Dong Sun Kim

Association of Low-Dose Exposure to Persistent Organic Pollutants with Global DNA Hypomethylation in Healthy Koreans

Background Global DNA methylation levels have been reported to be inversely associated with blood levels of persistent organic pollutants (POPs), xenobiotics that accumulate in adipose tissue. Whether these associations extend to a population with much lower concentrations of POPs is not known. Objectives This study was performed to examine whether low-dose exposure to POPs was associated with global DNA hypomethylation in Koreans. Methods The amount of global DNA hypomethylation was estimated by the percent 5-methyl-cytosine (%5-mC) in Alu and LINE-1 assays in 86 apparently healthy Koreans. Among various POPs, organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), and polybrominated diphenylethers (PBDEs) were measured. Results Most OC pesticides were inversely and significantly associated with %5-mC in the Alu assay, with correlation coefficients in the range −0.2 to −0.3 after adjusting for age, sex, body mass index, smoking, and alcohol. The strongest OC pesticide associations with %5-mC in the Alu assay were observed with oxychlordane, trans-nonachlor, and p,p′-dichlorodiphenyldichloroethylene. The correlation coefficient of age with %5-mC in the Alu assay was −0.24, similar to correlations of OC pesticides with %5-mC in the Alu assay. Most PCBs and PBDEs showed nonsignificant inverse trends with %5-mC in the Alu assay, but for some PCBs the U-shaped association was significant. On the other hand, POPs were not associated with %5-mC in the LINE-1 assay. Conclusions We found that low-dose exposure to POPs, in particular OC pesticides, was associated with global DNA hypomethylation in apparently healthy Koreans.

Hypomethylation of the protein gene product 9.5 promoter region in gallbladder cancer and its relationship with clinicopathological features

Protein gene product 9.5 (PGP9.5) is a neurospecific peptide that removes ubiquitin from ubiquitinated proteins and prevents them being targeted for degradation by proteosomes. Its expression is a potential marker of non‐small lung cancer, invasive colorectal cancer and esophageal squamous cell carcinoma. Gallbladder (GB) cancer is the most common malignant tumor of the biliary tract and is usually associated with gallstone disease, a late diagnosis, unsatisfactory treatment and a poor prognosis. To understand the role of PGP9.5 in GB cancer, we examined the methylation status of its promoter and its expression in surgical biopsy samples. Formalin‐fixed, paraffin‐embedded tumors and non‐neoplastic GB tissues (22 carcinomas, eight adenomas, 26 normal epithelia) were collected from patients who had undergone surgical resection. The methylation status of the promoter region of the PGP9.5 gene was determined by methylation‐specific polymerase chain reaction, and the expression of PGP9.5 was examined by immunohistochemistry using tissue microarrays. PGP9.5 promoter was methylated in 84.6% (22/26) of normal GB epithelium, 37.5% (3/8) of adenomas and 27.2% (6/22) of carcinomas. Most tumors with an unmethylated promoter exhibited positive staining for PGP9.5 in epithelial and neoplastic cells, but no PGP9.5 expression was observed in normal epithelia or in tumor tissues with a methylated promoter. No correlation was found between promoter hypomethylation of PGP9.5 and clinicopathological findings (i.e. age, sex, histological type or grade, N‐status, invasion depth or tumor stage) whereas PGP9.5 hypomethylation was found to be inversely correlated with the presence of a gallstone (P = 0.015). These results suggest that PGP9.5 promoter hypomethylation could be a reliable marker for GB cancer and that DNA hypomethylation might play an important role in re‐expression of the PGP9.5 gene in GB cancer. (Cancer Sci 2006; 97: 1205–1210)

Polymorphisms in the CASPASE Genes and Survival in Patients With Early-Stage Non–Small-Cell Lung Cancer

PURPOSE This study was conducted to determine the impact of potentially functional polymorphisms in the CASPASE (CASP) genes on the survival of early-stage non-small-cell lung cancer (NSCLC) patients. PATIENTS AND METHODS Four hundred eleven consecutive patients with surgically resected NSCLC were enrolled. Nine potentially functional polymorphisms in the CASP3, CASP7, CASP8, CASP9, and CASP10 genes were investigated. The genotype and haplotype associations with overall survival (OS) and disease-free survival (DFS) were analyzed. RESULTS Patients with the rs2227310 GG genotype had a significantly decreased OS and DFS compared with patients with the CC + CG genotype (adjusted hazard ratio [aHR] for OS, 1.67; 95% CI, 1.19 to 2.35; P = .003; aHR for DFS, 1.62; 95% CI, 1.19 to 2.22; P = .002). The rs4645981C>T genotype also had a significant effect on OS and DFS (under a recessive model; aHR for OS, 2.00; 95% CI, 1.04 to 3.85; P = .04; aHR for DFS, 2.76; 95% CI, 1.58 to 4.80; P = .0003). When the rs2227310 and rs4645981 genotypes were combined, patients with one or two bad genotypes had worse OS and DFS compared with those who had zero bad genotypes (aHR for OS, 1.75; 95% CI, 1.25 to 2.45; P = .001; aHR for DFS, 1.66; 95% CI, 1.23 to 2.26; P = .001). CONCLUSION The CASP7 rs2227310 and CASP9 rs4645981 polymorphisms may affect survival in early-stage NSCLC. The analysis of these polymorphisms can help identify patients at high risk for a poor disease outcome.

