Gene Summary

Gene:H2AFX; H2A histone family, member X
Aliases: H2AX, H2A.X, H2A/X
Summary:Histones are basic nuclear proteins that are responsible for the nucleosome structure of the chromosomal fiber in eukaryotes. Two molecules of each of the four core histones (H2A, H2B, H3, and H4) form an octamer, around which approximately 146 bp of DNA is wrapped in repeating units, called nucleosomes. The linker histone, H1, interacts with linker DNA between nucleosomes and functions in the compaction of chromatin into higher order structures. This gene encodes a member of the histone H2A family, and generates two transcripts through the use of the conserved stem-loop termination motif, and the polyA addition motif. [provided by RefSeq, Jul 2008]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:histone H2AX
Source:NCBIAccessed: 27 February, 2015


What does this gene/protein do?
Show (25)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 27 February 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Transcriptional Activation
  • Mitosis
  • Chromosome 11
  • DNA Damage
  • Phosphorylation
  • Double-Stranded DNA Breaks
  • H2AFX
  • Cell Cycle Proteins
  • bcl-2-Associated X Protein
  • Cell Cycle
  • DNA Repair
  • Reactive Oxygen Species
  • Cell Survival
  • Translocation
  • Signal Transduction
  • Sequence Homology, Nucleic Acid
  • Breast Cancer
  • Superoxides
  • Ataxia Telangiectasia Mutated Proteins
  • Radiotherapy
  • Apoptosis
  • Cell Proliferation
  • Oxidative Stress
  • Young Adult
  • Tumor Stem Cell Assay
  • Radiotherapy, Conformal
  • Antineoplastic Agents
  • DNA-Binding Proteins
  • Risk Factors
  • Cervical Cancer
  • Virus Latency
  • Viral Proteins
  • Cancer Gene Expression Regulation
  • Angiogenesis
  • Ubiquitin-Protein Ligases
  • Risk Assessment
  • fms-Like Tyrosine Kinase 3
  • Mutation
  • Histones
  • Testis
Tag cloud generated 27 February, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (2)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: H2AFX (cancer-related)

Huemer M, Rebhandl S, Zaborsky N, et al.
AID induces intraclonal diversity and genomic damage in CD86(+) chronic lymphocytic leukemia cells.
Eur J Immunol. 2014; 44(12):3747-57 [PubMed] Free Access to Full Article Related Publications
The activation-induced cytidine deaminase (AID) mediates somatic hypermutation and class switch recombination of the Ig genes by directly deaminating cytosines to uracils. As AID causes a substantial amount of off-target mutations, its activity has been associated with lymphomagenesis and clonal evolution of B-cell malignancies. Although it has been shown that AID is expressed in B-cell chronic lymphocytic leukemia (CLL), a clear analysis of in vivo AID activity in this B-cell malignancy remained elusive. In this study performed on primary human CLL samples, we report that, despite the presence of a dominant VDJ heavy chain region, a substantial intraclonal diversity was observed at VDJ as well as at IgM switch regions (Sμ), showing ongoing AID activity in vivo during disease progression. This AID-mediated heterogeneity was higher in CLL subclones expressing CD86, which we identified as the proliferative CLL fraction. Finally, CD86 expression correlated with shortened time to first treatment and increased γ-H2AX focus formation. Our data demonstrate that AID is active in CLL in vivo and thus, AID likely contributes to clonal evolution of CLL.

He HL, Lee YE, Shiue YL, et al.
Overexpression of REG4 confers an independent negative prognosticator in rectal cancers receiving concurrent chemoradiotherapy.
J Surg Oncol. 2014; 110(8):1002-10 [PubMed] Related Publications
BACKGROUND AND OBJECTIVES: Neoadjuvant concurrent chemoradiotherapy (CCRT) followed by surgery is the standard treatment for locally advanced rectal cancer. Through data mining from published transcriptomic database, we identified Regenerating Gene Type IV (REG4) as the most significantly associated gene with resistance to CCRT. This study examined the prognostic impact of REG4 expression in patients with rectal cancer receiving neoadjuvant CCRT.
METHODS: REG4 immunohistochemistry was retrospectively assessed for pre-treatment biopsy specimens from 172 rectal cancer patients who received neoadjuvant CCRT followed by surgery without initial distant metastasis. The results were correlated with the clinicopathological variables, disease-specific survival (DSS), local recurrence-free survival (LRFS), and distant metastasis-free survival (DMFS), as well as γ-H2AX expression in post-treatment tumor samples.
RESULTS: High expression of REG4 was associated with advanced pre-treatment nodal status (P = 0.026), advanced post-treatment tumor status (P = 0.006), advanced post-treatment nodal status (P = 0.001), advanced post-treatment tumor stage (P < 0.001), and inferior tumor regression grade (P = 0.001). Of note, high expression of REG4 emerged as an adverse prognosticator for DSS (P = 0.0004), LRFS (P = 0.0009), and MeFS (P = 0.0254). After multivariate comparisons, it remained independently prognostic for worse DSS (hazard ratio [HR] = 2.731; P = 0.025) and LRFS (HR = 2.676; P = 0.029). High expression of REG4 was also negatively associated with γ-H2AX expression (P < 0.0001, r = -0.708).
CONCLUSIONS: High expression of REG4 is associated with poor therapeutic response, adverse outcome and an aggressive phenotype in rectal cancer patients treated with neoadjuvant CCRT, justifying REG4 is a surrogate marker to predict CCRT resistance.

Ning G, Bijron JG, Yamamoto Y, et al.
The PAX2-null immunophenotype defines multiple lineages with common expression signatures in benign and neoplastic oviductal epithelium.
J Pathol. 2014; 234(4):478-87 [PubMed] Article available free on PMC after 01/12/2015 Related Publications
The oviducts contain high-grade serous cancer (HGSC) precursors (serous tubal intraepithelial neoplasia or STINs), which are γ-H2AX(p) - and TP53 mutation-positive. Although they express wild-type p53, secretory cell outgrowths (SCOUTs) are associated with older age and serous cancer; moreover, both STINs and SCOUTs share a loss of PAX2 expression (PAX2(n) ). We evaluated PAX2 expression in proliferating adult and embryonic oviductal cells, normal mucosa, SCOUTs, Walthard cell nests (WCNs), STINs, and HGSCs, and the expression of genes chosen empirically or from SCOUT expression arrays. Clones generated in vitro from embryonic gynaecological tract and adult Fallopian tube were Krt7(p) /PAX2(n) /EZH2(p) and underwent ciliated (PAX2(n) /EZH2(n) /FOXJ1(p) ) and basal (Krt7(n) /EZH2(n) /Krt5(p) ) differentiation. Similarly, non-ciliated cells in normal mucosa were PAX2(p) but became PAX2(n) in multi-layered epithelium undergoing ciliated or basal (WCN) cell differentiation. PAX2(n) SCOUTs fell into two groups: type 1 were secretory or secretory/ciliated with a 'tubal' phenotype and were ALDH1(n) and β-catenin(mem) (membraneous only). Type 2 displayed a columnar to pseudostratified (endometrioid) phenotype, with an EZH2(p) , ALDH1(p) , β-catenin(nc) (nuclear and cytoplasmic), stathmin(p) , LEF1(p) , RCN1(p) , and RUNX2(p) expression signature. STINs and HGSCs shared the type 1 immunophenotype of PAX2(n) , ALDH1(n) , β-catenin(mem) , but highly expressed EZH2(p) , LEF1(p) , RCN1(p) , and stathmin(p) . This study, for the first time, links PAX2(n) with proliferating fetal and adult oviductal cells undergoing basal and ciliated differentiation and shows that this expression state is maintained in SCOUTs, STINs, and HGSCs. All three entities can demonstrate a consistent perturbation of genes involved in potential tumour suppressor gene silencing (EZH2), transcriptional regulation (LEF1), regulation of differentiation (RUNX2), calcium binding (RCN1), and oncogenesis (stathmin). This shared expression signature between benign and neoplastic entities links normal progenitor cell expansion to abnormal and neoplastic outgrowth in the oviduct and exposes a common pathway that could be a target for early prevention.

