ATM associates with and phosphorylates p53: mapping the region of interaction

Glioma oncoprotein Bcl2L12 inhibits the p53 tumor suppressor

Glioblastoma multiforme (GBM) is a lethal brain tumor characterized by intense apoptosis resistance and extensive necrosis. Bcl2L12 (for Bcl2-like 12) is a cytoplasmic and nuclear protein that is overexpressed in primary GBM and functions to inhibit post-mitochondrial apoptosis signaling. Here, we show that nuclear Bcl2L12 physically and functionally interacts with the p53 tumor suppressor, as evidenced by the capacity of Bcl2L12 to (1) enable bypass of replicative senescence without concomitant loss of p53 or p19 (Arf), (2) inhibit p53-dependent DNA damage-induced apoptosis, (3) impede the capacity of p53 to bind some of its target gene promoters, and (4) attenuate endogenous p53-directed transcriptomic changes following genotoxic stress. Correspondingly, The Cancer Genome Atlas profile and tissue protein analyses of human GBM specimens show significantly lower Bcl2L12 expression in the setting of genetic p53 pathway inactivation. Thus, Bcl2L12 is a multifunctional protein that contributes to intense therapeutic resistance of GBM through its ability to operate on two key nodes of cytoplasmic and nuclear signaling cascades.

Switching p53-dependent growth arrest to apoptosis via the inhibition of DNA damage-activated kinases

Cisplatin and doxorubicin are widely used anticancer drugs that cause DNA damage, which activates the ATM-Chk2-p53 pathway in cancer cells. This activation leads to cell cycle block or apoptosis, depending on the nature of the DNA damage. In an attempt to enhance the effects of these agents, we inhibited ATM/ATR and Chk2, which are known upstream regulators of p53. The cancer cell lines A2780 and ARN8, bearing the wild-type p53 protein, were used to study changes in p53 activation and trans-activation. Our results suggest that the G(1)-checkpoint, normally activated by DNA damage, is functionally overcome by the action of kinase inhibitors that sensitize cells to apoptosis. Both inhibitors show these effects, albeit with variable intensity in different cell lines, which is promising for other studies and theoretically for use in clinical practice.

Nuclear ataxias

Historically basic neuroscience research has made several important contributions to the cell biology of the nucleus, in particular the elucidation of nuclear structures and compartments. As research progressed towards elucidating the mechanism of neurological disease at the cellular and molecular levels, it is now providing insight into the importance and basis of coordination of nuclear pathways within the nucleus and with other cellular compartments. Ataxias, lethal neurodegenerative diseases that are distinguished by a progressive loss of motor coordination, stem from disruption of nuclear function.

Systems-wide proteomic characterization of combinatorial post-translational modification patterns

Protein post-translational modifications (PTMs) have been widely shown to influence protein-protein interactions, direct subcellular location and transduce a variety of both internal and externally generated signals into cellular/phenotypic outcomes. Mass spectrometry has been a key tool for the elucidation of several types of PTMs in both qualitative and quantitative manners. As large datasets on the proteome-wide level are now being generated on a daily basis, the identification of combinatorial PTM patterns has become feasible. A survey of the recent literature in this area shows that many proteins undergo multiple modifications and that sequential or hierarchal patterns exist on many proteins; the biology of these modification patterns is only starting to be unraveled. This review will outline combinatorial PTM examples in biology, and the mass spectrometry-based techniques and applications utilized in the investigations of these combinatorial PTMs.

p53 represses class switch recombination to IgG2a through its antioxidant function

Ig class switch recombination (CSR) occurs in activated mature B cells, and causes an exchange of the IgM isotype for IgG, IgE, or IgA isotypes, which increases the effectiveness of the humoral immune response. DNA ds breaks in recombining switch (S) regions, where CSR occurs, are required for recombination. Activation-induced cytidine deaminase initiates DNA ds break formation by deamination of cytosines in S regions. This reaction requires reactive oxygen species (ROS) intermediates, such as hydroxyl radicals. In this study we show that the ROS scavenger N-acetylcysteine inhibits CSR. We also demonstrate that IFN-gamma treatment, which is used to induce IgG2a switching, increases intracellular ROS levels, and activates p53 in switching B cells, and show that p53 inhibits IgG2a class switching through its antioxidant-regulating function. Finally, we show that p53 inhibits DNA breaks and mutations in S regions in B cells undergoing CSR, suggesting that p53 inhibits the activity of activation-induced cytidine deaminase.

Epigenetic regulation of p16Ink4a and Arf by JDP2 in cellular senescence

In response to accumulating cellular stress, cells protect themselves from abnormal growth by entering the senescent stage. Senescence is controlled mainly by gene products from the p16Ink4a/Arf locus. In mouse cells, the expression of p16Ink4a and Arf increases continuously during proliferation in cell culture. Transcription from the locus is under complex control. p16Ink4a and Arf respond independently to positive and negative signals, and the entire locus is epigenetically suppressed by histone methylation that depends on the Polycomb repressive complex-1 and -2 (PRC1 and PRC2). In fact, the PRCs associate with the p16Ink4a/Arf locus in young proliferating cells and dissociate in aged senescent cells. Thus, it seems that chromatin-remodeling factors that regulate association and dissociation of PRCs might be important players in the senescence program. Here, we summarize the molecular mechanisms that mediate cellular aging and introduce the Jun dimerization protein 2 (JDP2) as a factor that regulates replicative senescence by mediating dissociation of PRCs from the p16Ink4a/Arf locus.

Radiation Sensitivity and Tumor Susceptibility in ATM Phospho-Mutant ATF2 Mice

The transcription factor ATF2 was previously shown to be an ATM substrate. Upon phosphorylation by ATM, ATF2 exhibits a transcription-independent function in the DNA damage response through localization to DNA repair foci and control of cell cycle arrest. To assess the physiological significance of this phosphorylation, we generated ATF2 mutant mice in which the ATM phosphoacceptor sites (S472/S480) were mutated (ATF2(KI)). ATF2(KI) mice are more sensitive to ionizing radiation (IR) than wild-type (ATF2 (WT)) mice: following IR, ATF2(KI) mice exhibited higher levels of apoptosis in the intestinal crypt cells and impaired hepatic steatosis. Molecular analysis identified impaired activation of the cell cycle regulatory protein p21(Cip/Waf1) in cells and tissues of IR-treated ATF2(KI) mice, which was p53 independent. Analysis of tumor development in p53(KO) crossed with ATF2(KI) mice indicated a marked decrease in amount of time required for tumor development. Further, when subjected to two-stage skin carcinogenesis process, ATF2(KI) mice developed skin tumors faster and with higher incidence, which also progressed to the more malignant carcinomas, compared with the control mice. Using 3 mouse models, we establish the importance of ATF2 phosphorylation by ATM in the acute cellular response to DNA damage and maintenance of genomic stability.

