Ataxia Telangiectasia Mutated Phosphorylation Research Articles

Quantitative analysis of ATM phosphorylation in lymphocytes

Since many anticancer therapies target DNA and DNA damage response pathways, biomarkers of DNA damage endpoints may prove valuable in basic and clinical cancer research. Ataxia telangiectasia-mutated (ATM) kinase is the principal regulator of cellular responses to DNA double-strand breaks (DSBs). In humans, ATM autophosphorylation at serine 1981 (p-S1981) is an immediate molecular response to nascent DSBs and ionizing radiation (IR). Here we describe the analytical characteristics and fit-for-purpose validation of a quantitative dual-labeled immunoblot that simultaneously measures p-S1981-ATM and pan-ATM in human peripheral blood mononuclear cells (PBMCs) following ex vivo exposure to 2 Gy IR, facilitating the calculation of %p-ATM. To validate our assay, we isolated PBMCs from 41 volunteers. We report that the median basal level of p-S1981-ATM and pan-ATM was 2.4 and 49.5 ng/107 PBMCs, respectively, resulting in %p-ATM of 4%. Following exposure of PBMCs to 2 Gy IR, p-S1981-ATM levels increased 12-fold to 29.8 ng/107 PBMCs resulting in %p-ATM of 63%. Interestingly, we show that PBMCs from women have a 2.6-fold greater median p-S1981-ATM level following IR exposure than men (44.4 versus 16.9 ng/107 cells; p < 0.01). This results in a significantly greater %p-ATM for women (68% versus 49%; p < 0.01). Our rigorous description of the analytical characteristics and reproducibility of phosphoprotein immunoblotting, along with our finding that the ATM DNA damage response is greater in women, has far reaching implications for biomedical researchers.

SIRT7-mediated ATM deacetylation is essential for its deactivation and DNA damage repair.

The activation of ataxia-telangiectasia mutated (ATM) upon DNA damage involves a cascade of reactions, including acetylation by TIP60 and autophosphorylation. However, how ATM is progressively deactivated after completing DNA damage repair remains obscure. Here, we report that sirtuin 7 (SIRT7)-mediated deacetylation is essential for dephosphorylation and deactivation of ATM. We show that SIRT7, a class III histone deacetylase, interacts with and deacetylates ATM in vitro and in vivo. In response to DNA damage, SIRT7 is mobilized onto chromatin and deacetylates ATM during the late stages of DNA damage response, when ATM is being gradually deactivated. Deacetylation of ATM by SIRT7 is prerequisite for its dephosphorylation by its phosphatase WIP1. Consequently, depletion of SIRT7 or acetylation-mimic mutation of ATM induces persistent ATM phosphorylation and activation, thus leading to impaired DNA damage repair. Together, our findings reveal a previously unidentified role of SIRT7 in regulating ATM activity and DNA damage repair.

ATM phosphorylation of the actin-binding protein drebrin controls oxidation stress-resistance in mammalian neurons and C. elegans

Drebrin (DBN) regulates cytoskeletal functions during neuronal development, and is thought to contribute to structural and functional synaptic changes associated with aging and Alzheimer’s disease. Here we show that DBN coordinates stress signalling with cytoskeletal dynamics, via a mechanism involving kinase ataxia-telangiectasia mutated (ATM). An excess of reactive oxygen species (ROS) stimulates ATM-dependent phosphorylation of DBN at serine-647, which enhances protein stability and accounts for improved stress resilience in dendritic spines. We generated a humanized DBN Caenorhabditis elegans model and show that a phospho-DBN mutant disrupts the protective ATM effect on lifespan under sustained oxidative stress. Our data indicate a master regulatory function of ATM-DBN in integrating cytosolic stress-induced signalling with the dynamics of actin remodelling to provide protection from synapse dysfunction and ROS-triggered reduced lifespan. They further suggest that DBN protein abundance governs actin filament stability to contribute to the consequences of oxidative stress in physiological and pathological conditions.

γ-Tocotrienol-Inhibited Cell Proliferation of Human Gastric Cancer by Regulation of Nuclear Factor-κB Activity.

