DNA Damage Response Signaling Pathways Research Articles

How telomeres solve the chromosome end‐protection problem

Chromosome ends can activate the DNA damage response (DDR) signaling pathways and become substrates for Double‐strand Break (DSB) repair. Telomeres solve this end‐protection problem by repressing all forms of DDR signaling and DSB repair. The telomeric DNA, maintained by telomerase, binds a six‐subunit protein complex, termed shelterin, that protects chromosome ends. Shelterin binds to the double‐stranded (ds) telomeric DNA through two subunits, TRF1 and TRF2. These proteins recruit a single‐stranded (ss) telomeric DNA binding factor, POT1, which binds to the ss telomeric repeats present at all chromosome ends. POT1 is linked to TRF1 and TRF2 via interactions involving TPP1 and TIN2. A sixth component, Rap1, interacts with TRF2. Conditional knockout experiments in mouse embryonic fibroblasts (MEFs) have revealed the mechanism by which this simple protein complex prevents activation of the ATM and ATR DNA damage signaling pathways, represses 5′ end resection, and prevents non‐homologous end joining (NHEJ) and homology directed repair (HDR) at telomeres. Shelterin is compartmentalized such that TRF2 represses ATM signaling and NHEJ, whereas ATR signaling is repressed by POT1. The mechanism by which TRF2 represses ATM signaling and NHEJ involves the remodeling of telomeres into the t‐loop structure, which essentially hides the chromosome end. POT1 represses ATR signaling by preventing the ssDNA sensor in the ATR pathway, RPA, from binding to telomeres. Progress on the mechanistic aspects of shelterin mediated chromosome end protection will be presented.Support or Funding InformationDr. de Lange is funded by awards from the NIH, American Cancer Society, the Breast Cancer Research Foundation, and the STARR Cancer ConsortiumThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Targeting the MYCN-PARP-DNA Damage Response Pathway in Neuroendocrine Prostate Cancer.

Purpose: We investigated MYCN-regulated molecular pathways in castration-resistant prostate cancer (CRPC) classified by morphologic criteria as adenocarcinoma or neuroendocrine to extend the molecular phenotype, establish driver pathways, and identify novel approaches to combination therapy for neuroendocrine prostate cancer (NEPC).Experimental Design and Results: Using comparative bioinformatics analyses of CRPC-Adeno and CRPC-Neuro RNA sequence data from public data sets and a panel of 28 PDX models, we identified a MYCN-PARP-DNA damage response (DDR) pathway that is enriched in CRPC with neuroendocrine differentiation (NED) and CRPC-Neuro. ChIP-PCR assay revealed that N-MYC transcriptionally activates PARP1, PARP2, BRCA1, RMI2, and TOPBP1 through binding to the promoters of these genes. MYCN or PARP1 gene knockdown significantly reduced the expression of MYCN-PARP-DDR pathway genes and NED markers, and inhibition with MYCNsi and/or PARPsi, BRCA1si, or RMI2si significantly suppressed malignant activities, including cell viability, colony formation, and cell migration, in C4-2b4 and NCI-H660 cells. Targeting this pathway with AURKA inhibitor PHA739358 and PARP inhibitor olaparib generated therapeutic effects similar to those of gene knockdown in vitro and significantly suppressed tumor growth in both C4-2b4 and MDACC PDX144-13C subcutaneous models in vivoConclusions: Our results identify a novel MYCN-PARP-DDR pathway that is driven by N-MYC in a subset of CRPC-Adeno and in NEPC. Targeting this pathway using in vitro and in vivo CRPC-Adeno and CRPC-Neuro models demonstrated a novel therapeutic strategy for NEPC. Further investigation of N-MYC-regulated DDR gene targets and the biological and clinical significance of MYCN-PARP-DDR signaling will more fully elucidate the importance of the MYCN-PARP-DDR signaling pathway in the development and maintenance of NEPC. Clin Cancer Res; 24(3); 696-707. ©2017 AACR.

Cutaneous exposure to lewisite causes acute kidney injury by invoking DNA damage and autophagic response.