RUNX3 modulates DNA damage-mediated phosphorylation of tumor suppressor p53 at Ser-15 and acts as a co-activator for p53

Although it has been shown that the gastric tumor suppressor RUNX3 has a growth inhibitory activity, the precise molecular mechanisms behind RUNX3-mediated tumor suppression remained unclear. In this study, we found that RUNX3 is closely involved in DNA damage-dependent phosphorylation of tumor suppressor p53 at Ser-15 and acts as a co-activator for p53. The small interference RNA-mediated knockdown of RUNX3 inhibited adriamycin (ADR)-dependent apoptosis in p53-proficient cells but not in p53-deficient cells in association with a significant reduction of p53-target gene expression as well as phosphorylation of p53 at Ser-15. In response to ADR, RUNX3 was induced to accumulate in the cell nucleus and co-localized with p53. Immunoprecipitation experiments demonstrated that RUNX3 forms a complex with p53 in cells. In vitro pulldown assays revealed that the COOH-terminal portion of p53 is required for the interaction with RUNX3. Forced expression of RUNX3 enhanced p53-mediated transcriptional activation. Additionally, RUNX3 had an ability to induce the phosphorylation of p53 at Ser-15, thereby promoting p53-dependent apoptosis. Intriguingly, RUNX3 interacted with phosphorylated forms of ataxia telangiectasia-mutated in response to ADR; however, it did not affect the extent of DNA damage. From the clinical point of view, coordinated p53 mutation and decreased expression of RUNX3 in 105 human lung adenocarcinomas were significantly associated with the poor outcome of patients (p = 0.0203). Thus, our present results strongly suggest that RUNX3 acts as a novel co-activator for p53 through regulating its DNA damage-induced phosphorylation at Ser-15 and also provide a clue to understanding the molecular mechanisms underlying RUNX3-mediated tumor suppression.

MUC1-C Oncoprotein Interacts Directly with ATM and Promotes the DNA Damage Response to Ionizing Radiation

The ataxia-telangiectasia mutated (ATM) kinase is activated in the cellular response to ionizing radiation (IR) and is of importance to the repair of DNA double strand breaks (DSBs). The MUC1 oncoprotein is aberrantly overexpressed in human breast carcinomas. The present work demonstrates that the MUC1 C-terminal subunit (MUC1-C) constitutively interacts with ATM in human breast cancer cells. We show that the MUC1-C cytoplasmic domain binds directly to ATM HEAT repeats. Our results also demonstrate that the MUC1-C cytoplasmic domain binds to the ATM substrate H2AX. The functional significance of these interactions is supported by the finding that MUC1-C promotes removal of IR-induced nuclear γH2AX foci. MUC1-C also protects against IR-induced chromosomal aberrations. In concert with these results, MUC1-C blocks IR-induced death by promoting repair of potentially lethal DNA damage. These findings indicate that the overexpression of MUC1 can protect against IR-induced DNA DSBs and may represent a physiologic response that has been exploited by malignant cells.

Potentiation of etoposide-induced apoptosis in HeLa cells by co-treatment with KG-135, a quality-controlled standardized ginsenoside formulation

Our previous studies demonstrated that KG-135, a quality-controlled red ginseng-specific formulation containing approximately equal amounts of three major ginsenosides (Rk1, Rg3 and Rg5), down-regulated G1 cyclin-dependent kinase in HeLa cells. In the present work, we have found that KG-135 potentates cytotoxicity of etoposide by modulating apoptotic signaling. Co-treatment of etoposide and KG-135 markedly elevated the expression and phosphorylation at the serine 15 residue of p53 as well as the cellular levels of Bax and p21(Waf1/Cip1). The increased accumulation and phosphorylation of p53 (Ser15) were attenuated by treatment of cells with wortmannin, a pan-phosphatidylinositol-3 kinase inhibitor. Moreover, co-treatment of etoposide and KG-135 enhanced mitochondrial localization of Bax. Our results indicate that etoposide-induced apoptosis in HeLa cells can be potentiated in the presence of KG-135 through a mechanism that involves the stabilization of p53 and the stimulation of Bax- and p21-mediated apoptotic signaling pathways. These findings suggest that KG-135 represents a useful candidate adjuvant for the treatment of cancers that could potentially minimize the adverse effects of current clinical chemotherapeutics.

SOCS1 links cytokine signaling to p53 and senescence

SOCS1 is lost in many human tumors, but its tumor suppression activities are not well understood. We report that SOCS1 is required for transcriptional activity, DNA binding, and serine 15 phosphorylation of p53 in the context of STAT5 signaling. In agreement, inactivation of SOCS1 disabled p53-dependent senescence in response to oncogenic STAT5A and radiation-induced apoptosis in T cells. In addition, SOCS1 was sufficient to induce p53-dependent senescence in fibroblasts. The mechanism of activation of p53 by SOCS1 involved a direct interaction between the SH2 domain of SOCS1 and the N-terminal transactivation domain of p53, while the C-terminal domain of SOCS1 containing the SOCS Box mediated interaction with the DNA damage-regulated kinases ATM/ATR. Also, SOCS1 colocalized with ATM at DNA damage foci induced by oncogenic STAT5A. Collectively, these results add another component to the p53 and DNA damage networks and reveal a mechanism by which SOCS1 functions as a tumor suppressor.

ATM augments nuclear stabilization of DYRK2 by inhibiting MDM2 in the apoptotic response to DNA damage

The tumor suppressor p53 is a transcription factor that regulates cell cycle, DNA repair, senescence, and apoptosis in response to DNA damage. Phosphorylation of p53 at Ser-46 is indispensable for the commitment to apoptotic cell death. A previous study has shown that upon exposure to genotoxic stress, DYRK2 translocates into the nucleus and phosphorylates p53 at Ser-46, thereby inducing apoptosis. However, less is known about mechanisms responsible for intracellular control of DYRK2. Here we show the functional nuclear localization signal at N-terminal domain of DYRK2. Under normal conditions, nuclear and not cytoplasmic DYRK2 is ubiquitinated by MDM2, resulting in its constitutive degradation. In the presence of proteasome inhibitors, we detected a stable complex of DYRK2 with MDM2 at the nucleus. Upon exposure to genotoxic stress, ATM phosphorylates DYRK2 at Thr-33 and Ser-369, which enables DYRK2 to escape from degradation by dissociation from MDM2 and to induce the kinase activity toward p53 at Ser-46 in the nucleus. These findings indicate that ATM controls stability and pro-apoptotic function of DYRK2 in response to DNA damage.

