Tumor suppressor p53 is required to modulate BRCA1 expression

Radiosensitization effect of quinoline-indole-schiff base derivative 10E on non-small cell lung cancer cells in vitro and in tumor xenografts

Radioresistance is an inevitable obstacle in the clinical treatment of inoperable patients with non-small cell lung cancer (NSCLC). Combining treatment with radiosensitizers may improve the efficacy of radiotherapy. Previously, the quinoline derivative 10E as new exporter of Nur77 has shown superior antitumor activity in hepatocellular carcinoma. Here, we aimed to investigate the radiosensitizing activity and acting mechanisms of 10E. In vitro, A549 and H460 cells were treated with control, ionizing radiation (IR), 10E, and 10E + IR. Cell viability, apoptosis, and cycle were examined using CCK-8 and flow cytometry assays. Protein expression and localization were examined using western blotting and immunofluorescence. Tumor xenograft models were established to evaluate the radiosensitizing effect of 10E in vivo. 10E significantly inhibited cell proliferation and increased their radiosensitivity while reducing level of p-BCRA1, p-DNA-PKs, and 53BP1 involved in the DNA damage repair pathway, indicating that its radiosensitizing activity is closely associated with repressing DNA damage repair. A549 cells showed low level of Nur77 and a low response to IR but 10E-treated A549 cells showed high level of Nur77 indicating that Nur77 is a core radiosensitivity factor and 10E restores the expression of Nur77. Nur77 and Ku80 extranuclear co-localization in the 10E-treated A549 cells suggested that 10E-modulated Nur77 nuclear exportation inhibits DNA damage repair pathways and increases IR-triggered apoptosis. The combination of 10E and IR significantly inhibits tumor growth in a tumor xenograft model. Our findings suggest that 10E acts as a radiosensitizer and that combining 10E with radiotherapy may be a potential strategy for NSCLC treatment.

BRCA Mutations and MicroRNA Expression Patterns in the Peripheral Blood of Breast Cancer Patients

Breast cancer (BC) persists as the predominant malignancy globally, standing as the foremost cause of cancer-related mortality among women. Despite notable advancements in prevention and treatment, encompassing the incorporation of targeted immunotherapies, a continued imperative exists for the development of innovative methodologies. These methodologies would facilitate the identification of women at heightened risk, enhance the optimization of therapeutic approaches, and enable the vigilant monitoring of emergent treatment resistance. Circulating microRNAs (miRNAs), found either freely circulating in the bloodstream or encapsulated within extracellular vesicles, have exhibited substantial promise for diverse clinical applications. These applications range from diagnostic and prognostic assessments to predictive purposes. This study aimed to explore the potential associations between BRCA mutations and specific miRNAs (miR-21, miR-155, miR-126, and miR-200c) expression that are known to be dysregulated in BC patient samples. Our findings indicate a robust correlation between miRNA expression status and disease subtypes. We found a correlation between the expression status of miRNAs and distinct disease subtypes. Intriguingly, however, no significant associations were discerned between disease status, subtypes, or miRNA expression levels and the presence of BRCA mutations. To advance the validation of miRNAs as clinically relevant biomarkers, additional investigations within larger and meticulously selected patient cohorts are deemed imperative. These microRNA entities hold the potential to emerge as groundbreaking and readily accessible tools, poised for seamless integration into the landscape of clinical practice.

Treatment of Sulfur Mustard Corneal Injury by Augmenting the DNA Damage Response (DDR): A Novel Approach

Sulfur mustard (SM) is a highly reactive organic chemical has been used as a chemical warfare agent and terrorist threat since World War I. The cornea is highly sensitive to SM toxicity and exposure to low vapor doses can cause incapacitating acute injuries. Exposure to higher doses can elicit persistent secondary keratopathies that cause reduced quality of life and impaired or lost vision. Despite a century of research, there are no specific treatments for acute or persistent ocular SM injuries. SM cytotoxicity emerges, in part, through DNA alkylation and double-strand breaks (DSBs). Because DSBs can naturally be repaired by DNA damage response pathways with low efficiency, we hypothesized that enhancing the homologous recombination pathway could pose a novel approach to mitigate SM injury. Here, we demonstrate that a dilithium salt of adenosine diphosphoribose (INV-102) increases protein levels of p53 and Sirtuin 6, upregulates transcription of BRCA1/2, enhances γH2AX focus formation, and promotes assembly of repair complexes at DSBs. Based on in vitro evidence showing INV-102 enhancement of DNA damage response through both p53-dependent and p53-independent pathways, we next tested INV-102 in a rabbit preclinical model of corneal injury. In vivo studies demonstrate a marked reduction in the incidence and severity of secondary keratopathies in INV-102-treated eyes compared with vehicle-treated eyes when treatment was started 24 hours after SM vapor exposure. These results suggest DNA repair mechanisms are a viable therapeutic target for SM injury and suggest topical treatment with INV-102 is a promising approach for SM as well as other conditions associated with DSBs. SIGNIFICANCE STATEMENT: Sulfur mustard gas corneal injury currently has no therapeutic treatment. This study aims to show the therapeutic potential of activating the body's natural DNA damage response to activate tissue repair.

PRIMA-1 synergizes olaparib-induced cell death in p53 mutant triple negative human breast cancer cell line via restoring p53 function, arresting cell cycle, and inducing apoptosis

This study concerned with assessing the effect of restoring p53 using PRIMA-1 on the anti-cancer activity of olaparib against TP53-mutant triple negative breast cancer (TNBC) cells and exploring the optimum synergistic concentrations and the underlying mechanism. Human BC cell lines, MDA-MB-231 with mutated TP53 gene, and MCF-7 with wild-type TP53 gene were treated with olaparib and/or PRIMA-1. The IC50 value for olaparib was significantly decreased by PRIMA-1 in MDA-MB-231 cells compared to MCF-7 cells. Contrary to MCF-7 cells, co-treatment with olaparib and PRIMA-1 had a synergistic anti-proliferative effect in MDA-MB-231 at all tested concentrations with the best synergistic combination at 45 and 8.5 µM, respectively, and furthermore PRIMA-1 enhanced olaparib-induced apoptosis. This synergistic apoptotic effect was associated with a significant boost in mRNA expression of TP53 gene, cell cycle arrest at G2/M phase, modulation of BRCA-1, BAX and Bcl2 proteins expressions, and induction of active caspase-3. These results present a clue for the utility of combined olaparib and PRIMA-1 in treatment of TP53-mutant TNBC invitro. PRIMA-1 triggers olaparib-induced MDA-MB-231 cell death in a synergistic manner via restoring TP53, decreasing BRCA-1 expression, cell cycle arrest, and enhancement of apoptosis via p53/BAX/Bcl2/caspase 3 pathway.

