. One such platform known for sharing health information is YouTube. The purpose of this study was to describe content related to BRCA1/2 mutations on YouTube. The sample included 100 English language videos, which were coded for content related to BRCA1/2 mutations. The 100 videos evaluated in this study were viewed 5.5 million times. In general, the BRCA1 and BRCA2 gene mutations were mentioned simultaneously, with only 15% of videos explaining the difference in prevalence or implication of the variants individually. A great number of videos (85.0%) discussed having genetic testing to determine the presence of BRCA mutations, but only 16.0% discussed the potential harms of BRCA mutation testing and 42.0% mentioned seeking genetic counseling to determine the need for testing and interpretation of the test results. Comparing the characteristics and content of videos created by healthcare professionals (n = 71) to those created by consumers and the media (n = 29), we found that consumer/media videos were viewed twice as many times as professional videos (3,704,351 vs. 1,851,825, p = 0.04). Videos from medical professionals should include consistent information on the recommendations for individuals who test positive for a BRCA mutation. Such content should include education about BRCA mutations, testing, implications of those results and ways to reduce risk, and recommendations for increased surveillance and enhanced screening for individuals positive for BRCA mutations.

Key genes and drug delivery systems to improve the efficiency of chemotherapy

Cancer cells can develop resistance to anticancer drugs, thereby becoming tolerant to treatment through different mechanisms. The biological mechanisms leading to the generation of anticancer treatment resistance include alterations in transmembrane proteins, DNA damage and repair mechanisms, alterations in target molecules, and genetic responses, among others. The most common anti-cancer drugs reported to develop resistance to cancer cells include cisplatin, doxorubicin, paclitaxel, and fluorouracil. These anticancer drugs have different mechanisms of action, and specific cancer types can be affected by different genes. The development of drug resistance is a cellular response which uses differential gene expression, to enable adaptation and survival of the cell to diverse threatening environmental agents. In this review, we briefly look at the key regulatory genes, their expression, as well as the responses and regulation of cancer cells when exposed to anticancer drugs, along with the incorporation of alternative nanocarriers as treatments to overcome anticancer drug resistance.

Clinical use and mechanisms of resistance for PARP inhibitors in homologous recombination-deficient cancers

Cells are continuously subjected to DNA damaging agents. DNA damages are repaired by one of the many pathways guarding genomic integrity. When one or several DNA damage pathways are rendered inefficient, cells can accumulate mutations, which modify normal cellular pathways, favoring abnormal cell growth. This supports malignant transformation, which can occur when cells acquire resistance to cell cycle checkpoints, apoptosis, or growth inhibition signals. Mutations in genes involved in the repair of DNA double strand breaks (DSBs), such as BRCA1, BRCA2, or PALB2, significantly increase the risk of developing cancer of the breast, ovaries, pancreas, or prostate. Fortunately, the inability of these tumors to repair DNA breaks makes them sensitive to genotoxic chemotherapies, allowing for the development of therapies precisely tailored to individuals' genetic backgrounds. Unfortunately, as with many anti-cancer agents, drugs used to treat patients carrying a BRCA1 or BRCA2 mutation create a selective pressure, and over time tumors can become drug resistant. Here, we detail the cellular function of tumor suppressors essential in DNA damage repair pathways, present the mechanisms of action of inhibitors used to create synthetic lethality in BRCA carriers, and review the major molecular sources of drug resistance. Finally, we present examples of the many strategies being developed to circumvent drug resistance.

Design, synthesis and in silico studies of new quinazolinone derivatives as antitumor PARP-1 inhibitors

Herein, we report an eco-friendly synthesis of a new series of quinazolinone-based derivatives as potential PARP-1 inhibitors. The 4-quinazolinone scaffold was utilized as a bioisostere to the phthalazinone core of the reference compound Olaparib. Most of the synthesized compounds displayed appreciable inhibitory activity against PARP-1. Compound 12c showed inhibitory activity at IC50 = 30.38 nM comparable to Olaparib, which has IC50 = 27.89 nM. Cell cycle analysis was performed for compounds 12a and 12c, and both exhibited cell growth arrest at G2/M phase in the MCF-7 cell line. In addition, both compounds increased the programmed apoptosis compared to the control. Furthermore, molecular docking of the final compounds into the PARP-1 active site was executed to explore their probable binding modes. Also, a computational QSAR and in silico ADMET study was performed. The results of this study revealed that some of the newly synthesized compounds could serve as a new framework to discover new PARP-1 inhibitors with anti-cancer activity.

First-Line Treatment with Olaparib for Early Stage BRCA-Positive Ovarian Cancer: May It Be Possible? Hypothesis Potentially Generating a Line of Research

Olaparib is currently approved in maintenance treatment of advanced ovarian cancer after response to first-line chemotherapy for breast related cancer antigens (BRCA) mutated patients. The use of this agent is based on data from SOLO1 study that observed a decreased risk of disease progression or death and a median progression-free survival about 36 months longer in case of therapy with olaparib. However, this trial recruited only patients with advanced stage ovarian cancer. The aim of this review is to retrace the available data in order to clarify the potential efficacy and feasibility of olaparib administration in newly diagnosed epithelial ovarian cancer also in early stages.

Exploiting the Prevalence of Homologous Recombination Deficiencies in High-Grade Serous Ovarian Cancer

High-grade serous ovarian cancer (HGSOC) remains the most lethal gynecologic cancer in the United States. Genomic analysis revealed roughly half of HGSOC display homologous repair deficiencies. An improved understanding of the genomic and somatic mutations that influence DNA repair led to the development of poly(ADP-ribose) polymerase inhibitors for the treatment of ovarian cancer. In this review, we explore the preclinical and clinical studies that led to the development of FDA approved drugs that take advantage of the synthetic lethality concept, the implementation of the early phase trials, the development of companion diagnostics and proposed mechanisms of resistance.

