Association of CYP1A1 and microsomal epoxide hydrolase polymorphisms with lung squamous cell carcinoma

The Association between EPHX1 Gene Polymorphisms and Lung Cancer among Jordanian People

OBJECTIVE

Genetic susceptibility to lung cancer is the subject of extensive research. We investigated whether polymorphisms in the microsomal epoxide hydrolase (EPHX1) gene is linked to lung cancer susceptibility in Jordanian patients.

METHODS

In this case-control study a total of 218 subjects from Jordan University Hospital and King Hussein Cancer Center were screened (108 lung cancer patients and 110 matched controls). Polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) was used to detect the two common polymorphisms in EPXH1 located in exons 3 and 4; namely, amino acid substitution from tyrosine to histidine at residue 113 of exon 3 (Tyr113His; low activity allele) and amino acid substitution from histidine to arginine at residue 139 of exon 4 (His139Arg; high activity allele).

RESULTS

There was no significant difference in genotype distribution between control subjects and lung cancer patients. In addition, no differences were found when evaluated according to age, gender or tobacco consumption. For exon 3 the adjusted OR was 0.970 (95% CI 0.473 - 1.991) for the Tyr113/His113 genotype and 0.692 (95% CI 0.301 - 1.590) for the Tyr113/Tyr113 genotype, respectively.  For exon 4 the adjusted OR was 0.596 (95% CI 0.297-1.197) for the His139/Arg139 genotype and 0.882 (95% CI 0.117- 6.660) for the Arg139/Arg139 genotype, respectively. Logistic regression analysis did not show differences in EPXH1 distributions between patients and controls when categorized according to predicted microsomal epoxide hydrolase activity.  Therefore, common polymorphisms within EPHX1 do not appear to be significant risk factors for lung cancer development in the Jordanian population.

CONCLUSION

No associations were observed between lung cancer risk and EPXH1 polymorphisms in the Jordanian population.

Genetic polymorphisms in the mEH gene in relation to tobacco smoking: role in lung cancer susceptibility and survival in north Indian patients with lung cancer undergoing platinum-based chemotherapy

Aim: Epoxide hydrolase is involved in oxidative defenses and is responsible for the activation of carcinogens. The relationship between EPHX1 polymorphisms (Tyr113His and His139Arg) and overall survival (OS) and lung cancer (LC) risk was investigated. Methods: The study comprised 550 cases and 550 controls. Genotyping and statistical analysis were applied. Results: The variant genotypes of EPHX1 polymorphisms exhibited no association with LC risk. The Tyr113His polymorphism exhibited twofold increased odds of lymph node invasion (p = 0.04). The Tyr/His genotype is a risk factor for smokers. Subjects carrying the combined genotype for His139Arg showed better median survival time (MST) and the heterozygous genotype revealed better MST in the case of small-cell lung cancer (SCLC; 11.30 vs 6.73 months; log-rank test: p = 0.02). The heterozygous genotype (His139Arg) had longer MST in patients receiving cisplatin/carboplatin and irinotecan (11.30 vs 7.23; log-rank test: p = 0.007) Conclusion: The Tyr113His polymorphism is associated with LC risk in smokers and is a potential prognostic factor for OS in patients with SCLC after irinotecan.

Polymorphisms in the Microsomal Epoxide Hydrolase Gene: Role in Lung Cancer Susceptibility and Prognosis

Aims and background

The aim of this study was to investigate the relationship between EPHXI exon 3 Tyr113His and exon 4 His139Arg polymorphisms, predicted microsomal epoxide hydrolase (mEH) activity, and lung cancer development. mEH is a protective enzyme involved in oxidative defences against a number of environmental chemicals and pollutants, but it is also responsible for the xenobiotic activation of carcinogens.

Methods

We investigated the two polymorphisms of the mEH gene (EPHX1) in 58 lung cancer patients and 41 controls using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

Results

The exon 3 Tyr113His polymorphism was associated with lung cancer (P <0.001). The frequency of the His113His homozygote genotype in exon 3 was significantly increased in patients compared with controls (P <0.001). In contrast, there was no significant difference in exon 4 polymorphisms between patients and controls. When the exon 3 and 4 polymorphisms were considered together, the combined EPHX1 His113His113/His139His139 genotype (very low predicted enzyme activity) was found to be associated with an increased risk of lung cancer (P = 0.044, OR = 3.063, CI = 0.932–10.069). We observed that patients with T3 + T4 tumors had an approximately 3-fold higher risk of the Tyr113/His113 genotype than patients with T1 + T2 tumors. Lung cancer patients carrying aheterozygote Tyr113/His113 genotype had a 2-fold increased risk of lymph node metastases (P = 0.051).

Conclusion

These findings suggest that the exon 3 Tyr113His and exon 4 His139Arg polymorphisms of EPHXI may be associated with a increased risk of lung cancer and a worse prognosis. Free full text available at www.tumorionline.it

Synergistic association of CYP1A1 polymorphisms with increased susceptibility to squamous cell lung cancer in north Indian smokers

OBJECTIVES

Studies in different populations have shown that polymorphisms within the CYP1A1 gene play an important role in determining individual susceptibility to lung cancer. However, the data obtained so far have been contradictory within the same or different populations. Few studies have focused on the synergistic effect of CYP1A1 polymorphisms on the susceptibility to lung cancer overall and to different histological subtypes along with the impact of smoking.

METHODS

A total of 704 individuals (353 lung cancer patients and 351 controls) were evaluated for CYP1A1 polymorphisms. CYP1A1 genotyping was done by means of PCR-RFLP.

RESULTS

A CYP1A1 mutant genotype was found to be significantly associated with lung cancer (OR = 3.15; 95% CI = 1.75-5.71; p = 0.0001) and this risk was 4-fold higher in case of squamous cell carcinoma (SCC). The CYP1A1 m2 allelic variant was found to be strongly associated with the risk of SCC and adenocarcinoma. The combined "at risk" genotypes of the CYP1A1 m1 and m2 allelic variants were associated with lung cancer risk and this risk was higher in case of SCC (OR = 2.0; 95% CI = 1.97-3.81; p = 0.028). Furthermore, the lung cancer risk was associated with smoking, especially in heavy smokers carrying CYP1A1 variant genotypes. We also observed that heavy smokers with the mutant m1 genotype were at increased risk of SCC (OR = 5.4; 95% CI = 2.4-11.9; p<0.0001). Furthermore, when stratified for smoking dose and histology, the effect was compounded in heavy smokers and SCC (OR = 7.5; 95% CI = 1.8-30.9; p = 0.004).