BIA-ALCL in patients with genetic predisposition for breast cancer: our experience and a review of the literature

Breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) is an emerging non-Hodgkin's lymphoma that occurs exclusively in patients with breast implants. The estimated risk of developing BIA-ALCL from exposure to breast implants is largely based on approximations about patients at risk. There is a growing body of evidence regarding the presence of specific germline mutations in patients developing BIA-ALCL, rising interest regarding possible markers of genetic predisposition to this type of lymphoma. The present paper focuses attention on BIA-ALCL in women with a genetic predisposition for breast cancer. We report our experience at the European Institute of Oncology, Milan, Italy, describing a case of BIA-ALCL in a BRCA1 mutation carrier who developed BIA-ALCL 5 years after implant-based post mastectomy reconstruction. She was treated successfully with an en-bloc capsulectomy. Additionally, we review the available literature on inherited genetic factors predisposing to the development of BIA-ALCL. In patients with genetic predisposition to breast cancer (mainly TP53 and BRCA1/2 germline mutations), BIA-ALCL prevalence seems to be higher and time to onset appears to be shorter in comparison to the general population. These high-risk patients are already included in close follow-up programs allowing the diagnosis of early-stage BIA-ALCL. For this reason, we do not believe that a different approach should be followed for postoperative surveillance.

Overcoming therapeutic resistance in pancreatic cancer: Emerging opportunities by targeting BRCAs and p53

Pancreatic cancer (PC) is characterized by (epi)genetic and microenvironmental alterations that negatively impact the treatment outcomes. New targeted therapies have been pursued to counteract the therapeutic resistance in PC. Aiming to seek for new therapeutic options for PC, several attempts have been undertaken to exploit BRCA1/2 and TP53 deficiencies as promising actionable targets. The elucidation of the pathogenesis of PC highlighted the high prevalence of p53 mutations and their connection with the aggressiveness and therapeutic resistance of PC. Additionally, PC is associated with dysfunctions in several DNA repair-related genes, including BRCA1/2, which sensitize tumours to DNA-damaging agents. In this context, poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) were approved for mutant BRCA1/2 PC patients. However, acquired drug resistance has become a major drawback of PARPi. This review emphasizes the importance of targeting defective BRCAs and p53 pathways for advancing personalized PC therapy, with particular focus on how this approach may provide an opportunity to tackle PC resistance.

A transcriptional program associated with cell cycle regulation predominates in the anti-inflammatory effects of CX-5461 in macrophage

CX-5461, a novel selective RNA polymerase I inhibitor, shows potential anti-inflammatory and immunosuppressive activities. However, the molecular mechanisms underlying the inhibitory effects of CX-5461 on macrophage-mediated inflammation remain to be clarified. In the present study, we attempted to identify the systemic biological processes which were modulated by CX-5461 in inflammatory macrophages. Primary peritoneal macrophages were isolated from normal Sprague Dawley rats, and primed with lipopolysaccharide or interferon-γ. Genome-wide RNA sequencing was performed. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used for gene functional annotations. Enrichment analysis was conducted using the ClusterProfiler package of R software. We found that CX-5461 principally induced a molecular signature related to cell cycle inhibition in primed macrophages, featuring downregulation of genes encoding cell cycle mediators and concomitant upregulation of cell cycle inhibitors. At the same concentration, however, CX-5461 did not induce a systemic anti-inflammatory transcriptional program, although some inflammatory genes such as IL-1β and gp91phox NADPH oxidase were downregulated by CX-5461. Our data further highlighted a central role of p53 in orchestrating the molecular networks that were responsive to CX-5461 treatment. In conclusion, our study suggested that limiting cell proliferation predominated in the inhibitory effects of CX-5461 on macrophage-mediated inflammation.

KRAS Pathway Alterations in Malignant Pleural Mesothelioma: An Underestimated Player

Simple Summary

Malignant pleural mesothelioma (MPM) is a rare, incurable cancer. KRAS pathway alterations are frequent in human MPM but have been likely underestimated by next generation sequencing studies.

Abstract

Malignant pleural mesothelioma (MPM) is a rare, incurable cancer of the mesothelial cells lining the lungs and the chest wall that is mainly caused by asbestos inhalation. The molecular mechanisms of mesothelial carcinogenesis are still unclear despite comprehensive studies of the mutational landscape of MPM, and the most frequently mutated genes BAP1, NF2, CDKN2A, TP53, and TSC1 cannot cause MPM in mice in a standalone fashion. Although KRAS pathway alterations were sporadically detected in older studies employing targeted sequencing, they have been largely undetected by next generation sequencing. We recently identified KRAS mutations and copy number alterations in a significant proportion of MPM patients. Here, we review and analyze multiple human datasets and the published literature to show that, in addition to KRAS, multiple other genes of the KRAS pathway are perturbed in a significant proportion of patients with MPM.

ATF6 prevents DNA damage and cell death in colon cancer cells undergoing ER stress

Colon cancer represents one of the most common and aggressive cancers in its advanced state. Among the most innovative anti-cancer approaches, the manipulation of UPR is a promising one, effective also against cancers carrying dysfunctional p53. Interestingly, it is emerging that UPR cross-talks with DDR and that targeting the interplay between these two adaptive responses may be exploited to overcome the resistance to the single DDR- and UPR-targeting treatments. Previous studies have highlighted the role of IRE1 alpha and PERK UPR sensors on DDR, while the impact of ATF6 on this process remains under-investigated. This study shows for the first time that ATF6 sustains the expression level of BRCA-1 and protects colon cancer cells from the cytotoxic effect of ER stressors DPE and Thapsigargin. At molecular level, ATF6 activates mTOR to sustain the expression of HSP90, of which BRCA-1 is a client protein. Therefore, pharmacological or genetic inhibition of ATF6 promoted BRCA-1 degradation and increased DNA damage and cell death, particularly in combination with Adriamycin. All together this study suggests that targeting ATF6 may not only potentiate the cytotoxic effect of drugs triggering ER stress but may render colon cancer cells more sensitive to Adriamycin and possibly to other DNA damaging agents used to treat colon cancer.

VPA and TSA Interrupt the Interplay between mutp53 and HSP70, Leading to CHK1 and RAD51 Down-Regulation and Sensitizing Pancreatic Cancer Cells to AZD2461 PARP Inhibitor

HDAC inhibitors (HDACi) represent promising anti-cancer treatments, as the acetylation of histone and non-histone proteins is often dysregulated in cancer and contributes to cancer onset and progression. HDACi have been also reported to increase the cytotoxicity of DNA-damaging agents, such as radiation or cisplatin. In this study, we found that TSA and, even more effectively, VPA synergized with AZD2461, PARP1, 2 and 3 inhibitor (PARPi) to induce DNA damage and reduce pancreatic cancer cell survival. At a molecular level, VPA and TSA down-regulated CHK1 and RAD51, which is correlated with the interruption of the cross-talk between mutp53 and HSP70. Moreover, VPA and to a lesser extent TSA reactivated wtp53 in these cells, which contributed to CHK1 and RAD51 reduction. These findings suggest that the combination of HDACi and PARPi might improve the treatment of pancreatic cancer, which remains one of the most aggressive and therapy-resistant cancers.