Replication Fork Remodeling and Therapy Escape in DNA Damage Response-Deficient Cancers

Most cancers have lost a critical DNA damage response (DDR) pathway during tumor evolution. These alterations provide a useful explanation for the initial sensitivity of tumors to DNA-targeting chemotherapy. A striking example is dysfunctional homology-directed repair (HDR), e.g., due to inactivating mutations in BRCA1 and BRCA2 genes. Extensive efforts are being made to develop novel targeted therapies exploiting such an HDR defect. Inhibitors of poly(ADP-ribose) polymerase (PARP) are an instructive example of this approach. Despite the success of PARP inhibitors, the presence of primary or acquired therapy resistance remains a major challenge in clinical oncology. To move the field of precision medicine forward, we need to understand the precise mechanisms causing therapy resistance. Using preclinical models, various mechanisms underlying chemotherapy resistance have been identified. Restoration of HDR seems to be a prevalent mechanism but this does not explain resistance in all cases. Interestingly, some factors involved in DNA damage response (DDR) have independent functions in replication fork (RF) biology and their loss causes RF instability and therapy sensitivity. However, in BRCA-deficient tumors, loss of these factors leads to restored stability of RFs and acquired drug resistance. In this review we discuss the recent advances in the field of RF biology and its potential implications for chemotherapy response in DDR-defective cancers. Additionally, we review the role of DNA damage tolerance (DDT) pathways in maintenance of genome integrity and their alterations in cancer. Furthermore, we refer to novel tools that, combined with a better understanding of drug resistance mechanisms, may constitute a great advance in personalized diagnosis and therapeutic strategies for patients with HDR-deficient tumors.

Olaparib in germline-mutated metastatic breast cancer: implications of the OlympiAD trial

Breast cancer remains a leading cause of death worldwide. Our increased understanding of cellular mechanisms inherent to cancer has led to the development of new therapeutic targets. One such therapy is that of poly(ADP-ribose) polymerase (PARP) inhibitors, with PARP playing a key role in the repair of single stranded DNA breaks. The development of drugs able to inhibit PARP led to their investigation in tumors that have defective DNA repair, including that of BRCA1/2-associated cancers. The PARP inhibitor Olaparib, has recently been evaluated in the Phase III OlympiAD trial, and demonstrated a significant progression-free survival advantage in patients with HER2-negative metastatic breast cancer and a germline BRCA-mutation. This article will review the findings and potential implications of the trial.

Mutational signatures and mutable motifs in cancer genomes

Cancer is a genetic disorder, meaning that a plethora of different mutations, whether somatic or germ line, underlie the etiology of the 'Emperor of Maladies'. Point mutations, chromosomal rearrangements and copy number changes, whether they have occurred spontaneously in predisposed individuals or have been induced by intrinsic or extrinsic (environmental) mutagens, lead to the activation of oncogenes and inactivation of tumor suppressor genes, thereby promoting malignancy. This scenario has now been recognized and experimentally confirmed in a wide range of different contexts. Over the past decade, a surge in available sequencing technologies has allowed the sequencing of whole genomes from liquid malignancies and solid tumors belonging to different types and stages of cancer, giving birth to the new field of cancer genomics. One of the most striking discoveries has been that cancer genomes are highly enriched with mutations of specific kinds. It has been suggested that these mutations can be classified into 'families' based on their mutational signatures. A mutational signature may be regarded as a type of base substitution (e.g. C:G to T:A) within a particular context of neighboring nucleotide sequence (the bases upstream and/or downstream of the mutation). These mutational signatures, supplemented by mutable motifs (a wider mutational context), promise to help us to understand the nature of the mutational processes that operate during tumor evolution because they represent the footprints of interactions between DNA, mutagens and the enzymes of the repair/replication/modification pathways.

Resistance to PARP Inhibitors: Lessons from Preclinical Models of BRCA-Associated Cancer

Inhibitors of poly(ADP-ribose) polymerase (PARP) have recently entered the clinic for the treatment of homologous recombination–deficient cancers. Despite the success of this approach, resistance to PARP inhibitors (PARPis) is a clinical hurdle, and it is poorly understood how cancer cells escape the deadly effects of PARPis without restoring BRCA1/2 function. By synergizing the advantages of next-generation sequencing with functional genetic screens in tractable model systems, novel mechanisms providing useful insights into DNA damage response (DDR) have been identified. BRCA1/2 models not only are tools to explore therapy escape mechanisms but also yield basic knowledge about DDR pathways and PARPis’ mechanism of action. Moreover, alterations that render cells resistant to targeted therapies may cause new synthetic dependencies that can be exploited to combat resistant disease.

Targeting Cyclin-Dependent Kinases for Treatment of Gynecologic Cancers

Ovarian, uterine/endometrial, and cervical cancers are major gynecologic malignancies estimated to cause nearly 30,000 deaths in 2018 in US. Defective cell cycle regulation is the hallmark of cancers underpinning the development and progression of the disease. Normal cell cycle is driven by the coordinated and sequential rise and fall of cyclin-dependent kinases (CDK) activity. The transition of cell cycle phases is governed by the respective checkpoints that prevent the entry into the next phase until cellular or genetic defects are repaired. Checkpoint activation is achieved by p53- and ATM/ATR-mediated inactivation of CDKs in response to DNA damage. Therefore, an aberrant increase in CDK activity and/or defects in checkpoint activation lead to unrestricted cell cycle phase transition and uncontrolled proliferation that give rise to cancers and perpetuate malignant progression. Given that CDK activity is also required for homologous recombination (HR) repair, pharmacological inhibition of CDKs can be exploited as a synthetic lethal approach to augment the therapeutic efficacy of PARP inhibitors and other DNA damaging modalities for the treatment of gynecologic cancers. Here, we overview the basic of cell cycle and discuss the mechanistic studies that establish the intimate link between CDKs and HR repair. In addition, we present the perspective of preclinical and clinical development in small molecule inhibitors of CDKs and CDK-associated protein targets, as well as their potential use in combination with hormonal therapy, PARP inhibitors, chemotherapy, and radiation to improve treatment outcomes.

Conceptual frameworks of synthetic lethality in clear cell carcinoma of the ovary

Targeting non-oncogenes may result in the selective death of cancer cells. Clear cell carcinoma of the ovary (CCC) may exhibit resistance against conventional chemotherapy and is associated with poor prognosis. The aim of the present report was to review synthetic lethality-based therapies for CCC. Previous English-language studies were reviewed to accumulate preclinical and clinical data on targeting synthetic lethal partners. Synthetic lethal interactions have a variety of types, involving components of a backup or parallel pathway with overlapping functions, components encoded by paralogous pairs, subunit components that form heteromeric complexes and components that are arranged in a single linear pathway. A set of candidate gene targets potentially resulting in synthetic lethality have been previously identified. HNF class homeobox, AT-rich interaction domain 1A, ATR serine/threonine kinase, ATM serine/threonine kinase, checkpoint kinase 1 and phosphatase and tensin homolog may be the key partner genes. A variety of loss of function genes in CCC are driver or passenger events and may function as synthetic lethal pairs under replication stress conditions. Further clinical studies will be required to investigate the safety and therapeutic effect of synthetic lethality pairs in CCC tumor types with replication stress.