El-Naggar M, Ebbing E, Bijnsdorp I, et al.
Radiosensitization by thymidine phosphorylase inhibitor in thymidine phosphorylase negative and overexpressing bladder cancer cell lines.
Nucleosides Nucleotides Nucleic Acids. 2014; 33(4-6):413-21 [PubMed] Related Publications
TAS-102 (trifluorothymidine [TFT] and thymidine phosphorylase inhibitor [TPI] in a molar ratio of 1:0.5) has activity in 5-fluorouracil resistant colon cancer. TPI is added to increase TFT's bioavailability. TFT has a dual mechanism of action by inhibiting thymidylate synthase and by its incorporation into DNA. Interesting radiosensitizing effects of TPI were recently reported. The aim of our study was to determine whether TP expression would affect radiosensitivity and to characterize the effect of TPI. Two bladder cancer cell lines RT112 (TP negative) and RT112/TP (TP overexpression) were tested for drug sensitivity and radiosensitivity (clonogenic assay), with and without TFT and/or TPI. Expression of γ H2AX was used as marker for DNA damage. RT112 cells were not more sensitive to TFT then RT112/TP cells. TPI alone did not inhibit cell growth of RT112 even at 100 μM, but inhibited that of RT112/TP by 27%. In both RT112 and RT112/TP cells 10 μM TPI did not or slightly affect radiosensitivity, but 100 μM TPI alone enhanced the radiation response (p<.05). TFT alone at 1 μM and in combination with 10 μM TPI did not affect the radiation response of both cell lines. TPI alone induced expression of ϒH2AX, which was increased in combination with radiation. In conclusion, TPI enhanced radiosensitivity at high concentrations, independent of TP expression, while TFT and TPI at a low concentration did not affect the radiosensitivity of RT112 and RT112/TP cell lines.

Xu XH, Liu XY, Su J, et al.
ShRNA targeting Bmi-1 sensitizes CD44⁺ nasopharyngeal cancer stem-like cells to radiotherapy.
Oncol Rep. 2014; 32(2):764-70 [PubMed] Related Publications
Accumulating evidence indicates that cancer stem cells (CSCs) are involved in resistance to radiation therapy (RT). Bmi-1, a member of the Polycomb family of transcriptional repressors, is essential for maintaining the self-renewal abilities of stem cells and overexpression of Bmi-1 correlates with cancer therapy failure. Our previous study identified that the CD44+ nasopharyngeal cancer (NPC) cells may be assumed as one of markers of nasopharyngeal carcinoma cancer stem cell-like cells (CSC-LCs) and Bmi-1 is overexpressed in CD44+ NPC. In the present study, we used RNA interference technology to knock down the expression of Bmi-1 in CD44+ NPC cells, and then measured the radiation response by clonogenic cell survival assay. DNA repair was monitored by γH2AX foci formation. Bmi-1 downstream relative gene and protein expression of p16, p14, p53 were assessed by western blotting and real-time PCR. Cell cycle and apoptosis were detected by flow cytometry assays. We found that Bmi-1 knockdown prolonged G1 and enhanced the radiation-induced G2/M arrest, inhibited DNA damage repair, elevated protein p16, p14 and p53 expression, leading to increased apoptosis in the radiated CD44+ cells. These data suggest that Bmi-1 downregulation increases the radiosensitivity to CD44+ NPC CSC-LCs. Bmi-1 is a potential target for increasing the sensitivity of NPC CSCs to radiotherapy.

Zhang L, Chen LH, Wan H, et al.
Exome sequencing identifies somatic gain-of-function PPM1D mutations in brainstem gliomas.
Nat Genet. 2014; 46(7):726-30 [PubMed] Article available free on PMC after 01/12/2015 Related Publications
Gliomas arising in the brainstem and thalamus are devastating tumors that are difficult to surgically resect. To determine the genetic and epigenetic landscape of these tumors, we performed exomic sequencing of 14 brainstem gliomas (BSGs) and 12 thalamic gliomas. We also performed targeted mutational analysis of an additional 24 such tumors and genome-wide methylation profiling of 45 gliomas. This study led to the discovery of tumor-specific mutations in PPM1D, encoding wild-type p53-induced protein phosphatase 1D (WIP1), in 37.5% of the BSGs that harbored hallmark H3F3A mutations encoding p.Lys27Met substitutions. PPM1D mutations were mutually exclusive with TP53 mutations in BSG and attenuated p53 activation in vitro. PPM1D mutations were truncating alterations in exon 6 that enhanced the ability of PPM1D to suppress the activation of the DNA damage response checkpoint protein CHK2. These results define PPM1D as a frequent target of somatic mutation and as a potential therapeutic target in brainstem gliomas.

Uzdensky A, Demyanenko S, Bibov M, et al.
Expression of proteins involved in epigenetic regulation in human cutaneous melanoma and peritumoral skin.
Tumour Biol. 2014; 35(8):8225-33 [PubMed] Related Publications
Epigenetic processes play a critical role in melanoma development. However, little is known about proteins responsible for epigenetic transformations in melanoma cells. The processes in the peritumoral skin within the excision margin are almost unstudied. We studied the changes in expression of 112 proteins involved in epigenetic regulation of gene expression in the human cutaneous melanoma and its peritumoral zone using "The Proteomic Antibody Microarrays" (GRAA2, Sigma-Aldrich). Dimethylated histone H3 at lysines 4 and 9 as well as proteins involved in the regulation of transcription (histone deacetylases HDAC-1 and HDAC-11, DNA methyl-binding protein Kaiso), cell cycle control (protein kinases Aurora-В and PKR, chromosome protein CENP-E , and phosphorylated and acetylated histone H3), DNA repair (phosphorylated histone H2AX), and nuclear protein import (importins α3 and α5/7) were over-expressed in the melanoma tissue as compared with normal skin. At the same time, HDAC-10 and proliferating cell nuclear antigen PCNA were downregulated. In the peritumoral skin, at the excision margin (1-2 cm from the melanoma edge), we observed similar changes in expression of these proteins and, additionally, over-expression of arginine methyltransferases PRMT5 and NAD-dependent histone deacetylase SIR2. Histone methyltransferase G9a and metastasis-associated protein 2 were downregulated. Therefore, epigenetic regulation that requires histone modifications and expression of some regulatory proteins is of importance for melanoma development and propagation. The observed changes in the peritumoral skin may indicate the epigenetic pre-tuning in this zone possibly involved in malignant transformation. These results can be potentially useful for melanoma diagnostics and targeted therapy.