γ-Tocotrienol (γ-T3) exhibits the activity of anticancer via regulating cell signaling pathways. Nuclear factor-κB (NF-κB), one of the crucial pro-inflammatory factors, is involved in the regulation of cell proliferation, apoptosis, invasion, and migration of tumor. In the present study, NF-κB activity inhibited by γ-T3 was investigated in gastric cancer cells. Cell proliferation, NF-κB activity, active protein phosphatase type 2A (PP2A), and ataxia-telangiectasia mutated (ATM) protein were explored using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT), methylene blue, enzyme-linked immunosorbent assay (ELISA), malachite green, luciferase, and Western blotting assays. The effects of γ-T3 on tumor growth and the expression of NF-κB and PP2A proteins were also further examined by implanting human gastric cancer cells in a BALB/c nude mouse model. The results showed that γ-T3 significantly inhibited the cell proliferation and attenuated the NF-κB activity in vitro and in vivo. γ-T3 dramatically increased PP2A activity and protein expression, which suppressed ATM phosphorylation and its translocation to the cytoplasm in gastric cancer cells. Thus, our findings may provide mechanistic insight into effects of γ-T3 on the regulation of NF-κB activity by a PP2A-dependent mechanism and suggest that PP2A may serve as a molecular target for a potential chemopreventive agent.

Chlamydia trachomatis Inhibits Homologous Recombination Repair of DNA Breaks by Interfering with PP2A Signaling.

Cervical and ovarian cancers exhibit characteristic mutational signatures that are reminiscent of mutational processes, including defective homologous recombination (HR) repair. How these mutational processes are initiated during carcinogenesis is largely unclear. Chlamydia trachomatis infections are epidemiologically associated with cervical and ovarian cancers. Previously, we showed that C. trachomatis induces DNA double-strand breaks (DSBs) but suppresses Ataxia-telangiectasia mutated (ATM) activation and cell cycle checkpoints. The mechanisms by which ATM regulation is modulated and its consequences for the repair pathway in C. trachomatis-infected cells remain unknown. Here, we found that Chlamydia bacteria interfere with the usual response of PP2A to DSBs. As a result, PP2A activity remains high, as the level of inhibitory phosphorylation at Y307 remains unchanged following C. trachomatis-induced DSBs. Protein-protein interaction analysis revealed that C. trachomatis facilitates persistent interactions of PP2A with ATM, thus suppressing ATM activation. This correlated with a remarkable lack of homologous recombination (HR) repair in C. trachomatis-infected cells. Chemical inhibition of PP2A activity in infected cells released ATM from PP2A, resulting in ATM phosphorylation. Activated ATM was then recruited to DSBs and initiated downstream signaling, including phosphorylation of MRE11 and NBS1 and checkpoint kinase 2 (Chk2)-mediated activation of the G2/M cell cycle checkpoint in C. trachomatis-infected cells. Further, PP2A inhibition led to the restoration of C. trachomatis-suppressed HR DNA repair function. Taking the data together, this study revealed that C. trachomatis modulates PP2A signaling to suppress ATM activation to prevent cell cycle arrest, thus contributing to a deficient high-fidelity HR pathway and a conducive environment for mutagenesis.IMPORTANCEChlamydia trachomatis induces DNA double-strand breaks in host cells but simultaneously inhibits proper DNA damage response and repair mechanisms. This may render host cells prone to loss of genetic integrity and transformation. Here we show that C. trachomatis prevents activation of the key DNA damage response mediator ATM by preventing the release from PP2A, leading to a complete absence of homologous recombination repair in host cells.

Unraveling the in vitro antitumor activity of Vismia baccifera against HepG2: role of hydrogen peroxide

Currently natural products derived from plants are receiving huge attention because of their antitumor activities. In previous work we reported that an aqueous leaf extract of Vismia baccifera induced toxicity in HepG2. The present study focuses on the mechanisms of the cytotoxic actions induced by the extract. Results showed that V. baccifera was innocuous in non-transformed human HH4 hepatocytes. In HepG2 it caused deregulation of antioxidant status (increasing superoxide dismutase expression and decreasing glutathione levels and glutathione peroxidase activity) and accumulation of reactive oxygen species, particularly hydrogen peroxide. The extract induced a) cell cycle arrest at G2/M phase, b) phosphorylation of ATM (protein kinase ataxia-telangiectasia mutated) and γH2AX (γ-histone family 2A variant), c) caspase-3 activation, and e) deregulation of the Bax/Bcl family, increasing pro-apoptotic proteins. ATM did not seem to be involved in γH2AX activation. Co-incubation with catalase prevented the alterations elicited by V. baccifera in HepG2. Taking together, these results indicate that hydrogen peroxide mediates the HepG2 cytotoxic response and provide evidence for more in-depth studies of the signaling involved.