DNA polymerase η mutational signatures are found in a variety of different types of cancer

DNA polymerase (pol) η is a specialized error-prone polymerase with at least two quite different and contrasting cellular roles: to mitigate the genetic consequences of solar UV irradiation, and promote somatic hypermutation in the variable regions of immunoglobulin genes. Misregulation and mistargeting of pol η can compromise genome integrity. We explored whether the mutational signature of pol η could be found in datasets of human somatic mutations derived from normal and cancer cells. A substantial excess of single and tandem somatic mutations within known pol η mutable motifs was noted in skin cancer as well as in many other types of human cancer, suggesting that somatic mutations in A:T bases generated by DNA polymerase η are a common feature of tumorigenesis. Another peculiarity of pol ηmutational signatures, mutations in YCG motifs, led us to speculate that error-prone DNA synthesis opposite methylated CpG dinucleotides by misregulated pol η in tumors might constitute an additional mechanism of cytosine demethylation in this hypermutable dinucleotide.

PARP inhibitors: review of mechanisms of action and BRCA1/2 mutation targeting

Poly(ADP-ribose) polymerases have shown true promise in early clinical studies due to reported activity in BRCA-associated cancers. PARP inhibitors may represent a potentially important new class of chemotherapeutic agents directed at targeting cancers with defective DNA-damage repair. In order to widen the prospective patient population that would benefit from PARP inhibitors, predictive biomarkers based on a clear understanding of the mechanism of action are required. In addition, a more sophisticated understanding of the toxicity profile is required if PARP inhibitors are to be employed in the curative, rather than the palliative, setting. PARP inhibitors have successfully moved into clinical practice in the past few years, with approval granted from the Food and Drug Administration (FDA) and European Medicines Agency (EMA) within the past two years. The United States FDA approval of olaparib applies to fourth-line treatment in germline BRCA-mutant ovarian cancer, and European EMA approval of olaparib for maintenance therapy in both germline and somatic BRCA-mutant platinum-sensitive ovarian cancer. This review covers the current understanding of PARP, its inhibition, and the basis of the excitement surrounding these new agents. It also evaluates future approaches and directions required to achieve full understanding of the intricate interplay of these agents at the cellular level.

A centrosome clustering protein, KIFC1, predicts aggressive disease course in serous ovarian adenocarcinomas

BACKGROUND

Amplified centrosomes are widely recognized as a hallmark of cancer. Although supernumerary centrosomes would be expected to compromise cell viability by yielding multipolar spindles that results in death-inducing aneuploidy, cancer cells suppress multipolarity by clustering their extra centrosomes. Thus, cancer cells, with the aid of clustering mechanisms, maintain pseudobipolar spindle phenotypes that are associated with low-grade aneuploidy, an edge to their survival. KIFC1, a nonessential minus end-directed motor of the kinesin-14 family, is a centrosome clustering molecule, essential for viability of extra centrosome-bearing cancer cells. Given that ovarian cancers robustly display amplified centrosomes, we examined the overexpression of KIFC1 in human ovarian tumors.

RESULTS

We found that in clinical epithelial ovarian cancer (EOC) samples, an expression level of KIFC1 was significantly higher when compared to normal tissues. KIFC1 expression also increased with tumor grade. Our In silico analyses showed that higher KIFC1 expression was associated with poor overall survival (OS) in serous ovarian adenocarcinoma (SOC) patients suggesting that an aggressive disease course in ovarian adenocarcinoma patients can be attributed to high KIFC1 levels. Also, gene expression levels of KIFC1 in high-grade serous ovarian carcinoma (HGSOC) highly correlated with expression of genes driving centrosome amplification (CA), as examined in publically-available databases. The pathway analysis results indicated that the genes overexpressed in KIFC1 high group were associated with processes like regulation of the cell cycle and cell proliferation. In addition, when we performed gene set enrichment analysis (GSEA) for identifying the gene ontologies associated to KIFC1 high group, we found that the first 100 genes enriched in KIFC1 high group were from centrosome components, mitotic cell cycle, and microtubule-based processes. Results from in vitro experiments on well-established in vitro models of HGSOC (OVSAHO, KURAMOCHI), OVCAR3 and SKOV3) revealed that they display robust centrosome amplification and expression levels of KIFC1 was directly associated (inversely correlated) to the status of multipolar mitosis. This association of KIFC1 and centrosome amplification with HGSOC might be able to explain the increased aggressiveness in this disease.

CONCLUSION

These findings compellingly underscore that KIFC1 can be a biomarker that predicts an aggressive disease course in ovarian adenocarcinomas.

Rampant centrosome amplification underlies more aggressive disease course of triple negative breast cancers

Centrosome amplification (CA), a cell-biological trait, characterizes pre-neoplastic and pre-invasive lesions and is associated with tumor aggressiveness. Recent studies suggest that CA leads to malignant transformation and promotes invasion in mammary epithelial cells. Triple negative breast cancer (TNBC), a histologically-aggressive subtype shows high recurrence, metastases, and mortality rates. Since TNBC and non-TNBC follow variable kinetics of metastatic progression, they constitute a novel test bed to explore if severity and nature of CA can distinguish them apart. We quantitatively assessed structural and numerical centrosomal aberrations for each patient sample in a large-cohort of grade-matched TNBC (n = 30) and non-TNBC (n = 98) cases employing multi-color confocal imaging. Our data establish differences in incidence and severity of CA between TNBC and non-TNBC cell lines and clinical specimens. We found strong correlation between CA and aggressiveness markers associated with metastasis in 20 pairs of grade-matched TNBC and non-TNBC specimens (p < 0.02). Time-lapse imaging of MDA-MB-231 cells harboring amplified centrosomes demonstrated enhanced migratory ability. Our study bridges a vital knowledge gap by pinpointing that CA underlies breast cancer aggressiveness. This previously unrecognized organellar inequality at the centrosome level may allow early-risk prediction and explain higher tumor aggressiveness and mortality rates in TNBC patients.