Phosphorylation of p53 serine 18 upregulates apoptosis to suppress Myc-induced tumorigenesis

ATM and p53 are critical regulators of the cellular DNA damage response and function as potent tumor suppressors. In cells undergoing ionizing radiation, ATM is activated by double-strand DNA breaks and phosphorylates the NH(2) terminus of p53 at serine residue 18. We have previously generated mice bearing an amino acid substitution at this position (p53S18A) and documented a role for p53 phosphorylation in DNA damage-induced apoptosis. In this present study, we have crossed E mu myc transgenic mice with our p53S18A mice to explore a role for ATM-p53 signaling in response to oncogene-induced tumorigenesis. Similar to DNA damage induced by ionizing radiation, expression of c-Myc in pre-B cells induces p53 serine 18 phosphorylation and Puma expression to promote apoptosis. E mu myc transgenic mice develop B-cell lymphoma more rapidly when heterozygous or homozygous for p53S18A alleles. However, E mu myc-induced tumorigenesis in p53S18A mice is slower than that observed in E mu myc mice deficient for either p53 or ATM, indicating that both p53-induced apoptosis and p53-induced growth arrest contribute to the suppression of B-cell lymphoma formation in E mu myc mice. These findings further reveal that oncogene expression and DNA damage activate the same ATM-p53 signaling cascade in vivo to regulate apoptosis and tumorigenesis.

gammaH2AX marks the main events of the spermatogenic process

Recent findings reveal that chromatin reorganization requires formation and repair of DNA double strand breaks (DSBs). Therefore, dynamic changes in chromatin structure taking place along the mitotic and the meiotic processes should be accompanied by histone H2AX phosphorylation and formation of gamma H2AX, a prominent event occurring at DSB sites. Accordingly, gamma H2AX has been detected at multiple developmental steps in adult germ cells. Nevertheless, no comprehensive study focusing on the main biological events occurring in the seminiferous epithelium has been carried out in mammals. Here I analyze H2AX phosphorylation in immunostained testis sections comparing PAS/cresyl violet counterstained, noncounterstained, and immuno-fluorescence preparations and show several waves of H2AX phosphorylation/dephosphorylation coupled to various developmental phases of spermatogonia and spermatocytes as well as to spermatid differentiation. The combined detection of DNA replication or free 3'-OH DNA ends highlight the possible significance of gamma H2AX at these locations.

Requirement of ATM for rapid p53 phosphorylation at Ser46 without Ser/Thr-Gln sequences

p53 phosphorylation at Ser46 following DNA damage is important for preferential transactivation of proapoptotic genes. Here, we report that ataxia-telangiectasia mutated (ATM) kinase is responsible for Ser46 phosphorylation of p53 during early-phase response to DNA damage. To elucidate the direct phosphorylation of p53 at Ser46 by ATM, an ATM mutant (ATM-AS) sensitive to ATP analogues was engineered. In vitro kinase assays revealed that p53 was phosphorylated at Ser46 by ATM-AS, even when ATP analogues were used as phosphate donors, although this phosphorylation site is not in an SQ motif, a consensus ATM site. Furthermore, Ser46 phosphorylation by ATM was dependent on the N- and C-terminal domains of p53, unlike Ser15 phosphorylation. Immunofluorescence analyses showed that Ser46-phosphorylated p53 was observed as foci in response to DNA damage and colocalized with gamma-H2AX or Ser1981-phosphorylated ATM. These results suggest that ATM phosphorylates a noncanonical serine residue on p53 by mechanisms different from those for the phosphorylation of Ser15.

Novel HIV-1 therapeutics through targeting altered host cell pathways

The emergence of drug-resistant HIV-1 strains presents a challenge for the design of new drugs. Anti-HIV compounds currently in use are the subject of advanced clinical trials using either HIV-1 reverse transcriptase, viral protease or integrase inhibitors. Recent studies show an increase in the number of HIV-1 variants resistant to anti-retroviral agents in newly infected individuals. Targeting host cell factors involved in the regulation of HIV-1 replication might be one way to combat HIV-1 resistance to the currently available anti-viral agents. A specific inhibition of HIV-1 gene expression could be expected from the development of compounds targeting host cell factors that participate in the activation of the HIV-1 LTR promoter. Here we discuss how targeting the host can be accomplished either by using small molecules to alter the function of the host's proteins such as p53 or cdk9, or by utilizing new advances in siRNA therapies to knock down essential host factors such as CCR5 and CXCR4. Finally, we will discuss how the viral protein interactomes should be used to better design therapeutics against HIV-1.

Phosphorylation of Exo1 modulates homologous recombination repair of DNA double-strand breaks

DNA double-strand break (DSB) repair via the homologous recombination pathway is a multi-stage process, which results in repair of the DSB without loss of genetic information or fidelity. One essential step in this process is the generation of extended single-stranded DNA (ssDNA) regions at the break site. This ssDNA serves to induce cell cycle checkpoints and is required for Rad51 mediated strand invasion of the sister chromatid. Here, we show that human Exonuclease 1 (Exo1) is required for the normal repair of DSBs by HR. Cells depleted of Exo1 show chromosomal instability and hypersensitivity to ionising radiation (IR) exposure. We find that Exo1 accumulates rapidly at DSBs and is required for the recruitment of RPA and Rad51 to sites of DSBs, suggesting a role for Exo1 in ssDNA generation. Interestingly, the phosphorylation of Exo1 by ATM appears to regulate the activity of Exo1 following resection, allowing optimal Rad51 loading and the completion of HR repair. These data establish a role for Exo1 in resection of DSBs in human cells, highlighting the critical requirement of Exo1 for DSB repair via HR and thus the maintenance of genomic stability.

Tumour suppression by p53: a role for the DNA damage response?

Loss of p53 function occurs during the development of most, if not all, tumour types. This paves the way for genomic instability, tumour-associated changes in metabolism, insensitivity to apoptotic signals, invasiveness and motility. However, the nature of the causal link between early tumorigenic events and the induction of the p53-mediated checkpoints that constitute a barrier to tumour progression remains uncertain. This Review considers the role of the DNA damage response, which is activated during the early stages of tumour development, in mobilizing the tumour suppression function of p53. The relationship between these events and oncogene-induced p53 activation through the ARF pathway is also discussed.