PARP Inhibition Activates STAT3 in Both Tumor and Immune Cells Underlying Therapy Resistance and Immunosuppression In Ovarian Cancer

Despite the promising activity of poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) in many cancer types with defects in the DNA damage response the majority of the treated patients acquire PARPi resistance and succumb to their diseases. Consequently, there is an urgent need to identify the mechanisms of PARPi resistance. Here, we show that PARPi treatment promotes STAT3 activation in ovarian cancer cells, tumor-associated immune cells and fibroblasts, resulting in PARPi resistance and immunosuppression. Comparison of ovarian cancer patient-matched tumor biopsies before and after PARPi therapy revealed that STAT3 activity was significantly higher in tumor cells and tumor-associated immune cells and fibroblasts post PARPi treatment. Moreover, one-time PARPi treatment activated STAT3 both in tumor cells as well as diverse immune subsets and fibroblasts. PARPi-treated immune cells exhibited decreased expression of immunostimulatory interferon (IFN)-γ and Granzyme B while increasing immunosuppressive cytokine IL-10. Finally, we demonstrate that the acquisition of PARPi resistance in ovarian cancer cells was accompanied by increased STAT3 activity. Ablating STAT3 inhibited PARPi-resistant ovarian tumor cell growth and/or restored PARPi sensitivity. Therefore, our study has identified a critical mechanism intrinsic to PARPi that promotes resistance to PARPi and induces immunosuppression during PARPi treatment by activating STAT3 in tumor cells and tumor-associated immune cells/fibroblasts.

KRAS signaling in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) arises from mesothelial cells lining the pleural cavity of asbestos‐exposed individuals and rapidly leads to death. MPM harbors loss‐of‐function mutations in BAP1, NF2, CDKN2A, and TP53, but isolated deletion of these genes alone in mice does not cause MPM and mouse models of the disease are sparse. Here, we show that a proportion of human MPM harbor point mutations, copy number alterations, and overexpression of KRAS with or without TP53 changes. These are likely pathogenic, since ectopic expression of mutant KRAS^G12D in the pleural mesothelium of conditional mice causes epithelioid MPM and cooperates with TP53 deletion to drive a more aggressive disease form with biphasic features and pleural effusions. Murine MPM cell lines derived from these tumors carry the initiating KRAS^G12D lesions, secondary Bap1 alterations, and human MPM‐like gene expression profiles. Moreover, they are transplantable and actionable by KRAS inhibition. Our results indicate that KRAS alterations alone or in accomplice with TP53 alterations likely play an important and underestimated role in a proportion of patients with MPM, which warrants further exploration.

Gene dosage effects of poly(A) track-engineered hypomorphs

Manipulation of gene activity through creation of hypomorphic mutants has been a long-standing tool in examining gene function. Our previous studies have indicated that hypomorphic mutants could be created by inserting cis-regulatory sequences composed of consecutive adenosine nucleotides called poly(A) tracks. Here we use poly(A) tracks to create hypomorphic mutants and functional characterization of membrane, secretory, and endogenous proteins. Insertion of poly(A) tracks into the sequences of interleukin-2 and membrane protein CD20 results in a programmable reduction of mRNA stability and attenuation of protein expression regardless of the presence of a signaling sequence. Likewise, CRISPR-Cas9 targeted insertion of poly(A) tracks into the coding sequence of the endogenous human genes AUF1 and TP53 results in a programmable reduction of targeted protein and mRNA levels. Functional analyses of AUF1-engineered hypomorphs indicate a direct correlation between AUF1 gene levels and the stability of AUF1-regulated mRNAs. Hypomorphs of TP53 affect expression of the target genes differentially depending on the severity of the hypomorphic mutation. Finally, decreases in TP53 protein affect the same cellular pathways in poly(A) track-engineered cells as in cancer cells, indicating these variants’ biological relevance. These results highlight this technology’s power to create predictable, stable hypomorphs in recombinant or endogenous genes in combination with CRISPR-Cas9 engineering tools.

Anticancer effect of AZD2461 PARP inhibitor against colon cancer cells carrying wt or dysfunctional p53

Colon cancer is one of the most common cancers, currently treated with traditional chemotherapies or alternative therapies. However, these treatments are still not enough effective and induce several side effects, so that the search of new therapeutic strategies is needed. The use of Poly-(ADP-ribose)-polymerase (PARP) inhibitors, although originally approved against BRCA-1 or BRCA-2 mutated cancers, has been extended, particularly in combination with other treatments, to cure cancers that do not display defects in DNA repair signaling pathways. The role of p53 oncosuppressor in the regulating the outcome of PARP inhibitor treatment remains an open issue. In this study, we addressed this topic by using a well-tolerated PARP 1/2/3 inhibitor, namely AZD2461, against colon cancer cell lines with different p53 status. We found that AZD2461 reduced cell proliferation in wtp53 and p53-/- cancer cells by increasing ROS and DNA damage, while R273H mutant (mut) p53 counteracted these effects. Moreover, AZD2461 improved the reduction of cell proliferation by low dose radiation (IR) in wtp53 cancer cells, in which a down-regulation of BRCA-1 occurred. AZD2461 did not affect cell proliferation of mutp53 colon cancer cells also in combination with low dose radiation, suggesting that only wt p53 or p53 null colon cancer cells could benefit AZD2461 treatment.

TP53 Co-Mutational Features and NGS-Calibrated Immunohistochemistry Threshold in Gastric Cancer

Purpose

TP53 is the most frequently mutated gene in gastric cancer and it can be potentially used for gastric cancer diagnosis and screening. However, standardized clinical approaches that could accurately and cost-effectively detect TP53 mutations in gastric cancer are largely lagged behind.

Patients and Methods

We conducted next-generation sequencing (NGS) analysis of 425 cancer-related genes in 42 gastric cancer patients in our cohort. A 1313-patient cohort derived from the cBioPortal database was used for validation. We performed immunohistochemistry (IHC) staining with four commonly used p53 antibodies, and the NGS results were used as the gold standard to optimize the IHC threshold for each antibody.

Results

By NGS analysis, we found that around 80% of gastric cancer patients in our cohort harbored TP53 alterations. Genetic alterations of BRCA1/2 or KMT2B were mostly exclusive with TP53 mutations, so were the MSI status or low grade of tumors. These results were further validated using the data from cBioPortal. We then used the NGS-derived TP53 status to optimize four commonly used IHC antibodies for detecting TP53 mutations. We showed that all antibodies could achieve more than 93% accuracy when proper IHC positivity thresholds were used, especially for the SP5 antibody that could reach 100% sensitivity and specificity with the 20% threshold.

Conclusion

Our results indicated that exclusivity between TP53 and BRCA mutations could be potentially used as a cost-effective way to predict BRCA status. Also, setting proper IHC thresholds for each specific antibody is critical to accurately detect TP53 mutations and facilitate disease diagnosis.

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.