Dong Y, Xiong M, Duan L, et al.
H2AX phosphorylation regulated by p38 is involved in Bim expression and apoptosis in chronic myelogenous leukemia cells induced by imatinib.
Apoptosis. 2014; 19(8):1281-92 [PubMed] Related Publications
Increasing evidence suggests that histone H2AX plays a critical role in regulation of tumor cell apoptosis and acts as a novel human tumor suppressor protein. However, the action of H2AX in chronic myelogenous leukemia (CML) cells is unknown. The detailed mechanism and epigenetic regulation by H2AX remain elusive in cancer cells. Here, we report that H2AX was involved in apoptosis of CML cells. Overexpression of H2AX increased apoptotic sensitivity of CML cells (K562) induced by imatinib. However, overexpression of Ser139-mutated H2AX (blocking phosphorylation) decreased sensitivity of K562 cells to apoptosis. Similarly, knockdown of H2AX made K562 cells resistant to apoptotic induction. These results revealed that the function of H2AX involved in apoptosis is strictly related to its phosphorylation (Ser139). Our data further indicated that imatinib may stimulate mitogen-activated protein kinase (MAPK) family member p38, and H2AX phosphorylation followed a similar time course, suggesting a parallel response. H2AX phosphorylation can be blocked by p38 siRNA or its inhibitor. These data demonstrated that H2AX phosphorylation was regulated by p38 MAPK pathway in K562 cells. However, the p38 MAPK downstream, mitogen- and stress-activated protein kinase-1 and -2, which phosphorylated histone H3, were not required for H2AX phosphorylation during apoptosis. Finally, we provided epigenetic evidence that H2AX phosphorylation regulated apoptosis-related gene Bim expression. Blocking of H2AX phosphorylation inhibited Bim gene expression. Taken together, these data demonstrated that H2AX phosphorylation regulated by p38 is involved in Bim expression and apoptosis in CML cells induced by imatinib.

Liou JS, Wu YC, Yen WY, et al.
Inhibition of autophagy enhances DNA damage-induced apoptosis by disrupting CHK1-dependent S phase arrest.
Toxicol Appl Pharmacol. 2014; 278(3):249-58 [PubMed] Related Publications
DNA damage has been shown to induce autophagy, but the role of autophagy in the DNA damage response and cell fate is not fully understood. BO-1012, a bifunctional alkylating derivative of 3a-aza-cyclopenta[a]indene, is a potent DNA interstrand cross-linking agent with anticancer activity. In this study, BO-1012 was found to reduce DNA synthesis, inhibit S phase progression, and induce phosphorylation of histone H2AX on serine 139 (γH2AX) exclusively in S phase cells. Both CHK1 and CHK2 were phosphorylated in response to BO-1012 treatment, but only depletion of CHK1, but not CHK2, impaired BO-1012-induced S phase arrest and facilitated the entry of γH2AX-positive cells into G2 phase. CHK1 depletion also significantly enhanced BO-1012-induced cell death and apoptosis. These results indicate that BO-1012-induced S phase arrest is a CHK1-dependent pro-survival response. BO-1012 also resulted in marked induction of acidic vesicular organelle (AVO) formation and microtubule-associated protein 1 light chain 3 (LC3) processing and redistribution, features characteristic of autophagy. Depletion of ATG7 or co-treatment of cells with BO-1012 and either 3-methyladenine or bafilomycin A1, two inhibitors of autophagy, not only reduced CHK1 phosphorylation and disrupted S phase arrest, but also increased cleavage of caspase-9 and PARP, and cell death. These results suggest that cells initiate S phase arrest and autophagy as pro-survival responses to BO-1012-induced DNA damage, and that suppression of autophagy enhances BO-1012-induced apoptosis via disruption of CHK1-dependent S phase arrest.

Qu A, Wang H, Li J, et al.
Biological effects of (125)i seeds radiation on A549 lung cancer cells: G2/M arrest and enhanced cell death.
Cancer Invest. 2014; 32(6):209-17 [PubMed] Related Publications
External beam radiation (EBRT) and (125)I seeds continuous low dose rate radiation (CLDR) were used to treat patients with lung cancer. We herein investigated the biological effects of EBRT and CLDR on lung cancer cells. A549 human lung cancer cell line was thus exposed to different doses of EBRT and CLDR. CLDR was more efficient to inhibit cell growth than EBRT. CLDR induced increased DNA damage as evidenced by long-lasting p-H2AX activity. The enhanced inhibitory effects of CLDR on lung cancer cell growth may be, at least in part, due to the increased Bax/Bcl2 ratio and cyclin B1-mediated G2/M arrest.

Yang H, Tang Y, Guo W, et al.
Up-regulation of microRNA-138 induce radiosensitization in lung cancer cells.
Tumour Biol. 2014; 35(7):6557-65 [PubMed] Related Publications
Deregulation of microRNAs (miRNAs) is implicated in tumor progression. We attempt to identify the association between miR-138 and Sentrin/SUMO-specific protease 1 (SENP1) as a radiosensitization-related gene and characterize the biological function by which SENP1 was regulated by miR-138 to influence radiosensitization in lung cancer cells. In this study, we showed that miRNA-138 is reduced in both lung cancer clinical specimens and cell lines and is effective to inhibit SENP1 expression. Moreover, high levels of miR-138 are associated with lower levels of lung cancer cell proliferation and colony formation. Then, we investigated the underlying mechanisms responsible for the increase in the radiosensitivity of lung cancer cells when SENP1 is inhibited by miR-138. We further show that the increased radiosensitivity may be the result of an increased γ-H2AX expression, an increased rate of apoptosis, and changes in the cell cycle. In conclusion, our data demonstrate that the miR-138/SENP1 cascade is relative to radiosensitization in lung cancer cells and is a potential radiotherapy target.

