Alteration of the ATM gene occurs in gastric cancer cell lines and primary tumors associated with cellular response to DNA damage

Working title: Molecular involvement of p53-MDM2 interactome in gastrointestinal cancers

The interaction between murine double minute 2 (MDM2) and p53, marked by transcriptional induction and feedback inhibition, orchestrates a functional loop dictating cellular fate. The functional loop comprising p53-MDM2 axis is made up of an interactome consisting of approximately 81 proteins, which are spatio-temporally regulated and involved in DNA repair mechanisms. Biochemical and genetic alterations of the interactome result in dysregulation of the p53-mdm2 axis that leads to gastrointestinal (GI) cancers. A large subset of interactome is well known and it consists of proteins that either stabilize p53 or MDM2 and proteins that target the p53-MDM2 complex for ubiquitin-mediated destruction. Upstream signaling events brought about by growth factors and chemical messengers invoke a wide variety of posttranslational modifications in p53-MDM2 axis. Biochemical changes in the transactivation domain of p53 impact the energy landscape, induce conformational switching, alter interaction potential and could change solubility of p53 to redefine its co-localization, translocation and activity. A diverse set of chemical compounds mimic physiological effectors and simulate biochemical modifications of the p53-MDM2 interactome. p53-MDM2 interactome plays a crucial role in DNA damage and repair process. Genetic aberrations in the interactome, have resulted in cancers of GI tract (pancreas, liver, colorectal, gastric, biliary, and esophageal). We present in this article a review of the overall changes in the p53-MDM2 interactors and the effectors that form an epicenter for the development of next-generation molecules for understanding and targeting GI cancers.

Genetic Profiles Affect the Biological Effects of Serine on Gastric Cancer Cells

A high serine content in body fluid was identified in a portion of patients with gastric cancer, but its biological significance was not clear. Here, we investigated the biological effect of serine on gastric cancer cells. Serine was added into the culture medium of MGC803 and HGC27 cancer cells, and its influence on multiple biological functions, such as cell growth, migration and invasion, and drug resistance was analyzed. We examined the global transcriptomic profiles in these cultured cells with high serine content. Both MGC803 and HGC27 cell lines were originated from male patients, however, their basal gene expression patterns were very different. The finding of cell differentiation-associated genes, ALPI, KRT18, TM4SF1, KRT81, A2M, MT1E, MUC16, BASP1, TUSC3, and PRSS21 in MGC803 cells suggested that this cell line was more poorly differentiated, compared to HGC27 cell line. When the serine concentration was increased to 150mg/ml in medium, the response of these two gastric cancer cell lines was different, particularly on cell growth, cell migration, and invasion and 5-FU resistance. In animal experiment, administration of high concentration of serine promoted cancer cell metastasis to local lymph node. Taken together, we characterized the basal gene expressing profiles of MGC803 and HGC27. The HGC27 cells were more differentiated than MGC803 cells. MGC803 cells were more sensitive to the change of serine content. Our results suggested that the responsiveness of cancer cells to microenvironmental change is associated with their genetic background.

MicroRNA (miR) dysregulation during Helicobacter pylori-induced gastric inflammation and cancer development: critical importance of miR-155

Dysregulation of noncoding microRNA molecules has been associated with immune cell activation in the context of Helicobacter pylori induced gastric inflammation as well as carcinogenesis, but also with downregulation of mismatch repair genes, and may interfere with immune checkpoint proteins that lead to the overexpression of antigens on gastric tumor cells. Numerous miR-molecules have been described as important tools and markers in gastric inflammation and cancer development -including miR-21, miR-143, miR-145, miR-201, and miR-335- all of which are downregulated in gastric tumors, and involved in cell cycle growth or tumor invasion. Among the many microRNAs involved in gastric inflammation, adenocarcinoma development and immune checkpoint regulation, miR-155 is notable in that its upregulation is considered a key marker of chronic gastric inflammation that predisposes a patient to gastric carcinogenesis. Among various other miRs, miR-155 is highly expressed in activated B and T cells and in monocytes/macrophages present in chronic gastric inflammation. Notably, miR-155 was shown to downregulate the expression of certain MMR genes, such as MLH1, MSH2, and MSH6. In tumor-infiltrating miR-155-deficient CD8⁺ T cells, antibodies against immune checkpoint proteins restored the expression of several derepressed miR-155 targets, suggesting that miR-155 may regulate overlapping pathways to promote antitumor immunity. It may thus be of high clinical impact that gastric pathologies mediated by miR-155 result from its overexpression. This suggests that it may be possible to therapeutically attenuate miR-155 levels for gastric cancer treatment and/or to prevent the progression of chronic gastric inflammation into cancer.