PARP inhibitors: A new era of targeted therapy

Personalized medicine seeks to utilize targeted therapies with increased selectivity and efficacy in preselected patient cohorts. One such molecularly targeted therapy is enabled by inhibiting the enzyme poly(ADP-ribose) polymerase (PARP) by small molecule inhibitors in tumors which have a defect in the homologous DNA recombination pathway, most characteristically due to BRCA mutations. Olaparib, a highly potent PARP inhibitor, has recently been the approved for ovarian cancer therapy by the FDA and European commission in patients with platinum-sensitive, recurrent, high-grade serous ovarian cancer with BRCA1 or BRCA2 mutations. Currently, clinical trials with several PARP inhibitors are being conducted to assess the toxicities, the efficacies and the benefit of the drugs as monotherapies or combined with radiation or other chemotherapeutic agents, in ovarian, breast, prostate, rectal, lung, pancreatic, peritoneal, head and neck, brain, squamous cell carcinomas and sarcomas, to list a few. In this review, our focus is to outline the emerging molecular mechanisms, preclinical evidence and clinical applications of PARP inhibitors especially in nonBRCA cancers, and review the combination strategies compatible with PARP inhibitor therapy.

Etiology of familial breast cancer with undetected BRCA1 and BRCA2 mutations: clinical implications

BACKGROUND

Familial breast cancer accounts for 20-30 % of all breast cancer cases. Mutations in the BRCA1 and BRCA2 genes account for the majority of high risk families with both early onset breast cancer and ovarian cancer. Most of the families with less than six breast cancer cases and no ovarian cancer do not carry BRCA1 or BRCA2 mutations that can be detected using routine sequencing protocols. Here, we aimed to review the etiology of familial breast cancer in cases without BRCA1 and BRCA2 mutations.

RESULTS

After excluding BRCA1 and BRCA2 mutations, factors proposed to contribute to familial breast cancer include: chance clustering of apparently sporadic cases, shared lifestyle, monogenic inheritance, i.e., dominant gene mutations associated with a high risk (TP53, PTEN, STK11), dominant gene mutations associated with a relatively low risk (ATM, BRIP1, RLB2), recessive gene mutations associated with horizontal inheritance patterns (sister-sister), and polygenic inheritance where susceptibility to familial breast cancer is thought to be conferred by a large number of low risk alleles.

CONCLUSIONS

Current evidence suggests that in the majority of cases with BRCA1 and BRCA2 negative familial breast cancer the etiology is due to interactions of intermediate or low risk alleles with environmental and lifestyle factors. Thus, a careful selection of patients submitted to genetic testing is needed. Clearly, further research is required to fully elucidate the etiology of non-BRCA familial breast cancer.

Bleomycin-induced mutagen sensitivity, passive smoking, and risk of breast cancer in Chinese women: a case-control study

BACKGROUND

It is well recognized that genetic variation as well as environmental factors modulates breast cancer risk. Deficiencies in DNA repair capacity are thought to associate with breast cancer risk. The main aim of this study was to use the mutagen sensitivity assay as an indirect measure of DNA repair capacity to assess breast cancer risk and the relationship between passive smoking and breast cancer risk among women in China.

METHODS

We carried out a case-control study, involving 196 Chinese patients with breast cancer and 211 controls without the disease and with no history of cancer. We investigated the association between mutagen sensitivity and breast cancer risk using bleomycin as the mutagen. Mutagen sensitivity was measured by quantifying the chromatid breaks induced by mutagens in short-term cultures of peripheral blood lymphocytes. Nonparametric tests and the Fisher's exact test were used to determine the statistical significance of the crude case-control comparisons, followed by logistic regression to adjust for important covariates.

RESULTS

The mean number of bleomycin-induced breaks per cell was 0.81 for cases compared with 0.73 for the controls (p = 0.016). A greater number of bleomycin-induced chromosomal breaks per cell was associated with an increased risk of breast cancer (adjusted odds ratio of 1.82, p trend <0.01). The association between bleomycin sensitivity and breast cancer risk was greater for women who were exposed to tobacco smoke (passive smokers). The combination of bleomycin sensitivity and exposure to tobacco smoke increased risk further; women passive smokers with high sensitivity to bleomycin had a 2.77-fold increased risk of breast cancer.

CONCLUSIONS

Our data indicate that increased bleomycin-induced mutagen sensitivity is significantly associated with an increased risk of breast cancer among Chinese women. Exposure to passive smoke is also associated with increased breast cancer risk, and the correlation is even greater for women with both longer passive exposure to tobacco smoke and high sensitivity to bleomycin.

Gamma-ray-induced mutagen sensitivity and risk of sporadic breast cancer in young women: a case-control study

Hypersensitivity to radiation exposure has been suggested to be a risk factor for the development of breast cancer. In this case-control study of 515 young women (≤ 55 years) with newly diagnosed sporadic breast cancer and 402 cancer-free controls, we examined the radiosensitivity as measured by the frequency of chromatid breaks induced by gamma-radiation exposure in the G2 phase of phytohemagglutinin-stimulated and short-term cultured fresh lymphocytes. We found that the average chromatid breaks per cell from 50 well-spread metaphases were statistically significantly higher in 403 non-Hispanic White breast cancer patients (0.52 ± 0.22) than that in 281 non-Hispanic White controls (0.44 ± 0.16) (P value < 0.001), and in 60 Mexican American breast cancer patients (0.52 ± 0.19) than that in 65 Mexican American controls (0.44 ± 0.16) (P value = 0.021), but the difference was not significant in African Americans (52 cases [0.45 ± 0.16] versus 56 controls [0.47 ± 0.16], P = 0.651). The frequency of chromatid breaks per cell above the median of control subjects was associated with two-fold increased risk for breast cancer in non-Hispanic Whites and Mexican Americans. A dose-response relationship was evident between radiosensitivity and risk for breast cancer (P (trend) < 0.001) in these two ethnic groups. We concluded that gamma-ray-induced mutagen sensitivity may play a role in susceptibility to breast cancer in young non-Hispanic White and Mexican American women.