Jia Y, Peng L, Rao Q, et al.
Oncogene iASPP enhances self-renewal of hematopoietic stem cells and facilitates their resistance to chemotherapy and irradiation.
FASEB J. 2014; 28(7):2816-27 [PubMed] Related Publications
iASPP is a member of the apoptosis-stimulating proteins of p53 (ASPP) family and negatively regulates the apoptotic function of p53. In a hematopoietic system, overexpression of iASPP results in blockage of apoptosis, which may play a role in regulating hematopoietic stem cell (HSC) numbers. To address this, we first analyzed the expression of iASPP in patients with acute leukemia (AL) and found it was highly expressed in patients with AL. We further established a transgenic mouse model in which human iASPP was specifically expressed in hematopoietic cells. Overexpression of iASPP led to an increase in the proportion of long-term HSCs, short-term HSCs, multipotent progenitors, and common myeloid progenitor. HSCs from iASPP transgenic mice had an advantage in long-term reconstitution potential. In addition, the hematopoietic cells from iASPP transgenic mice exhibited a significantly lower level of p53 dependent apoptosis. After irradiation damage, hematopoietic cells of iASPP transgenic mice had a higher level of γ-H2AX expression, which lasted for a longer time. These results provide the first evidence that the iASPP can increase HSC populations and reconstitution capacity. Interestingly, in response to cell damage stimuli, hematopoietic cells can be protected against apoptosis by iASPP; meanwhile these apoptosis-resistant cells would have more mutation accumulation, which might be the potential risk for malignant transformation.-Jia, Y., Peng, L., Rao, Q., Xing, H., Huai, L., Yu, P., Chen, Y., Wang, C., Wang, M., Mi, Y., Wang, J. Oncogene iASPP enhances self-renewal of hematopoietic stem cells and facilitates their resistance to chemotherapy and irradiation.

Flores-Pérez A, Rafaelli LE, Ramírez-Torres N, et al.
RAD50 targeting impairs DNA damage response and sensitizes human breast cancer cells to cisplatin therapy.
Cancer Biol Ther. 2014; 15(6):777-88 [PubMed] Article available free on PMC after 01/06/2015 Related Publications
In tumor cells the effectiveness of anti-neoplastic agents that cause cell death by induction of DNA damage is influenced by DNA repair activity. RAD50 protein plays key roles in DNA double strand breaks repair (DSBs), which is crucial to safeguard genome integrity and sustain tumor suppression. However, its role as a potential therapeutic target has not been addressed in breast cancer. Our aim in the present study was to analyze the expression of RAD50 protein in breast tumors, and evaluate the effects of RAD50-targeted inhibition on the cytotoxicity exerted by cisplatin and anthracycline and taxane-based therapies in breast cancer cells. Immunohistochemistry assays on tissue microarrays indicate that the strong staining intensity of RAD50 was reduced in 14% of breast carcinomas in comparison with normal tissues. Remarkably, RAD50 silencing by RNA interference significantly enhanced the cytotoxicity of cisplatin. Combinations of cisplatin with doxorubicin and paclitaxel drugs induced synergistic effects in early cell death of RAD50-deficient MCF-7, SKBR3, and T47D breast cancer cells. Furthermore, we found an increase in the number of DSBs, and delayed phosphorylation of histone H2AX after cisplatin treatment in RAD50-silenced cells. These cellular events were associated to a dramatical increase in the frequency of chromosomal aberrations and a decrease of cell number in metaphase. In conclusion, our data showed that RAD50 abrogation impairs DNA damage response and sensitizes breast cancer cells to cisplatin-combined therapies. We propose that the development and use of inhibitors to manipulate RAD50 levels might represent a promising strategy to sensitize breast cancer cells to DNA damaging agents.

Konstantinopoulos PA, Wilson AJ, Saskowski J, et al.
Suberoylanilide hydroxamic acid (SAHA) enhances olaparib activity by targeting homologous recombination DNA repair in ovarian cancer.
Gynecol Oncol. 2014; 133(3):599-606 [PubMed] Related Publications
OBJECTIVES: Approximately 50% of serous epithelial ovarian cancers (EOC) contain molecular defects in homologous recombination (HR) DNA repair pathways. Poly(ADP-ribose) polymerase inhibitors (PARPi) have efficacy in HR-deficient, but not in HR-proficient, EOC tumors as a single agent. Our goal was to determine whether the histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), can sensitize HR-proficient ovarian cancer cells to the PARPi AZD-2281 (olaparib).
METHODS: Ovarian cancer cell lines (SKOV-3, OVCAR-8, NCI/ADR-Res, UWB1.289 BRCA1null and UWB1.289+BRCA1 wild-type) were treated with saline vehicle, olaparib, SAHA or olaparib/SAHA. Sulforhodamine B (SRB) assessed cytotoxicity and immunofluorescence and Western blot assays assessed markers of apoptosis (cleaved PARP) and DNA damage (pH2AX and RAD51). Drug effects were also tested in SKOV-3 xenografts in Nude mice. Affymetrix microarray experiments were performed in vehicle and SAHA-treated SKOV-3 cells.
RESULTS: In a microarray analysis, SAHA induced coordinated down-regulation of HR pathway genes, including RAD51 and BRCA1. Nuclear co-expression of RAD51 and pH2AX, a marker of efficient HR repair, was reduced approximately 40% by SAHA treatment alone and combined with olaparib. SAHA combined with olaparib induced apoptosis and pH2AX expression to a greater extent than either drug alone. Olaparib reduced cell viability at increasing concentrations and SAHA enhanced these effects in 4 of 5 cell lines, including BRCA1 null and wild-type cells, in vitro and in SKOV-3 xenografts in vivo.
CONCLUSIONS: These results provide preclinical rationale for targeting DNA damage response pathways by combining small molecule PARPi with HDACi as a mechanism for reducing HR efficiency in ovarian cancer.

Miyasaka A, Oda K, Ikeda Y, et al.
Anti-tumor activity of olaparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, in cultured endometrial carcinoma cells.
BMC Cancer. 2014; 14:179 [PubMed] Article available free on PMC after 01/06/2015 Related Publications
BACKGROUND: PTEN inactivation is the most frequent genetic aberration in endometrial cancer. One of the phosphatase-independent roles of PTEN is associated with homologous recombination (HR) in nucleus. Poly (ADP-ribose) polymerase (PARP) plays key roles in the repair of DNA single-strand breaks, and a PARP inhibitor induces synthetic lethality in cancer cells with HR deficiency. We examined the anti-tumor activity of olaparib, a PARP inhibitor, and its correlation between the sensitivity and status of PTEN in endometrial cancer cell lines.
METHODS: The response to olaparib was evaluated using a clonogenic assay with SF50 values (concentration to inhibit cell survival to 50%) in 16 endometrial cancer cell lines. The effects of PTEN on the sensitivity to olaparib and ionizing radiation (IR) exposure were compared between parental HEC-6 (PTEN-null) and HEC-6 PTEN + (stably expressing wild-type PTEN) cells by clonogenic assay, foci formation of RAD51 and γH2AX, and induction of cleaved PARP. The effects of siRNA to PTEN were analyzed in cells with wild-type PTEN.
RESULTS: The SF50 values were 100 nM or less in four (25%: sensitive) cell lines; whereas, SF50 values were 1,000 nM or more in four (25%: resistant) cell lines. PTEN mutations were not associated with sensitivity to olaparib (Mutant [n = 12]: 746 ± 838 nM; Wild-type [n = 4]: 215 ± 85 nM, p = 0.26 by Student's t test). RAD51 expression was observed broadly and was not associated with PTEN status in the 16 cell lines. The number of colonies in the clonogenic assay, the foci formation of RAD51 and γH2AX, and the induction of apoptosis were not affected by PTEN introduction in the HEC-6 PTEN + cells. The expression level of nuclear PTEN was not elevated within 24 h following IR in the HEC-6-PTEN + cells. In addition, knocking down PTEN by siRNA did not alter the sensitivity to olaparib in 2 cell lines with wild-type PTEN.
CONCLUSIONS: Our results suggest that olaparib, a PARP inhibitor, is effective on certain endometrial cancer cell lines. Inactivation of PTEN might not affect the DNA repair function. Predictive biomarkers are warranted to utilize olaparib in endometrial cancer.