CONCLUSIONS

Polymorphism in the CYP1A1 gene is an important risk modifier for lung cancer.

The modifying effect of CYP2E1, GST, and mEH genotypes on the formation of hemoglobin adducts of acrylamide and glycidamide in workers exposed to acrylamide

This study assesses the association of acrylamide (AA) and glycidamide (GA) hemoglobin adducts (AAVal and GAVal) and their ratios with genetic polymorphisms of the metabolic enzymes cytochrome P450 2E1 (CYP2E1), exon 3 and 4 of microsomal epoxide hydrolase (mEH3 and mEH4), glutathione transferase theta (GSTT1), and mu (GSTM1) or/and the combinations of these polymorphisms, involved in the activation and detoxification of AA in humans. Fifty-one AA-exposed workers and 34 controls were recruited and provided a post-shift blood sample. AAVal and GAVal were determined simultaneously using isotope-dilution liquid chromatography-electronspray ionization/tandem mass spectrometry (LC-ESI-MS/MS). Genetic polymorphisms of CYP2E1, mEH3 and 4, GSTT1, and GSTM1 were also analyzed. Our results reveal that the GAVal/AAVal ratio, potentially reflecting the proportion of AA metabolized to GA, ranged from 0.13 to 0.45 with a mean at 0.27. Multivariate regression analysis demonstrates that the joint effect of CYP2E1, GSTM1, and mEH4 genotypes was significantly associated with AAVal and GAVal levels after adjustment for AA exposures. These results suggest that mEH4 and the combined genotypes of CYP2E1, GSTM1 and mEH4 may be associated with the formation of AAVal and GAVal. Further studies may be needed to shed light on the roles that phase I and II enzymes play in AA metabolism.

An Interethnic Comparison of Polymorphisms of the Genes Encoding Drug-Metabolizing Enzymes and Drug Transporters: Experience in Singapore

Much of the interindividual variability in drug response is attributable to the presence of single nucleotide polymorphisms (SNPs) in genes encoding drug-metabolizing enzymes and drug transporters. In recent years, we have investigated the polymorphisms in a number of genes encoding phase I and II drug-metabolizing enzymes including CYPIA1, CYP3A4, CYP3A5, GSTM1, NAT2, UGT1A1, and TPMT and drug transporter (MDR1) in three distinct Asian populations in Singapore, namely the Chinese, Malays, and Indians. Significant differences in the frequencies of common alleles encoding these proteins have been observed among these three ethnic groups. For example, the frequency of the variant A2455G polymorphism of CYP1A1 was 28% in Chinese and 31% in Malays, but only 18% in Indians. CYP3A4*4 was detected in two of 110 Chinese subjects, but absent in Indians and Malays. Many Chinese and Malays (61-63%) were homozygous for the GSTM1*0 null genotype compared with 33% of Indians. The frequency of the UGTIA1*28 allele was highest in the Indian population (35%) compared to similar frequencies that were found in the Chinese (16%) and Malay (19%) populations. More importantly, our experience over the years has shown that the pharmacogenetics of these drug-metabolizing enzymes and MDR1 in the Asian populations are different from these in the Caucasian and African populations. For example, the CYP3A4*1B allele, which contains an A-290G substitution in the promoter region of CYP3A4, is absent in all three Asian populations of Singapore studied, but occurs in more than 54% of Africans and 5% of Caucasians. There were no difference in genotype and allelic variant frequencies in exon 12 of MDR1 between the Chinese, Malay, and Indian populations. When compared with other ethnic groups, the distribution of the wild-type C allele in exon 12 in the Malays (34.2%) and Indians (32.8%) was relatively high and similar to the Japanese (38.55%) and Caucasians (41%) but different from African-Americans (15%). The frequency of wild-type TT genotype in Asians (43.5% to 52.1%) and Japanese (61.5%) was much higher than those found in Caucasians (13.3%). All the proteins we studied represent the primary hepatic or extrahepatic enzymes, and their polymorphic expression may be implicated in disease risk and the disposition of drugs or endogenous substances. As such, dose requirements of certain drugs may not be optimal for Asian populations, and a second look at the factors responsible for this difference is necessary.

Glutathione S-transferase M1 (GSTM1) polymorphisms and lung cancer: a literature-based systematic HuGE review and meta-analysis

Multiple genes have been studied for potential associations with lung cancer. The gene most frequently associated with increased risk has been glutathione S-transferase M1 (GSTM1). The glutathione S-transferase enzyme family is known to catalyze detoxification of electrophilic compounds, including carcinogens, therapeutic drugs, environmental toxins, and products of oxidative stress. In this review, the authors summarize the available evidence associating lung cancer with the GSTM1 gene. They describe results from an updated meta-analysis of 98 published genetic association studies investigating the relation between the GSTM1 null variant and lung cancer risk including 19,638 lung cancer cases and 25,266 controls (counting cases and controls in each study only once). All studies considered, the GSTM1 null variant was associated with an increased risk of lung cancer (odds ratio (OR) = 1.22, 95% confidence interval (CI): 1.14, 1.30), but no increase in risk was seen (OR = 1.01, 95% CI: 0.91, 1.12) when only the five largest studies (>500 cases each) were considered. Furthermore, while GSTM1 null status conferred a significantly increased risk of lung cancer to East Asians (OR = 1.38, 95% CI: 1.24, 1.55), such a genotype did not confer increased risk to Caucasians. More data regarding the predictive value of GSTM1 genetic testing are needed before population-based testing may be reasonably considered.

Polymorphisms of CYP1A1 and GSTM1 genes and susceptibility to oral cancer

PURPOSE

Oral cancer is the fifth most common form of cancer in the world and comprises 6.5% of all cancer deaths. Since one of the major risk factors for oral cancer is tobacco use, we hypothesized that polymorphic genes coding for tobacco carcinogen-metabolizing enzymes may play a role in oral cancer susceptibility.

MATERIALS AND METHODS

To investigate the association between polymorphisms of the CYP1A1 and GSTM1 genes and risks for oral squamous cell carcinoma (OSCC) in the Korean population, the prevalence of the CYP1A1 Mspl and GSTM1 null polymorphisms were examined in 72 patients with histologically confirmed primary OSCC, as well as in 221 healthy control subjects.