BRCA2 is a mediator of RAD51- and DMC1-facilitated homologous recombination in Arabidopsis thaliana

• Mutations in the breast cancer susceptibility gene 2 (BRCA2) are correlated with hereditary breast cancer in humans. Studies have revealed that mammalian BRCA2 plays crucial roles in DNA repair. Therefore, we wished to define the role of the BRCA2 homologs in Arabidopsis in detail. • As Arabidopsis contains two functional BRCA2 homologs, an Atbrca2 double mutant was generated and analyzed with respect to hypersensitivity to genotoxic agents and recombination frequencies. Cytological studies addressing male and female meiosis were also conducted, and immunolocalization was performed in male meiotic prophase I. • The Atbrca2 double mutant showed hypersensitivity to the cross-linking agent mitomycin C and displayed a dramatic reduction in somatic homologous recombination frequency, especially after double-strand break induction. The loss of AtBRCA2 also led to severe defects in male meiosis and development of the female gametophyte and impeded proper localization of the synaptonemal complex protein AtZYP1 and the recombinases AtRAD51 and AtDMC1. • The results demonstrate that AtBRCA2 is important for both somatic and meiotic homologous recombination. We further show that AtBRCA2 is required for proper meiotic synapsis and mediates the recruitment of AtRAD51 and AtDMC1. Our results suggest that BRCA2 controls single-strand invasion steps during homologous recombination in plants.

MYC and Breast Cancer

MYC is a key regulator of cell growth, proliferation, metabolism, differentiation, and apoptosis. MYC deregulation contributes to breast cancer development and progression and is associated with poor outcomes. Multiple mechanisms are involved in MYC deregulation in breast cancer, including gene amplification, transcriptional regulation, and mRNA and protein stabilization, which correlate with loss of tumor suppressors and activation of oncogenic pathways. The heterogeneity in breast cancer is increasingly recognized. Breast cancer has been classified into 5 or more subtypes based on gene expression profiles, and each subtype has distinct biological features and clinical outcomes. Among these subtypes, basal-like tumor is associated with a poor prognosis and has a lack of therapeutic targets. MYC is overexpressed in the basal-like subtype and may serve as a target for this aggressive subtype of breast cancer. Tumor suppressor BRCA1 inhibits MYC's transcriptional and transforming activity. Loss of BRCA1 with MYC overexpression leads to the development of breast cancer-especially, basal-like breast cancer. As a downstream effector of estrogen receptor and epidermal growth factor receptor family pathways, MYC may contribute to resistance to adjuvant therapy. Targeting MYC-regulated pathways in combination with inhibitors of other oncogenic pathways may provide a promising therapeutic strategy for breast cancer, the basal-like subtype in particular.

YB-1 evokes susceptibility to cancer through cytokinesis failure, mitotic dysfunction and HER2 amplification

Y-box binding protein-1 (YB-1) expression in the mammary gland promotes breast carcinoma that demonstrates a high degree of genomic instability. In the present study, we developed a model of premalignancy to characterize the role of this gene during breast cancer initiation and early progression. Antibody microarray technology was used to ascertain global changes in signal transduction following the conditional expression of YB-1 in human mammary epithelial cells (HMEC). Cell cycle associated proteins were frequently altered with the most dramatic being LIM Kinase 1/2 (LIMK1/2). Consequently, the misexpression of LIMK1/2 was associated with cytokinesis failure that acted as a precursor to centrosome amplification. Detailed investigation revealed that YB-1 localized to the centrosome in a phosphorylation-dependent manner where it complexed with pericentrin and γ-tubulin. This was found to be essential in maintaining the structural integrity and microtubule nucleation capacity of the organelle. Prolonged exposure to YB-1 led to rampant acceleration toward tumourigenesis with the majority of cells acquiring numerical and structural chromosomal abnormalities. Slippage through the G₁/S checkpoint due to overexpression of cyclin E promoted continued proliferation of these genomically compromised cells. As malignancy further progressed, we identified a subset of cells harbouring HER2 amplification. Our results recognize YB-1 as a cancer susceptibility gene with the capacity to prime cells for tumourigenesis.

Ubiquitin becomes ubiquitous in cancer: emerging roles of ubiquitin ligases and deubiquitinases in tumorigenesis and as therapeutic targets

By virtue of its ability to regulate both protein turnover and non-proteolytic signalling functions, ubiquitin protein conjugation has been implicated in the control of multiple cellular processes, including protein localization, cell cycle control, transcription regulation, DNA damage repair, and endocytosis. Ubiquitin metabolism enzymes have been identified as either oncogenes or tumor suppressors in a variety of cancers. Given that ubiquitin metabolism is governed by enzymes--E1, E2, E3, E4, deubiquitinases (DUBs), and the proteasome- the system as a whole is ripe for target and drug discovery in cancer. Of the ubiquitin/proteasome system components, the E3's and DUBs can recognize substrates with the most specificity, and are thus of key interest as drug targets in cancer. This review examines the molecular role in cancer, relevant substrates, and potential for pharmacologic development, of E3's and DUBs that have been associated thus far with human malignancies as oncogenes or tumor suppressors.

Triple-negative breast cancer: present challenges and new perspectives

Triple-negative breast cancers (TNBC), characterized by absence of estrogen receptor (ER), progesterone receptor (PR) and lack of overexpression of human epidermal growth factor receptor 2 (HER2), are typically associated with poor prognosis, due to aggressive tumor phenotype(s), only partial response to chemotherapy and present lack of clinically established targeted therapies. Advances in the design of individualized strategies for treatment of TNBC patients require further elucidation, by combined 'omics' approaches, of the molecular mechanisms underlying TNBC phenotypic heterogeneity, and the still poorly understood association of TNBC with BRCA1 mutations. An overview is here presented on TNBC profiling in terms of expression signatures, within the functional genomic breast tumor classification, and ongoing efforts toward identification of new therapy targets and bioimaging markers. Due to the complexity of aberrant molecular patterns involved in expression, pathological progression and biological/clinical heterogeneity, the search for novel TNBC biomarkers and therapy targets requires collection of multi-dimensional data sets, use of robust multivariate data analysis techniques and development of innovative systems biology approaches.