Lewisite (2-chlorovinyldichloroarsine) is an organic arsenical chemical warfare agent that was developed and weaponized during World Wars I/II. Stockpiles of lewisite still exist in many parts of the world and pose potential environmental and human health threat. Exposure to lewisite and similar chemicals causes intense cutaneous inflammatory response. However, morbidity and mortality in the exposed population is not only the result of cutaneous damage but is also a result of systemic injury. Here, we provide data delineating the pathogenesis of acute kidney injury (AKI) following cutaneous exposure to lewisite and its analog phenylarsine oxide (PAO) in a murine model. Both agents caused renal tubular injury, characterized by loss of brush border in proximal tubules and tubular cell apoptosis accompanied by increases in serum creatinine, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1. Interestingly, lewisite exposure enhanced production of reactive oxygen species (ROS) in the kidney and resulted in the activation of autophagic and DNA damage response (DDR) signaling pathways with increased expression of beclin-1, autophagy-related gene 7, and LC-3A/B-II and increased phosphorylation of γ-H2A.X and checkpoint kinase 1/2, respectively. Terminal deoxyribonucleotide-transferase-mediated dUTP nick-end labeling-positive cells were detected in renal tubules along with enhanced proapoptotic BAX/cleaved caspase-3 and reduced antiapoptotic BCL2. Scavenging ROS by cutaneous postexposure application of the antioxidant N-acetyl-l-cysteine reduced lewisite-induced autophagy and DNA damage. In summary, we provide evidence that topical exposure to lewisite causes AKI. The molecular mechanism underlying these changes involves ROS-dependent activation of autophagy and DDR pathway associated with the induction of apoptosis.

Epstein-Barr Virus Hijacks DNA Damage Response Transducers to Orchestrate Its Life Cycle.

The Epstein–Barr virus (EBV) is a ubiquitous virus that infects most of the human population. EBV infection is associated with multiple human cancers, including Burkitt’s lymphoma, Hodgkin’s lymphoma, a subset of gastric carcinomas, and almost all undifferentiated non-keratinizing nasopharyngeal carcinoma. Intensive research has shown that EBV triggers a DNA damage response (DDR) during primary infection and lytic reactivation. The EBV-encoded viral proteins have been implicated in deregulating the DDR signaling pathways. The consequences of DDR inactivation lead to genomic instability and promote cellular transformation. This review summarizes the current understanding of the relationship between EBV infection and the DDR transducers, including ATM (ataxia telangiectasia mutated), ATR (ATM and Rad3-related), and DNA-PK (DNA-dependent protein kinase), and discusses how EBV manipulates the DDR signaling pathways to complete the replication process of viral DNA during lytic reactivation.

Integrated genome analysis of uterine leiomyosarcoma to identify novel driver genes and targetable pathways.

Uterine leiomyosarcomas (uLMS) are rare, aggressive malignancies for which limited treatment options are available. To gain novel molecular insights into uLMS and identify potential novel therapeutic targets, we characterized 84 uLMS samples for genome-wide somatic copy number alterations, mutations, gene fusions and gene expression and performed a data integration analysis. We found that alterations affecting TP53, RB1, PTEN, MED12, YWHAE and VIPR2 were present in the majority of uLMS. Pathway analyses additionally revealed that the PI3K/AKT/mTOR, estrogen-mediated S-phase entry and DNA damage response signaling pathways, for which inhibitors have already been developed and approved, frequently harbored genetic changes. Furthermore, a significant proportion of uLMS was characterized by amplifications and overexpression of known oncogenes (CCNE1, TDO2), as well as deletions and reduced expression of tumor suppressor genes (PTEN, PRDM16). Overall, it emerged that the most frequently affected gene in our uLMS samples was VIPR2 (96%). Interestingly, VIPR2 deletion also correlated with unfavorable survival in uLMS patients (multivariate analysis; HR = 4.5, CI = 1.4-14.3, p = 1.2E-02), while VIPR2 protein expression was reduced in uLMS vs. normal myometrium. Moreover, stimulation of VIPR2 with its natural agonist VIP decreased SK-UT-1 uLMS cell proliferation in a dose-dependent manner. These data suggest that VIPR2, which is a negative regulator of smooth muscle cell proliferation, might be a novel tumor suppressor gene in uLMS. Our work further highlights the importance of integrative molecular analyses, through which we were able to uncover the genes and pathways most frequently affected by somatic alterations in uLMS.