RESULTS

A significant risk increase for oral cancer was observed among subjects with the homozygous CYP1A1 (m2/m2) genotype (OR=3.8, 95% CI=1.9-7.7), but not the GSTM1 null genotype (OR=0.7, 95% CI=0.4-1.3). Risk for oral cancer was significantly increased in subjects with the homozygous CYP1A1 (m2/m2)genotype, regardless of smoking history (smokers; OR=4.4; 95% CI=1.2-16.3; non- smokers OR=4.9; 95% CI=1.9-12.5). Using the potentially most protective genotype GSTM1 (+)/CYP1A1 [(m1/m1)+ (m1/m2)] as the reference group, an increased risk for oral cancer was observed among subjects with the GSTM1 (+)/ CYP1A1 (m2/m2) (OR= 2.0, 95% CI=0.8-5.2), and GSTM1 (-)/ CYP1A1 (m2/m2) (OR=4.9, 95% CI=1.5-15.5) genotypes (p < 0.009, (chi2 trend test).

CONCLUSION

Our results suggest that individuals with a genotype of CYP1A1 (m2/m2) and GSTM1 (-) are highly susceptible for OSCC and that the CYP1A1 (m2/m2) genotype is closely associated with increased risk of OSCC in Koreans.

EPHX1 polymorphisms and the risk of lung cancer: a HuGE review

BACKGROUND

Microsomal epoxide hydrolase 1 (EPHX1) plays an important role in both the activation and detoxification of tobacco-derived carcinogens. Polymorphisms at exons 3 and 4 of the EPHX1 gene have been reported to be associated with variations in EPHX1 activity. The aim of this study is to review and summarize the available molecular epidemiologic studies of lung cancer and EPHX1.

METHODS

We searched MEDLINE, Current Contents, and Web of Science databases for studies published before August 2004. We conducted a systematic review and meta-analysis of 13 case-control studies. Summary odds ratios and summary prevalence of the variant allele (genotype) of both polymorphisms in the EPHX1 gene were calculated using the DerSimonian and Laird method.

RESULTS

The low-activity (variant) genotype of EPHX1 polymorphism at exon 3 was associated with decreased risk of lung cancer (odds ratio = 0.65; 95% confidence interval = 0.44-0.96) in lung cancer risk among whites. In white populations, the high-activity (variant) genotype of EPHX1 polymorphism at exon 4 was associated with a modest increase in risk of lung cancer (1.22; 0.79-1.90) and the predicted low activity was associated with a modest decrease in risk (0.72; 0.43-1.22).

CONCLUSIONS

EPHX1 enzyme may act as a phase I enzyme in lung carcinogenesis. The low-activity genotype of EPHX1 gene is associated with decreased risk of lung cancer among whites.

Genetic analysis of microsomal epoxide hydrolase gene and its association with lung cancer risk

The human microsomal epoxide hydrolase (EH) gene contains polymorphic alleles, which may be linked to increased risk for tobacco-related lung cancer. The purpose of this study is to screen new polymorphisms and determine whether these polymorphisms can be used to predict individual susceptibility to lung cancer. The polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis was used to screen for polymorphisms in the coding region of the EH gene. Eleven polymorphisms, including previously reported polymorphisms, were identified and the prevalence of these variants was assessed in at least 50 healthy Caucasians and African-Americans. Among the 11 polymorphisms, the prevalence of the amino acid-changing EH polymorphisms in codons 43, 113 and 139 was examined in 182 Caucasian incident cases with primary lung cancer, as well as in 365 frequency-matched controls to examine the role of EH polymorphisms in lung cancer risk. A significant increase in lung cancer risk was observed for predicted high EH activity genotypes (odds ratio (OR) 2.3, 95% confidence interval (CI) 1.2-4.3) as compared with low EH activity genotypes. This association was more pronounced among patients with lung adenocarcinoma (OR 4.7, 95% CI 1.7-13.1). These results suggest that the EH polymorphism plays an important role in lung cancer risk and is linked to tobacco smoke exposure.

Cytochrome P-450 1A1 gene polymorphisms and risk of breast cancer: a HuGE review

Cytochrome P-450 (CYP) 1A1 plays a key role in phase I metabolism of polycyclic aromatic hydrocarbons and in estrogen metabolism. It is expressed predominantly in extrahepatic tissues, including the breast. Four CYP1A1 gene polymorphisms (3801T --> C, Ile462Val, 3205T --> C, and Thr461Asp) have been studied in relation to breast cancer. The 3801C variant is more common than the Val variant. Both variants occur more frequently in Asians than in White populations. The 3205T --> C polymorphism has been observed in African Americans only. Little data are available on the geographic/ethnic distribution of the Thr461Asp polymorphism. The functional significance of the polymorphisms is unclear. In 17 studies, no consistent association between breast cancer and CYP1A1 genotype was found. Meta-analysis found no significant risk for the genotypes 1) 3801C/C (relative risk (RR) = 0.97, 95% confidence interval (CI): 0.52, 1.80) or 3801T/C (RR = 0.91, 95% CI: 0.70, 1.19) versus 3801T/T, 2) Val/Val (RR = 1.04, 95% CI: 0.63, 1.74) or Ile/Val (RR = 0.92, 95% CI: 0.76, 1.10) versus Ile/Ile, or 3) Asp/Asp (RR = 0.95, 95% CI: 0.20, 4.49) or Thr/Asp (RR = 1.12, 95% CI: 0.87, 1.43) versus Thr/Thr. Future studies should explore possible interactions between CYP1A1 and sources of polycyclic aromatic hydrocarbons, markers of estrogen exposure, other lifestyle factors influencing hormonal levels, and other genes involved in polycyclic aromatic hydrocarbon metabolism or hormonal biosynthesis.

Functional analysis of human microsomal epoxide hydrolase genetic variants

Human microsomal epoxide hydrolase (EPHX1) is active in the metabolism of many potentially carcinogenic or otherwise genotoxic epoxides, such as those derived from the oxidation of polyaromatic hydrocarbons. EPHX1 is polymorphic and encodes allelic variation at least two amino acid positions, Y113H and H139R. In a number of recent molecular epidemiological investigations, EPHX1 polymorphism has been suggested as a susceptibility factor for several human diseases. To better evaluate the functional contribution of EPHX1 genetic polymorphism, we characterized the enzymatic properties associated with each of the respective variant proteins. Enzymatic profiles were evaluated with cis-stilbene oxide (cSO) and benzo[a]pyrene-4,5-epoxide (BaPO), two prototypical substrates for the hydrolase. In one series of experiments, activities of recombinant EPHX1 proteins were analyzed subsequent to their expression using the pFastbac baculovirus vector in Spodoptera frugiperda-9 (Sf9) insect cells, and purification by column chromatography. In parallel studies, EPHX1 activities were evaluated with human liver microsomes derived from individuals of known EPHX1 genotype. Using the purified protein preparations, rates of cSO and BaPO hydrolysis for the reference protein, Y113/H139, were approximately 2-fold greater than those measured with the other EPHX1 allelic variants. However, when activities were analyzed using human liver microsomal fractions, no major differences were evident in the reaction rates generated among preparations representing the different EPHX1 alleles. Collectively, these results suggest that the structural differences encoded by the Y113H and H139R variant alleles exert only modest impact on EPHX1-specific enzymatic activities in vivo.