Bokobza SM, Jiang Y, Weber AM, et al.
Short-course treatment with gefitinib enhances curative potential of radiation therapy in a mouse model of human non-small cell lung cancer.
Int J Radiat Oncol Biol Phys. 2014; 88(4):947-54 [PubMed] Related Publications
PURPOSE: To evaluate the combination of radiation and an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) in preclinical models of human non-small cell lung cancer.
METHODS AND MATERIALS: Sensitivity to an EGFR TKI (gefitinib) or radiation was assessed using proliferation assays and clonogenic survival assays. Effects on receptor signal transduction pathways (pEGFR, pAKT, pMAPK) and apoptosis (percentage of cleaved PARP Poly (ADP-ribose) polymerase (PARP)) were assessed by Western blotting. Radiation-induced DNA damage was assessed by γH2AX immunofluorescence. Established (≥ 100 mm(3)) EGFR-mutated (HCC287) or EGFR wild-type (A549) subcutaneous xenografts were treated with radiation (10 Gy, day 1) or gefitinib (50 mg/kg, orally, on days 1-3) or both.
RESULTS: In non-small cell lung cancer (NSCLC) cell lines with activating EGFR mutations (PC9 or HCC827), gefitinib treatment markedly reduced pEGFR, pAKT, and pMAPK levels and was associated with an increase in cleaved PARP but not in γH2AX foci. Radiation treatment increased the mean number of γH2AX foci per cell but did not significantly affect EGFR signaling. In contrast, NSCLC cell lines with EGFR T790M (H1975) or wild-type EGFR (A549) were insensitive to gefitinib treatment. The combination of gefitinib and radiation treatment in cell culture produced additive cell killing with no evidence of synergy. In xenograft models, a short course of gefitinib (3 days) did not significantly increase the activity of radiation treatment in wild-type EGFR (A549) tumors (P=.27), whereas this combination markedly increased the activity of radiation (P<.001) or gefitinib alone (P=.002) in EGFR-mutated HCC827 tumors, producing sustained tumor regressions.
CONCLUSIONS: Gefitinib treatment increases clonogenic cell killing by radiation but only in cell lines sensitive to gefitinib alone. Our data suggest additive rather than synergistic interactions between gefitinib and radiation and that a combination of short-course gefitinib and high-dose/-fraction radiation may have the greatest potential against the subsets of lung cancers harboring activating mutations in the EGFR gene.

García-Baquero R, Puerta P, Beltran M, et al.
Methylation of tumor suppressor genes in a novel panel predicts clinical outcome in paraffin-embedded bladder tumors.
Tumour Biol. 2014; 35(6):5777-86 [PubMed] Related Publications
DNA methylation of tumor suppressor genes (TSGs) represents a frequent and early epigenetic event with potential applications for cancer detection and disease evolution. Our aim was to examine the stratification and prognostic biomarker role of the methylation of a novel panel of TSGs in bladder cancer. The methylation status of 18 TSGs was evaluated in bladder cancer cells (n=14) and paraffin-embedded primary bladder tumors (n=61), using a methylation-specific multiplex ligation-dependent probe amplification assay (MS-MLPA). Recurrence, progression, and disease-specific survival were analyzed using univariate and multivariate Cox models. PRDM2, HLTF, ID4, DLC1, BNIP3, H2AFX, CACNA1G, TGIF, and CACNA1A were discovered methylated in bladder cancer. The methylation of RUNX3 (p=0.026), TWIST1 (p=0.009), SFRP4 (p=0.002), and CCND2 (p=0.027) correlated to tumor stage. Univariate analyses indicated prognostic associations for recurrence (DLC1, SFRP5, H2AFX, CACNA1G), progression (DLC1, SFRP5, CACNA1G), disease-specific (PRDM2, DLC1, SFRP5, CACNA1G, and TIMP3), and overall survival (SFRP5 and TIMP3). In multivariate analyses, several TSGs remained as independent prognosticators for recurrence (SFRP5, H2AFX), progression (CACNA1G), and disease-specific survival (SFRP5). Thus, a novel set of TSGs was identified, frequently methylated in bladder cancer cells and tumors. TSG methylation allowed histopathologic and outcome stratification using paraffin-embedded tumors. This is clinically relevant by offering a strategy for the management of patients affected with uroepithelial neoplasias in pathology routine laboratories.

Guerzoni C, Amatori S, Giorgi L, et al.
An aza-macrocycle containing maltolic side-arms (maltonis) as potential drug against human pediatric sarcomas.
BMC Cancer. 2014; 14:137 [PubMed] Article available free on PMC after 01/06/2015 Related Publications
BACKGROUND: Identification of new drugs against paediatric sarcomas represents an urgent clinical need that mainly relies on public investments due to the rarity of these diseases. In this paper we evaluated the in vitro and in vivo efficacy of a new maltol derived molecule (maltonis), belonging to the family of molecules named hydroxypyrones.
METHODS: Maltonis was screened for its ability to induce structural alteration of DNA molecules in comparison to another maltolic molecule (malten). In vitro antitumour efficacy was tested using a panel of sarcoma cell lines, representative of Ewing sarcoma, osteosarcoma and rhabdomyosarcoma, the three most common paediatric sarcomas, and in normal human mesenchymal primary cell cultures. In vivo efficacy was tested against TC-71 Ewing sarcoma xenografts.
RESULTS: Maltonis, a soluble maltol-derived synthetic molecule, was able to alter the DNA structure, inhibit proliferation and induce apoptotic cell death in paediatric sarcoma cells, either sensitive or resistant to some conventional chemotherapeutic drugs, such as doxorubicin and cisplatin. In addition, maltonis was able to induce: i) p21, p15 and Gadd45a mRNA upregulation; ii) Bcl-2, survivin, CDK6 and CDK8 down-regulation; iii) formation of γ-H2AX nuclear foci; iv) cleavage of PARP and Caspase 3. Two independent in vivo experiments demonstrated the tolerability and efficacy of maltonis in the inhibition of tumour growth. Finally maltonis was not extruded by ABCB1, one of the major determinants of chemotherapy failure, nor appeared to be a substrate of the glutathione-related detoxification system.
CONCLUSIONS: Considering that treatment of poorly responsive patients still suffers for the paucity of agents able to revert chemoresistance, maltonis may be considered for the future development of new therapeutic approaches for refractory metastatic patients.