Dysregulation of the Tumor Suppressor Tip60 and ATM Signaling Paradigm by the HIV Transactivator of Transcription

Despite the longevity afforded by modern anti‐retroviral therapy, long‐term HIV infection increases the risk for pulmonary co‐morbidities associated with cell cycle dysregulation including lung cancer and pulmonary arterial hypertension. As such, we postulate that select viral factors, in particular the HIV transactivator of transcription (Tat), interfere with cellular processes involving tumor suppressors and other cell cycle regulators during chronic infection. Tat is well known to inhibit the activity of the tumor suppressor Tat Interacting Protein 60 kDa (Tip60), an acetyltransferase critical in the progression to cell cycle arrest and/or apoptosis. In response to stressors such as DNA damage and oxidative stress, Tip60 activates the cell cycle master regulator kinase Ataxia Telangiectasia Mutated (ATM) via acetylation, initiating a signaling cascade that culminates in the activation of a DNA damage response resulting in both short and long term cellular arrest. Thus, we hypothesize that inhibition of Tip60 by Tat interferes with cellular arrest in responses to these stressors and results in abnormal proliferation. We addressed the hypothesis using HeLa cells stably transfected to express Tat (HeLa‐TatIII). Utilizing an ATP based luminescent cell viability assay, we observed accelerated cell proliferation in HeLa‐TatIII compared to its HeLa wild‐type counterpart. Furthermore, immunoprecipitation experiments in HeLa‐WT cells confirmed a physical interaction between Tat and Tip60. Acetylation by Tip60 results in autophosphorylation of ATM at ser1981, and this phosphorylation event is a canonical marker for ATM activation. As such, we determined the phosphorylation state of ATM ser1981 after treatment with doxorubicin in HeLa‐WT and HeLa‐TatIII cells. We found that, following treatment with doxorubicin, ATM phosphorylation at ser1981 was severely attenuated in HeLa‐TatIII cells compared to HeLa‐WTs, suggesting a role for Tat in the inhibition of ATM activation. Taken together, these data support the role of the HIV Tat protein in dysregulation of cell cycle arrest via ATM signaling pathways. Whether HIV promotes cellular proliferation in co‐morbidities such as lung cancer and pulmonary arterial hypertension via these pathways remains to be addressed.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

P3.02-077 Platin Sensitivity and ATM-Deficiency in Non-Small Cell Lung Cancer

Platinum based antineoplastic therapies (platins) are a first line treatment for non-small cell lung cancer (NSCLC) that generate DNA breaks and stimulate DNA damage response pathways. An inability to repair damage generated by these agents leads to cytotoxicity and cell death. A key mediator of the DNA damage response is ataxia telangiectasia mutated (ATM), an activator of downstream targets involved in DNA repair, cell cycle arrest, and apoptosis. Our lab has demonstrated that cell lines lacking ATM show increased sensitivity to platins. We hypothesize that platin exposure will activate ATM and that cells deficient in ATM will be innately sensitive to platins. Here we assess the molecular action of ATM in response to platins to determine if ATM-deficiency is predictive of platin sensitivity. ATM status was determined in five NSCLC cell lines using western blotting and RT-qPCR. Cell lines were treated with varying concentrations cisplatin, carboplatin and oxaliplatin for 18-hours and assessed for ATM phosphorylation by western blot. Additionally, downstream targets of ATM (KAP-1, p53, and gamma-H2AX) were investigated to determine ATM pathway activation. Knockdown cell lines were generated using shRNA to ATM before testing for IR and cisplatin sensitivity using clonogenic assay. ATR and ATM inhibitors were tested on knockdown cell lines to investigate pathway response differences after cisplatin and IR. NSCLC cell lines NCI-H226, NCI-H460, and NCI-H522 were found to be ATM-proficient whereas cell lines NCI-H23 and NCI-H1373 were found to be ATM-deficient. ATM-proficient cell lines demonstrated an increased level of phosphorylated-ATM in response to treatments with cisplatin, carboplatin, and oxaliplatin. ATM knockdown cell lines were found to have increased sensitivity to IR, however analysis of cisplatin sensitivity was inconclusive with only 1 out of 4 showing increased sensitivity. ATR inhibition in combination with cisplatin caused a large increase in DNA damage response from ATM and DNA-PKcs suggesting an avenue for synthetic lethality. It is clear that platin exposure induced an ATM mediated signaling response and that cells lacking ATM showed deficiencies in the phosphorylation of key downstream targets. Cells deficient in ATM may therefore be more susceptible to platin therapy due to an impaired DNA repair response. However, the predictive capabilities of ATM loss for platin sensitivity is still unclear. This data suggests that individuals with low or non-functioning ATM may be candidates for precision low dose therapies that exploit this deficiency.