Ets1 was significantly activated by ERK1/2 in mutant K-ras stably transfected human adrenocortical cells

In our previous study on the tumorigenesis of human functional adrenal tumors, we observed a high frequency of point mutation in the K-ras gene in clinical adrenal tumors. Therefore, we analyzed gene profiles of mutant K-ras transfected adrenocortical cells by DNA microarray to determine the expression pattern of genes related to cell cycle, signal transduction, apoptosis, tumorigenesis, steroidogenesis, and other expressed sequence tags (ESTs). Then we analyzed all of the significant differentially expressed genes by bioinformatics tools, "Matchminer" and "Gominer." The results revealed that expression of mutant K-ras gene induced by IPTG upregulated Ets1, which was mainly related to cell proliferation. After carefully being analyzed by software "DAVID" and "Pathart," Ets1 was found to be activated by being phosphorylated at theronine 38 by ERK1/2, and in turn, to regulate the following genes: uPA, MMP-3, and prolactin (Ling et al., 2003; Duffy and Daggan, 2004; Maupas-Schwalm et al., 2004; van Themsche et al., 2004). The result of Western blotting analysis confirmed that Ets1 was really phosphorylated when mutant K-ras was activated. On the other hand, the membrane blotting analyses indicated that the expression levels of uPA, MMP-3, and prolactin in human adrenocortical cells stably transfected with the mutant K-ras gene were significantly higher than those in normal control cells. Compared to control cells, the level of prolactin raised 1.4-fold, the level of MMP-3 raised 1.8-fold, and the level of uPA raised 2.1-fold in the transfected cells. From the results of this study, we proposed a mechanism of Ets1 in human adrenocortical cells expressing a mutated K-ras gene.

Genetic polymorphism of the CYP1A1, CYP2E1, GSTM1 and GSTT1 genes and lung cancer susceptibility in a north indian population

CYP1A1, CYP2E1, GSTM1 and GSTT1 polymorphisms were evaluated in north Indian lung cancer patients and controls. The estimated relative risk for lung cancer associated with the CYP1A1*2C allele was 2.68. Apart from the CYP1A1*2C genotype, there was no attributable risk in relation to other genotypes when analyzed singly. However, in the presence of a single copy of the variant CYP1A1 (CYP1A1*1/2A) and null GSTT1 genes, there was a three-fold increased risk for lung cancer; when stratified histologically the relative risk increased to 3.7 in case of SQCC. Similarly individuals carrying the mutant CYP1A1*2C genotype and single copy of the variant CYP1A1 Mspl allele, had a relative risk of 2.85 for lung cancer. In case of the GSTM1 and CYP1A1 genotypes, null GSTM1 and variant Msp1 alleles had two-fold elevated risk for SQCC. On the other hand CYP1A1*2C and null GSTM1 genotype had a 3.5-fold elevated risk for SCLC. Stratified analysis indicated a multiplicative interaction between tobacco smoking and variant CYP1A1 genotypes on the risk for SQCC and SCLC. The heavy smokers (BI > 400) with CYP1A1*2C genotype were at a very high risk to develop SCLC with an OR of 29.30 (95% CI = 2.42-355, p = 0.008). Taken together, these findings, the first to be analyzed in north Indian population, suggest that combined GSTT1 , GSTM1 and CYP1A1 polymorphisms could be susceptible to lung cancer induced by bidi (an Indian cigarette) smoking.

GSTM1, GSTT1, GSTP1 and CYP1A1 genetic polymorphisms and susceptibility to esophageal cancer in a French population: Different pattern of squamous cell carcinoma and adenocarcinoma

AIM: To evaluate the association between CYP1A1 and GSTs genetic polymorphisms and susceptibility to esophageal squamous cell carcinoma (SCC) and esophageal adenocarcinoma (ADC) in a high risk area of northwest of France.

METHODS: A case-control study was conducted to investigate the genetic polymorphisms of these enzymes (CYP1A1*2C and GSTP1 exon 7 Val alleles, GSTM1*2/*2 and GSTT1*2/*2 null genotypes). A total of 79 esophageal cancer cases and 130 controls were recruited.

RESULTS: GSTM1*2/*2 and CYP1A1*1A/*2C genotype frequencies were higher among squamous cell carcinomas at a level close to statistical significance (OR = 1.83, 95%CI 0.88-3.83, P = 0.11; OR = 3.03, 95%CI 0.93-9.90, P = 0.07, respectively). For GSTP1 polymorphism, no difference was found between controls and cases, whatever their histological status. Lower frequency of GSTT1 deletion was observed in ADC group compared to controls with a statistically significant difference (OR = 13.31, 95%CI 1.66-106.92, P < 0.01).

CONCLUSION: In SCC, our results are consistent with the strong association of this kind of tumour with tobacco exposure. In ADC, our results suggest 3 distinct hypotheses: (1) activation of exogenous procarcinogens, such as small halogenated compounds by GSTT1; (2) contribution of GSTT1 to the inflammatory response of esophageal mucosa, which is known to be a strong risk factor for ADC, possibly through leukotriene synthesis; (3) higher sensitivity to the inflammatory process associated with intracellular depletion of glutathione.