Noncoding RNAs in DNA Damage Response: Opportunities for Cancer Therapeutics.

DNA repair machinery preserves genomic integrity, which is frequently challenged through endogenous and exogenous toxic insults, and any sort of repair machinery malfunctioning ultimately manifests in the form of several types of terrible human diseases such as cancers (Hoeijmakers, Nature 411(6835): 366-374, 2001). Noncoding RNAs (ncRNAs) are crucial players of DNA repair machinery in a cell and play a vital role in maintaining genomic stability, which is essential for its survival and normal functioning thus preventing tumorigenesis. To preserve the integrity of the genome, cells initiate a specific cellular response, recognized as DNA damage response (DDR), which includes several distinct DNA repair pathways. These repair pathways permit normal cells to repair DNA damage or induce apoptosis and cell cycle arrest in case the damage is irreparable. Disruption of these pathways in cancer leads to an increase in genomic instability and mutagenesis. Recently, emerging evidence suggests that ncRNAs play a critical role in the regulation of DDR. There is an extensive crosstalk between ncRNAs and the canonical DDR signaling pathway. DDR-induced expression of ncRNAs can provide a regulatory mechanism to accurately control the expression of DNA damage responsive genes in a spatio-temporal manner. DNA damage alters expression of a variety of ncRNAs at multiple levels including transcriptional regulation, post-transcriptional regulation, and RNA degradation and vice versa, wherein ncRNAs can directly regulate cellular processes involved in DDR by altering expression of their targeting genes, with a particular emphasis on microRNAs (miRNAs) and long noncoding RNAs (lncRNAs). Relationship between the defects in the DDR and deregulation of related ncRNAs in human cancers is one of the established, which is growing stronger with the advent of high-throughput sequencing techniques such as next-generation sequencing. Understanding of the mechanisms that explain the association between ncRNAs and DDR/DNA repair pathways will definitely increase our understanding on human tumor biology and on different responses to diverse drugs. Different ncRNAs interact with distinct DDR components and are promising targets for improving the effects to overcome the resistance to conventional chemotherapeutic agents. In this chapter, we will focus the role of ncRNAs in the DNA damage, repair, and cancer.

Analysis of Genomes and Transcriptomes of Hepatocellular Carcinomas Identifies Mutations and Gene Expression Changes in the Transforming Growth Factor-β Pathway

Development of hepatocellular carcinoma (HCC) is associated with alterations in the transforming growth factor-beta (TGF-β) signaling pathway, which regulates liver inflammation and can have tumor suppressor or promoter activities. Little is known about the roles of specific members of this pathway at specific of HCC development. We took an integrated approach to identify and validate the effects of changes in this pathway in HCC and identify therapeutic targets. We performed transcriptome analyses for a total of 488 HCCs that include data from The Cancer Genome Atlas. We also screened 301 HCCs reported in the Catalogue of Somatic Mutations in Cancer and 202 from Cancer Genome Atlas for mutations in genome sequences. We expressed mutant forms of spectrin beta, non-erythrocytic 1 (SPTBN1) in HepG2, SNU398, and SNU475 cells and measured phosphorylation, nuclear translocation, and transcriptional activity of SMAD family member 3 (SMAD3). We found somatic mutations in at least 1 gene whose product is a member of TGF-β signaling pathway in 38% of HCC samples. SPTBN1 was mutated in the largest proportion of samples (12 of 202, 6%). Unsupervised clustering of transcriptome data identified a group of HCCs with activation of the TGF-β signaling pathway (increased transcription of genes in the pathway) and a group of HCCs with inactivation of TGF-β signaling (reduced expression of genes in this pathway). Patients with tumors with inactivation of TGF-β signaling had shorter survival times than patients with tumors with activation of TGF-β signaling (P= .0129). Patterns of TGF-β signaling correlated with activation of the DNA damage response and sirtuin signaling pathways. HepG2, SNU398, and SNU475 cells that expressed the D1089Y mutant or with knockdown of SPTBN1 had increased sensitivity to DNA crosslinking agents and reduced survival compared with cells that expressed normal SPTBN1 (controls). In genome and transcriptome analyses of HCC samples, we found mutations in genes in the TGF-β signaling pathway in almost 40% of samples. These correlated with changes in expression of genes in the pathways; up-regulation of genes in this pathway would contribute to inflammation and fibrosis, whereas down-regulation would indicate loss of TGF-β tumor suppressor activity. Our findings indicate that therapeutic agents for HCCs can be effective, based on genetic features of the TGF-β pathway; agents that block TGF-β should be used only in patients with specific types of HCCs.