Upregulation of the APE1 and H2AX genes and miRNAs involved in DNA damage response and repair in gastric cancer

Gastric cancer remains one of the leading causes of cancer-related death worldwide, and most of the cases are associated with Helicobacter pylori infection. This bacterium promotes the production of reactive oxygen species (ROS), which cause DNA damage in gastric epithelial cells. In this study, we evaluated the expression of important genes involved in the recognition of DNA damage (ATM, ATR, and H2AX) and ROS-induced damage repair (APE1) and the expression of some miRNAs (miR-15a, miR-21, miR-24, miR-421 and miR-605) that target genes involved in the DNA damage response (DDR) in 31 fresh tissues of gastric cancer. Cytoscape v3.1.1 was used to construct the postulated miRNA:mRNA interaction network. Analysis performed by real-time quantitative PCR exhibited significantly increased levels of the APE1 (RQ = 2.55, p < 0.0001) and H2AX (RQ = 2.88, p = 0.0002) genes beyond the miR-421 and miR-605 in the gastric cancer samples. In addition, significantly elevated levels of miR-21, miR-24 and miR-421 were observed in diffuse-type gastric cancer. Correlation analysis reinforced some of the gene:gene (ATM/ATR/H2AX) and miRNA:mRNA relationships obtained also with the interaction network. Thus, our findings show that tumor cells from gastric cancer presents deregulation of genes and miRNAs that participate in the recognition and repair of DNA damage, which could confer an advantage to cell survival and proliferation in the tumor microenvironment.

The miR27b-CCNG1-P53-miR-508-5p axis regulates multidrug resistance of gastric cancer

Multidrug resistance (MDR) correlates with treatment failure and poor prognosis among gastric cancer (GC) patients. In a previous study using high-throughput functional screening, we identified 11 microRNAs (miRNAs) that regulate MDR in GC and found that miR-508-5p reversed MDR by targeting ABCB1 and ZNRD1. However, the mechanism by which miR-508-5p was decreased in chemo-resistant GC cells was unclear. In this study, we found that ectopic miR-27b is sufficient to sensitize tumors to chemotherapy in vitro and in vivo. Moreover, miR-27b directly targets the 3′ untranslated regions (3′-UTRs) of CCNG1, a well-known negative regulator of P53 stability. Interestingly, miR-27b up-regulation leads to increased miR-508-5p expression, and this phenomenon is mediated by CCNG1 and P53. Further investigation indicated that miR-508-5p is directly regulated by P53. Thus, the miR-27b/CCNG1/P53/miR-508-5p axis plays important roles in GC-associated MDR. In addition, miR-27b and miR-508-5p expression was detected in GC tissues with different chemo-sensitivities, and we found that tissues in which miR-27b and miR-508-5p are up-regulated are more sensitive to chemotherapy. Together, these data suggest that the combination of miR-27b and miR-508-5p represents a potential marker of MDR. Restoring the miR-27b and miR-508-5p levels might contribute to MDR reversion in future clinical practice.

Targeting deficient DNA damage repair in gastric cancer

INTRODUCTION

Over recent years our understanding of DNA damage repair has evolved leading to an expansion of therapies attempting to exploit DNA damage repair deficiencies across multiple solid tumours. Gastric cancer has been identified as a tumour where a subgroup of patients demonstrates deficiencies in the homologous recombination pathway providing a potential novel treatment approach for this poor prognosis disease.

AREA COVERED

This review provides an overview of DNA damage repair and how this has been targeted to date in other tumour types exploiting the concept of synthetic lethality. This is followed by a discussion of how deficiencies in homologous recombination may be identified across tumour types and on recent progress in targeting DNA repair deficiencies in gastric cancer.