Genetic susceptibility to tobacco-related cancer

Although cigarette smoking is the dominant risk factor for several epithelial cancers, only a small fraction of individuals with tobacco exposure develop cancer. The underlying hypothesis is that genetic factors may render certain smokers more susceptible to cancer than others. Genetic alterations in critical regulatory pathways may predispose cells to carcinogenesis. These pathways include regulation of xenobiotic metabolism; control of genomic stability, including DNA repair mechanisms, cell-cycle checkpoints, apoptosis and telomere length; and control of microenvironmental factors, such as matrix metalloproteinases, inflammation and growth factors. In addition, epigenetic events, such as promoter hypermethylation and loss of imprinting, are also involved in carcinogenesis. In this review, we will summarize recent advances in genetic susceptibility to tobacco-related cancer. Emphasizing on risk assessment, we will describe how genetic variations in the above-mentioned genetic pathways modify the tobacco-related cancer risk. In addition, we will discuss how genetic variations may assist in predicting clinical outcome, such as the natural history of cancer and treatment response. The measurements of genetic susceptibility by both genotypic and phenotypic assays are covered in the text. Finally, we present a number of current concerns that need to be addressed as the exciting field of molecular cancer epidemiology advances rapidly.

Retinoblastoma protein (pRB) was significantly phosphorylated through a Ras-to-MAPK pathway in mutant K-ras stably transfected human adrenocortical cells

Our previous studies have shown that the cell proliferation rate, mRNA levels of p450scc, p450c17, and 3betaHSD, and secretion of cortisol were significantly increased in human adrenocortical cells stably transfected with mutated K-ras expression plasmid "pK568MRSV" after being inducted with IPTG. In addition, the increased level was a time-dependent manner. However, the levels of p450, p450scc, p450c17, 3betaHSD, cortisol, and cell proliferation rate were inhibited by a MEK phospholation inhibitor, PD098059. The above results prove that mutated K-ras oncogene is able to regulate tumorigenesis and steroidogenesis through a Ras-RAF-MEK-MAPK signal transduction pathway. The aim of this study was to investigate regulated factors in this pathway and also examine whether the other signal transduction pathways or other moles involved in tumorigenesis or steroidogenesis. In the first year, we analyzed gene profiles of mutant K-ras-transfected adrenocortical cells by DNA microarray to determine the gene expression related to cell cycle, signal transduction, apoptosis, tumorigenesis, steroidogenesis, and other expressed sequence tag. After being affected by the K-ras mutant, gene expression was significantly increased in some upregulated genes. Human zinc-finger protein 22 increased by 28.5 times, Osteopontin increased by 5.8 times, LIM domain Kinase 2 (LIMK2) increased by 3.3 times, Homo sapiens dual-specificity tyrosine-(Y)-phosphorylation regulated Kinase 2 (DYRK2) increased by 2.2 times, and human syntaxin 3 increased by two times. On the other hand, significant decreases in gene expression were also observed in some downregulated genes. Retinoblastoma binding protein 1 (RBBP1) decreased by four times, Homo sapiens craniofacial development protein 1 (CFDP1) decreased by 2.4 times, DAP Kinase-related apoptosis-inducing protein Kinase 1 (DRAK1) decreased by 2.3 times, SKI-interacting protein (SKIP) decreased by 2.2 times, and human poly(A)-Binding protein (PABP) decreased by 2.1 times. In all significant differentially expressed genes, preliminary analysis by bioinformatics revealed that after induced K-ras mutant expression by isopropyl thiogalctoside (IPTG), the downregulation of RBBP1 gene was most correlated to cell proliferation. RBBP1 can bind with RB/E2F to form a mSIN3-HDAC complex, which induces cell cycle arrest in the G1/G0 stage by repressing transcription of E2F-regulated genes. The result of a Northern blot showed that RBBP1 were inhibited after an induction of IPTG for 36 h. Another Northern blot analysis proved that mRNA levels of cyclin D1 and c-myc increased in proportion to K-ras expression. Finally, Western blot was carried out, and the results showed that phosphorylated pRB also increased. Taken together, we infer that the mutant K-ras oncogene promoted the cells to proceed to the G1/S stage by the inhibiting the formation of RB/RBBP1-dependent repressor complex from binding with the SIN3-HDAC complex, which resulted in the acetylation of histone to active transcription of E2F-regulated genes. However, the roles of the other differentially expressed genes involved in cell proliferation, cell morphologic change, tumorigenesis, or steroidogenesis still need further investigation.

Effect of epoxide hydrolase polymorphisms on chromosome aberrations and risk for lung cancer

Microsomal epoxide hydrolase (mEH) gene is polymorphic and its enzyme is involved in the activation and subsequent detoxification of several tobacco carcinogens, for example polycyclic aromatic hydrocarbons. Therefore, we have investigated the association of two polymorphisms at exons 3 and 4 of the mEH gene with the development of lung cancer in 110 patients and 119 matched controls. In addition, we have investigated the relationship between the different mEH alleles and the frequency of chromosome aberrations (CA), as an approach to understand the role of genetic susceptibility on cancer risk. Our results show that only the homozygous exon 4 fast genotype is significantly associated with increased risk for lung cancer (odds ratio [OR]=6.26; 95% confidence interval [CI]=1.02-38.3). When the exons 3 and 4 polymorphisms are considered together, patients carrying the high enzyme activity genotype have a significantly increased risk for lung cancer (OR=2.46; 95% CI=1.06-5.68). More importantly, the increased risk for this group is confirmed by their having the highest frequency of CA compared to any other genotype groups. In addition, genotypes with higher risk had consistently more CA than those with lower risk. Our CA data also indicates that the low activity genotype may exert a protective role in cigarette smokers, as it was associated with a significant decrease in CA compared to the high and intermediate activity genotypes. In conclusion, the CA data provides evidence to support that susceptibility mEH alleles are significantly involved with the development of lung cancer from cigarette smoking.

Association of microsomal epoxide hydrolase polymorphisms and lung cancer risk

Microsomal epoxide hydrolase (mEH) plays a dual role in the detoxification and activation of tobacco procarcinogens. Two polymorphisms affecting enzyme activity have been described in the exons 3 and 4 of the mEH gene, which result in the substitution of amino acids histidine to tyrosine at residue 113, and arginine to histidine at residue 139, respectively. We performed a hospital-based case-control study consisting of 277 newly diagnosed lung cancer patients and 496 control subjects to investigate a possible association between these two polymorphisms and lung cancer risk. The polymorphisms were determined by polymerase chain reaction/restriction fragment length polymorphism and TaqMan assay using DNA from peripheral white blood cells. Logistic regression was performed to calculate odds ratios (ORs), confidence limits (CL) and to control for possible confounders. The exon 3 polymorphism of the mEH gene was associated with a significantly decreased risk of lung cancer. The adjusted OR, calculated relative to subjects with the Tyr113/Tyr113 wild type, for the His113/His113 genotype was 0.38 (95% CL 0.20-0.75). An analysis according to histological subtypes revealed a statistically significant association for adenocarcinomas; the adjusted OR for the His113/His113 genotype was 0.40 (95% CL 0.17-0.94). In contrast, no relationship between the exon 4 polymorphism and lung cancer risk was found. The adjusted OR, calculated relative to the His139/His139 wild type, was for the Arg139/Arg139 genotype 1.83 (0.76-4.44). Our results support the hypothesis that genetically reduced mEH activity may be protective against lung cancer.