Rare, evolutionarily unlikely missense substitutions in ATM confer increased risk of breast cancer

The susceptibility gene for ataxia telangiectasia, ATM, is also an intermediate-risk breast-cancer-susceptibility gene. However, the spectrum and frequency distribution of ATM mutations that confer increased risk of breast cancer have been controversial. To assess the contribution of rare variants in this gene to risk of breast cancer, we pooled data from seven published ATM case-control mutation-screening studies, including a total of 1544 breast cancer cases and 1224 controls, with data from our own mutation screening of an additional 987 breast cancer cases and 1021 controls. Using an in silico missense-substitution analysis that provides a ranking of missense substitutions from evolutionarily most likely to least likely, we carried out analyses of protein-truncating variants, splice-junction variants, and rare missense variants. We found marginal evidence that the combination of ATM protein-truncating and splice-junction variants contribute to breast cancer risk. There was stronger evidence that a subset of rare, evolutionarily unlikely missense substitutions confer increased risk. On the basis of subset analyses, we hypothesize that rare missense substitutions falling in and around the FAT, kinase, and FATC domains of the protein may be disproportionately responsible for that risk and that a subset of these may confer higher risk than do protein-truncating variants. We conclude that a comparison between the graded distributions of missense substitutions in cases versus controls can complement analyses of truncating variants and help identify susceptibility genes and that this approach will aid interpretation of the data emerging from new sequencing technologies.

Candidate protein biodosimeters of human exposure to ionizing radiation

PURPOSE

To conduct a literature review of candidate protein biomarkers for individual radiation biodosimetry of exposure to ionizing radiation.

MATERIALS AND METHODS

Reviewed approximately 300 publications (1973 - April 2006) that reported protein effects in mammalian systems after either in vivo or in vitro radiation exposure.

RESULTS

We found 261 radiation-responsive proteins including 173 human proteins. Most of the studies used high doses of ionizing radiation (>4 Gy) and had no information on dose- or time-responses. The majority of the proteins showed increased amounts or changes in phosphorylation states within 24 h after exposure (range: 1.5- to 10-fold). Of the 47 proteins that are responsive at doses of 1 Gy and below, 6 showed phosphorylation changes at doses below 10 cGy. Proteins were assigned to 9 groups based on consistency of response across species, dose- and time-response information and known role in the radiation damage response.

CONCLUSIONS

ATM (Ataxia telengiectasia mutated), H2AX (histone 2AX), CDKN1A (Cyclin-dependent kinase inhibitor 1A), and TP53 (tumor protein 53) are top candidate radiation protein biomarkers. Furthermore, we recommend a panel of protein biomarkers, each with different dose and time optima, to improve individual radiation biodosimetry for discriminating between low-, moderate-, and high-dose exposures. Our findings have applications for early triage and follow-up medical assessments.

The CXXC finger 5 protein is required for DNA damage-induced p53 activation

The tumor suppressor p53 is a critical component of the DNA damage response pathway that induces a set of genes responsible for cell cycle arrest, senescence, apoptosis, and DNA repair. The ataxia telangiectasia mutated protein kinase (ATM) responds to DNA-damage stimuli and signals p53 stabilization and activation, thereby facilitating transactivation of p53 inducible genes and maintainence of genome integrity. In this study, we identified a CXXC zinc finger domain containing protein termed CF5 as a critical component in the DNA damage signaling pathway. CF5 induces p53 transcriptional activity and apoptosis in cells expressing wild type p53 but not in p53-deficient cells. Knockdown of CF5 inhibits DNA damage-induced p53 activation as well as cell cycle arrest. Furthermore, CF5 physically interacts with ATM and is required for DNA damage-induced ATM phosphorylation but not its recruitment to chromatin. These findings suggest that CF5 plays a crucial role in ATM-p53 signaling in response to DNA damage.

Phosphorylation of ATM by Cdk5 mediates DNA damage signalling and regulates neuronal death

The phosphatidylinositol-3-kinase-like kinase ATM (Ataxia – telangiectasia mutated) plays a central role in coordinating the DNA damage responses including cell cycle checkpoint control, DNA repair, and apoptosis. Mutations of ATM cause a spectrum of defects ranging from neurodegeneration to cancer predisposition. However, the mechanism by which DNA damage activates ATM is poorly understood. We show that Cdk5 (cyclin-dependent kinase 5), activated by DNA damage, directly phosphorylates ATM at serine 794 in postmitotic neurons. Phosphorylation at serine 794 precedes and is required for ATM autophosphorylation at serine 1981, and activates ATM kinase activity. Cdk5-ATM signal regulates phosphorylation and function of ATM targets p53 and H2AX. Interruption of Cdk5-ATM pathway attenuates DNA damage-induced neuronal cell cycle reentry and expression of p53 targets PUMA and Bax, protecting neurons from DNA damage-induced death. Thus, activation of Cdk5 by DNA damage serves as a critical signal to initiate ATM response and regulate ATM-dependent cellular processes.

Relationship Between San-Huang-Xie-Xin-Tang and its herbal components on the gene expression profiles in HepG2 cells

Traditional Chinese medicine (TCM) has been used for thousands of years. Most Chinese herbal formulae consist of several herbal components and have been used to treat various diseases. However, the mechanisms of most formulae and the relationship between formulae and their components remain to be elucidated. Here we analyzed the putative mechanism of San-Huang-Xie-Xin-Tang (SHXXT) and defined the relationship between SHXXT and its herbal components by microarray technique. HepG2 cells were treated with SHXXT or its components and the gene expression profiles were analyzed by DNA microarray. Gene set enrichment analysis indicated that SHXXT and its components displayed a unique anti-proliferation pattern via p53 signaling, p53 activated, and DNA damage signaling pathways in HepG2 cells. Network analysis showed that most genes were regulated by one molecule, p53. In addition, hierarchical clustering analysis showed that Rhizoma Coptis shared a similar gene expression profile with SHXXT. These findings may explain why Rhizoma Coptis is the principle herb that exerts the major effect in the herbal formula, SHXXT. Moreover, this is the first report to reveal the relationship between formulae and their herbal components in TCM by microarray and bioinformatics tools.

Ataxia-telangiectasia: from a rare disorder to a paradigm for cell signalling and cancer

First described over 80 years ago, ataxia-telangiectasia (A-T) was defined as a clinical entity 50 years ago. Although not encountered by most clinicians, it is a paradigm for cancer predisposition and neurodegenerative disorders and has a central role in our understanding of the DNA-damage response, signal transduction and cell-cycle control. The discovery of the protein A-T mutated (ATM) that is deficient in A-T paved the way for rapid progress on understanding how ATM functions with a host of other proteins to protect against genome instability and reduce the risk of cancer and other pathologies.