No association between polymorphisms in the histone deacetylase genes and the risk of lung cancer.

Although cigarette smoking is the major cause of lung cancer, only a fraction of smokers develop lung cancer during their lifetime, and this suggests that genetic and epigenetic factors are of importance in determining an individuals susceptibility to lung cancer. Histone deacetylases (HDAC)

Effect of body mass index on global DNA methylation in healthy Korean women.

Obesity is known to be strongly associated with cardiovascular disease and cancer, the leading causes of mortality worldwide, and develops owing to interactions between genes and the environment. DNA methylation can act as a downstream effector of environmental signals, and analysis of this process therefore holds substantial promise for identifying mechanisms through which genetic and environmental factors jointly contribute to disease risk. Global DNA methylation of peripheral blood cells has recently been proposed as a potential biomarker for disease risk. Repetitive element DNA methylation has been shown to be associated with prominent obesity-related chronic diseases, but little is known about its relationship with weight status. In this study, we quantified the methylation of Alu elements in the peripheral blood DNA of 244 healthy women with a range of body mass indexes (BMIs) using pyrosequencing technology. Among the study participants, certain clinical laboratory parameters, including hemoglobin, serum glutamic oxaloacetic transaminase, serum glutamic-pyruvic transaminase, total cholesterol, and triglyceride levels were found to be strongly associated with BMI. Moreover, a U-shaped association between BMI and Alu methylation was observed, with the lowest methylation levels occurring at BMIs of between 23 and 30 kg/m2. However, there was no significant association between Alu methylation and age, smoking status, or alcohol consumption. Overall, we identified a differential influence of BMI on global DNA methylation in healthy Korean women, indicating that BMI-related changes in Alu methylation might play a complex role in the etiology and pathogenesis of obesity. Further studies are required to elucidate the mechanisms underlying this relationship.

Infrequent hypermethylation of the PTEN gene in Korean non‐small‐cell lung cancers

CpG islands (CGIs) hypermethylation is implicated in the pathogenesis of many cancers, including lung cancer. The phosphate and tension homolog (PTEN) is a tumor suppressor that controls a variety of biological processes including cell proliferation, growth, migration, and death. The defects in PTEN regulation have a profound impact on carcinogenesis. Herein, we have examined the methylation status of the human PTEN gene in 137 primary non‐small‐cell lung cancers (NSCLCs) by using a methylation‐specific PCR and correlated the results with clinicopathological features. Promoter methylation of the PTEN gene was observed in 5.1%, 2.9%, and 0.0% of three different CpG regions, which were localized at −1460 to −1263, −984 to −848, and −300 to −128 nucleotides upstream of the translation start site, respectively. Reverse transcription‐PCR and immunohistochemical analysis showed the methylation of the CGI region at −984 to −848 correlated more accurately with PTEN expression. In addition, no significant correlation was found between PTEN methylation and clinicopathological factors, including the survival rates. These findings suggest that promoter methylation is not an important mechanism for PTEN deregulation in NSCLCs from Koreans. (Cancer Sci 2010; 101: 568–572)

Polycyclic aromatic hydrocarbons are associated with insulin receptor substrate 2 methylation in adipose tissues of Korean women

Polycyclic aromatic hydrocarbons (PAHs) are highly lipid soluble and are an increasing concern for general populations given their various adverse health effects, including obesity-related metabolic dysfunction. DNA methylation can act as a downstream effector for the biological effects of environmental exposures, but whether PAHs influence DNA methylation is unclear. To test for possible adverse effects of PAHs on adipose tissue (AT), we determined the promoter methylation status of 12 genes involved in glucose and lipid metabolism (CS, GLUT4, IR, IRS1, IRS2, LIPIN1, MCAD, PCK1, PCK2, PPARGC1Β, SDHA, and SREBP1) in visceral AT of Korean women by using methylation-specific PCR (MSP). IRS2 methylation alone was significantly associated with concentrations of individual PAH chemicals. When the PAH summary measure was used, the odds ratios of IRS2 hypermethylation across quartile of the PAH summary measure were 1, 1.7, 2.0, and 11.2 (95% confidence interval: 1.5-84.0) after adjusting for age and BMI (P trend=0.02). The strength of association between PAH summary measure and IRS2 hypermethylation was as similar as that of BMI. Collectively, these results suggested that lipophilic PAHs might be contributing factors to the pathogenesis of insulin resistance through methylation-mediated suppression of the IRS2 gene. However, further studies with large sample size are needed to confirm our findings.