Abstract 1418: G9a methyltransferase plays a role in ATM-dependent DNA damage response

Abstract Induction of DNA damage leads to a choreographed set of local chromatin changes that ensures an efficient recruitment of DNA repair factors. One principal regulator of the DNA Damage Response (DDR) signaling pathway is ATM kinase, which phosphorylates key factors at early stages of the response. G9a protein methyltransferase has been identified as a novel substrate for ATM. We have found that G9a localizes to sites of DNA damage in an ATM-dependent fashion and that inhibition of its activity affects recruitment of multiple DNA repair factors. Moreover G9a catalytic inhibition using UNC0638 leads to hyperactivation of ATM induced by DNA breaks. This was associated with an increased ATM-dependent “spreading” of pH2AX and MDC1 signals seen at regions of localized DNA breaks induced by UV-laser scissors. These data suggest that G9a activity is required for regulating the extent of ATM activation as well as for efficient recruitment of downstream DNA repair factors. Biochemical data will be presented that explore potential mechanisms for these findings. Overall our data suggests that G9a plays a critical role in the regulation of ATM-dependent signaling during the DNA damage response, and raises the possibility of using G9a inhibitors to target cancers with certain DNA repair defects. Citation Format: Lizahira Rodriguez-Colon, Vasudeva Ginjala, Atul Kulkarni, Safia Ansari, Shridar Ganesan. G9a methyltransferase plays a role in ATM-dependent DNA damage response [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 1418. doi:10.1158/1538-7445.AM2017-1418

Immature Lymphocytes Inhibit Rag1 and Rag2 Transcription and V(D)J Recombination in Response to DNA Double-Strand Breaks.

Mammalian cells have evolved a common DNA damage response (DDR) that sustains cellular function, maintains genomic integrity, and suppresses malignant transformation. In pre-B cells, DNA double-strand breaks (DSBs) induced at Igκ loci by the Rag1/Rag2 (RAG) endonuclease engage this DDR to modulate transcription of genes that regulate lymphocyte-specific processes. We previously reported that RAG DSBs induced at one Igκ allele signal through the ataxia telangiectasia mutated (ATM) kinase to feedback-inhibit RAG expression and RAG cleavage of the other Igκ allele. In this article, we show that DSBs induced by ionizing radiation, etoposide, or bleomycin suppress Rag1 and Rag2 mRNA levels in primary pre-B cells, pro-B cells, and pro-T cells, indicating that inhibition of Rag1 and Rag2 expression is a prevalent DSB response among immature lymphocytes. DSBs induced in pre-B cells signal rapid transcriptional repression of Rag1 and Rag2, causing downregulation of both Rag1 and Rag2 mRNA, but only Rag1 protein. This transcriptional inhibition requires the ATM kinase and the NF-κB essential modulator protein, implicating a role for ATM-mediated activation of canonical NF-κB transcription factors. Finally, we demonstrate that DSBs induced in pre-B cells by etoposide or bleomycin inhibit recombination of Igκ loci and a chromosomally integrated substrate. Our data indicate that immature lymphocytes exploit a common DDR signaling pathway to limit DSBs at multiple genomic locations within developmental stages wherein monoallelic Ag receptor locus recombination is enforced. We discuss the implications of our findings for mechanisms that orchestrate the differentiation of monospecific lymphocytes while suppressing oncogenic Ag receptor locus translocations.