EXPERT OPINION

Gastric cancer remains a difficult malignancy to treat and the possibility of targeting deficient DNA repair in a subgroup of patients is an exciting prospect. Future combinations with immunotherapy and radiotherapy are appealing and appear to have a sound biological rationale. However, much work remains to be done to understand the significance of the genetic and epigenetic alterations involved, to elucidate the optimum predictive signatures or biomarkers and to consider means of overcoming treatment resistance.

Mutation at intronic repeats of the ataxia-telangiectasia mutated (ATM) gene and ATM protein loss in primary gastric cancer with microsatellite instability

Ataxia-telangiectasia mutated (ATM) is a Ser/Thr protein kinase that plays a critical role in DNA damage-induced signaling and initiation of cell cycle checkpoint signaling in response to DNA-damaging agents such as ionizing radiation. We have previously reported the ATM protein loss by immunohistochemistry (IHC) in 16% of human gastric cancer (GC) tissue. We hypothesized that ATM gene intron mutations targeted by microsatellite instability (MSI) cause ATM protein loss in a subset of GC. We studied mononucleotide mutations at the intron of ATM gene, ATM IHC and MSI in GC. Ten human gastric cancer cell lines were studied for the ATM gene mutation at introns, RT-PCR, direct sequencing, and immunohistochemistry. GC tissues of 839 patients were analyzed for MSI and ATM IHC. Among them, 604 cases were analyzed for the ATM mutations at introns preceding exon 6, exon 10 and exon 20. Two human GC cell lines (SNU-1 and -638) showed ATM intron mutations, deletion in RT-PCR and direct sequencing, and ATM protein loss by IHC. The frequencies of ATM mutation, MSI, and ATM protein loss were 12.9% (78/604), 9.2% (81/882) and 15.2% (134/839), respectively. Analysis of associations among MSI, ATM gene mutation, and ATM protein loss revealed highly co-existing ATM gene alterations and MSI. ATM intron mutation and ATM protein loss were detected in 69.3% (52/75) and 53.3% (40/75) of MSI positive GC. MSI positivity and ATM protein loss were present in 68.4% (52/76) and 48.7% (37/76) of GC with ATM intron mutation. ATM mutation and ATM protein loss had characteristics of old age, distal location of tumor, large tumor size, and histologic intestinal type. Our study might be interpreted as that ATM gene mutation at intron might be targeted by MSI and lead to ATM protein loss in a selected group of GC.

DNA damage response-related proteins in gastric cancer: ATM, Chk2 and p53 expression and their prognostic value

OBJECTIVES

The aims of this study were to assess expressions of the DNA damage response (DDR)-related proteins and to investigate their clinical significances in gastric carcinoma.

METHODS

Two independent cohorts, a training set (n=524) and validation set (n=394), of gastric cancer patients were enrolled. Ataxia telangiectasia mutated (ATM), checkpoint kinase 2 (Chk2), and p53 expressions were examined by immunohistochemistry using tissue microarray.

RESULTS

ATM loss, Chk2 loss, and p53 positivity were observed in 21.8, 14.1, and 36.1% of the training set, and in 17.3, 12.2, and 35.8% of the validation set, respectively. In the training set, the aberrant expressions of ATM, Chk2, or p53 were significantly associated with an advanced TNM stage and poor disease-specific survival. This association was verified in the validation set. Chk2 positivity and p53 negativity were significantly related to a prolonged disease-specific survival. Also, patients with nonaberrant expressional levels of all 3 DDR-related proteins had a more favorable outcome than others. Multivariate analyses showed that Chk2 loss and at least 1 aberrant DDR-related protein remained as independent prognostic factors of poor disease-specific survival.

CONCLUSIONS

This study elucidated the prognostic implications of DDR-related proteins, and suggests that their aberrant expressions play critical roles in the development and progression of gastric cancer.