Oligo-Fucoidan prevents IL-6 and CCL2 production and cooperates with p53 to suppress ATM signaling and tumor progression

Low-molecular-weight Fucoidan (Oligo-Fucoidan) is a sulfated polysaccharide that has a variety of biological effects and has also been shown to have beneficial health effects. However, the molecular mechanisms underlying the therapeutic effects of Oligo-Fucoidan in patients with cancer remain unclear. Using human colorectal cancer HCT116 cells with (p53+/+) or without (p53−/−) normal p53 expression, we found that Oligo-Fucoidan treatment reduces the occurrence of spontaneous DNA lesions. Etoposide induces double strand DNA breaks. Subsequent administration of Oligo-Fucoidan to etoposide-treated cells promotes p53 accumulation, p21 expression and significant decreases in ataxia-telangiectasia-mutated (ATM), checkpoint kinase 1 (Chk1) and γ-H2AX phosphorylation in p53+/+ cells compared with p53−/− cells. Similarly, co-administration of Oligo-Fucoidan with etoposide inhibits ATM, Chk1 and γ-H2AX phosphorylation, particularly in the presence of p53. Furthermore, Oligo-Fucoidan supplementation increases cancer cell death and attenuates the adverse effects induced by etoposide that decreases production of the pro-inflammatory cytokine IL-6 and chemokine CCL2/MCP-1. Importantly, Oligo-Fucoidan decreases the tumor-promoting M2 macrophages in microenvironment as well as collaborates with p53 and works in combination with etoposide to prevent HCT116 tumorigenicity. Our results first demonstrate that p53 enables Oligo-Fucoidan to effectively inhibit tumor progression, and Oligo-Fucoidan minimizes the side effects of chemotherapy and alters tumor microenvironment.

ATM-activated autotaxin (ATX) propagates inflammation and DNA damage in lung epithelial cells: a new mode of action for silica-induced DNA damage?

Silica exposure is a common risk factor for lung cancer. It has been claimed that key elements in cancer development are activation of inflammatory cells that indirectly induce DNA damage and proliferative stimuli in respiratory epithelial cells. We studied DNA damage induced by silica particles in respiratory epithelial cells and focused the role of the signaling enzyme autotaxin (ATX). A549 and 16 bronchial epithelial cells (16HBE) lung epithelial cells were exposed to silica particles. Reactive oxygen species (ROS), NOD-like receptor family pyrin domain containing-3 (NLRP3) inflammasome activation, ATX, ataxia telangiectasia mutated (ATM), and DNA damage (γH2AX, pCHK1, pCHK2, comet assay) were end points. Low doses of silica induced NLRP3 activation, DNA damage accumulation, and ATM phosphorylation. A novel finding was that ATM induced ATX generation and secretion. Not only silica but also rotenone, camptothecin and H2O2 activated ATX via ATM, suggesting that ATX is part of a generalized ATM response to double-strand breaks (DSBs). Surprisingly, ATX inhibition mitigated DNA damage accumulation at later time points (6-16 h), and ATX transfection caused NLRP3 activation and DNA damage. Furthermore, the product of ATX enzymatic activity, lysophosphatidic acid, recapitulated the effects of ATX transfection. These data indicate an ATM-ATX-dependent loop that propagates inflammation and DSB accumulation, making low doses of silica effective inducers of DSBs in epithelial cells. We conclude that an ATM-ATX axis interconnects DSBs with silica-induced inflammation and propagates these effects in epithelial cells. Further studies of this adverse outcome pathway may give an accurate assessment of the lowest doses of silica that causes cancer.

Methyleugenol and selected oxidative metabolites affect DNA-Damage signalling pathways and induce apoptosis in human colon tumour HT29 cells

Previously the food carcinogen methyleugenol was found to be cytotoxic and genotoxic in multiple cell lines and in primary hepatocytes. In this study, the question addressed was whether methyleugenol and the selected oxidative metabolites, 1′-hydroxymethyleugenol, methyleugenol-2′,3′-epoxide and 3′-oxomethylisoeugenol trigger a DNA damage response in the human colon carcinoma HT29 cell line. Most notably investigations by flow cytometry revealed that the metabolites induce an accumulation of HT29 cells in the G2 phase of the cell cycle. DNA damage response is characterised by a time-delayed phosphorylation of ATM (ataxia-telangiectasia, mutated)/ATR (ATM- and Rad3-related) kinases and checkpoint kinase 1 after 2 h of incubation, and the tumour suppressor protein p53 only after 24 h of incubation. The test compounds induced apoptotic cell death indicated by cleavage of caspase 3 and poly-(ADP-ribose)-polymerase after a prolonged incubation time up to 72 h. In addition, activation of ATM/ATR-signalling cascade might contribute to apoptosis induction to a certain extent. However, clarification of this relationship awaits experimental confirmation.