Lal S, Burkhart RA, Beeharry N, et al.
HuR posttranscriptionally regulates WEE1: implications for the DNA damage response in pancreatic cancer cells.
Cancer Res. 2014; 74(4):1128-40 [PubMed] Related Publications
HuR (ELAV1), an RNA-binding protein abundant in cancer cells, primarily resides in the nucleus, but under specific stress (e.g., gemcitabine), HuR translocates to the cytoplasm in which it tightly modulates the expression of mRNA survival cargo. Here, we demonstrate for the first time that stressing pancreatic ductal adenocarcinoma (PDA) cells by treatment with DNA-damaging anticancer agents (mitomycin C, oxaliplatin, cisplatin, carboplatin, and a PARP inhibitor) results in HuR's translocation from the nucleus to the cytoplasm. Importantly, silencing HuR in PDA cells sensitized the cells to these agents, whereas overexpressing HuR caused resistance. HuR's role in the efficacy of DNA-damaging agents in PDA cells was, in part, attributed to the acute upregulation of WEE1 by HuR. WEE1, a mitotic inhibitor kinase, regulates the DNA damage repair pathway, and therapeutic inhibition of WEE1 in combination with chemotherapy is currently in early phase trials for the treatment of cancer. We validate WEE1 as a HuR target in vitro and in vivo by demonstrating (i) direct binding of HuR to WEE1's mRNA (a discrete 56-bp region residing in the 3' untranslated region) and (ii) HuR siRNA silencing and overexpression directly affects the protein levels of WEE1, especially after DNA damage. HuR's positive regulation of WEE1 increases γ-H2AX levels, induces Cdk1 phosphorylation, and promotes cell-cycle arrest at the G2-M transition. We describe a novel mechanism that PDA cells use to protect against DNA damage in which HuR posttranscriptionally regulates the expression and downstream function of WEE1 upon exposure to DNA-damaging agents.

Garufi A, D'Orazi V, Arbiser JL, D'Orazi G
Gentian violet induces wtp53 transactivation in cancer cells.
Int J Oncol. 2014; 44(4):1084-90 [PubMed] Article available free on PMC after 01/06/2015 Related Publications
Recent studies suggest that gentian violet (GV) may have anticancer activity by inhibiting for instance NADPH oxidases (Nox genes) whose overexpression is linked to tumor progression. Nox1 overexpression has been shown to inhibit transcriptional activity of the oncosuppressor p53, impairing tumor cell response to anticancer drugs. The tumor suppressor p53 is a transcription factor that, upon cellular stress, is activated to induce target genes involved in tumor cell growth inhibition and apoptosis. Thus, its activation is important for efficient tumor eradication. In this study, we examined the effect of GV on wild-type (wt) p53 activity in cancer cells. We found that GV was able to overcome the inhibitory effect of the NADPH oxidase Nox1 on p53 transcriptional activity. For the first time we show that GV was able to directly induce p53/DNA binding and transcriptional activity. In vitro, GV markedly induced cancer cell death and apoptotic marker PARP cleavage in wtp53-carrying cells. GV-induced cell death was partly inhibited in cells deprived of p53, suggesting that the anticancer activity of GV may partly depend on p53 activation. GV is US Food and Drug Administration approved for human use and may, therefore, have therapeutic potential in the management of cancer through p53 activation.

Xie C, Wang H, Cheng H, et al.
RAD18 mediates resistance to ionizing radiation in human glioma cells.
Biochem Biophys Res Commun. 2014; 445(1):263-8 [PubMed] Related Publications
Radioresistance remains a major challenge in the treatment of glioblastoma multiforme (GBM). RAD18 a central regulator of translesion DNA synthesis (TLS), has been shown to play an important role in regulating genomic stability and DNA damage response. In the present study, we investigate the relationship between RAD18 and resistance to ionizing radiation (IR) and examined the expression levels of RAD18 in primary and recurrent GBM specimens. Our results showed that RAD18 is an important mediator of the IR-induced resistance in GBM. The expression level of RAD18 in glioma cells correlates with their resistance to IR. Ectopic expression of RAD18 in RAD18-low A172 glioma cells confers significant resistance to IR treatment. Conversely, depletion of endogenous RAD18 in RAD18-high glioma cells sensitized these cells to IR treatment. Moreover, RAD18 overexpression confers resistance to IR-mediated apoptosis in RAD18-low A172 glioma cells, whereas cells deficient in RAD18 exhibit increased apoptosis induced by IR. Furthermore, knockdown of RAD18 in RAD18-high glioma cells disrupts HR-mediated repair, resulting in increased accumulation of DSB. In addition, clinical data indicated that RAD18 was significantly higher in recurrent GBM samples that were exposed to IR compared with the corresponding primary GBM samples. Collectively, our findings reveal that RAD18 may serve as a key mediator of the IR response and may function as a potential target for circumventing IR resistance in human GBM.

Chen L, Fu L, Kong X, et al.
Jumonji domain-containing protein 2B silencing induces DNA damage response via STAT3 pathway in colorectal cancer.
Br J Cancer. 2014; 110(4):1014-26 [PubMed] Article available free on PMC after 01/06/2015 Related Publications
BACKGROUND: Jumonji domain-containing protein 2B (JMJD2B), directly targeted by hypoxia-inducible factor 1α, maintains the histone methylation balance important for the transcriptional activation of many oncogenes. Jumonji domain-containing protein 2B has been implicated in colorectal cancer (CRC) progression; however, the mechanism remains unclear.
METHODS: Immunofluorescence and western blotting detected phosphorylated histone H2AX, characteristic of double-strand breaks, and comet assay was used to investigate DNA damage, in CRC cells after JMJD2B small interfering RNA (siRNA) transfection. We assessed the resulting in vitro responses, that is, cell cycle progression, apoptosis, and senescence coupled with JMJD2B silencing-induced DNA damage, studying the regulatory role of signal transducers and activators of transcription 3 (STAT3). The JMJD2B silencing anti-cancer effect was determined using an in vivo CRC xenograft model.
RESULTS: Jumonji domain-containing protein 2B knockdown induced DNA damage via ataxia telangiectasia-mutated (ATM) and ATM and Rad3-related pathway activation, resulting in cell cycle arrest, apoptosis, and senescence in both normoxia and hypoxia. Signal transducers and activators of transcription 3 suppression by JMJD2B silencing enhanced DNA damage. Intratumoural injection of JMJD2B siRNA suppressed tumour growth in vivo and activated the DNA damage response (DDR).
CONCLUSIONS: Jumonji domain-containing protein 2B has an essential role in cancer cell survival and tumour growth via DDR mediation, which STAT3 partially regulates, suggesting that JMJD2B is a potential anti-cancer target.