Concordance of ATM (ataxia telangiectasia mutated) immunohistochemistry between biopsy or metastatic tumor samples and primary tumors in gastric cancer patients

ATM (ataxia telangiectasia mutated) is one of several DNA repair proteins that are suggested to sensitize tumor cells to the poly(ADP-ribose) polymerase inhibitor olaparib when deficient. The aim of this study was to assess the spatiotemporal concordance of ATM immunohistochemistry (IHC) in gastric cancer in order to determine if measurements made at the level of various sample types and times could be inferred as having the potential to be relevant to treatment decisions made at the patient level. Two independent cohorts composed of 591 gastric cancer patients divided into a gastrectomy cohort (n = 450) and a metastasis cohort (n = 141) were used in this study. A total of 2,705 ATM IHC samples were examined, including 450 whole tissue, 3 sets of 450 tissue microarray (TMA), 301 biopsy, 222 metastatic tumor and 2 additional whole tissue samples of 50 cases from the gastrectomy cohort, and 141 pairs of primary and metastatic tumors from the metastasis cohort. The prevalence of ATM negativity was 13.1% in biopsies, 13.9, 15.1, and 16.0% in TMAs and 15.9% in whole tissue samples of the gastrectomy cohort, and 21.4% in primary tumor and 21.5% in metastatic tumor samples of the metastasis cohort. coefficients were 0.341 for biopsy, 0.572 as the average of 3 TMAs and 0.415 for the largely synchronous metastatic tumors of the gastrectomy cohort, and 0.153 for the largely asynchronous metastatic tumors of the metastasis cohort. Using whole tissue sections from tumor resections or primary tumor, respectively, as the reference standards, specificity and sensitivity were 91.6 and 41.0% for biopsy, 93.9 and 61.9% as the average of 3 TMAs, and 86.6 and 58.8% for metastatic tumors of the gastrectomy cohort and 81.7 and 33.3% for metastatic tumors of the metastasis cohort, respectively. Although we have demonstrated that the IHC assay for ATM was robust and reproducible in gastric tumor samples, we have also found that measurements were subject to significant discordance across multiple sample types from the same patient. Further work will be necessary to determine if classification may be made more consistent by multiple sampling. However, the lack of agreement between primary and asynchronous metastatic samples suggests that such sampling would need to be performed at the time of any treatment decision.

Metastasis of neuroendocrine tumors are characterized by increased cell proliferation and reduced expression of the ATM gene

PURPOSE

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are rare group of tumors with a wide spectrum of clinical behavior. However, there are no known clinically relevant biomarkers to predict metastasis.

EXPERIMENTAL DESIGN

To investigate differential gene expression signatures of metastatic vs non-metastatic NETs, we studied cell cycle regulatory genes in 19 metastatic and 22 non-metastatic colorectal NETs by PCR arrays. Immunohistochemistry (IHC) and quantitative real-time RT-PCR were performed to verify the results and another set of 38 GEP-NETs were further studied for validation.

RESULTS

We first delineated six candidate genes for metastasis including ATM, CCND2, RBL2, CDKN3, CCNB1, and GTSE1. ATM was negatively correlated with metastatic NETs (p<0.001) with more than 2-fold change compared to non-metastatic NETs. Overexpression of ATM protein by IHC was strongly correlated with high ATM mRNA levels and low Ki-67 labeling index. Patients with ATM-negativity by IHC showed significantly decreased overall survival than patients with ATM-positivity (median OS, metastatic vs non-metastatic NETs; 2.7 years vs not reached; p = 0.003) and 85.7% of metastatic NETs were ATM-negative. In another validation set of GEP-NETs, decreased mRNA of ATM gene was associated with metastasis and remained significant (p = 0.023).

CONCLUSIONS

ATM down-regulation was strongly associated with metastatic NETs when compared with non-metastatic NETs and ATM may be a potential predictive marker for metastasis as well as a novel target in metastatic GEP-NETs.

Analysis of D1853N ATM polymorphism in radiosensitive patients with cervical carcinoma

Clinical oncologists have been focusing their efforts on attempting to define risk groups of patients with unusual biological reactions to the recommended therapy regimens using molecular biology techniques.

THE AIMS OF OUR STUDY WERE

(i) to find a design and validate a method for fast and reliable analysis of the D1853N (5557G>A) genetic polymorphism in the ATM (ataxia-telangiectasia mutated) gene; (ii) to use side-directed mutagenesis to generate ATM 5557A-positive DNA (reference ATM5557A DNA); and (iii) to analyze a group of patients suffering from cervical carcinoma with adverse responses to radiotherapy. The 5557A variant was found in three of twenty women (15%). Our data show that the prevalence of the 5557A allelic variant in cervical cancer subjects with adverse responses after irradiation probably does not differ from the prevalence common in Caucasians. A larger population study should confirm these preliminary results.