Epoxide hydrolase genotype and orolaryngeal cancer risk: interaction with GSTM1 genotype

The human microsomal epoxide hydrolase (EH) gene contains polymorphic alleles which are associated with altered EH activity and may be linked to increased risk for tobacco-related cancers. The objective was to examine the role of EH polymorphisms in orolaryngeal cancer risk. The prevalence of the EH codons 113 and 139 polymorphisms were examined in 81 African American and 142 Caucasian incident orolaryngeal cancer patients and 335 controls frequency-matched on age, sex, and race. In Caucasians, a significant risk increase was observed for subjects with the EH(113Tyr) variant (OR=2.1, 95% CI=1.1-4.0) and predicted high-activity EH genotypes in heavy-smokers (>or=35 pack-years; OR=3.4, 95% CI=1.2-9.6). A significant association between predicted high EH activity genotypes and orolaryngeal cancer risk was observed in Caucasian subjects with the GSTM1 null (OR=3.5, 95% CI=1.3-9.3) but not GSTM [+] (OR=0.9, 95%CI=0.4-2.1) genotype. These results suggest that EH polymorphisms play an important role in risk for orolaryngeal cancer in Caucasians.

Association of GSTM1, CYP1A1 and CYP2E1 genetic polymorphisms with susceptibility to lung adenocarcinoma: a case-control study in Chinese population

A case-control study of 164 lung adenocarcinoma (AC) patients with 181 age- and gender-matched healthy controls was conducted in order to assess any associations between glutathione-S-transferase M1 (GSTM1), cytochrome P4501A1 (CYP1A1) and cytochrome P4502E1 (CYP2E1) polymorphisms and susceptibility to lung AC in Chinese. The presence of CYP2E1 variant allele was significantly less frequent in cases than in controls, while the distribution of GSTM1 null genotype and variant CYP1A1 Msp1 allele did not vary between cases and controls. After adjustment for age, gender, smoking and all other genotypes, the CYP2E1 Rsa1 variant allele was significantly associated with decreased risk of lung AC [odds ratio 0.534 (95% confidence interval, 0.340-0.837)]. Furthermore, 3.0-fold increased risk was found in individuals with combined GSTM1 null genotype and CYP2E1 Rsa1 wild type versus those with combined GSTM1 non-null type and CYP2E1 variant allele. Our results suggest that CYP2E1 Rsa1 variant allele is associated with a decreased risk of lung AC, and combined GSTM1 null genotype and CYP2E1 Rsa1 wild type has a promoting effect on susceptibility to lung AC.

Environmental exposure and lung cancer among nonsmokers: an example of Taiwanese female lung cancer

Lung cancer is the leading cause of cancer death worldwide and in Taiwan. Cigarette smoking is considered to be the most important risk factor, since about 90% of lung cancer can be related to cigarette smoking. Despite the recent decrease of cigarette smoking, lung cancer is still the leading cause of cancer death in the United States. In Taiwan, only around 50% of lung cancer incidence could be associated with cigarette smoking, particularly less than 10% of Taiwanese women are smokers. Thus, the aetiology of lung cancer for nonsmokers remains unknown. DNA damages including bulky and oxidative damage may be related with mutation of tumor suppressor genes, such as p53 gene. The high DNA adduct levels in female may be associated with frequent exposure to indoor cooking oil fumes (COF) and outdoor heavy air pollution. Oxidative stress induced by COF was also discussed. Different p53 mutation spectra and mutation frequency between genders reflected that different environmental factors may be involved in nonsmoking male and female lung cancer development. Most importantly, our recent report has demonstrated that human papillomavirus (HPV) infection was associated with nonsmoking female lung cancer. Based on our studies with Taiwanese nonsmoking lung cancer as the model, the possible aetiological factors of lung cancer incidence in Taiwanese nonsmokers were elucidated.

Non-synonymous single nucleotide alterations in the microsomal epoxide hydrolase gene and their functional effects

1. By sequencing genomic DNA from 72 established cell lines derived from Japanese individuals, we detected 25 single nucleotide alterations in the microsomal epoxide hydrolase (EPHX1) gene. Of them, five were exonic alterations resulting in amino acid alterations (77C>G, T26S; 128G>C, R43T; 337T>C, Y113H; 416A>G, H139R; 823A>G, T275A). The T26S, R43T, Y113H and H139R substitutions were found at relatively high frequencies and seemed to be polymorphic, and T26S and T275A were novel. 2. To examine the effects of these amino acid alterations on EPHX1 function, EPHX1 cDNA constructs of wild-type and five variants were transfected into COS-1 cells, and their hydrolytic activities for cis-stilbene oxide were determined in vitro. Although all of the transfectants expressed EPHX1 mRNA and protein at similar levels, the variant H139R protein was expressed at a significantly higher level (128% of the wild-type). K(m) values were not significantly different between the wild-type and variants. 3. Increase (140%) in the enzymatic activity (V(max)) of the variant H139R was accompanied by the increased EPHX1 protein level without any significant change in the intrinsic EPHX1 activity. On the other hand, the variant R43T showed increased values for V(max) and clearance (V(max)/K(m)) (around 130%) both on a microsomal protein basis and on a EPHX1 protein basis. 4. These results suggest that R43T as well as H139R increase epoxide hydrolase activity.

Overexpression of aryl hydrocarbon receptor in human lung carcinomas

Exposure to polycylic aromatic hydrocarbons (PAH) has been associated with increased risk of lung cancer. Aryl hydrocarbon receptor (AhR) is known to play an essential role in PAH-induced toxicity. The objectives of this study were to identify and evaluate AhR expression in normal human lung tissues and in lung carcinomas. AhR protein and mRNA levels in human lung cell lines were evaluated with immunoblot and quantitative real-time RT-PCR assays, respectively. AhR protein expression was high in cytosol homogenates of adenocarcinoma (AD) cell lines and AhR mRNA levels corresponded well with AhR protein levels in these cell lines. AhR expression in human lung tissues and carcinomas were examined by means of immunohistochemical staining method. In normal lung tissues, immunostaining was found in the cytosol of bronchiolar epithelial cells. AhR immunostaining was more intense in AD than in squamous cell carcinomas. When AhR expression was compared with noral bronchiolar epithelial cells and neoplastic cells in the same specimens, the neoplastic cells, especially those of AD, demonstrated an increased staining. The upregulation of AhR mRNA expression was also demonstrated among 2 of 4 paired tissues with the quantitative real-time RT-PCR assay. Our data indicated that AhR expression was upregulated in lung AD and suggested that AhR and its expression might play an important role in the development of lung AD.