Abstract 3215: Therapeutic potential of dual-function small molecules for breast cancers

Abstract Epigenetic silencing of tumor suppressors is an important mechanism in tumor initiation and progression. A tumor suppressor gene, BRCA1, is part of complex molecules in the repair of DNA double-strand breaks (DSBs), and loss of BRCA1 contributes to both sporadic and inherited breast tumor progression. Furthermore, recent studies have shown that the ataxia-telangiectasia mutated (ATM) activity is abnormal in breast cancer. Therefore, we tested the hypothesis that the dual-functional drug that fused the HDAC inhibitor with an ATM activator may enhance killing of breast cancer (BC) cells by increasing ATM activation. In addition, the expression of ATM may enhance the synergistic antitumor effects of HDAC inhibitors in combination with radiotherapy. To determine the HDAC inhibitory potency, SP-1-303 was screened against a panel of Class I and Class II HDAC enzymes in vitro and identified as a pan-HDAC inhibitor (IC50=120 nM). Western blot confirmed that SP-1-303 increased acetylated histone H3/H4, α-tubulin, and phosphorylation of ATM within 30 min - 4 h in a time-dependent manner. Using two ER positive BC cell lines (MCF7 and T-47D), two triple negative breast cancer (TNBC) cell lines (MDA-MB-231 and HCC 1937), and one normal breast epithelial cell line as a control (MCF10A), the effects of SP-1-303 on cell growth and cell death were examined by performing cytotoxicity assays and flow cytometry. SAHA and Tamoxifen were used as controls. SP-1-303 conferred the values of cytotoxicity (IC50) for the ER positive BC cells in a range of 0.25-0.4 μM, while the values are in a range of 1-3 μM for TNBC and 12 μM for normal breast epithelial cells, respectively. Flow cytometry (FACS) analyses demonstrated significant increases in G1 arrest (81%) in MCF7 cells and a further enhancement in the G1 phase (91%) in combination with radiation. The data implies the mechanism of action from this drug—cancer cells are being arrested in the G1 phase of the cell cycle, a radiation sensitive phase, suggesting that SP-1-303 may have a synergistic effect with radiation on cell killing. Taken together, SP-1-303 had the largest impact on ER positive breast cancer over TNBC. These data imply that an increased cell death is occurring in ER positive breast cancers from these dual-action molecules through HDAC inhibition and increased ATM activation, suggesting that SP-1-303 alone or its combination with radiotherapy may improve clinical efficacy. Citation Format: Nicole Nicholas, Alfredo Velena, Scott Grindrod, Mira Jung. Therapeutic potential of dual-function small molecules for breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3215. doi:10.1158/1538-7445.AM2017-3215

Abstract 3317: Autophagy protects ovarian cancer cells from olaparib-induced toxicity

Abstract Ovarian cancer (OC) is the most lethal gynecologic malignancy. Persistence of dormant, drug resistant cancer cells is one of the major factors that contribute to poor outcomes. The Poly (ADP) ribose polymerase (PARP) inhibitor, olaparib, has shown promising anti-cancer activity and has been approved by the FDA for the treatment of ovarian cancer with BRCA1/2 mutations. Olaparib targets DNA repair mechanisms within cancer cells and induces apoptosis. Both preclinical and clinical data indicate that efficacy of olaparib can be decreased by acquired resistance. One mechanism of resistance involves autophagy. Autophagy can degrade organelles and long-lived proteins to provide energy for cancer cells under nutrient poor conditions or in the presence of stress. The energy provided from autophagy is used to fuel the DNA repair process and metabolic needs in cancer cells. Autophagy can protect cancer cells from chemotherapy or can enhance the response to certain drugs. In this study, we have asked whether autophagy protects OC cells against the cytotoxic effects of olaparib or augments damage. We first determined PARP activity using a modified PARP activity assay in different OC cell lines. Olaparib-induced autophagy was determined by punctate localization of GFP-LC3, conversion of LC3I to LC3II on protein blots and electron microscopy. To test whether autophagy contributes to the resistance of OC cells to olaparib, we determined the impact of autophagy inhibition on the sensitivity of OC cells to olaparib by either using the pharmacologic inhibitors chloroquine (CQ), LYS05 or short interfering RNA (siRNA) against ATG7. Upon investigation of a potential mechanism of olaparib-induced autophagy we evaluated the production of reactive oxygen species (ROS) and the expression of JNK, Ataxia-telangiectasia mutated (ATM), mTOR and p70S6K. Inhibition of PARP by olaparib treatment, decreased PARP activity in a dose- dependent manner, leading to DNA damage judged by phosphorylation of γ-H2AX. Olaparib treatment decreased cell growth, caused cell cycle arrest and significantly enhanced apoptosis in 5 of 5 OC cell lines. Olaparib induced autophagy in 8 of 8 OC cell lines. Both pharmacologic and genetic inhibition of autophagy increased OC cells sensitivity to olaparib and induced apoptosis in 5 of 6 OC cell lines. Furthermore, flow cytometry and western blot analysis demonstrated that olaparib treatment increased ROS production and increased the phosphorylation of JNK and ATM while decreasing the phosphorylation of mTOR and p70S6K. Taken together, our data described autophagy as a potential mechanism of olaparib resistance in OC that may depend upon the activation of ATM and JNK by ROS downregulating pmTOR and p70S6K. Combination of olaparib with CQ, LYS05 or other autophagy inhibitor may provide a novel strategy to increase the efficacy of olaparib in OC. Current studies are underway to test our hypothesis in vivo. Citation Format: Janice M. Santiago-O'Farrill, Safia Essien, Mary Figueroa, Lan Pang, Ravi Amaravadi, Zhen Lu, Robert C. Bast. Autophagy protects ovarian cancer cells from olaparib-induced toxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3317. doi:10.1158/1538-7445.AM2017-3317