DNA-binding properties of T4 UvsY recombination mediator protein: polynucleotide wrapping promotes high-affinity binding to single-stranded DNA

To carry out homologous recombination events in the cell, recombination proteins must be able to recognize and form presynaptic filaments on single-stranded DNA (ssDNA) in the presence of a vast excess of double-stranded DNA (dsDNA). Therefore recombination machineries stringently discriminate between ssDNA and dsDNA lattices. Recent single-molecule studies of bacteriophage T4 recombination proteins revealed that, surprisingly, the UvsY recombination mediator protein binds stronger to stretched dsDNA molecules than to stretched ssDNA. Here, we show that for relaxed DNA lattices, the opposite is true: UvsY exhibits a 1000-fold intrinsic affinity preference for ssDNA over dsDNA at moderate salt concentrations. This finding suggests that UvsY preferentially loads UvsX recombinase onto ssDNA under physiological conditions. The biochemical basis for high-affinity UvsY–ssDNA binding was investigated by hydrodynamic and cross-linking methods. Results show that UvsY forms ring-like hexamers in solution, and that ssDNA binds to multiple subunits within each hexamer, consistent with ssDNA wrapping. The data support a model in which ssDNA wrapping by UvsY protein is important for the selective nucleation of presynaptic filaments on ssDNA versus dsDNA, and for the coordinated transfer of ssDNA from Gp32 (SSB) to UvsY (RMP) to UvsX (recombinase) during filament assembly.

Identification of a novel pathogenic mutation in BRCA2 in a Spanish breast-ovarian cancer family

Germline mutations in the BRCA1/2 genes contribute to most of inherited breast and ovarian cancers. We analyzed a family fulfilling classical criteria of hereditary breast/ovarian cancer. After complete sequencing of coding regions and splice junctions of both genes, a nonpreviously reported mutation in BRCA2 was detected in the index case. Direct mutation detection was performed with their relatives, and three of them were also mutation carriers, two healthy males and a patient afflicted with borderline ovarian cancer. The c.2999delCT, consists of a deletion of two bases in exon 11, in the limits of the ovarian cancer cluster region. This is a frameshift mutation that causes a disruption of the translational reading frame resulting in a stop codon 10 amino acids downstream in the 934 position of the BRCA2 protein, causing a truncation protein. This often causes a loss of function in the protein as critical parts of the amino acid chain are no longer created. Because of it, this mutation must be classified as pathogenic and can be regarded as the cause of the cancers in this family.

Hereditary ovarian cancer

At least 10% of ovarian tumors are hereditary and associated with highly penetrant, autosomal, dominant genetic predisposition. Three clinical manifestations of hereditary ovarian cancer have been identified: site-specific ovarian cancer, hereditary breast and/or ovarian cancer (HBOC) and hereditary non-polyposis colorectal cancer (HNPCC) syndromes. BRCA germline mutations account for more than 90% of all hereditary epithelial ovarian tumors whereas most of the remaining 10% are caused by MLH1 and MSH2 mutations, which are susceptibility genes of HNPCC. Genetic testing is available for each of the three hereditary syndromes above mentioned. The recommendations for OC surveillance in high-risk women having a strong family history or BRCA mutation carriers include transvaginal pelvic ultrasound with color Doppler and serum CA125 every 6 months. Bilateral salpingo-oophorectomy appears to be effective to reduce the risk of ovarian cancer in BRCA mutation carriers. Hysterosalpingo-oophorectomy should be considered in HNPCC women who undergo surgery for colorectal carcinoma.

Indole-3-carbinol as a chemopreventive and anti-cancer agent

During the course of oncogenesis and tumor progression, cancer cells constitutively upregulate signaling pathways relevant to cell proliferation and survival as a strategy to overcome genomic instability and acquire resistance phenotype to chemotherapeutic agents. In light of this clinical and molecular heterogeneity of human cancers, it is desirable to concomitantly target these genetic abnormalities by using an agent with pleiotropic mode of action. Indole-3-carbinol and its metabolite 3,3'-diindoylmethane (DIM) target multiple aspects of cancer cell-cycle regulation and survival including Akt-NF kappa B signaling, caspase activation, cyclin-dependent kinase activities, estrogen metabolism, estrogen receptor signaling, endoplasmic reticulum stress, and BRCA gene expression. This broad spectrum of anti-tumor activities in conjunction with low toxicity underscores the translational value of indole-3-carbinol and its metabolites in cancer prevention/therapy. Furthermore, novel anti-tumor agents with overlapping underlying mechanisms have emerged via structural optimization of indole-3-carbinol and DIM, which may provide considerable therapeutic advantages over the parental compounds with respect to chemical stability and anti-tumor potency. Together, these agents might foster new strategies for cancer prevention and therapy.

Minding the gap: the underground functions of BRCA1 and BRCA2 at stalled replication forks

The hereditary breast and ovarian cancer predisposition genes, BRCA1 and BRCA2, participate in the repair of DNA double strand breaks by homologous recombination. Circumstantial evidence implicates these genes in recombinational responses to DNA polymerase stalling during the S phase of the cell cycle. These responses play a key role in preventing genomic instability and cancer. Here, we review the current literature implicating the BRCA pathway in HR at stalled replication forks and explore the hypothesis that BRCA1 and BRCA2 participate in the recombinational resolution of single stranded DNA lesions termed "daughter strand gaps", generated during replication across a damaged DNA template.

Glutathione S-transferase polymorphisms associated with risk of breast cancer in southern Taiwan

In this study, the genetic polymorphisms associated with breast cancer in southern Taiwan were investigated. Two categories of genes were analyzed: (1) BRCA1, BRCA2, and Rad51, the DNA repair factors involved in homologous recombinational repair; and (2) CYP1A1, COMT, GST, and NAT2, the xenobiotic-metabolizing enzymes (XME) involved in estrogen metabolism. We found that the number of deletions and/or mutations in the GST genes was highly correlated with the occurrence of breast cancer. These data suggest that the GST enzymes, which detoxify the catechol estrogen quinones, are important target molecules for screening in populations at high risk of breast cancer.