Endosulfan induces cell dysfunction through cycle arrest resulting from DNA damage and DNA damage response signaling pathways

Our previous study showed that endosulfan increases the risk of cardiovascular disease. To identify toxic mechanism of endosulfan, we conducted an animal study for which 32 male Wistar rats were randomly and equally divided into four groups: Control group (corn oil only) and three treatment groups (1, 5 and 10mgkg−1·d−1). The results showed that exposure to endosulfan resulted in injury of cardiac tissue with impaired mitochondria integrity and elevated 8-OHdG expression in myocardial cells. Moreover, endosulfan increased the expressions of Fas, FasL, Caspase-8, Cleaved Caspase-8, Caspase-3 and Cleaved Caspase-3 in cardiac tissue. In vitro, human umbilical vein endothelial cells (HUVECs) were treated with different concentrations of endosulfan (1, 6 and 12μgmL−1) for 24h. An inhibitor for Ataxia Telangiectasia Mutated Protein (ATM) (Ku-55933, 10μM) was added in 12μgmL−1 group for 2h before exposure to endosulfan. Results showed that endosulfan induced DNA damage and activated DNA damage response signaling pathway (ATM/Chk2 and ATR/Chk1) and consequent cell cycle checkpoint. Furthermore, endosulfan promoted the cell apoptosis through death receptor pathway resulting from oxidative stress. The results provide a new insight for mechanism of endosulfan-induced cardiovascular toxicity which will be helpful in future prevention of cardiovascular diseases induced by endosulfan.

Synergistic effects of a novel lipid-soluble extract from Pinellia pedatisecta Schott and cisplatin on human cervical carcinoma cell lines through the regulation of DNA damage response signaling pathway.

Herbal medicines have been recognized as an attractive approach for cancer therapy with minimal side effects. The present study investigated the type of interaction between a novel lipid-soluble extract from Pinellia pedatisecta Schott (PE) and cisplatin (CDDP) on human cervical cancer SiHa and CaSki cell lines in vitro. The mechanism of this combination was studied using cell proliferation, invasion and apoptosis assays, and by analyzing cell cycle distribution and protein expression, with a focus on DNA damage response (DDR) activation. Equipotent combinations of PE and CDDP were determined by isobologram analysis, in order to evaluate potential synergy. The combination index for SiHa cells was 0.43, and the index for CaSki cells was 0.68, indicating synergy. Treatment with PE and CDDP combined resulted in a significantly greater inhibition of invasion in the two cells, compared with either drug alone (SiHa, P<0.01; CaSki, P<0.001). This co-treatment induced significantly more apoptosis in the two cell lines, and arrested cells at the G0/G1 phase and G2/M phase in SiHa and CaSki, respectively, with a significant decrease (P<0.01) in S phase cells in the two cell lines. Combined PE and CDDP targeting synergistically enhanced the expression of markers of DDR (phosphorylation of ataxia-telangiectasia mutated, checkpoint kinase (Chk)-1, Chk-2, and γ-H2A histone family member X) in cells. These results suggest that PE and cisplatin act synergistically in cervical cancer cells with high DDR activation. The approach presented in the present study may have important implications for the pharmacological mechanism of Pinellia pedatisecta Schott and cervical cancer therapeutic strategies.

Autophagy in UV Damage Response.

UV radiation exposure from sunlight and artificial tanning beds is the major risk factor for the development of skin cancer and skin photoaging. UV-induced skin damage can trigger a cascade of DNA damage response signaling pathways, including cell cycle arrest, DNA repair and, if damage is irreparable, apoptosis. Compensatory proliferation replaces the apoptotic cells to maintain skin barrier integrity. Disruption of these processes can be exploited to promote carcinogenesis by allowing the survival and proliferation of damaged cells. UV radiation also induces autophagy, a catabolic process that clears unwanted or damaged proteins, lipids and organelles. The mechanisms by which autophagy is activated following UV exposure, and the functions of autophagy in UV response, are only now being clarified. Here, we summarize the current understanding of the mechanisms governing autophagy regulation by UV, the roles of autophagy in regulating cellular response to UV-induced photodamage and the implications of autophagy modulation in the treatment and prevention of photoaging and skin cancer.