Variants in the ATM gene associated with a reduced risk of contralateral breast cancer

Between 5% and 10% of women who survive a first primary breast cancer will subsequently develop a second primary cancer in the contralateral breast. The Women's Environment, Cancer, and Radiation Epidemiology Study was designed to identify genetic and environmental determinants of contralateral breast cancer (CBC). In this study, 708 women with asynchronous CBC served as cases and 1,397 women with unilateral breast cancer served as controls. ATM, a serine-threonine kinase, controls the cellular response to DNA double-strand breaks, and has been implicated in breast cancer risk. Complete mutation screening of the ATM gene in all 2,105 study participants identified 240 distinct sequence variants; only 15 were observed in >1% of subjects. Among the rare variants, deleterious alleles resulting in loss of ATM function were associated with a nonsignificant increase in risk of CBC. In contrast, carriers of common variants had a statistically significant reduction in risk of CBC. Four of these 15 variants were individually associated with a significantly decreased risk of second primary breast cancer [c.1899-55T>G, rate ratio (RR), 0.5; 95% confidence interval (CI), 0.3-0.8; c.3161C>G, RR, 0.5; 95% CI, 0.3-0.9; c.5558A>T, RR, 0.2; 95% CI, 0.1-0.6; c.6348-54T>C RR, 0.2; 95% CI, 0.1-0.8]. These data suggest that some alleles of ATM may exert an antineoplastic effect, perhaps by altering the activity of ATM as an initiator of DNA damage responses or a regulator of p53.

A novel Tel1/ATM N-terminal motif, TAN, is essential for telomere length maintenance and a DNA damage response

Tel1/ATM, a conserved phosphatidylinositol 3-kinase-related kinase (PIKK), acts in the response to DNA damage and regulates telomere maintenance. PIKK family members share an extended N-terminal region of low sequence homology. Sequence alignment of the N terminus of Tel1/ATM orthologs revealed a conserved, novel motif we term TAN (for Tel1/ATM N-terminal motif). Point mutations in conserved residues of the TAN motif resulted in telomere shortening, and its deletion caused the same short telomere phenotype as complete deletion of Tel1 did. Overexpressing Tel1 TAN mutants did not rescue telomere shortening. The TAN motif was also essential for the function of Tel1 in the response to DNA damage, as TAN-deleted Tel1 was indistinguishable from the complete lack of Tel1 in causing reduced viability and signaling through Rad53 upon DNA damage. Strikingly, TAN deletion reduced recruitment of Tel1 to a double-strand DNA break. Together, these results define a conserved sequence motif within an otherwise poorly defined region of the Tel1/ATM kinase family proteins that is essential for normal Tel1 function in Saccharomyces cerevisiae.

Risk of cancer by ATM missense mutations in the general population

PURPOSE

Truncating and missense mutations in the ATM gene, which cause insufficient DNA damage surveillance, allow damaged cells to proceed into mitosis, which eventually results in increased cancer susceptibility. We tested the hypotheses that ATM Ser49Cys and ATM Ser707Pro heterozygosity increase the risk of cancer overall, of breast cancer, and of 26 other cancer subtypes in the general population.

PATIENTS AND METHODS

We genotyped 10,324 individuals from the Danish general population who were observed prospectively for 36 years, during which 2,056 developed cancer.

RESULTS

Multifactorially adjusted hazard ratios for ATM Ser49Cys heterozygotes versus noncarriers were 1.2 (95% CI, 0.9 to 1.5) for cancer overall, 0.8 (95% CI, 0.3 to 2.0) for breast cancer, 4.8 (95% CI, 2.2 to 11) for melanoma, 2.3 (95% CI, 1.1 to 5.0) for prostate cancer, and 3.4 (95% CI, 1.1 to 11) for cancer of the oral cavity/pharynx. Multifactorially adjusted hazard ratios for ATM Ser707Pro heterozygotes versus noncarriers were 0.8 (95% CI, 0.6 to 1.2) for cancer overall, 0.6 (95% CI, 0.2 to 1.6) for breast cancer, 10 (95% CI, 1.1 to 93) for thyroid/other endocrine tumors, and 2.7 (95% CI, 1.0 to 7.6) for cancer of corpus uteri.

CONCLUSION

ATM missense mutations do not increase the risk of cancer overall or of breast cancer in the general population; however, we observed in exploratory analyses that ATM missense mutations may be associated with an increased risk of other cancer subtypes. As we did multiple comparisons, some of these findings could represent chance findings rather than real phenomena.

Critical involvement of the ATM-dependent DNA damage response in the apoptotic demise of HIV-1-elicited syncytia

DNA damage can activate the oncosuppressor protein ataxia telangiectasia mutated (ATM), which phosphorylates the histone H2AX within characteristic DNA damage foci. Here, we show that ATM undergoes an activating phosphorylation in syncytia elicited by the envelope glycoprotein complex (Env) of human immunodeficiency virus-1 (HIV-1) in vitro. This was accompanied by aggregation of ATM in discrete nuclear foci that also contained phospho-histone H2AX. DNA damage foci containing phosphorylated ATM and H2AX were detectable in syncytia present in the brain or lymph nodes from patients with HIV-1 infection, as well as in a fraction of blood leukocytes, correlating with viral status. Knockdown of ATM or of its obligate activating factor NBS1 (Nijmegen breakage syndrome 1 protein), as well as pharmacological inhibition of ATM with KU-55933, inhibited H2AX phosphorylation and prevented Env-elicited syncytia from undergoing apoptosis. ATM was found indispensable for the activation of MAP kinase p38, which catalyzes the activating phosphorylation of p53 on serine 46, thereby causing p53 dependent apoptosis. Both wild type HIV-1 and an HIV-1 mutant lacking integrase activity induced syncytial apoptosis, which could be suppressed by inhibiting ATM. HIV-1-infected T lymphoblasts from patients with inactivating ATM or NBS1 mutations also exhibited reduced syncytial apoptosis. Altogether these results indicate that apoptosis induced by a fusogenic HIV-1 Env follows a pro-apoptotic pathway involving the sequential activation of ATM, p38MAPK and p53.

Single-stranded DNA-binding protein hSSB1 is critical for genomic stability

Single-strand DNA (ssDNA)-binding proteins (SSBs) are ubiquitous and essential for a wide variety of DNA metabolic processes, including DNA replication, recombination, DNA damage detection and repair. SSBs have multiple roles in binding and sequestering ssDNA, detecting DNA damage, stimulating nucleases, helicases and strand-exchange proteins, activating transcription and mediating protein-protein interactions. In eukaryotes, the major SSB, replication protein A (RPA), is a heterotrimer. Here we describe a second human SSB (hSSB1), with a domain organization closer to the archaeal SSB than to RPA. Ataxia telangiectasia mutated (ATM) kinase phosphorylates hSSB1 in response to DNA double-strand breaks (DSBs). This phosphorylation event is required for DNA damage-induced stabilization of hSSB1. Upon induction of DNA damage, hSSB1 accumulates in the nucleus and forms distinct foci independent of cell-cycle phase. These foci co-localize with other known repair proteins. In contrast to RPA, hSSB1 does not localize to replication foci in S-phase cells and hSSB1 deficiency does not influence S-phase progression. Depletion of hSSB1 abrogates the cellular response to DSBs, including activation of ATM and phosphorylation of ATM targets after ionizing radiation. Cells deficient in hSSB1 exhibit increased radiosensitivity, defective checkpoint activation and enhanced genomic instability coupled with a diminished capacity for DNA repair. These findings establish that hSSB1 influences diverse endpoints in the cellular DNA damage response.