Persistent organic pollutants and promoter hypermethylation of the O6-methylguanine-DNA methyltransferase gene

Abstract Promoter hypermethylation of the O6-methylguanine-DNA methyltransferase (MGMT) DNA repair gene is important during carcinogenesis. We explored whether organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), were associated with hypermethylation of the MGMT gene promoter in peripheral leukocytes among 368 Koreans without cancer. Hypermethylation decreased as OCPs increased (Ptrend = 0.02), while PCB concentrations showed an inverted U-shaped association (Pquadratic < 0.01). The prevalence of MGMT promoter hypermethylation was highest within the 2nd quintile of the PCB summary score (28.4%), while it was only 2.7% in the upper 10% score. Chronic exposure to these chemicals may affect methylation of the MGMT promoter, with possibly non-monotonic dose response relationships.

Promoter methylation of Wrap53α, an antisense transcript of p53, is associated with the poor prognosis of patients with non‑small cell lung cancer

Lung cancer, of which non-small cell lung cancer (NSCLC) accounts for ~85% of cases, remains a leading cause of cancer-associated mortality and morbidity worldwide. Tumor suppressor p53 is a master regulator of diverse cellular processes and is a therapeutic target in cancer. However, many aspects of its transcriptional regulation are still not well defined. WD repeat containing antisense to TP53α (Wrap53α) a newly identified natural antisense transcript of p53, can regulate p53 expression following DNA damage. The present study determined the methylation status of the Wrap53α promoter in primary lung tissues using methylation-specific polymerase chain reaction and evaluated its associations with clinicopathological features and survival in patients with NSCLC. The Wrap53α promoter was methylated in 12 (8.2%) of 146 malignant tissues. Its methylation was associated with the downregulation of its transcription and was frequently detected in patients with stages II–IIIA (P=0.03), and p53 mutation-negative cases (P=0.08). Methylation of Wrap53α promoter was associated with worse overall survival of total patients with a borderline significance [adjusted Hazard Ratio (HR)=2.44, 95% Confidence Interval (CI)=0.98–6.04, P=0.05]. Notably, Wrap53α promoter methylation significantly associated with poor overall survival in p53 mutation-negative patients (log-rank P=0.01, adjusted HR=2.92, 95% CI=1.00–8.60, P=0.05), but not in patients with p53 mutations. The results of the present study suggest that Wrap53α may serve a role in the pathogenesis of a subset of lung cancer, and its methylation may be considered to be a prognostic marker for surgically resected NSCLC patients. However, further studies with a larger sample size are required to confirm this finding.

Hypermethylation of normal mucosa of esophagus‑specific 1 is associated with an unfavorable prognosis in patients with non‑small cell lung cancer

Lung cancer is the leading cause of cancer-associated mortality due to high incidence and poor survival rates, irrespective of global variations in its biology and treatment. Changes in DNA methylation are frequent in cancer and constitute an important mechanism in tumorigenesis. Normal mucosa of esophagus-specific 1 (NMES1) is expressed in epithelial tissue and is believed to be a tumor suppressor gene. The present study investigated the methylation status of the NMES1 promoter in 178 cases of primary non-small cell lung cancer (NSCLC) by pyrosequencing and evaluated the prognostic value of this methylation. NMES1 methylation-positive tumors above the background threshold for non-malignant tissue were found in 15 cases (8.4%) and were detected exclusively in malignant tissues. In addition, univariate and multivariate analyses showed that methylation-positive patients experienced worse overall survival rate (OSR) compared with methylation-negative patients (adjusted hazard ratio, 2.62; 95% confidence interval, 1.20–5.69; P=0.02). Notably, within the methylation-positive group, patients with strong methylation tended to experience worse OSR compared with those with weak methylation (adjusted hazard ratio, 2.45 vs. 3.05; Ptrend=0.02). These findings suggest that NMES1 may serve an important role in lung cancer pathogenesis, and its methylation could be considered a prognostic marker for NSCLC. Further studies with large numbers of samples are required to confirm this conclusion.