DNA damage-induced nuclear factor-kappa B activation and its roles in cancer progression.

DNA damage is a vital challenge to cell homeostasis. Cellular responses to DNA damage (DDR) play essential roles in maintaining genomic stability and survival, whose failure could lead to detrimental consequences such as cancer development and aging. Nuclear factor-kappa B (NF-κB) is a family of transcription factors that plays critical roles in cellular stress response. Along with p53, NF-κB modulates transactivation of a large number of genes which participate in various cellular processes involved in DDR. Here the authors summarize the recent progress in understanding DNA damage response and NF-κB signaling pathways. This study particularly focuses on DNA damage-induced NF-κB signaling cascade and its physiological and pathological significance in B cell development and cancer therapeutic resistance. The authors also discuss promising strategies for selectively targeting this genotoxic NF-κB signaling aiming to antagonize acquired resistance and resensitize refractory cancer cells to cytotoxic treatments.

MOB Co-activators Associate with NDR/LATS Kinases to Function in DNA Damage Response Signaling and Hippo Pathways

MOB Co-activators Associate with NDR/LATS Kinases to Function in DNA Damage Response Signaling and Hippo Pathways

Targeting Ribonucleotide Reductase M1 and M2 in Multiple Myeloma

Ribonucleotide reductase (RR) is an enzyme that catalyzes the conversion of ribonucleotide diphosphate to deoxyribonucleotide diphosphate and is essential for de novo DNA synthesis, DNA repair, and cell growth. RR primarily exists as a heterodimer tetramer composed of regulatory subunit RRM1, and catalytic subunit RRM2. Overexpression or polymorphisms of RR are described non-small cell lung, pancreas, breast, and ovarian cancers. Moreover, RRM1 and RRM2 expression is highly correlated with patient survival in non-small cell lung and pancreas cancers. To date, the biologic significance in multiple myeloma (MM) has not yet been elucidated. In this study, we characterized the role of RRM1 and RRM2 in MM pathogenesis.By examining 3 independent expression data from GEO database, we found that RR (especially RRM1) expression is higher in MM plasma cells than normal plasma cells. We examined RRM1 and RRM2 expression in 6 MM cell lines and 3 MM patients' tumor cells by quantitative real-time PCR and immunoblotting and confirmed that both RRM1 and RRM2 are highly expressed in these cells. We next knocked down both RRM1 and RRM2 in 4 MM cell lines (NCI-H929, MM.1S, RPMI8226, and KMS-11) using siRNA. Knockdown of RRM1 and RRM2 triggered significant growth inhibition, associated with apoptotic cells death evidenced by AnnexinV/PI staining, in NCI-H929 and MM.1S, but not RPMI8226 or KMS-11 cells. We next examined molecular mechanisms whereby RRM1 downregulation triggers MM cell death. Gene expression profiling showed that p53 regulated genes were overexpressed after RRM1 knockdown. We therefore further examined DNA damage response (phosphorylated-ATM, -ATR, -Chk1, and -Chk2, and gamma-Histone H2A.X) and p53 (phosphorylated-p53, p21, Noxa, Puma, Bax) signaling pathways and found that these pathways were activated in NCI-H929 and MM.1S (both p53 wild-type), but not in RPMI8226 (p53 mutant) or KMS-11 (p53 null) cells after RRM1 knockdown. To validate the role of RRM1 of in vivo, we subcutaneously injected MM.1S cells transduced with shRNA against RRM1 or shLuc into our mouse xenograft model and observed that tumor growth was significantly reduced in shRRM1-MM.1S cells versus shLuc-MM.1S cells. Clofarabine (CLO), a purine nucleoside analog, which allosterically inhibits both DNA polymerases and RRM1 is used to treat acute leukemia and chronic lymphocytic leukemia and has been studied preclinically in MM (Valdez et. al. Experimental Hematology 2013). We therefore next examined CLO as a potential therapeutic agent in MM. Consistent with RRM1 knockdown, CLO induced growth arrest in p53 wild-type cell lines (NCI-H929, MM.1S, and MOLP-8), but not in p53 mutant (RPMI8226, OPM2, U266) or null (KMS-11) cells. Moreover, CLO treatment combined with DNA damaging agents (Melphalan, Doxorubicin) triggered synergetic cell death in p53 wild-type MM cells.Our results therefore demonstrate that RR, especially RRM1, is a novel therapeutic target in patients with wild-type p53 MM, and provide the basis for clinical evaluation of CLO, alone or in combination with DNA damaging agents, to improve patient outcome. DisclosuresHideshima:Acetylon: Consultancy; C4 Therapeutics: Equity Ownership. Anderson:Celgene: Membership on an entity's Board of Directors or advisory committees; Oncoprep: Equity Ownership; Gilead: Membership on an entity's Board of Directors or advisory committees; Oncoprep: Equity Ownership; Gilead: Membership on an entity's Board of Directors or advisory committees; Acetylon: Equity Ownership; Celgene: Membership on an entity's Board of Directors or advisory committees; Acetylon: Equity Ownership; Millennuim: Membership on an entity's Board of Directors or advisory committees; Millennuim: Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Equity Ownership; C4 Therapeutics: Equity Ownership; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees.