Islam MA, Thomas SD, Murty VV, et al.
c-Myc quadruplex-forming sequence Pu-27 induces extensive damage in both telomeric and nontelomeric regions of DNA.
J Biol Chem. 2014; 289(12):8521-31 [PubMed] Article available free on PMC after 21/03/2015 Related Publications
Quadruplex-forming DNA sequences are present throughout the eukaryotic genome, including in telomeric DNA. We have shown that the c-Myc promoter quadruplex-forming sequence Pu-27 selectively kills transformed cells (Sedoris, K. C., Thomas, S. D., Clarkson, C. R., Muench, D., Islam, A., Singh, R., and Miller, D. M. (2012) Genomic c-Myc quadruplex DNA selectively kills leukemia. Mol. Cancer Ther. 11, 66-76). In this study, we show that Pu-27 induces profound DNA damage, resulting in striking chromosomal abnormalities in the form of chromatid or chromosomal breaks, radial formation, and telomeric DNA loss, which induces γ-H2AX in U937 cells. Pu-27 down-regulates telomeric shelterin proteins, DNA damage response mediators (RAD17 and RAD50), double-stranded break repair molecule 53BP1, G2 checkpoint regulators (CHK1 and CHK2), and anti-apoptosis gene survivin. Interestingly, there are no changes of DNA repair molecules H2AX, BRCA1, and the telomere maintenance gene, hTERT. ΔB-U937, where U937 cells stably transfected with deleted basic domain of TRF2 is partially sensitive to Pu-27 but exhibits no changes in expression of shelterin proteins. However, there is an up-regulation of CHK1, CHK2, H2AX, BRCA1, and survivin. Telomere dysfunction-induced foci assay revealed co-association of TRF1with γ-H2AX in ATM deficient cells, which are differentially sensitive to Pu-27 than ATM proficient cells. Alt (alternating lengthening of telomere) cells are relatively resistant to Pu-27, but there are no significant changes of telomerase activity in both Alt and non-Alt cells. Lastly, we show that this Pu-27-mediated sensitivity is p53-independent. The data therefore support two conclusions. First, Pu-27 induces DNA damage within both telomeric and nontelomeric regions of the genome. Second, Pu-27-mediated telomeric damage is due, at least in part, to compromise of the telomeric shelterin protein complex.

Huang H, Tian H, Duan Z, et al.
microRNA-383 impairs phosphorylation of H2AX by targeting PNUTS and inducing cell cycle arrest in testicular embryonal carcinoma cells.
Cell Signal. 2014; 26(5):903-11 [PubMed] Related Publications
Male germ cells with aberrant DNA damage are the weighted factor contributing to male infertility. Mounting evidence shows that DNA damage in male germ cells impairs spermatogenesis and lowers fecundity. MicroRNAs (miRNAs) regulating expression of multiple genes play a significant role in spermatogenesis. Our previous results have shown that microRNA-383 (miR-383) is one of the notable down-regulated microRNAs in the testes of sterile males with maturation arrest (MA) and is located predominantly in spermatogonia and primary spermatocytes. However, the role that miR-383 plays in DNA damage during spermatogenesis remains unknown. In this study, we found that miR-383 inhibited the focal formation and abundance of γH2AX, which is the major marker of sites of DNA damage, with or without ultraviolet irradiation and cisplatin in testicular embryonal carcinoma (NT-2) cells. In addition, NT-2 cells were remarkably sensitized to DNA damage reagent (cisplatin) by forcing expression of miR-383 and silencing expression of protein phosphatase 1, regulatory subunit 10 (PNUTS). By constructing Renilla luciferase reporters and co-transfecting miR-383 and reporters in NT-2 cells, we identified that PNUTS was a valid target of miR-383. Further results demonstrated that the repression of the phosphorylated form of H2AX by miR-383 was due to independent depletion of PNUTS and cell cycle arrest. In conclusion, we found a novel function of miR-383 in the DNA damage pathway. miR-383 impairs the phosphorylation of H2AX by targeting PNUTS and inducing cell cycle arrest independently, as well as sensitizing NT-2 cells to cisplatin.

Dilley RL, Poh W, Gladstone DE, et al.
Poly(ADP-ribose) polymerase inhibitor CEP-8983 synergizes with bendamustine in chronic lymphocytic leukemia cells in vitro.
Leuk Res. 2014; 38(3):411-7 [PubMed] Article available free on PMC after 01/03/2015 Related Publications
DNA repair aberrations and associated chromosomal instability is a feature of chronic lymphocytic leukemia (CLL). To evaluate if DNA repair insufficiencies are related to methylation changes, we examined the methylation of nine promoter regions of DNA repair proteins by bisulfide sequencing in 26 CLL primary samples and performed quantitative PCR on a subset of samples to examine BRCA1 expression. We also investigated if changes in cytogenetic or expression level of DNA repair proteins led to changes in sensitivity to a novel PARP inhibitor, CEP-8983, alone and in combination with bendamustine. No changes in promoter methylation were identified in BRCA1, BRCA2, FANC-C, FANC-F, FANC-L, ATM, MGMT, hMLH1 and H2AX except for two cases of minor BRCA1 hypermethylation. CLL samples appeared to have reduced BRCA1 mRNA expression uniformly in comparison to non-malignant lymphocytes irrespective of promoter hypermethylation. CEP-8983 displayed single agent cytotoxicity and the combination with bendamustine demonstrated synergistic cytotoxicity in the majority of CLL samples. These results were consistent across cytogenetic subgroups, including 17p deleted and previously treated patients. Our results provide rationale for further exploration of the combination of a PARP inhibitor and DNA damaging agents as a novel therapeutic strategy in CLL.

El-Saghire H, Vandevoorde C, Ost P, et al.
Intensity modulated radiotherapy induces pro-inflammatory and pro-survival responses in prostate cancer patients.
Int J Oncol. 2014; 44(4):1073-83 [PubMed] Article available free on PMC after 01/03/2015 Related Publications
Intensity modulated radiotherapy (IMRT) is one of the modern conformal radiotherapies that is widely used within the context of cancer patient treatment. It uses multiple radiation beams targeted to the tumor, however, large volumes of the body receive low doses of irradiation. Using γ-H2AX and global genome expression analysis, we studied the biological responses induced by low doses of ionizing radiation in prostate cancer patients following IMRT. By means of different bioinformatics analyses, we report that IMRT induced an inflammatory response via the induction of viral, adaptive, and innate immune signaling. In response to growth factors and immune-stimulatory signaling, positive regulation in the progression of cell cycle and DNA replication were induced. This denotes pro-inflammatory and pro-survival responses. Furthermore, double strand DNA breaks were induced in every patient 30 min after the treatment and remaining DNA repair and damage signaling continued after 18-24 h. Nine genes belonging to inflammatory responses (TLR3, SH2D1A and IL18), cell cycle progression (ORC4, SMC2 and CCDC99) and DNA damage and repair (RAD17, SMC6 and MRE11A) were confirmed by quantitative RT-PCR. This study emphasizes that the risk assessment of health effects from the out-of-field low doses during IMRT should be of concern, as these may increase the risk of secondary cancers and/or systemic inflammation.