Drug 9AA reactivates p21/Waf1 and Inhibits HIV-1 progeny formation

It has been demonstrated that the p53 pathway plays an important role in HIV-1 infection. Previous work from our lab has established a model demonstrating how p53 could become inactivated in HIV-1 infected cells through binding to Tat. Subsequently, p53 was inactivated and lost its ability to transactivate its downstream target gene p21/waf1. P21/waf1 is a well-known cdk inhibitor (CKI) that can lead to cell cycle arrest upon DNA damage. Most recently, the p21/waf1 function was further investigated as a molecular barrier for HIV-1 infection of stem cells. Therefore, we reason that the restoration of the p53 and p21/waf1 pathways could be a possible theraputical arsenal for combating HIV-1 infection. In this current study, we show that a small chemical molecule, 9-aminoacridine (9AA) at low concentrations, could efficiently reactivate p53 pathway and thereby restoring the p21/waf1 function. Further, we show that the 9AA could significantly inhibit virus replication in activated PBMCs, likely through a mechanism of inhibiting the viral replication machinery. A mechanism study reveals that the phosphorylated p53ser15 may be dissociated from binding to HIV-1 Tat protein, thereby activating the p21/waf1 gene. Finally, we also show that the 9AA-activated p21/waf1 is recruited to HIV-1 preintegration complex, through a mechanism yet to be elucidated.

Ataxia-telangiectasia mutated is not required for p53 induction and apoptosis in irradiated epithelial tissues

The ataxia-telangiectasia mutated (Atm) protein kinase is a central regulator of the cellular response to DNA damage. Although Atm can regulate p53, it is not known if this Atm function varies between tissues. Previous studies showed that the induction of p53 and apoptosis by whole-body ionizing radiation varies greatly between tissue and tumor types, so here we asked if Atm also had a tissue-specific role in the ionizing radiation response. Irradiated Atm-null mice showed impaired p53 induction and apoptosis in thymus, spleen, and brain. In contrast, radiation-induced p53, apoptosis, phosphorylation of Chk2, and G(2)-M cell cycle arrest were slightly delayed in Atm(-/-) epithelial cells of the small intestine but reached wild-type levels by 4 h. Radiation-induced p53 and apoptosis in Atm(-/-) hair follicle epithelial cells were not impaired at any of the time points examined. Thus, Atm is essential for radiation-induced apoptosis in lymphoid tissues but is largely dispensable in epithelial cells. This indicates that marked differences in DNA damage signaling pathways exist between tissues, which could explain some of the tissue-specific phenotypes, especially tumor suppression, associated with Atm deficiency.

The involvement of DNA-damage and -repair defects in neurological dysfunction

A genetic link between defects in DNA repair and neurological abnormalities has been well established through studies of inherited disorders such as ataxia telangiectasia and xeroderma pigmentosum. In this review, we present a comprehensive summary of the major types of DNA damage, the molecular pathways that function in their repair, and the connection between defective DNA-repair responses and specific neurological disease. Particular attention is given to describing the nature of the repair defect and its relationship to the manifestation of the associated neurological dysfunction. Finally, the review touches upon the role of oxidative stress, a leading precursor to DNA damage, in the development of certain neurodegenerative pathologies, such as Alzheimer's and Parkinson's.

The DNA damage response pathways: at the crossroad of protein modifications

Post-translational modifications play a crucial role in coordinating cellular response to DNA damage. Recent evidence suggests an interplay between multiple protein modifications, including phosphorylation, ubiquitylation, acetylation and sumoylation, that combine to propagate the DNA damage signal to elicit cell cycle arrest, DNA repair, apoptosis and senescence. Utility of specific post-translational modifiers allows temporal and spatial control over protein relocalization and interactions, and may represent a means for trans-regulatory activation of protein activities. The ability to recognize these specific modifiers also underscores the capacity for signal amplification, a crucial step for the maintenance of genomic stability and tumor prevention. Here we have summarized recent findings that highlight the complexity of post-translational modifications in coordinating the DNA damage response, with emphasis on the DNA damage signaling cascade.

ATM-NF-kappaB connection as a target for tumor radiosensitization

Ionizing radiation (IR) plays a key role in both areas of carcinogenesis and anticancer radiotherapy. The ATM (ataxia-telangiectasia mutated) protein, a sensor to IR and other DNA-damaging agents, activates a wide variety of effectors involved in multiple signaling pathways, cell cycle checkpoints, DNA repair and apoptosis. Accumulated evidence also indicates that the transcription factor NF-kappaB (nuclear factor-kappaB) plays a critical role in cellular protection against a variety of genotoxic agents including IR, and inhibition of NF-kappaB leads to radiosensitization in radioresistant cancer cells. NF-kappaB was found to be defective in cells from patients with A-T (ataxia-telangiectasia) who are highly sensitive to DNA damage induced by IR and UV lights. Cells derived from A-T individuals are hypersensitive to killing by IR. Both ATM and NF-kappaB deficiencies result in increased sensitivity to DNA double strand breaks. Therefore, identification of the molecular linkage between the kinase ATM and NF-kappaB signaling in tumor response to therapeutic IR will lead to a better understanding of cellular response to IR, and will promise novel molecular targets for therapy-associated tumor resistance. This review article focuses on recent findings related to the relationship between ATM and NF-kappaB in response to IR. Also, the association of ATM with the NF-kappaB subunit p65 in adaptive radiation response, recently observed in our lab, is also discussed.