Microsomal epoxide hydrolase and glutathione S-transferase polymorphisms in relation to laryngeal carcinoma risk

Two polymorphic sites of the microsomal epoxide hydrolase gene (EPHX1, 113Tyr-->113His, 139His-->139Arg) and four glutathione S-transferase genes (GSTM1, GSTM3, GSTP1, GSTT1) were genotyped in a group of patients with larynx cancer (N=204) and in a group of healthy controls (N=203), all Spanish caucasians. After adjusting for gender, age, and tobacco smoking, none of the polymorphisms alone were found to be associated with larynx cancer risk. The analysis of EPHX1/GST combinations, however, showed a significant over-representation of patients with a combination of 113Tyr/113Tyr EPHX1 and 105Ile/105Ile GSTP1 (adjusted odds ratio (OR): 1.95; 95% confidence interval (CI): 1.02-3.78). The calculation of the predicted epoxide hydrolase (EH) activity also showed an increased risk for the individuals with both predicted high activity EH and 105Ile/105Ile GSTP1 (OR: 2.90; 95% CI: 1.10-7.67). These results on larynx cancer tend to confirm a former study on lung cancer (Cancer Lett. 173 (2001) 155) suggesting the existence of an interaction between variants of EH and GSTpi, both enzymes being involved in the metabolism of aromatic hydrocarbons, that may increase susceptibility to tobacco-related cancers.

Genetic polymorphisms and lung cancer susceptibility: a review

Lung cancer is a major cause of cancer-related death in the developed countries and the overall survival rate has still an extremely poor. Cigarette smoking is an established risk factor for lung cancer although a possible role for genetic susceptibility in the development of lung cancer has been inferred from familial clustering of the disease and segregation analyzes. Everyone may have a unique combination of polymorphic traits that modify genetic susceptibility and response to drugs, chemicals and carcinogens. Developments in molecular biology have led to growing interest in investigation of biological markers, which may increase predisposition to lung carcinogenesis. Therefore, the high-risk genotype of an individual could be determined easily. As there are the great number of carcinogen-activating and -detoxifying enzymes, the variation in their expression and the complexity of exposures to tobacco carcinogens, the existence of multiple alleles at loci of those enzymes may result in differential susceptibilities of individuals. This review summarize data addressing the relationships of lung cancer to markers of genetic susceptibility genes, including metabolic polymorphisms other than well-investigated cytochrome P450s or glutathione S-transferases, DNA repair genes and the p53 tumor suppressor gene. Among genetic polymorphisms reviewed here, myeloperoxidase gene (a G to A mutation) and microsomal epoxide hydrolase exon 4 polymorphism (substitution of Arg for His) were significantly associated with lung cancer risk. As lung cancer is a multifactorial disease, an improved understanding of the interplay of environmental and genetic polymorphisms at multiple loci may help identify individuals who are at increased risk for lung cancer. Hopefully, in the future we will be able to screen for lung cancer susceptibility by using specific biomarkers.

Microsomal epoxide hydrolase polymorphisms and lung cancer risk: a quantitative review

To investigate the role of microsomal epoxide hydrolase (mEH) polymorphisms in the aetiology of lung cancer and to assess the interaction between mEH polymorphisms and smoking, we performed a meta-analysis of seven published studies, which included 2078 cases and 3081 controls, and a pooled analysis of eight studies (four published and four unpublished at that time) with a total of 986 cases and 1633 controls. The combined meta-analysis odds ratios (ORs) were 0.98 (95% confidence interval [CI] = 0.72-1.35) for polymorphism at amino acid 113 in exon 3 (His/His versus Tyr/Tyr genotype) and 1.00 (95% CI = 0.71-1.41) for polymorphism at amino acid 139 in exon 4 (Arg/Arg versus His/His genotype). In the pooled analysis, we observed a significant decrease in lung cancer risk (OR = 0.70, 95% CI = 0.51-0.96) for exon 3 His/His genotype after adjustment for age, sex, smoking and centre. The protective effect of exon 3 polymorphism seems stronger for adenocarcinoma of the lung than for other histological types. The OR for high predicted mEH activity, compared with low activity, was 1.54 (95% CI = 0.77-3.07) in the meta analysis and 1.18 (95% CI = 0.92-1.52) in the pooled analysis. We did not find a consistent modification of the carcinogenic effect of smoking according to mEH polymorphism, although the risk of lung cancer decreased among never smokers with high mEH activity and among heavy smokers with the exon 3 His/His genotype. In conclusion, this study suggests a possible effect of mEH polymorphisms at exon 3 in modulating lung cancer. If present, this effect may vary among different populations, possibly because of interaction with genetic or environmental factors.

Genetic polymorphism of enzymes involved in xenobiotic metabolism and the risk of lung cancer

Chronic inhalation of cigarette smoke is a major risk factor for the development of lung cancer. It has been suggested that genetic susceptibility may contribute to the risk, because only a small portion of smokers develops the disease. Several polymorphisms that involve the metabolic activation or detoxification of carcinogens derived from cigarette smoke have been found to be associated with lung cancer risk. Many studies have focused on the relation between the distribution of polymorphic variants of different forms of the metabolic enzymes and lung cancer susceptibility. In this respect two groups of genetic polymorphisms of enzymes involved in xenobiotic metabolism, cytochrome P450 (CYP) and glutathione S-transferases (GSTs), have been discussed.CYP multigene superfamily consists of 10 subfamilies (CYP1-CYP10). A positive association between development of lung cancer and the mutant homozygous genotype ofCYP1A1 gene has been reported in several Japanese populations but such an association has not been observed in either Caucasians or African-Americans. The relation betweenCYP2D6 and lung cancer remains conflicting and inconclusive. Several polymorphisms have been identified at theCYP2E1 locus. No definitive link between the polymorphisms ofCYP2E1 and the risk of lung cancer has, however, been identified. The role of otherCYP2 isoforms in lung carcinogenesis has not been sufficiently investigated.GSTs form a superfamily of genes consisting of five distinct families, namedGSTA, GSTM, GSTP, GSTT andGSTS. The role ofGSTM, GSTT1 orGSTP1 polymorphism in modifying the lung cancer risk may be more limited than has been so far anticipated.Although some genetic polymorphisms discussed here have not shown significant increases/decreases in risk, individuals with differing genotypes may have different susceptibilities to lung cancer. Hopefully, in future studies it will be possible to screen for lung cancer using specific biomarkers.