The role of BRCA1 in non-homologous end-joining

From the genotypic viewpoint, single nucleotide polymorphisms in the genes of the non-homologous end-joining (NHEJ) pathway, which is important in the repair of DNA double-strand breaks, have been shown to be associated with increased breast cancer risk. However, more phenotypic evidence is needed to strengthen the link between defective NHEJ genes and breast cancer development. Recently, BRCA1-deficient mouse embryonic fibroblasts were found to have significantly reduced NHEJ activity, suggesting an accessory role of BRCA1 in NHEJ. Since BRCA1 is a well-documented breast cancer susceptibility gene, this association between NHEJ and BRCA1 not only suggests a role of BRCA1 in NHEJ, but also provides support for the tumorigenic contribution of the NHEJ pathway to breast cancer development. Interestingly, the phenotypic data show that BRCA1 may promote only specific subtypes of NHEJ, e.g. in vivo precise and terminal end-joining capacities, and have either a suppressive or no effect on others. However, these findings have remained inconclusive, and the lack of consistency between these results may be at least partly explained by the use of different assays, which may measure different subtypes of NHEJ, and of different cell lines investigated. Although some insights have been obtained, the whole picture of NHEJ repair in mammalian cells is far from complete, and the questions of how many subpathways are involved or how we can investigate each subpathway have not yet been adequately addressed.

DNA damage hypersensitivity in cells lacking BRCA2: a review of in vitro and in vivo data

Since the discovery of the tumour suppressor BRCA2 (encoded by breast-cancer susceptibility gene 2), cells lacking the fully functional protein have consistently been found to show increased sensitivity to a variety of DNA-damaging agents, particularly those that cross-link DNA. In this short review, we will bring together these findings and discuss them in the light of our recent in vivo data in the mouse small intestine, which suggests that deletion of cells lacking Brca2 is necessary to avoid the development of potentially tumorigenic clones in this tissue, a system that may be less effective in the mammary glands of humans with germline mutations in BRCA2.

Showing your ID: intrinsic disorder as an ID for recognition, regulation and cell signaling

Regulation, recognition and cell signaling involve the coordinated actions of many players. To achieve this coordination, each participant must have a valid identification (ID) that is easily recognized by the others. For proteins, these IDs are often within intrinsically disordered (also ID) regions. The functions of a set of well-characterized ID regions from a diversity of proteins are presented herein to support this view. These examples include both more recently described signaling proteins, such as p53, alpha-synuclein, HMGA, the Rieske protein, estrogen receptor alpha, chaperones, GCN4, Arf, Hdm2, FlgM, measles virus nucleoprotein, RNase E, glycogen synthase kinase 3beta, p21(Waf1/Cip1/Sdi1), caldesmon, calmodulin, BRCA1 and several other intriguing proteins, as well as historical prototypes for signaling, regulation, control and molecular recognition, such as the lac repressor, the voltage gated potassium channel, RNA polymerase and the S15 peptide associating with the RNA polymerase S-protein. The frequent occurrence and the common use of ID regions in important protein functions raise the possibility that the relationship between amino acid sequence, disordered ensemble and function might be the dominant paradigm for the molecular recognition that serves as the basis for signaling and regulation by protein molecules.

Towards a dietary prevention of hereditary breast cancer

Inheritance of a deleterious mutation in BRCA1 or BRCA2 confers a high lifetime risk of developing breast cancer. Variation in penetrance between individuals suggests that factors other than the gene mutation itself may influence the risk of cancer in susceptible women. Several risk factors have been identified which implicate estrogen-induced growth stimulation as a probable contributor to breast cancer pre-disposition. The protein products of both of these genes appear to help preserve genomic integrity via their participation in the DNA damage response and repair pathways. To date, the evidence for a cancer-protective role of dietary nutrients, for the most part those with antioxidant properties, has been based on women without any known genetic pre-disposition and it is important to identify and evaluate dietary factors which may modify the risk of cancer in BRCA carriers. Here we propose that diet modification may modulate the risk of hereditary breast cancer by decreasing DNA damage (possibly linked to estrogen exposure) or by enhancing DNA repair. The prevention of hereditary breast cancer through diet is an attractive complement to current management strategies and deserves exploration.

Brca2 deficiency in the murine small intestine sensitizes to p53-dependent apoptosis and leads to the spontaneous deletion of stem cells

The gene encoding the human BRCA2 tumour suppressor is mutated in a number of different tumour types, most notably inherited breast cancers. The primary role of BRCA2 is thought to lie in the maintenance of genomic stability via its role in the homologous recombination pathway. We generated mice in which Brca2 was deleted from virtually all cells within the adult small intestine, using a CYP1A1-driven Cre-Lox approach. We noted a significant p53-dependent increase in the levels of spontaneous apoptosis which persisted for several months after removal of the gene and ultimately we observed the spontaneous deletion of Brca2-deficient stem cells. Brca2 deficiency did not lead to gross changes in intestinal physiology but did enhance sensitivity to a variety of DNA crosslinking agents. Taken together, our results indicate that Brca2 plays an important role in the response to DNA damage in the small intestine. Furthermore, we show that Brca2 deficiency results in the spontaneous deletion of stem cells, thereby protecting the small intestine against tumorigenesis.

The cell-type-specificity of inherited predispositions to tumours: review and hypothesis

Most hereditary predispositions to tumours affect only one particular cell type of the body but the genes bearing the relevant germ-line mutation are not cell-type-specific. Some predisposition syndromes include increased risks of lesions (developmental or tumourous) of unrelated cell types, in any individual predisposed to the main lesion (e.g. osteosarcoma in patients predisposed to retinoblastoma). Other predispositions to additional lesions occur only in members of some families with the predisposition to the basic lesion (e.g. Gardner's syndrome in some families suffering familial adenomatous polyposis). In yet other predisposition syndromes, different mutations of the same gene are associated with markedly differing family-specific clinical syndromes. In particular, identical germline mutations (e.g. in APC, RET and PTEN genes), have been found associated with differing clinical syndromes in different families. This paper reviews previously suggested mechanisms of the cell-type specificity of inherited predispositions to tumour. Models of tumour formation in predisposition syndromes are discussed, especially those involving a germline mutation (the first 'hit') of a tumour suppressor gene (TSG) and a second (somatic) hit on the second allele of the same TSG. A modified model is suggested, such that the second hit is a co-mutation of the second allele of the TSG and a regulator which is specific for growth and/or differentiation of the cell type which is susceptible to the tumour predisposition. In some cases of tumour, the second hit may be large enough to be associated with a cytogenetically-demonstrable abnormality of the part of the chromosome carrying the TSG, but in other cases, the co-mutation may be of 'sub-cytogenetic' size (i.e. 10(2)-10(5) bases). For the latter, mutational mechanisms of frameshift and impaired fidelity of replication of DNA by DNA polyerases may sometimes be involved. Candidate cell-type-specific regulators may include microRNAs and perhaps transcription factors. It is suggested that searching the introns within 10(5)-10(6) bases either side of known of exonic mutations of TSGs associated with inherited tumour predisposition might reveal microRNA cell-type-specific regulators. Additional investigations may involve fluorescent in situ hybridisations on interphase tumour nuclei.