Untangling the crosstalk between BRCA1 and R-loops during DNA repair

R-loops are RNA:DNA hybrids assembled during biological processes but are also linked to genetic instability when formed out of their natural context. Emerging evidence suggests that the repair of DNA double-strand breaks requires the formation of a transient R-loop, which eventually must be removed to guarantee a correct repair process. The multifaceted BRCA1 protein has been shown to be recruited at this specific break-induced R-loop, and it facilitates mechanisms in order to regulate R-loop removal. In this review, we discuss the different potential roles of BRCA1 in R-loop homeostasis during DNA repair and how these processes ensure faithful DSB repair.

Advanced Approaches to Breast Cancer Classification and Diagnosis

The International Agency for Research on Cancer (IARC) has recently reported a 66% increase in the global number of cancer deaths since 1960. In the US alone, about one in eight women is expected to develop invasive breast cancer(s) (breast cancer) at some point in their lifetime. Traditionally, a BC diagnosis includes mammography, ultrasound, and some high-end molecular bioimaging. Unfortunately, these techniques detect BC at a later stage. So early and advanced molecular diagnostic tools are still in demand. In the past decade, various histological and immuno-molecular studies have demonstrated that BC is highly heterogeneous in nature. Its growth pattern, cytological features, and expression of key biomarkers in BC cells including hormonal receptor markers can be utilized to develop advanced diagnostic and therapeutic tools. A cancer cell's progression to malignancy exhibits various vital biomarkers, many of which are still underrepresented in BC diagnosis and treatment. Advances in genetics have also enabled the development of multigene assays to detect genetic heterogeneity in BC. However, thus far, the FDA has approved only four such biomarkers-cancer antigens (CA); CA 15-3, CA 27-29, Human epidermal growth factor receptor 2 (HER2), and circulating tumor cells (CTC) in assessing BC in body fluids. An adequately structured portable-biosensor with its non-invasive and inexpensive point-of-care analysis can quickly detect such biomarkers without significantly compromising its specificity and selectivity. Such advanced techniques are likely to discriminate between BC and a healthy patient by accurately measuring the cell shape, structure, depth, intracellular and extracellular environment, and lipid membrane compositions. Presently, BC treatments include surgery and systemic chemo- and targeted radiation therapy. A biopsied sample is then subjected to various multigene assays to predict the heterogeneity and recurrence score, thus guiding a specific treatment by providing complete information on the BC subtype involved. Thus far, we have seven prognostic multigene signature tests for BC providing a risk profile that can avoid unnecessary treatments in low-risk patients. Many comparative studies on multigene analysis projected the importance of integrating clinicopathological information with genomic-imprint analysis. Current cohort studies such as MINDACT, TAILORx, Trans-aTTOM, and many more, are likely to provide positive impact on long-term patient outcome. This review offers consolidated information on currently available BC diagnosis and treatment options. It further describes advanced biomarkers for the development of state-of-the-art early screening and diagnostic technologies.

Myricetin Exerts its Apoptotic Effects on MCF-7 Breast Cancer Cells through Evoking the BRCA1-GADD45 Pathway

OBJECTIVE

Myricetin is a polyphenol flavonoid with nutraceutical values which is abundantly found as the main ingredient of various foods and beverages. It has been reported that the function of myricetin is to trigger apoptosis in several types of cancers. The present study intended to investigate the apoptotic effects of myricetin on MCF-7 breast cancer cells and to assess its possible mechanisms of action.

MATERIALS AND METHODS

MCF-7 breast cancer cells were assigned to four groups: Control (cells in normal condition); myricetin (cells treated with the IC50 dosage of myricetin) in three different incubation times (24, 48, and 72 h). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, annexin V assay, flow cytometry, real-time polymerase chain reaction (PCR), and caspase-3 assay were used to estimate the apoptosis function of myricetin in breast cancer.

RESULTS

The expression levels of apoptosis-related genes caspase-3, caspase-8, caspase-9, and the BAX /Bcl-2 ratio as well as the expression of p53, BRCA1, GADD45 genes were significantly increased following the treatment of MCF-7 breast cancer cells with myricetin. The annexin V assay demonstrated the significant expression of annexin which was also detected by flow cytometry.

CONCLUSION

Myricetin efficiently induces apoptosis in MCF-7 breast cancer cells by evoking both extrinsic and intrinsic apoptotic pathways. Myricetin may exert its apoptotic effects on MCF-7 cells by inducing the BRCA1- GADD45 pathway.
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Breast-Specific Epigenetic Regulation of DeltaNp73 and Its Role in DNA-Damage-Response of BRCA1-Mutated Human Mammary Epithelial Cells

The function of BRCA1/2 proteins is essential for maintaining genomic integrity in all cell types. However, why women who carry deleterious germline mutations in BRCA face an extremely high risk of developing breast and ovarian cancers specifically has remained an enigma. We propose that breast-specific epigenetic modifications, which regulate tissue differentiation, could team up with BRCA deficiency and affect tissue susceptibility to cancer. In earlier work, we compared genome-wide methylation profiles of various normal epithelial tissues and identified breast-specific methylated gene promoter regions. Here, we focused on deltaNp73, the truncated isoform of p73, which possesses antiapoptotic and pro-oncogenic functions. We showed that the promoter of deltaNp73 is unmethylated in normal human breast epithelium and methylated in various other normal epithelial tissues and cell types. Accordingly, deltaNp73 was markedly induced by DNA damage in human mammary epithelial cells (HMECs) but not in other epithelial cell types. Moreover, the induction of deltaNp73 protected HMECs from DNA damage-induced cell death, and this effect was more substantial in HMECs from BRCA1 mutation carriers. Notably, when BRCA1 was knocked down in MCF10A, a non-malignant breast epithelial cell line, both deltaNp73 induction and its protective effect from cell death were augmented upon DNA damage. Interestingly, deltaNp73 induction also resulted in inhibition of BRCA1 and BRCA2 expression following DNA damage. In conclusion, breast-specific induction of deltaNp73 promotes survival of BRCA1-deficient mammary epithelial cells upon DNA damage. This might result in the accumulation of genomic alterations and allow the outgrowth of breast cancers. These findings indicate deltaNp73 as a potential modifier of breast cancer susceptibility in BRCA1 mutation carriers and may stimulate novel strategies of prevention and treatment for these high-risk women.

Short-term effects of simulated microgravity on morphology and gene expression in human breast cancer cells

Introduction

Microgravity has been shown to impose various effects on breast cancer cells. We exposed human breast cancer cells to simulated microgravity and studied morphology and alterations in gene expression.

Materials and methods

Human breast cancer cells were exposed to simulated microgravity in a random positioning machine (RPM) for 24 h. Morphology was observed under light microscopy, and gene alteration was studied by qPCR.