Genetic and structural variation in the gastric cancer kinome revealed through targeted deep sequencing

Genetic alterations in kinases have been linked to multiple human pathologies. To explore the landscape of kinase genetic variation in gastric cancer (GC), we used targeted, paired-end deep sequencing to analyze 532 protein and phosphoinositide kinases in 14 GC cell lines. We identified 10,604 single-nucleotide variants (SNV) in kinase exons including greater than 300 novel nonsynonymous SNVs. Family-wise analysis of the nonsynonymous SNVs revealed a significant enrichment in mitogen-activated protein kinase (MAPK)-related genes (P < 0.01), suggesting a preferential involvement of this kinase family in GC. A potential antioncogenic role for MAP2K4, a gene exhibiting recurrent alterations in 2 lines, was functionally supported by siRNA knockdown and overexpression studies in wild-type and MAP2K4 variant lines. The deep sequencing data also revealed novel, large-scale structural rearrangement events involving kinases including gene fusions involving CDK12 and the ERBB2 receptor tyrosine kinase in MKN7 cells. Integrating SNVs and copy number alterations, we identified Hs746T as a cell line exhibiting both splice-site mutations and genomic amplification of MET, resulting in MET protein overexpression. When applied to primary GCs, we identified somatic mutations in 8 kinases, 4 of which were recurrently altered in both primary tumors and cell lines (MAP3K6, STK31, FER, and CDKL5). These results demonstrate that how targeted deep sequencing approaches can deliver unprecedented multilevel characterization of a medically and pharmacologically relevant gene family. The catalog of kinome genetic variants assembled here may broaden our knowledge on kinases and provide useful information on genetic alterations in GC.

Arsenic trioxide induces apoptosis and G2/M phase arrest by inducing Cbl to inhibit PI3K/Akt signaling and thereby regulate p53 activation

Arsenic trioxide (ATO) strongly induces apoptosis in acute promyelocytic leukemia (APL), but it induces cell cycle arrest in most solid tumors. In this study, we investigated the mechanism of ATO action on APL-derived NB4 cells and gastric cancer cell lines. ATO decreased the viability of both cell lines, but gastric cancer cells were much less susceptible. ATO-induced G2/M phase arrest and p53 degradation in gastric cancer MGC803 cells. In contrast, ATO-induced apoptosis in NB4 cells without degradation of p53. Both processes were accompanied by transient activation of Akt. The PI3K/Akt inhibitor LY294002 significantly increased the amount of p53 protein and ATO-induced apoptosis in both cell lines and decreased G2/M phase arrest of MGC803 cells. In addition, ATO up-regulated the expression of Cbl proteins in both cell lines. Inhibition of Cbl with the proteasome inhibitor Ps341 decreased apoptosis in NB4 cells and increased the G2/M phase arrest of MGC803 cells, and it also prolonged the activation of PI3K/Akt by ATO. Consistent results with those in MGC803 cells were showed in gastric cancer cell BGC823 and SGC7901 after ATO treatment. These results demonstrate that inhibition of PI3K/Akt signaling by Cbl is involved in both ATO-induced apoptosis of NB4 cells and ATO-induced G2/M phase arrest of gastric cancer cells. Cbl achieved these effects probably via its regulating PI3K/Akt pathway, and thereby modulated p53 activation.

ATM sequence variants associate with susceptibility to non-small cell lung cancer