Characterization of segments from the central region of BRCA1: an intrinsically disordered scaffold for multiple protein-protein and protein-DNA interactions?

The BRCA1 tumor suppressor gene encodes an 1863 amino acid gene product that is implicated in many cellular pathways including transcription, cell-cycle checkpoint control, apoptosis and DNA repair. Much attention has been focused on the structural and biochemical characterization of the N-terminal RING and tandem C-terminal BRCT domains of BRCA1. Here we used NMR spectroscopy in conjunction with CD spectroscopy and limited proteolysis to investigate the biophysical properties of the approximately 1500 residue central region of BRCA1. Our results show that although there are a few small, mildly protease-resistant regions, the majority of the BRCA1 central region lacks any pre-existing independently folded globular domains. Electrophoretic mobility shift assay and intrinsic tryptophan fluorescence experiments also demonstrate that, although intrinsically disordered, polypeptides from the central region are able to mediate interactions with DNA and p53 with affinities in the low micromolar range. This supports a model in which the central region may act as a long flexible scaffold for intermolecular interactions, thereby helping to integrate multiple signals in the DNA damage response pathway.

Chemosensitivity and radiosensitivity profiles of four new human epithelial ovarian cancer cell lines exhibiting genetic alterations in BRCA2, TGFbeta-RII, KRAS2, TP53 and/or CDNK2A

To address the cellular basis for the response to ovarian cancer treatment, we characterized the chemosensitivity and radiosensitivity of four human epithelial ovarian cancer cell lines that harbor different genetic alterations. The TOV-21G, TOV-81D, OV-90, and TOV-112D cell lines were derived from ovarian tumors (TOV) or ascites (OV) from chemotherapy- and radiotherapy-naive patients and were characterized by their mutation spectrum of BRCA2, TGFbeta-RII, KRAS2, TP53, and CDKN2A. Cells were monitored for survival following exposure at various concentrations to different cytotoxic agents including cisplatin, camptothecin or paclitaxel or to different doses of gamma-irradiation. At the lowest doses, the TGFbeta-RII-mutated and KRAS2-mutated cell line, TOV-21G, and the BRCA2-mutated cell line, TOV-81D, demonstrated a significantly higher sensitivity to cisplatin and gamma-irradiation than the TP53-mutated cell lines, TOV-112D and OV-90. At higher doses, differences between the TP53-mutated lines were observed with TOV-112D being less sensitive to cisplatin than OV-90 that also harbors a CDNK2A mutation. All cell lines were similarly sensitive to high doses of gamma-irradiation. In contrast, sensitivity to camptothecin or paclitaxel was not significantly different between all cell lines, irrespective of the mutation status of BRCA1, BRCA2, TGFbeta-RII, KRAS2, TP53, and CDKN2A. The observed responses to treatment are consistent with the current knowledge concerning BRCA2, TGFbeta-RII, KRAS2, TP53, and/or CDKN2A aberrant function.

BRCA1 and BRCA2 in breast cancer predisposition and recombination control

Hereditary predisposition to breast and ovarian cancer is determined in large part by loss-of-function mutations in one of two genes, BRCA1 and BRCA2 . Early discoveries that the two genes function in the control of homologous recombination and the prevention of genomic instability have been strongly supported by subsequent work. Our aim here is to highlight new advances in the study of BRCA1 and BRCA2 , and to place these advances in the context of existing knowledge.

DNA double strand break repair and its association with inherited predispositions to breast cancer

Mutations in BRCA1 account for the majority of familial aggregations of early onset breast and ovarian cancer (~70%) and about 1/5 of all early onset breast cancer families; in contrast, mutations in BRCA2 account for a smaller proportion of breast/ovarian cancer families and a similar proportion of early onset breast cancer families. BRCA2 has also been shown to be associated with a much more pleiotropic disease spectrum compared to BRCA1. Since the identification of both BRCA1 and BRCA2 investigations into the functions of these genes have revealed that both are associated with the maintenance of genomic integrity via their apparent roles in cellular response to DNA damage, especially their involvement in the process of double strand DNA break repair. This review will focus on the specific roles of both genes and how functional differences may account for the diverse clinical findings observed between families that harbour BRCA1 or BRCA2 mutations.

RecQ helicases: suppressors of tumorigenesis and premature aging

The RecQ helicases represent a subfamily of DNA helicases that are highly conserved in evolution. Loss of RecQ helicase function leads to a breakdown in the maintenance of genome integrity, in particular hyper-recombination. Germ-line defects in three of the five known human RecQ helicases give rise to defined genetic disorders associated with cancer predisposition and/or premature aging. These are Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome, which are caused by defects in the genes BLM, WRN and RECQ4 respectively. Here we review the properties of RecQ helicases in organisms from bacteria to humans, with an emphasis on the biochemical functions of these enzymes and the range of protein partners that they operate with. We will discuss models in which RecQ helicases are required to protect against replication fork demise, either through prevention of fork breakdown or restoration of productive DNA synthesis.

Gene expression profile of human cells irradiated in G1 and G2 phases of cell cycle

The response of cells to ionizing radiation has long been known to result in alterations in gene expression. Here we examined the expression patterns of synchronized HeLa cells in G1 or G2, after exposure to 2Gy of X-rays on microarrays allowing evaluation of over 12,000 human genes. The analysis showed induction of at least twofold for 257 different genes, after irradiation of cells in G1 and down-regulation of 42. The altered transcription patterns involved genes belonging to cell cycle pathways, DNA repair, oncogenes, histones, heat shock genes, mitochondrial and ribosomal proteins, transcription and translational regulators and genes encoding cytoskeleton components. HeLa cells are deficient in p53 and none of the induced genes have previously been identified as regulated by p53. One hundred and seventy-seven genes were up-regulated and 26 genes were down-regulated after irradiation in G2. Surprisingly most of the up-regulated genes in both phases of the cell cycle encode ribosomal proteins. These studies have revealed cell cycle dependence on radiation-induced gene induction and have permitted the identification of previously known as well as unknown genes associated with radiation-induced altered expression.