Results

After 24 h, formation of three-dimensional structures (spheroids) occurred. BRCA1 expression was significantly increased (1.9×, p < 0.05) in the adherent cells under simulated microgravity compared to the control. Expression of KRAS was significantly decreased (0.6×, p < 0.05) in the adherent cells compared to the control. VCAM1 was significantly upregulated (6.6×, 2.0×, p < 0.05 each) in the adherent cells under simulated microgravity and in the spheroids. VIM expression was significantly downregulated (0.45×, 0.44×, p < 0.05 each) in the adherent cells under simulated microgravity and in the spheroids. There was no significant alteration in the expression of MAPK1, MMP13, PTEN, and TP53.

Conclusions

Simulated microgravity induces spheroid formation in human breast cancer cells within 24 h and alters gene expression toward modified adhesion properties, enhanced cell repair, and phenotype preservation. Further insights into the underlying mechanisms could open up the way toward new therapies.

The clinical characteristics and prognosis of endometrial carcinomas that occur after breast cancer: does hormone receptor status of breast cancer matter?

OBJECTIVE

To evaluate the clinical and pathological features of endometrial cancer (EC) following breast cancer and to assess the effect of the breast cancer hormone receptor status on subsequent EC.

MATERIALS

A retrospective study based on SEER data of EC patients with a history of breast cancer.

RESULTS

A total of 2142 cases met the inclusion criteria. Compared to that of the general population, the incidence of EC following estrogen receptor-positive (ER+) breast cancer and hormone receptor-negative (HR-) breast cancer increased by approximately 16-fold and 15-fold, respectively. Histologically, the proportions of type II EC following ER+ breast cancer, HR- breast cancer and primary EC were 39.6%, 39.4% and 31.2%, respectively (P < 0.001). The proportions of G3 ECs were 26.9%, 28.2% and 19.8%, respectively (P < 0.001). The proportion of patients who died from miscellaneous malignant tumors among EC patients following breast cancer was significantly higher than the proportion of patients among primary ECs. The overall survival rate was worse for EC patients with a history of breast cancer (P < 0.001). There were no significant differences between patients with EC following ER+ breast cancer and those with EC following HR- breast cancer with regard to stage, lymphatic metastasis, outcome or cause of death.

CONCLUSIONS

Compared to the general population, the incidence of EC in patients with breast cancer was increased markedly. Patients with EC following ER+ or HR- breast cancer shared the same clinicopathological features and prognoses. All patients need close monitoring regardless of breast cancer hormone receptor status.

Hypoxia Causes Transgenerational Impairment of Ovarian Development and Hatching Success in Fish

Hypoxia is a pressing environmental problem in both marine and freshwater ecosystems globally, and this problem will be further exacerbated by global warming in the coming decades. Recently, we reported that hypoxia can cause transgenerational impairment of sperm quality and quantity in fish (in F0, F1, and F2 generations) through DNA methylome modifications. Here, we provide evidence that female fish ( Oryzias melastigma) exposed to hypoxia exhibit reproductive impairments (follicle atresia and retarded oocyte development), leading to a drastic reduction in hatching success in the F2 generation of the transgenerational group, although they have never been exposed to hypoxia. Further analyses show that the observed transgenerational impairments in ovarian functions are related to changes in the DNA methylation and expression pattern of two gene clusters that are closely associated with stress-induced cell cycle arrest and cell apoptosis. The observed epigenetic and transgenerational alterations suggest that hypoxia may pose a significant threat to the sustainability of natural fish populations.

BRCA1-Dependent Transcriptional Regulation: Implication in Tissue-Specific Tumor Suppression

Germ-line mutations in breast cancer susceptibility gene 1 (BRCA1) predominantly predispose women to breast and ovarian cancers. BRCA1 is best known for its functions in maintenance of genomic integrity including repairing DNA double-strand breaks through homologous recombination and suppressing DNA replication stress. However, whether these universally important BRCA1 functions in maintenance of genomic stability are sufficient to account for its tissue-specific tumor-suppressing function remains unclear. Accumulating evidence indicates that there are previously underappreciated roles of BRCA1 in transcriptional regulation and chromatin remodeling. In this review, we discuss the functional significance of interactions between BRCA1 and various transcription factors, its role in epigenetic regulation and chromatin dynamics, and BRCA1-dependent crosstalk between the machineries of transcription and genome integrity. Furthermore, we propose a model of how transcriptional regulation could contribute to tissue-dependent tumor-suppressing function of BRCA1.

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

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

A role for the p53 tumour suppressor in regulating the balance between homologous recombination and non-homologous end joining

Loss of p53, a transcription factor activated by cellular stress, is a frequent event in cancer. The role of p53 in tumour suppression is largely attributed to cell fate decisions. Here, we provide evidence supporting a novel role for p53 in the regulation of DNA double-strand break (DSB) repair pathway choice. 53BP1, another tumour suppressor, was initially identified as p53 Binding Protein 1, and has been shown to inhibit DNA end resection, thereby stimulating non-homologous end joining (NHEJ). Yet another tumour suppressor, BRCA1, reciprocally promotes end resection and homologous recombination (HR). Here, we show that in both human and mouse cells, the absence of p53 results in impaired 53BP1 focal recruitment to sites of DNA damage induced by ionizing radiation. This effect is largely independent of cell cycle phase and the extent of DNA damage. In p53-deficient cells, diminished localization of 53BP1 is accompanied by a reciprocal increase in BRCA1 recruitment to DSBs. Consistent with these findings, we demonstrate that DSB repair via NHEJ is abrogated, while repair via homology-directed repair (HDR) is stimulated. Overall, we propose that in addition to its role as an ‘effector’ protein in the DNA damage response, p53 plays a role in the regulation of DSB repair pathway choice.

Identification of informative genes and pathways using an improved penalized support vector machine with a weighting scheme

Incorporation of pathway knowledge into microarray analysis has brought better biological interpretation of the analysis outcome. However, most pathway data are manually curated without specific biological context. Non-informative genes could be included when the pathway data is used for analysis of context specific data like cancer microarray data. Therefore, efficient identification of informative genes is inevitable. Embedded methods like penalized classifiers have been used for microarray analysis due to their embedded gene selection. This paper proposes an improved penalized support vector machine with absolute t-test weighting scheme to identify informative genes and pathways. Experiments are done on four microarray data sets. The results are compared with previous methods using 10-fold cross validation in terms of accuracy, sensitivity, specificity and F-score. Our method shows consistent improvement over the previous methods and biological validation has been done to elucidate the relation of the selected genes and pathway with the phenotype under study.

Conserved molecular mechanisms underlying the effects of small molecule xenobiotic chemotherapeutics on cells

For proper determination of the apoptotic potential of chemoxenobiotics in synergism, it is important to understand the modes, levels and character of interactions of chemoxenobiotics with cells in the context of predicted conserved biophysical properties. Chemoxenobiotic structures are studied with respect to atom distribution over molecular space, the predicted overall octanol-to-water partition coefficient (Log OWPC; unitless) and molecular size viz a viz van der Waals diameter (vdWD). The Log OWPC-to-vdWD (nm^-1 ) parameter is determined, and where applicable, hydrophilic interacting moiety/core-to-vdWD (nm^-1 ) and lipophilic incorporating hydrophobic moiety/core-to-vdWD (nm^-1 ) parameters of their part-structures are determined. The cellular and sub-cellular level interactions of the spectrum of xenobiotic chemotherapies have been characterized, for which a classification system has been developed based on predicted conserved biophysical properties with respect to the mode of chemotherapeutic effect. The findings of this study are applicable towards improving the effectiveness of existing combination chemotherapy regimens and the predictive accuracy of personalized cancer treatment algorithms as well as towards the selection of appropriate novel xenobiotics with the potential to be potent chemotherapeutics for dendrimer nanoparticle-based effective transvascular delivery.