The ataxia telangiectasia-mutated target site Ser18 is required for p53-mediated tumor suppression

The p53 tumor suppressor is phosphorylated at multiple sites within its NH(2)-terminal region. One of these phosphorylation sites (mouse Ser(18) and human Ser(15)) is a substrate for the ataxia telangiectasia-mutated (ATM) and ATM-related (ATR) protein kinases. Studies of p53(S18A) mice (with a germ-line mutation that replaces Ser(18) with Ala) have indicated that ATM/ATR phosphorylation of p53 Ser(18) is required for normal DNA damage-induced PUMA expression and apoptosis but not for DNA damage-induced cell cycle arrest. Unlike p53-null mice, p53(S18A) mice did not succumb to early-onset tumors. This finding suggested that phosphorylation of p53 Ser(18) was not required for p53-dependent tumor suppression. Here we report that the survival of p53(S18A) mice was compromised and that they spontaneously developed late-onset lymphomas (between ages 1 and 2 years). These mice also developed several malignancies, including fibrosarcoma, leukemia, leiomyosarcoma, and myxosarcoma, which are unusual in p53 mutant mice. Furthermore, we found that lymphoma development was linked with apoptotic defects. In addition, p53(S18A) animals exhibited several aging-associated phenotypes early, and murine embryonic fibroblasts from these animals underwent early senescence in culture. Together, these data indicate that the ATM/ATR phosphorylation site Ser(18) on p53 contributes to tumor suppression in vivo.

DNA repair and the immune system: From V(D)J recombination to aging lymphocytes

B and T lymphocytes are exposed to various genotoxic stresses during their life, which originate from programmed molecular mechanisms during their development and maturation or are secondary to cellular metabolism during acute phases of cell proliferation and activation during immune responses. How lymphocytes handle these multiple genomic assault has become a focus of interest over the years, perhaps beginning with the identification of the murine scid model in the early 80s when it was recognized that DNA repair deficiencies had profound consequences on the immune system. In this respect, the immune system represents an ideal model to study DNA damage responses (DDR) and the survey of immune deficiency conditions in humans or the development of specific animal models provided many major contributions in our understanding of the various biochemical pathways at play during DDR in general. Although the role of DNA repair in the early phases of B and T cell development has been analyzed thoroughly, the role of these functions in various aspects of the mature immune system (homeostasis, immunological memory, ageing) is less well understood. Lastly, the analysis of DNA repair in the immune system has provided many insights in the more general understanding of cancer.

Mystery of DNA repair: the role of the MRN complex and ATM kinase in DNA damage repair

Genomes are subject to a number of exogenous or endogenous DNA-damaging agents that cause DNA double-strand breaks (DSBs). These critical DNA lesions can result in cell death or a wide variety of genetic alterations, including deletions, translocations, loss of heterozygosity, chromosome loss, or chromosome fusions, which enhance genome instability and can trigger carcinogenesis. The cells have developed an efficient mechanism to cope with DNA damages by evolving the DNA repair machinery. There are 2 major DSB repair mechanisms: nonhomologous end joining (NHEJ) and homologous recombination (HR). One element of the repair machinery is the MRN complex, consisting of MRE11, RAD50 and NBN (previously described as NBS1), which is involved in DNA replication, DNA repair, and signaling to the cell cycle checkpoints. A number of kinases, like ATM (ataxia-telangiectasia mutated), ATR (ataxia-telangiectasia and Rad-3-related), and DNA PKcs (DNA protein kinase catalytic subunit), phosphorylate various protein targets in order to repair the damage. If the damage cannot be repaired, they direct the cell to apoptosis. The MRN complex as well as repair kinases are also involved in telomere maintenance and genome stability. The dysfunction of particular elements involved in the repair mechanisms leads to genome instability disorders, like ataxia telangiectasia (A-T), A-T-like disorder (ATLD) and Nijmegen breakage syndrome (NBS). The mutated genes responsible for these disorders code for proteins that play key roles in the process of DNA repair. Here we present a detailed review of current knowledge on the MRN complex, kinases engaged in DNA repair, and genome instability disorders.

Soy-derived isoflavones inhibit the growth of adult T-cell leukemia cells in vitro and in vivo

Adult T-cell leukemia occurs in human T-lymphotropic virus type I-infected individuals and is endemic to the south-western area of Kyushu in Japan. In this communication, we examined the effect of soy isoflavones on the growth of adult T-cell leukemia cells in vitro and in vivo. In the in vitro study, daidzein and genistein but not glycitein significantly inhibited the proliferation of ED-40515 and Hut102 cells in a dose-dependent manner. Among the isoflavones studied, genistein had the highest growth-inhibitory effect; however, genistein did not exert an apparent growth-inhibitory effect on Jurkat and Molt-4 cells, which were non-adult T-cell leukemia cells. Genistein prevented the G(1)/S or G(2)/M transition at 3 and 10 or 30 microM, respectively. Genistein upregulated p21 protein expression together with p53 accumulation. In addition, treatment with 30 microM genistein strongly induced phosphorylation of checkpoint kinase (CHK) 2 and p53 at serines 15, 20 and 37. Caffeine, an inhibitor of ataxia-telangiectasia mutated protein kinase, alleviated the genistein-induced p53 and CHK2 phosphorylation, suggesting the involvement of DNA damage at 30 microM. However, marked phosphorylation of CHK2 and p53 could not be detected at 3 and 10 microM genistein. These data indicate that genistein has biphasic growth-inhibitory properties. The in vivo studies demonstrated that soy-derived isoflavones significantly inhibit ED-40515 cell growth and infiltration into various organs in non-obese diabetic severe combined-immunodeficiency common gamma-chain knockout mice. Taken together, it is evident that soy isoflavones might serve as a promising compound for the treatment of adult T-cell leukemia.

ATM kinase activity modulates Fas sensitivity through the regulation of FLIP in lymphoid cells

Ataxia telangiectasia (A-T) is a rare cancer-predisposing genetic disease, caused by the lack of functional ATM kinase, a major actor of the double strand brakes (DSB) DNA-damage response. A-T patients show a broad and diverse phenotype, which includes an increased rate of lymphoma and leukemia development. Fas-induced apoptosis plays a fundamental role in the homeostasis of the immune system and its defects have been associated with autoimmunity and lymphoma development. We therefore investigated the role of ATM kinase in Fas-induced apoptosis. Using A-T lymphoid cells, we could show that ATM deficiency causes resistance to Fas-induced apoptosis. A-T cells up-regulate FLIP protein levels, a well-known inhibitor of Fas-induced apoptosis. Reconstitution of ATM kinase activity was sufficient to decrease FLIP levels and to restore Fas sensitivity. Conversely, genetic and pharmacologic ATM kinase inactivation resulted in FLIP protein up-regulation and Fas resistance. Both ATM and FLIP are aberrantly regulated in Hodgkin lymphoma. Importantly, we found that reconstitution of ATM kinase activity decreases FLIP protein levels and restores Fas sensitivity in Hodgkin lymphoma-derived cells. Overall, these data identify a novel molecular mechanism through which ATM kinase may regulate the immune system homeostasis and impair lymphoma development.

How important are post-translational modifications in p53 for selectivity in target-gene transcription and tumour suppression?