Retraction Note to: The Crucial Role of Cyclin-Dependent Kinase-5-Ataxia-Telangiectasia Mutated Axis in ICH-Induced Neuronal Injury of Rat Model.

Cyclin-dependent kinase 5 (CDK5) and ataxia-telangiectasia mutated (ATM) are involved in normal human neurodevelopment and serves as a switch between neuronal survival and death. However, the molecular mechanisms underlying CDK5-ATM-induced neuronal injury caused by intracerebral hemorrhage (ICH) remain unclear. In this work, we used rat ICH models and thrombin-induced cell models to investigate the potential role of CDK5-ATM signals. Our findings revealed that CDK5 protein levels and kinase activities (p-histone H1 expression) were enforced in hematoma-surrounding neuron tissues following ICH. Besides, the expression of p25, p-ATM, and active caspase-3 protein was also upregulated after ICH. According to in vitro assays, the expression of CDK5, p-ATM, and active caspase-3 was all upregulated in cell viability-decreasing ICH cell models. However, blocking of either CDK5 or ATM suppressed the phosphorylation of ATM and the expression of active caspase-3, and attenuated the inhibition of neuronal survival. When p35/p25 was silenced, CDK5-ATM pathway was further inhibited, and cell viability was obviously ameliorated. In conclusion, this work suggested that ATM could be phosphorylated by CDK5 to induce the active caspase-3 and neuronal injury when intracerebral hemorrhage or ischemia occurred. Thus, the CDK5-AMT signal pathway has an important role in ICH process and may be a therapeutic target to prevent brain injury.

Abstract B09: DNA damage inducible phosphorylation of ATR at threonine 1989 and quantitative analysis of the effect of ATR inhibition on DNA damage signaling using PTMScan

Abstract DNA repair pathways and checkpoint control are crucial in the maintenance of genome integrity. Agents that cause DNA damage, and agents that perturb DNA repair pathways, have been used successfully in the treatment of human cancer. The PI3K-like protein kinases ATR (ATM and Rad3-related) and ATM (ataxia telangiectasia mutated) are critical regulators of the DNA damage response (DDR), signaling to downstream effector molecules that in turn regulate cellular responses such as DNA repair, cell cycle arrest, and cell death. ATM is activated in response to DNA damage in part via autophosphorylation at serine 1981. ATR was long thought to exist in a constitutively active state in cells, with DNA damage-induced signaling occurring via recruitment of ATR to single stranded DNA and sites of replication stress. Recent work, however, has shown autophosphorylation of ATR at threonine 1989, a homologous site to ATM Ser1981. Like ATM Ser1981, phosphorylation of ATR Thr1989 occurs in response to DNA damage, indicating that phosphorylation at this site is important in ATR-mediated signaling. We have generated highly specific antibodies to both ATM Ser1981 and ATR Thr1989. Using these antibodies, we have identified conditions under which these sites are phosphorylated in cultured human cell lines. While phosphorylation of ATM was induced in response to a wide variety of DNA damage-inducing agents, phosphorylation of ATR was induced under a small subset of these conditions, most robustly with the alkylating agent mitomycin C, the ribonucleotide reductase inhibitor hydroxyurea and the topoisomerase II inhibitor etoposide. All of these agents inhibit DNA synthesis, albeit through different mechanisms. We then identified changes downstream of ATM and ATR under conditions of ATR Thr1989 phosphorylation. Checkpoint kinases Chk1 and Chk2 are phosphorylated and activated by ATR and ATM, respectively, though there is crosstalk between the two signaling pathways. Phosphorylation of ATR Thr1989, as well as phosphorylation of the ATR substrate Chk1 Ser317, but not phosphorylation of ATM Ser1981 or Chk2 Thr68, was abrogated by treatment with the ATR inhibitor VE-821. Using western blotting, we also detected a DNA damage-induced electrophoretic mobility shift of CtIP (CtBP-interacting protein), a protein involved in the generation of single stranded DNA. The change in CtIP was partially abrogated by the ATR inhibitor, indicating that posttranslational modification of CtIP may be related to ATR Thr1989 phosphorylation. Using cell lines with and without DNA damage, and in the presence or absence of kinase inhibitor, we performed PTMScan proteomic analysis to identify and quantify changes in phosphorylation levels of proteins and sites containing a consensus ATM/ATR substrate motif (S*Q/T*Q). Changes in phosphopeptide abundance between samples monitored by PTMScan provides insight into signaling components regulated by the ATM and ATR DNA damage response. Citation Format: Hayley J. Roberts, Matthew P. Stokes, Xiaoying Jia, Kimberly A. Lee, Susan M. Keezer. DNA damage inducible phosphorylation of ATR at threonine 1989 and quantitative analysis of the effect of ATR inhibition on DNA damage signaling using PTMScan [abstract]. In: Proceedings of the AACR Special Conference on DNA Repair: Tumor Development and Therapeutic Response; 2016 Nov 2-5; Montreal, QC, Canada. Philadelphia (PA): AACR; Mol Cancer Res 2017;15(4_Suppl):Abstract nr B09.