Increased ID4 expression, accompanied by mutant p53 accumulation and loss of BRCA1/2 proteins in triple-negative breast cancer, adversely affects survival

AIMS

Breast cancer 1 (BRCA1) expression is down-regulated in a significant proportion of non-hereditary breast cancers, in the absence of any mutation. This phenomenon is more pronounced in oestrogen (ER)-negative tumours. Recent studies have suggested that inhibitor of DNA binding 4 (ID4), as well as p53, participate in the transcriptional regulation of BRCA1.

METHODS

Immunohistochemical expression of ID4, BRCA1, BRCA2 and p53 in 699 women with triple-negative breast cancer was investigated using tissue microarrays. The prognostic role of these biomarkers was also evaluated. Survival outcomes were estimated with the Kaplan-Meier method and compared between groups with log-rank statistics.

RESULTS

Loss of BRCA1 and BRCA2 expression and overexpression of ID4 and p53 was observed in 75%, 90%, 95% and 66% of tumours, respectively. ID4 expression was increased in higher tumour grade (P < 0.001) and was associated significantly with basal-like subtype (P < 0.001), BRCA2 down-regulation (P = 0.037) and p53 accumulation (P < 0.001). Patients with strong ID4 expression displayed worse disease-free survival in both triple-negative breast cancers (P = 0.041) and basal-like triple-negative breast cancers (P = 0.026).

CONCLUSION

There is frequent ID4 expression and concomitant loss of BRCA proteins in triple-negative breast cancer. We hypothesize that strong ID4 expression could be useful as a prognostic marker in triple-negative breast cancer, predicting early tumour recurrence.

Control of signaling-mediated clearance of apoptotic cells by the tumor suppressor p53

The inefficient clearance of dying cells can lead to abnormal immune responses, such as unresolved inflammation and autoimmune conditions. We show that tumor suppressor p53 controls signaling-mediated phagocytosis of apoptotic cells through its target, Death Domain1α (DD1α), which suggests that p53 promotes both the proapoptotic pathway and postapoptotic events. DD1α appears to function as an engulfment ligand or receptor that engages in homophilic intermolecular interaction at intercellular junctions of apoptotic cells and macrophages, unlike other typical scavenger receptors that recognize phosphatidylserine on the surface of dead cells. DD1α-deficient mice showed in vivo defects in clearing dying cells, which led to multiple organ damage indicative of immune dysfunction. p53-induced expression of DD1α thus prevents persistence of cell corpses and ensures efficient generation of precise immune responses.

p53 suppresses hyper-recombination by modulating BRCA1 function

Both p53 and BRCA1 are tumor suppressors and are involved in a number of cellular processes including cell cycle arrest, apoptosis, transcriptional regulation, and DNA damage repair. Some studies have suggested that the association of BRCA1 and p53 is required for transcriptional regulation of genes involved in cell replication and DNA repair pathways. However, the relationship between the two proteins in molecular mechanisms of DNA repair is still not clear. Therefore, we sought to determine whether there is a functional link between p53 and BRCA1 in DNA repair. Firstly, using a plasmid recombination substrate, pDR-GFP, integrated into the genome of breast cancer cell line MCF7, we have demonstrated that p53 suppressed Rad51-mediated hyper-recombinational repair by two independent cell models of HPV-E6 induced p53 inactivation and p53 knockdown assay. Our study further indicated that p53 mediated homologous recombination (HR) through inhibiting BRCA1 over-function via mechanism of transcription regulation in response to DNA repair. Since it was found p53 and BRCA1 existed in a protein complex, indicating both proteins may be associated at post-transcriptional level. Moreover, defective p53-induced hyper-recombination was associated with cell radioresistance and chromosomal stability, strongly supporting the involvement of p53 in the inhibition of hyper-recombination, which led to genetic stability and cellular function in response to DNA damage. In addition, it was found that p53 loss rescued BRCA1 deficiency via recovering HR and chromosomal stability, suggesting that p53 is also involved in the HR-inhibition independently of BRCA1. Thus, our data indicated that p53 was involved in inhibiting recombination by both BRCA1-dependent and -independent mechanisms, and there is a functional link between p53-suppression and BRCA1-promotion in regulation of HR activity at transcription level and possible post-transcription level.

A novel radiation-induced p53 mutation is not implicated in radiation resistance via a dominant-negative effect

Understanding the mutations that confer radiation resistance is crucial to developing mechanisms to subvert this resistance. Here we describe the creation of a radiation resistant cell line and characterization of a novel p53 mutation. Treatment with 20 Gy radiation was used to induce mutations in the H460 lung cancer cell line; radiation resistance was confirmed by clonogenic assay. Limited sequencing was performed on the resistant cells created and compared to the parent cell line, leading to the identification of a novel mutation (del) at the end of the DNA binding domain of p53. Levels of p53, phospho-p53, p21, total caspase 3 and cleaved caspase 3 in radiation resistant cells and the radiation susceptible (parent) line were compared, all of which were found to be similar. These patterns held true after analysis of p53 overexpression in H460 cells; however, H1299 cells transfected with mutant p53 did not express p21, whereas those given WT p53 produced a significant amount, as expected. A luciferase assay demonstrated the inability of mutant p53 to bind its consensus elements. An MTS assay using H460 and H1299 cells transfected with WT or mutant p53 showed that the novel mutation did not improve cell survival. In summary, functional characterization of a radiation-induced p53 mutation in the H460 lung cancer cell line does not implicate it in the development of radiation resistance.

Progress in research of the BRCA1 gene in gastric cancer

Chemotherapy occupies an important position in the treatment of gastric cancer. Platinum drugs are commonly chemotherapy drugs for gastric cancer; however, sensitivity to these drugs varies among different patients. The breast cancer susceptibility gene 1 (BRCA1) is a tumor suppressor gene that is associated with sensitivity to platinum drugs. At present, the research on the BRCA1 gene is mainly focused on breast cancer, and there have been fewer studies on gastric cancer. This paper will give an overview of the structure and function of the BRCA1 gene and the relationship between BRCA1 and gastric cancer.