A number of elegant studies exploring the consequences of expression of various mutant forms of p53 in mice have been published over the last years. The results and conclusions drawn from these studies often contradict results previously obtained in biochemical assays and cell biology studies, questioning their relevance for p53 function in vivo. Owing to the multitude of post-translational modifications imposed on p53, however, the in vivo validation of their relevance for proper protein function and tumour suppression is constantly lagging behind new biochemical discoveries. Nevertheless, mouse genetics presents again its enormous power. Despite being relatively slow and tedious, it has become indispensable for researchers to sort out the wheat from the chaff in an endless sea of publications on p53.

p53 mediates interstitial cystitis antiproliferative factor (APF)-induced growth inhibition of human urothelial cells

Antiproliferative factor (APF) is a sialoglycopeptide elevated in the urine of patients with interstitial cystitis, a urinary bladder disorder of unknown etiology that is characterized by chronic pelvic pain. The present study was directed toward uncovering a pathway through which APF signals. Treatment of human urothelial cells with native APF resulted in growth inhibition accompanied by blockade of cell cycle transit and increased p53. Reduced expression of p53 by RNA interference diminished, while ectopic expression of p53 mimicked, the effects of APF. These are the first findings implicating the network of p53 target genes in urothelial defects associated with interstitial cystitis.

The complexity of p53 stabilization and activation

A number of proteins are activated by stress stimuli but none so spectacularly or with the degree of complexity as the tumour suppressor p53 (human p53 gene or protein). Once stabilized, p53 is responsible for the transcriptional activation of a series of proteins involved in cell cycle control, apoptosis and senescence. This protein is present at low levels in resting cells but after exposure to DNA-damaging agents and other stress stimuli it is stabilized and activated by a series of post-translational modifications that free it from MDM2 (mouse double minute 2 but used interchangeably to denote human also), a ubiquination ligase that ubiquitinates it prior to proteasome degradation. The stability of p53 is also influenced by a series of other interacting proteins. In this review, we discuss the post-translational modifications to p53 in response to different stresses and the consequences of these changes.

Fibroblast Growth Factor 1 inhibits p53-dependent apoptosis in PC12 cells

The survival activity of FGF1 and the pro-apoptotic activity of p53 were characterized in vitro and/or in vivo for different types of neurons after different stresses and in different neurodegenerative pathologies. To investigate whether or not FGF1 and p53 pathways interact in neuronal cells, we studied the effect of FGF1 on p53-dependent apoptosis in PC12 cells. We first characterized p53-dependent PC12 cell death induced by etoposide (a DNA damaging agent). We showed that etoposide increased p53 stabilization, phosphorylation (Ser-15), nuclear translocation and transcriptional activity. In particular, p53 promoted mdm2, p21, puma and noxa expression in PC12 cells. The activation of p53 initiated a classical mitochondrial apoptosis process associated with caspases activation and nuclear degradation. We demonstrated that FGF1 protected PC12 cells from p53-dependent apoptosis upstream from mitochondrial and nuclear events. FGF1 inhibited etoposide-induced p53 phosphorylation, stabilization, nuclear translocation and transcriptional activity. This study presents the first evidence that FGF1 and p53 pathways interact in neuronal cells, and that FGF1 protects neuronal cells from p53-dependent apoptosis, suggesting that alterations of FGF1/p53 crosstalk could be involved in a large range of neurons and in neurological disorders.

Ataxia telangiectasia mutated (ATM) signaling network is modulated by a novel poly(ADP-ribose)-dependent pathway in the early response to DNA-damaging agents

Poly(ADP-ribosyl)ation is a post-translational modification that is instantly stimulated by DNA strand breaks creating a unique signal for the modulation of protein functions in DNA repair and cell cycle checkpoint pathways. Here we report that lack of poly(ADP-ribose) synthesis leads to a compromised response to DNA damage. Deficiency in poly(ADP-ribosyl)ation metabolism induces profound cellular sensitivity to DNA-damaging agents, particularly in cells deficient for the protein kinase ataxia telangiectasia mutated (ATM). At the biochemical level, we examined the significance of poly(ADP-ribose) synthesis on the regulation of early DNA damage-induced signaling cascade initiated by ATM. Using potent PARP inhibitors and PARP-1 knock-out cells, we demonstrate a functional interplay between ATM and poly(ADP-ribose) that is important for the phosphorylation of p53, SMC1, and H2AX. For the first time, we demonstrate a functional and physical interaction between the major DSB signaling kinase, ATM and poly(ADP-ribosyl)ation by PARP-1, a key enzyme of chromatin remodeling. This study suggests that poly(ADP-ribose) might serve as a DNA damage sensory molecule that is critical for early DNA damage signaling.

DNA damage, p53, apoptosis and vascular disease

Atherosclerosis is the commonest cause of death in the Western world. The atherosclerotic plaque shows evidence of DNA damage, activation of damage repair pathways, p53 expression and apoptosis, involving a variety of different cell types. This review summarises the evidence for DNA damage in atherosclerosis, the likely stimuli inducing damage, and the increasing role of p53 in mediating apoptosis and its consequences in atherosclerosis.

Characterization of the breast cancer associated ATM 7271T>G (V2424G) mutation by gene expression profiling

Mutations in ATM are responsible for the autosomal recessive disorder ataxia telangiectasia. Heterozygous mutations in ATM have been associated with an elevated risk of breast cancer. We previously reported one breast cancer family in which ATM 7271T>G (V2424G) segregated with disease, and apparently acted in a dominant negative manner. We now report the screening of 782 multiple-case breast cancer families that identified two additional index cases with ATM 7271T>G. Phylogenetic sequence analysis showed that V2424 is a highly conserved residue, and that the 2424G variant is likely to interfere with function. To elucidate the consequences of this mutation, we expression profiled wild-type, heterozygous, and homozygous lymphoblastoid cell lines (LCLs) from Scottish and Australian families using an oligonucleotide microarray. Cluster analysis revealed 77 genes that were differentially expressed in homozygous and heterozygous V2424G cells (compared to wild-type) and 11 genes differentially expressed in the homozygous cells. We also evaluated the profiles of LCLs after exposure to ionizing radiation (IR) and identified 77 genes that were differentially expressed in wild-type cells, but not in homozygous or heterozygous V2424G cells. We validated the expression differences by RT-PCR in additional heterozygous V2424G LCLs from another breast cancer family. We found no consistent cytotoxicity or abrogation of ATM kinase activity after IR in seven heterozygous V2424G LCLs, compared to wild-type LCLs, but did find an increase in the number of chromosomal aberrations. These data suggest that the V2424G missense mutation acts largely as a dominant negative in terms of the associated expression profiles.