ATM gene mutations have been implicated in many human cancers. However, the role of ATM polymorphisms in lung carcinogenesis is largely unexplored. We conducted a case-control analysis of 556 Caucasian non-small-cell lung cancer (NSCLC) patients and 556 controls frequency-matched on age, gender and smoking status. We genotyped 11 single nucleotide polymorphisms of the ATM gene and found that compared with the wild-type allele-containing genotypes, the homozygous variant genotypes of ATM08 (rs227060) and ATM10 (rs170548) were associated with elevated NSCLC risk with ORs of 1.55 (95% CI: 1.02-2.35) and 1.51 (0.99-2.31), respectively. ATM haplotypes and diplotypes were inferred using the Expectation-Maximization algorithm. Haplotype H5 was significantly associated with reduced NSCLC risk in former smokers with an OR of 0.47 (0.25-0.96) compared with the common H1 haplotype. Compared with the H1-H2 diplotype, H2-H2 and H3-H4 diplotypes were associated with increased NSCLC risk with ORs of 1.58 (0.99-2.54) and 2.29 (1.05-5.00), respectively. We then evaluated genotype-phenotype correlation in the control group using the comet assay to determine DNA damage and DNA repair capacity. Compared with individuals with at least 1 wild-type allele, the homozygous variant carriers of either ATM08 or ATM10 exhibited significantly increased DNA damage as evidenced by a higher mean value of the radiation-induced olive tail moment (ATM08: 4.86 +/- 2.43 vs. 3.79 +/- 1.51, p = 0.04; ATM10: 5.14 +/- 2.37 vs. 3.79 +/- 1.54, p = 0.01). Our study presents the first epidemiologic evidence that ATM genetic variants may affect NSCLC predisposition, and that the risk-conferring variants might act through down-regulating the functions of ATM in DNA repair activity upon genetic insults such as ionizing radiation.

Possible involvement of CCT5, RGS3, and YKT6 genes up-regulated in p53-mutated tumors in resistance to docetaxel in human breast cancers

BACKGROUND

Present study was aimed to investigate the relationship of p53 mutation status with response to docetaxel in breast cancers. In addition, attempts were made to identify the genes differentially expressed between p53-wild and p53-mutated breast tumors and to study their relationship with response to docetaxel.

METHODS

Mutational analysis of p53 was done in 50 breast tumor samples obtained from primary breast cancer patients (n = 33) and locally recurrent breast cancer patients (n = 17) before docetaxel therapy. Response to docetaxel was evaluated clinically. Gene expression profiling (n = 2,412) was conducted by adapter-tagged competitive-PCR in 186 tumor samples, which were also analyzed in their p53 mutational status in order to identify the differentially expressed genes according to p53 mutation status and their relationship with response to docetaxel.

RESULTS

Response rate of p53-mutated tumors (44%) was lower than that of p53-wild tumors (62%) though there was no statistical significance (P = 0.23). Of 2412 genes, mRNA expression of 13 genes was significantly different between p53-wild and p53-mutated tumors. Of these 13 genes, mRNA expression of CCT5, RGS3, and YKT6 was significantly up-regulated in p53-mutated tumors and associated with a low response rate to docetaxel. Treatment of MCF-7 cells with siRNA specific for CCT5, RGS3, or YKT6 resulted in a significant enhancement of docetaxel-induced apoptosis.

CONCLUSIONS

CCT5, RGS3, and YKT6 mRNA expressions, which are up-regulated in p53-mutated breast tumors, might be implicated in resistance to docetaxel and clinically useful in identifying the subset of breast cancer patients who may or may not benefit from docetaxel treatment.

Complications of ophthalmic regional blocks: their treatment and prevention

Complications following ophthalmic regional anaesthesia are rare but are reported during both needle (intraconal and extraconal blocks) and blunt cannula (sub-Tenon's block) techniques. At present there is no perfect technique of ophthalmic regional anaesthesia. This article reports on the complications, treatment and prevention of commonly used ophthalmic regional blocks. Thorough knowledge of the measures required to deal with complications when they occur are of paramount importance for safe clinical practice.

Matrix metalloproteinase 11 depletion inhibits cell proliferation in gastric cancer cells

Our previous study has shown that matrix metalloproteinase 11 (MMP11) is highly expressed in tumor cell lines and primary tumor of gastric cancer (GC). In order to reveal the correlation between expression of MMP11 and biological features of GC cell, we have constructed the recombinant plasmids producing hairpin small interfering RNA (siRNA) to target MMP11 mRNA using a vector-based RNA interference technology. Stable transfection of recombinants into GC cell line BGC823 specifically depleted the mRNA and protein of MMP11 as demonstrated by RT-PCR and Western blotting analysis. The siRNA-treated cells exhibited significantly decreased growth ability compared with mock transfectants and parental BGC823 cells. Furthermore, colony formation of MMP11 deficient cells was dramatically inhibited in soft agar and tumorigenicity was reduced in nude mice, respectively. These results provide new insights into the function of MMP11 and suggest that MMP11 may play an important role in the control of cell proliferation and tumor development in GC.