A guide for functional analysis of BRCA1 variants of uncertain significance

Germline mutations in the tumor suppressor gene BRCA1 confer an estimated lifetime risk of 56-80% for breast cancer and 15-60% for ovarian cancer. Since the mid 1990s when BRCA1 was identified, genetic testing has revealed over 1,500 unique germline variants. However, for a significant number of these variants, the effect on protein function is unknown making it difficult to infer the consequences on risks of breast and ovarian cancers. Thus, many individuals undergoing genetic testing for BRCA1 mutations receive test results reporting a variant of uncertain clinical significance (VUS), leading to issues in risk assessment, counseling, and preventive care. Here, we describe functional assays for BRCA1 to directly or indirectly assess the impact of a variant on protein conformation or function and how these results can be used to complement genetic data to classify a VUS as to its clinical significance. Importantly, these methods may provide a framework for genome-wide pathogenicity assignment.

One function--multiple mechanisms: the manifold activities of p53 as a transcriptional repressor

Maintenance of genome integrity is a dynamic process involving complex regulation systems. Defects in one or more of these pathways could result in cancer. The most important tumor-suppressor is the transcription factor p53, and its functional inactivation is frequently observed in many tumor types. The tumor suppressive function of p53 is mainly attributed to its ability to regulate numerous target genes at the transcriptional level. While the mechanism of transcriptional induction by p53 is well characterized, p53-dependent repression is not understood in detail. Here, we review the manifold mechanisms of p53 as a transcriptional repressor. We classify two different categories of repressed genes based on the underlying mechanism, and novel mechanisms which involve regulation through noncoding RNAs are discussed. The complete elucidation of p53 functions is important for our understanding of its tumor-suppressor activity and, therefore, represents the key for the development of novel therapeutic approaches.

Estrogen receptor beta decreases survival of p53-defective cancer cells after DNA damage by impairing G₂/M checkpoint signaling

Estrogen receptor beta (ERβ) inhibits proliferation in different cellular systems by regulating components of the cell cycle machinery. Eukaryotic cells respond to DNA damage by arresting in G₁, S, or G₂ phases of the cell cycle to initiate DNA repair. Most tumor cells due to disruptions in the p53-dependent G₁ pathway are dependent on S-phase and G₂/M checkpoints to maintain genomic integrity in response to DNA damage. We report that induction of ERβ expression causes abrogation of the S-phase, and the Chk1/Cdc25C-mediated G₂/M checkpoints after cisplatin and doxorubicin exposure in p53-defective breast cancer cells but not in p53 wild-type mammary cells. This impairment of DNA damage response that involves BRCA1 downregulation and caspase-2 activation results in mitotic catastrophe and decreased cancer cell survival. These results indicate that in cancers where p53 is defective, assessment of the presence of ERβ may be of predictive value for the successful response to chemotherapy.

Membrane-bound melatonin receptor MT1 down-regulates estrogen responsive genes in breast cancer cells

Melatonin possesses anti-estrogenic effects on estrogen receptor expressing (ER+) breast cancer cells in culture by reducing cell cycle progression and cell proliferation. There is increasing agreement that on a cellular level the effects of melatonin are primarily induced by the membrane-bound receptor MT1. The participation of a second, nuclear receptor of the group of ligand-dependent transcription factors, called RZRalpha, is under debate. In this study we used a number of breast cancer cell lines differing in their expression of the estrogen receptor and the two known melatonin receptors. In MCF-7 breast cancer cells transfected with a vector carrying the MT1 gene (MCF-7Mel1a) binding of CREB-protein to the cAMP-responsive element of the breast cancer suppressing gene BRCA-1 was more strongly reduced by treatment with melatonin than in the parental cells. Expression of estrogen responsive genes was determined in serum-starved cells, cells stimulated for 16 hr with estradiol and cells subsequently treated with melatonin. Expression of BRCA-1, p53, p21(WAF) and c-myc were up-regulated by estradiol. Treatment of the stimulated cells with melatonin counteracted the increase induced by estradiol almost completely. The more MT1 a cell line expressed, the stronger was the reduction of the expression of the estradiol-induced genes. There was no correlation between the expression of the nuclear receptor RZRalpha and the effects of melatonin on these genes.

Altered expression of proliferation-inducing and proliferation-inhibiting genes might contribute to acquired doxorubicin resistance in breast cancer cells

This study was designed to investigate the molecular changes that may develop during exposure of breast cancer cells to anticancer agents and that may lead to acquired resistance. We used two breast cancer cell lines, a parental (MCF7/WT) and a doxorubicin-resistant (MCF7/DOX) one. Cell survival, cell cycle distribution and RT-PCR expression level of genes involved in DNA damage response, MDR1, GST and TOPOIIalpha were measured. MCF7/DOX cells were five-fold more resistant to doxorubicin (DOX) than the MCF7/WT cells. DOX treatment causes arrest of MCF7/DOX cells in G1 and G2 phases of cell cycle whereas MCF7/WT cells were arrested in S-phase. The molecular changes in both cell lines due to DOX treatment could be classified into: (1) the basal level of p53, p21, BRCA1, GST and TOPOIIalpha mRNA was higher in MCF7/DOX than MCF7/WT. During DOX treatment, the expression level of these genes decreased in both cell lines but the rate of down-regulation was faster in MCF7/WT than MCF7/DOX cells. (2) The expression level of MDR1 was the same in both cell lines but 48 and 72 h of drug treatment, MDR1 disappeared in MCF7/WT but still expressed in MCF7/DOX. (3) There was no change in the expression level of BAX, FAS and BRCA2 in both cell lines. Conclusively, after validation in clinical samples, overexpression of genes like BRCA1, p53, p21, GST, MDR1 and TOPOIIalpha could be used as a prognostic biomarker for detection of acquired resistance in breast cancer and as therapeutic targets for the improvement of breast cancer treatment strategies.

Induction of PPM1D following DNA-damaging treatments through a conserved p53 response element coincides with a shift in the use of transcription initiation sites

PPM1D (Wip1), a type PP2C phosphatase, is expressed at low levels in most normal tissues but is overexpressed in several types of cancers. In cells containing wild-type p53, the levels of PPM1D mRNA and protein increase following exposure to genotoxic stress, but the mechanism of regulation by p53 was unknown. PPM1D also has been identified as a CREB-regulated gene due to the presence of a cyclic AMP response element (CRE) in the promoter. Transient transfection and chromatin immunoprecipitation experiments in HCT116 cells were used to characterize a conserved p53 response element located in the 5' untranslated region (UTR) of the PPM1D gene that is required for the p53-dependent induction of transcription from the human PPM1D promoter. CREB binding to the CRE contributes to the regulation of basal expression of PPM1D and directs transcription initiation at upstream sites. Following exposure to ultraviolet (UV) or ionizing radiation, the abundance of transcripts with short 5' UTRs increased in cells containing wild-type p53, indicating increased utilization of downstream transcription initiation sites. In cells containing wild-type p53, exposure to UV resulted in increased PPM1D protein levels even when PPM1D mRNA levels remained constant, indicating post-transcriptional regulation of PPM1D protein levels.