Erbaykent-Tepedelen B, Karamil S, Gonen-Korkmaz C, Korkmaz KS
DNA damage response (DDR) via NKX3.1 expression in prostate cells.
J Steroid Biochem Mol Biol. 2014; 141:26-36 [PubMed] Related Publications
It has been reported that NKX3.1 an androgen-regulated homeobox gene restricted to prostate and testicular tissues, encodes a homeobox protein, which transcriptionally regulates oxidative damage responses and enhances topoisomerase I re-ligation by a direct interaction with the ATM protein in prostate cells. In this study, we aimed to investigate the role of NKX3.1 in DNA double-strand break (DSB) repair. We demonstrate that the DNA damage induced by CPT-11 (irinotecan, a topo I inhibitor), doxorubicin (a topo II inhibitor), and H2O2 (a mediator of oxidative damage), but not by etoposide (another topo II inhibitor), is negatively influenced by NKX3.1 expression. We also examined γH2AX((S139)) foci formation and observed that the overexpression of NKX3.1 resulted a remarkable decrease in the formation of γH2AX((S139)) foci. Intriguingly, we observed in NKX3.1 silencing studies that the depletion of NKX3.1 correlated with a significant decrease in the levels of p-ATM((S1981)) and γH2AX((S139)). The data imply that the DNA damage response (DDR) can be altered, perhaps via a decrease in the topoisomerase I re-ligation function; this is consistent with the physical association of NKX3.1 with DDR mediators upon treatment of both PC-3 and LNCaP cells with CPT-11. Furthermore, the depletion of NKX3.1 resulted in a G1/S progression via the facilitation of an increase in E2F stabilization concurrent with the suppressed DDR. Thus, the topoisomerase I inhibitor-mediated DNA damage enhanced the physical association of NKX3.1 with γH2AX((S139)) on the chromatin in LNCaP cells, whereas NKX3.1 in the soluble fraction was associated with p-ATM((S1981)) and RAD50 in these cells. Overall, the data suggest that androgens and NKX3.1 expression regulate the progression of the cell cycle and concurrently activate the DDR. Therefore, androgen withdrawal may augment the development of an error-prone phenotype and, subsequently, the loss of DNA damage control during prostate cancer progression.

Bélanger F, Rajotte V, Drobetsky EA
A majority of human melanoma cell lines exhibits an S phase-specific defect in excision of UV-induced DNA photoproducts.
PLoS One. 2014; 9(1):e85294 [PubMed] Article available free on PMC after 01/03/2015 Related Publications
It is well established that efficient removal of highly-promutagenic UV-induced dipyrimidine photoproducts via nucleotide excision repair (NER) is required for protection against sunlight-associated malignant melanoma. Nonetheless, the extent to which reduced NER capacity might contribute to individual melanoma susceptibility in the general population remains unclear. Here we show that among a panel of 14 human melanoma strains, 11 exhibit significant inhibition of DNA photoproduct removal during S phase relative to G0/G1 or G2/M. Evidence is presented that this cell cycle-specific NER defect correlates with enhanced apoptosis and reduced clonogenic survival following UV irradiation. In addition, melanoma strains deficient in S phase-specific DNA photoproduct removal manifest significantly lower levels of phosphorylated histone H2AX at 1 h post-UV, suggesting diminished activation of ataxia telangiectasia and Rad 3-related (ATR) kinase, i.e., a primary orchestrator of the cellular response to UV-induced DNA replication stress. Consistently, in the case of DNA photoproduct excision-proficient melanoma cells, siRNA-mediated depletion of ATR (but not of its immediate downstream effector kinase Chk1) engenders deficient NER specifically during S. On the other hand simultaneous siRNA-mediated depletion of ataxia telangiectasia mutated kinase (ATM) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) exerts no significant effect on either phosphorylation of H2AX at 1 h post-UV or the efficiency of DNA photoproduct removal. Our data suggest that defective NER exclusively during S phase, possibly associated with decreased ATR signaling, may constitute an heretofore unrecognized determinant in melanoma pathogenesis.

van Oorschot B, Hovingh SE, Moerland PD, et al.
Reduced activity of double-strand break repair genes in prostate cancer patients with late normal tissue radiation toxicity.
Int J Radiat Oncol Biol Phys. 2014; 88(3):664-70 [PubMed] Related Publications
PURPOSE: To investigate clinical parameters and DNA damage response as possible risk factors for radiation toxicity in the setting of prostate cancer.
METHODS AND MATERIALS: Clinical parameters of 61 prostate cancer patients, 34 with (overresponding, OR) and 27 without (non-responding, NR) severe late radiation toxicity were assembled. In addition, for a matched subset the DNA damage repair kinetics (γ-H2AX assay) and expression profiles of DNA repair genes were determined in ex vivo irradiated lymphocytes.
RESULTS: Examination of clinical data indicated none of the considered clinical parameters to be correlated with the susceptibility of patients to develop late radiation toxicity. Although frequencies of γ-H2AX foci induced immediately after irradiation were similar (P=.32), significantly higher numbers of γ-H2AX foci were found 24 hours after irradiation in OR compared with NR patients (P=.03). Patient-specific γ-H2AX foci decay ratios were significantly higher in NR patients than in OR patients (P<.0001). Consequently, NR patients seem to repair DNA double-strand breaks (DSBs) more efficiently than OR patients. Moreover, gene expression analysis indicated several genes of the homologous recombination pathway to be stronger induced in NR compared with OR patients (P<.05). A similar trend was observed in genes of the nonhomologous end-joining repair pathway (P=.09). This is congruent with more proficient repair of DNA DSBs in patients without late radiation toxicity.
CONCLUSIONS: Both gene expression profiling and DNA DSB repair kinetics data imply that less-efficient repair of radiation-induced DSBs may contribute to the development of late normal tissue damage. Induction levels of DSB repair genes (eg, RAD51) may potentially be used to assess the risk for late radiation toxicity.

Ibuki Y, Toyooka T, Zhao X, Yoshida I
Cigarette sidestream smoke induces histone H3 phosphorylation via JNK and PI3K/Akt pathways, leading to the expression of proto-oncogenes.
Carcinogenesis. 2014; 35(6):1228-37 [PubMed] Related Publications
Post-translational modifications in histones have been associated with cancer. Although cigarette sidestream smoke (CSS) as well as mainstream smoke are carcinogens, the relationship between carcinogenicity and histone modifications has not yet been clarified. Here, we demonstrated that CSS induced phosphorylation of histones, involving a carcinogenic process. Treatment with CSS markedly induced the phosphorylation of histone H3 at serine 10 and 28 residues (H3S10 and H3S28), which was independent from the cell cycle, in the human pulmonary epithelial cell model, A549 and normal human lung fibroblasts, MRC-5 and WI-38. Using specific inhibitors and small interfering RNA, the phosphorylation of H3S10 was found to be mediated by c-jun N-terminal kinase (JNK) and phosphoinositide 3-kinase (PI3K)/Akt pathways. These pathways were different from that of the CSS-induced phosphorylation of histone H2AX (γ-H2AX) mediated by Ataxia telangiectasia-mutated (ATM) and ATM-Rad3-related (ATR) protein kinases. A chromatin immunoprecipitation assay revealed that the phosphorylation of H3S10 was increased in the promoter sites of the proto-oncogenes, c-fos and c-jun, which indicated that CSS plays a role in tumor promotion. Because the phosphorylation of H3S10 was decreased in the aldehyde-removed CSS and was significantly induced by treatment with formaldehyde, aldehydes are suspected to partially contribute to this phosphorylation. These findings suggested that any chemicals in CSS, including aldehydes, phosphorylate H3S10 via JNK and PI3K/Akt pathways, which is different from the DNA damage response, resulting in tumor promotion.

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