The DNA damage response promotes polyomavirus JC infection by nucleus to cytoplasm NF- kappaB activation

BackgroundInfection of glial cells by human neurotropic polyomavirus JC (JCV), the causative agent of the CNS demyelinating disease progressive multifocal leukoencephalopathy (PML), rapidly inflicts damage to cellular DNA. This activates DNA damage response (DDR) signaling including induction of expression of DNA repair factor Rad51. We previously reported that Rad51 co-operates with the transcription factor NF-κB p65 to activate JCV early transcription. Thus Rad51 induction by JCV infection may provide positive feedback for viral activation early in JCV infection. DDR is also known to stimulate NF-κB activity, a phenomenon known as nucleus to cytoplasm or “inside-out” NF-κB signaling, which is initiated by Ataxia telangiectasia mutated (ATM) protein, a serine/threonine kinase recruited and activated by DNA double-strand breaks. Downstream of ATM, there occurs a series of post-translational modifications of NF-κB essential modulator (NEMO), the γ regulatory subunit of inhibitor of NF-κB (IκB) kinase (IKK), resulting in NF-κB activation.MethodsWe analyzed the effects of downstream pathways in the DDR by phosphospecific Western blots and analysis of the subcellular distribution of NEMO by cell fractionation and immunocytochemistry. The role of DDR in JCV infection was analyzed using a small molecule inhibitor of ATM (KU-55933). NEMO sumoylation was investigated by Western and association of ATM and NEMO by immunoprecipitation/Western blots.ResultsWe show that JCV infection caused phosphorylation and activation of ATM while KU-55933 inhibited JCV replication. JCV infection caused a redistribution of NEMO from cytoplasm to nucleus. Co-expression of JCV large T-antigen and FLAG-tagged NEMO showed the occurrence of sumoylation of NEMO, while co-expression of ATM and FLAG-NEMO demonstrated physical association between ATM and NEMO.ConclusionsWe propose a model where JCV infection induces both overexpression of Rad51 protein and activation of the nucleus to cytoplasm NF-κB signaling pathway, which then act together to enhance JCV gene expression.

MiR-30a radiosensitizes non-small cell lung cancer by targeting ATF1 that is involved in the phosphorylation of ATM.

Increasing number of studies report that microRNAs play important roles in radiosensitization. miR-30a has been proved to perform many functions in the development and treatment of cancer, and it is downregulated in non-small cell lung cancer (NSCLC) tissues and cells. This study was conducted to understand if miR-30a plays a role in the radiosensitivity of NSCLC cells. Radiosensitivity was examed by colony survival assay and tumor volume changing in vitro and in vivo, respectively. Bioinformatic analysis and luciferase reporter assays were used to distinguish the candidate target of miR-30a. qRT-PCR and western blotting were carried out to detect the relative expression of mRNAs and proteins. Cell cycle and cell apoptosis were determined by flow cytometry. Our results illustrated miR-30a could increase the radiosensitivity of NSCLC, especially in A549 cell line. In vivo experiment also showed the potential radiosensitizing possibility of miR-30a. Further exploration validated that miR-30a was directly targeting activating transcription factor 1 (ATF1). In studying the ataxia-telangiectasia mutated (ATM) associated effects on cell radiosensitivity, we found that miR-30a could reduce radiation induced G2/M cell cycle arrest and may also affect radiation induced apoptosis. Together, our results demonstrated that miR-30a may modulate the radiosensitivity of NSCLC through reducing the function of ATF1 in phosphorylation of ATM and have potential therapeutic value.