Altered gene expression profiles and higher frequency of spontaneous DNA strand breaks in APEX2-null thymus

A second class II AP endonuclease, APEX2, possesses strong 3'-5' exonuclease and 3'-phosphodiesterase activities but only very weak AP-endonuclease activity. APEX2 associates with proliferating cell nuclear antigen (PCNA), and the progression of S phase of the cell cycle is accompanied by its expression. APEX2-null mice exhibit severe dyslymphopoiesis in thymus as well as moderate dyshematopoiesis and growth retardation. Comparative gene expression profiling of wild-type and APEX2-null mice using an oligonucleotide microarray revealed that APEX2-null thymus has significantly altered gene expression profiles, reflecting its altered populations of thymocytes. Beyond these altered populations, APEX2-null thymus exhibits significant alterations in expression of genes involved in DNA replication, recombination and repair, including Apex1, Exo1 and Fen1 as well as master genes for the DNA damage response, such as E2f1, Chek1, and proapoptotic genes. We therefore examined the extent of DNA strand breakage, and found that both of single-strand breaks detected as comets and double-strand breaks detected as gammaH2AX foci were significantly higher in frequency in most APEX2-null thymocytes compared to wild-type thymocytes. This higher frequency of DNA breaks was accompanied by increased expression of PCNA and increased phosphorylation of p53 at Ser23 and to a lesser extent, at Ser18. The present study clearly demonstrates that APEX2-null lymphocytes have a higher frequency of DNA breaks, indicating that APEX2 may play an important role(s) during their generation and/or repair.

Prepubertal physical activity up-regulates estrogen receptor beta, BRCA1 and p53 mRNA expression in the rat mammary gland

Findings in BRCA1 mutation carriers suggest that physical activity, particularly during childhood, may be linked to a reduced risk of developing breast cancer. We investigated whether physical activity at puberty alters the expression of BRCA1 and two other tumor suppressor genes--p53 and estrogen receptor (ER)-beta--in rats. In addition, the effects on ER-alpha expression, mammary proliferation and functional epithelial differentiation were investigated as markers of altered mammary cancer risk in rats exposed to regular physical activity at puberty. Female Sprague Dawley rat pups were randomized to voluntary exercise, sham-exercise control and non-manipulated control groups. Treadmill training (20-25 m/min, 15% grade, 30 min/day, 5 days/week) started on postnatal day 14 and continued through day 32. Third thoracic mammary glands (n = 5 per group and age) were obtained at days 32, 48 and 100 and assessed for changes in morphology through wholemounts, and at 100 days cell proliferation by using Ki67 staining, protein levels of ER-alpha and ER-beta by immunohistochemistry, and mRNA expression levels of BRCA1, p53, ER-alpha and ER-beta by real-time PCR. Mammary glands of rats exposed to exercise during puberty contained fewer terminal end buds (TEBs) and a higher number of differentiated alveolar buds and lobules than the sham controls. However, cell proliferation was not significantly altered among the groups. ER-alpha protein levels were significantly reduced, while ER-beta levels were increased in the mammary ducts and lobular epithelial structures of 100-day old rays which were voluntarily exercised at puberty, compared to sham controls. ER-beta, BRCA1 and p53 mRNA levels were significantly higher in the mammary glands of 100-day-old exercised versus sham control rats. Pubertal physical activity reduced mammary epithelial targets for neoplastic transformation through epithelial differentiation and it also up-regulated tumor suppressor genes BRCA1, p53 and ER-beta, and reduced ER-alpha/ER-beta ratio in the mammary gland. It remains to be determined whether the up-regulation of BRCA1, and perhaps p53, explains the protective effect of childhood physical activity against breast cancer in women who carry a germline mutation in one of the BRCA1 alleles.

BRCA1-mediated ubiquitination inhibits topoisomerase II alpha activity in response to oxidative stress

Topoisomerase IIalpha is known to be critically involved in both cell proliferation and cell death. The mechanisms responsible for stress-dependent topoisomerase IIalpha alterations, however, remain unclear. This study focused on the behavior of topoisomerase IIalpha in response to oxidative stress induced by hydrogen peroxide (H(2)O(2)). The catalytic activity of topoisomerase IIalpha in MOLT-4 cells treated with H(2)O(2) decreased in parallel with the alteration of topoisomerase IIalpha expression. The ubiquitination of topoisomerase IIalpha was dependent on oxidative stress. BRCA1, a tumor-suppressor gene, appeared to be involved in these alterations in topoisomerase IIalpha. Furthermore, the retinoblastoma protein (pRb) was required for the ubiquitination of topoisomerase IIalpha by BRCA1. We conclude that the functions of topoisomerase IIalpha are regulated by ubiquitination on exposure to oxidative stress.

p53, BRCA1 and breast Cancer chemoresistance

The tumor suppressor genes p53 and BRCA1 are involved in hereditary as well as sporadic breast cancer development and therapeutic responses. While p53 mutations contribute to resistance to chemo- and radiotherapy, BRCA1 dysfunction leads to enhanced sensitivity to DNA damaging therapeutic agents. The biochemical pathways used by p53 and BRCA1 for signaling tumor suppression involve some cross-talk including repression of BRCA1 transcription by p53 and altered selectivity of p53-dependent gene activation by BRCA1. In this chapter we review clinical and preclinical data implicating p53 and BRCA1 in breast cancer chemosensitivity. We discuss the known signaling pathways downstream of p53 or BRCA1 that contribute to their modulation of therapeutic responses, and we discuss the implications of p53 or BRCA1 mutation in therapeutic design.

CHK2-Dependent Phosphorylation of BRCA1 in Hypoxia

Hypoxia induces a diverse spectrum of changes in the expression and activity of numerous DNA repair factors within the tumor microenvironment. In particular, we and others have shown that hypoxia induces phosphorylation and activation of the checkpoint kinase, CHK2, in an ATM-dependent manner. One downstream target of CHK2, the BRCA1 protein, plays a critical role in both DNA repair and cell cycle checkpoint regulation in mammalian cells. Here we report that BRCA1 is specifically phosphorylated on Serine 988 in response to hypoxic stress, and phosphorylation at this site is dependent on CHK2 expression. These findings enhance our understanding of ATM-CHK2 pathway activation in hypoxia, and they identify a novel role for BRCA1 in the response to hypoxic stress.

Caveolin-1 controls BRCA1 gene expression and cellular localization in human breast cancer cells

The role of caveolae and the caveolin proteins in cancer has been the subject of extensive research. BRCA1 participates in multiple biological pathways including DNA damage repair, transcriptional control, cell growth, apoptosis, and others. Little information, however, is available regarding the cellular mechanisms that control BRCA1 gene expression. The present study examined the potential regulation of BRCA1 gene expression and subcellular localization by Cav-1. Results of Western blots, RT-PCR, and transfection experiments showed that Cav-1 enhances BRCA1 protein and mRNA levels via a mechanism that involves transactivation of the BRCA1 promoter and which is p53-dependent. In addition, immunostaining experiments demonstrate that Cav-1 induced the cytoplasmic sequestration of BRCA1.