Abstract 1815: ATM inhibition potentiates death of androgen receptor-inactivated prostate cancer cells with telomere dysfunction

Abstract Prostate cancer is the most commonly diagnosed non-skin cancer, and second leading cause of cancer deaths, in American men. The androgen receptor (AR) plays a critical role in the survival of prostate cancer (PCa) cells. Therefore, treatments that inactivate AR, either by decreasing the androgen level or by inhibiting AR directly, are used to treat advanced PCa. However, these treatments are not curative, and disease progression generates castration-resistant prostate cancer (CRPC). Our studies point to a novel role of AR in telomere stability that, in our opinion, can be exploited to enhance the effectiveness of AR-targeted therapies for CRPC. Telomere stability is essential for cell proliferation and survival. We previously reported that AR plays a role in maintaining telomere stability in prostate cancer cells. Since telomere dysfunction activates the DNA damage response (DDR) signaling pathway which can activate cell cycle checkpoints, repair damaged DNA, and promote cell survival, we tested a hypothesis that AR-inactivated telomere dysfunction activates a DDR signaling pathway protein, called ATM (ataxia telangiectasia mutated) kinase, and ATM inhibitor potentiates cell death by averting telomeric DNA repair in AR-inactivated PCa cells. ATM pathway was assessed by the phosphorylation of ATM and its downstream target Chk2 through Western blotting, inhibition of telomere DNA repair was evaluated by counting RPA (DNA replication protein A) foci at damaged telomeres, and the cell viability was determined by PARP cleavage and colony formation assays. We observed that telomere dysfunction by AR-antagonists (Casodex or MDV3100) or AR-siRNA was associated with a dramatic increase in phosphorylation of ATM and Chk2 and the presence of phosphorylated ATM at telomeres, indicating the activation of DNA damage response signaling at telomeres. Moreover, Casodex washout led to the reversal of telomere dysfunction, indicating repair of damaged telomeres. ATM inhibitor blocked ATM phosphorylation and induced PARP cleavage, suggesting that ATM inhibitors induce apoptosis in AR-inactivated cells by blocking the repair of damaged DNA at telomere. This was further corroborated by a conspicuous localization of RPA at damaged telomeres; presence of RPA foci is indicative of unrepaired stretch of single-stranded DNA at telomeres. Finally, colony formation assay revealed a dramatic decrease in the survival of cells co-treated with Casodex and ATM inhibitor as compared with those treated with either Casodex or ATM inhibitor alone. These observations indicate that inhibitors of DDR signaling pathways may offer a unique opportunity to enhance the potency of AR-targeted therapies for the treatment of androgen-sensitive as well as castration- resistant prostate cancer. Citation Format: Sahn-Ho Kim, Vidyavathi Reddy, Min Wu, Evelyn R. Barrack, G. Prem-Veer Reddy. ATM inhibition potentiates death of androgen receptor-inactivated prostate cancer cells with telomere dysfunction. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1815.