Targeting DNA Damage Response in Prostate Cancer by Inhibiting Androgen Receptor-CDC6-ATR-Chk1 Signaling

Cell division cycle 6 (CDC6), an androgen receptor (AR) target gene, is implicated in regulating DNA replication and checkpoint mechanisms. CDC6 expression is increased during prostate cancer (PCa) progression and positively correlates with AR in PCa tissues. ARor CDC6 knockdown, together with AZD7762, aChk1/2 inhibitor, results in decreased TopBP1-ATR-Chk1 signaling and markedly increased ataxia-telangiectasia-mutated (ATM) phosphorylation, a biomarker of DNA damage, and synergistically increases treatment efficacy. Combination treatment with the AR signaling inhibitor enzalutamide (ENZ) and the Chk1/2 inhibitor AZD7762 demonstrates synergy with regard toinhibition of AR-CDC6-ATR-Chk1 signaling, ATM phosphorylation induction, andapoptosis in VCaP (mutant p53) and LNCaP-C4-2b (wild-type p53) cells. CDC6 overexpression significantly reduced ENZ- and AZD7762-induced apoptosis. Additive or synergistic therapeutic activities are demonstrated in AR-positive animal xenograft models. These findings have important clinical implications, since they introduce a therapeutic strategy for AR-positive, metastatic, castration-resistant PCa, regardless of p53 status, through targeting AR-CDC6-ATR-Chk1 signaling.

Study of ATM Phosphorylation by Cdk5 in Neuronal Cells.

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. We previously showed that Cdk5 (cyclin-dependent kinase 5) is activated by DNA damage and 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 pathway plays a crucial role in DNA damage-induced neuronal injury. This chapter describes protocols used in analyzing ATM phosphorylation by Cdk5 in CGNs (cerebellar granule neurons) and its effects on neuronal survival.

P2.01-090 Platin Induced Phosphorylation of ATM and ATM-Deficiency as a Predictive Marker of Platin Sensitivity in Non-Small Cell Lung Cancer

Platinum-based antineoplastic therapies (platins) are a first line treatment for non-small cell lung cancer (NSCLC) that generate DNA adducts leading to the formation of both single and double stranded DNA breaks. Effective DNA damage response pathways contribute to cell survival and resistance to these agents. Ataxia telangiectasia mutated (ATM) is an important mediator of the DNA damage response involved in the activation of key components of DNA repair, cell cycle arrest, and apoptosis. Our lab has demonstrated that cell lines lacking ATM show increased sensitivity to platins. We hypothesize that platin exposure will activate ATM and that cells deficient in ATM will be innately sensitivity to platins due to an impaired DNA damage response. Here we assess the molecular action of ATM in response to platins to determine if ATM-deficiency is predictive of platin sensitivity. ATM status was determined in five NSCLC cell lines using western blotting and rt-qPCR. Cell lines were treated with varying concentrations cisplatin, carboplatin and oxaliplatin for 18 hours and assessed for ATM phosphorylation by western blot. Additionally, downstream targets of ATM (KAP-1, p53, and g-H2AX) were investigated to determine ATM pathway activation. Finally, transient and stable ATM knockdowns were generated using siATM and shATM. These cells were then tested for platin sensitivity by trypan blue viability or clonogenic assays. NSCLC cell lines NCI-H226, NCI-H460, and NCI-H522 were found to be ATM-proficient whereas cell lines NCI-H23 and NCI-H1373 were found to be ATM-deficient. ATM-proficient cell lines demonstrated an increased level of phosphorylated-ATM in response to platins. In addition, KAP-1, a downstream target of ATM showed increased phosphorylation in response to these treatments when compared to non-treated controls. In contrast, ATM-deficient cell lines showed no increased levels of phosphorylated ATM or KAP-1 in response to platins. Preliminary analysis of siATM transient knockdowns in NCI-H226 shows an increased sensitivity to cisplatin. It is clear that platin exposure activated an ATM mediated signalling response and that cells lacking ATM showed deficiencies in the phosphorylation of key downstream targets of this pathway. Cells deficient in ATM may therefore be more susceptible to platin therapy due to an impaired DNA damage response. This data suggests that individuals with low or non-functioning ATM may be candidates for precision low does therapies that exploit this deficiency.