Mitotic genes are transcriptionally upregulated in the fibroblast irradiated with very low doses of UV-C.

Ultraviolet (UV) radiation induces a variety of biological effects, including DNA damage response and cell signaling pathways. We performed transcriptome analysis using microarray in human primary cultured fibroblasts irradiated with UV-C (0.5 or 5 J/m2) and harvested at 4 or 12 h following UV exposure. All transcript data were analyzed by comparison with the corresponding results in non-irradiated (control) cells. The number of genes with significantly altered expression (≥2-fold difference relative to the control) is higher in the sample irradiated with high dose of UV, suggesting that gene expression was UV dose-dependent. Pathway analysis on the upregulated genes at 12 h indicates that the expression of some cell cycle-related genes was predominantly induced irrespective of UV-dose. Interestingly, almost all the genes with significant altered expression were cell cycle-related genes designated as ‘Mitotic Genes’, which function in the spindle assembly checkpoint. Therefore, even a low dose of UV could affect the transcriptional profile.

Biological function and regulation of histone and non-histone lysine methylation in response to DNA damage.

DNA damage response (DDR) signaling network is initiated to protect cells from various exogenous and endogenous damage resources. Timely and accurate regulation of DDR proteins is required for distinct DNA damage repair pathways. Post-translational modificationsof histone and non-histone proteins play a vital role in the DDR factor foci formation and signaling pathway. Phosphorylation, ubiquitylation, SUMOylation, neddylation, poly(ADP-ribosyl)ation, acetylation, and methylation are all involved in the spatial-temporal regulation of DDR, among which phosphorylation and ubiquitylation are well studied. Studies in the past decade also revealed extensive roles of lysine methylation in response to DNA damage. Lysine methylation is finely regulated by plenty of lysine methyltransferases, lysinedemethylases, and can be recognized by proteins with chromodomain, plant homeodomain, Tudor domain, malignant brain tumor domain, or proline-tryptophan-tryptophan-proline domain. In this review, we outline the dynamics and regulation of histone lysine methylation at canonical (H3K4, H3K9, H3K27, H3K36, H3K79, and H4K20) and non-canonical sites after DNA damage, and discuss their context-specific functions in DDR protein recruitment or extraction, chromatin environment establishment, and transcriptional regulation. We also present the emerging advances of lysine methylation in non-histone proteins during DDR.

GOLPH3 and oncogenesis: What is the molecular link?

The Golgi phosphoprotein 3 (GOLPH3) is encoded by a gene that is located in a region of the human genome that is often amplified in different solid tumours. GOLPH3, an evolutionary conserved phosphatidylinositol 4-phosphate (PI4P) binding protein, is mainly localised at trans Golgi network (TGN). It regulates several cellular functions like Golgi vesicular trafficking, Golgi glycosylation and mitochondrial cardiolipin production. Recently, GOLPH3 was discovered to be part of the DNA damage response signalling pathway, with a role in cell survival following DNA damage. In this review, we will explore the cellular functions regulated by GOLPH3 and discuss if and how they contribute to the oncogenic activity of this intriguing Golgi localized oncoprotein.

Detection of polymorphism ofATM gene in Leukemia

The Ataxia telangiectasia mutated gene encodes the ATM protein, a key element in the DNA damage response (DDR) signalling pathway responsible for maintaining genomic integrity within the cell. In order to study the genetic changes of ATM gene in Lukaemia, we collected the blood samples of healthy persons for control and leukaemia persons for disease samples. We isolated DNA and performed PCR to analyse by Gene sequencing. As a result we found less number of sequencing result in nucleotide BLAST due to which we are unable to detect the compared result of mutation. Larger and/or combined association studies are needed to conclude the result.