Morphologic change and elevation of cortisol secretion in cultured human normal adrenocortical cells caused by mutant p21K-ras protein

In our previous study on the tumorigenesis of human functional adrenal tumors, we observed a high frequency of K-ras point mutations in clinical specimens. Furthermore, we cloned the mutated K-ras gene from the tumors and inserted it into vectors to transfect normal bovine adrenocortical cells to express the mutated K-ras gene. The mRNA level of steroidogenic enzymes such as cholesterol sidechain cleavage enzyme (P450SCC), 17alpha-hydroxylase/17,20-lyase (P450c17), and 3beta-hydroxysteroid dehydrogenase (3betaHSD) in the mutant K-ras stably transfected cells were elevated. Cultured normal adrenocortical cells from donors and patients with adrenocortical tumors were then transfected with mutant K-ras expression plasmids constructed from human adrenal tumors. Stable transfectants grew faster than normal cells. Additionally, morphologic change was observed in the transfected cells. Moreover, when the synthesis of hormones was analyzed, the mRNA of P450SCC, P450C17, and 3betaHSD was found to have increased, and the level of cortisol was 18 to 25 times that in control cells. The increased steroid hormone production in mutant K-ras-transfected cells was reversed by lovastatin, a pharmacologic inhibitor of p21ras function. These results, combined with previous reports of steroidogenic K-ras in bovine adrenocortical cells, suggest that the K-ras oncogene is involved in steroidogenesis in human adrenocortical cells.

Lung cancer susceptibility in relation to combined polymorphisms of microsomal epoxide hydrolase and glutathione S-transferase P1

Human microsomal epoxide hydrolase (mEH) catalyzes a key step in the biotransformation of benzo[a]pyrene that yields the highly mutagenic (+)-anti-7,8-diol-9,10 epoxide (BPDE). Two polymorphisms have been described in the coding region of the mEH gene (EPHX1) that produce two protein variants: 113Tyr-->113His (exon 3) and 139His-->139Arg (exon 4). We performed a case-control study among Northwestern Mediterranean Caucasians to investigate a possible association between these EPHX1 variants and lung cancer risk. Both EPHX1 polymorphisms were analyzed in a group of lung cancer patients (n=176) and in a control group of healthy smokers (n=187). The results showed a significantly decreased risk for the rare homozygous 113His/113His (adjusted odds ratio (OR): 0.44, 95% confidence interval (CI): 0.27-0.71) and 139Arg/139Arg (adjusted OR: 0.55, 95% CI: 0.33-0.91) compared with the major wild-types 113Tyr/113Tyr and 139His/139His, respectively, as the references. Thereafter, we analyzed the EPHX1 variants in combination with three glutathione S-transferase polymorphic genes (GSTM1, GSTT1, and GSTP1) and we found a significant overepresentation of cancer patients with a combination of exon 3 113Tyr/113Tyr EPHX1 and exon 5 105Ile/105Ile GSTP1 (adjusted OR: 2.34, 95% CI: 1.21-4.52). The polymorphic site within the exon 5 of GSTP1 results in a Ile-->Val substitution, and the isoleucine GSTpi isoform has been found in vitro to be less active than the valine isoform towards the conjugation of BPDE. The 113 Tyr/Tyr EPHX1 encodes for a high-activity mEH. Our results agree with these observations in vitro and suggest that a genetically determined combination of a high-activity mEH and a low-activity GSTpi may increase lung cancer risk among smokers.

Genetic polymorphisms of NAD(P)H quinone oxidoreductase, CYP1A1 and microsomal epoxide hydrolase and lung cancer risk in Nanjing, China

Genetic variations in metabolic activation or detoxification enzymes have been thought to contribute to individual differences in lung cancer susceptibility. Genetic polymorphisms of NAD(P)H quinone oxidoreductase (NQO1), cytochrome P4501A1 (CYP1A1) and microsomal epoxide hydrolase (HYL1) have been associated with increased lung cancer risk in Asian populations. In the present study, the possibility of an association of NQO1, CYP1A1 and HYL1 genetic polymorphisms with lung cancer was examined among residents in Nanjing, China. A total of 84 lung cancer patients and 84 control subjects were matched by age, gender, occupation and smoking status. No significant association was observed for these genetic polymorphisms with the overall incidence of lung cancer. When the groups were stratified according to smoking status, we found that smokers carrying the HYL1*2 allele had a higher relative risk for lung cancer Odds ratio ((OR), 5.66; 95% confidence interval (95% CI), 1.71-18.68). The association was also found with squamous cell carcinoma (OR, 3.23; 95% CI, 1.00-10.38). Our results suggest that HYL1*2 polymorphism might be a risk factor for smoking-associated lung cancer in China.

Significantly increased cortisol secretion in normal adrenocortical cells transfected with K-ras mutants derived from human functional adrenocortical tumors

Our previous study showed that the mutation hotspots of the K-ras proto-oncogene in human functional adrenocortical tumors are in codons 15, 16, 18, and 31, thus differing from the sites in other tumors. In addition, analyzing the K-Ras protein by a recombinant DNA technique showed that the activity of endogenic GTPase and the GTPase-activating protein (GAP)-binding ability were significantly decreased in patients with these tumors. The aim of this study was to understand whether those K-ras mutants, which were found only in human adrenocortical tumors, play an important role in these tumors. Thus, the mutant K-ras cDNA was constructed with mammalian expression vectors and transfected into normal adrenocortical cells. The amount of cortisol secreted by the transfected cells was 20 to 30 times that of normal cells. Furthermore, Northern blot analysis revealed that the expression of the three steroidogenesis-related genes P450(scc) (cholesterol side-chain cleavage enzyme), P450(C17) (17alpha-hydroxylase/17, 20-lyase), and P450(C21) (steroid 21-hydroxylase) gene increased in the transfected cells. The K-ras oncogene significantly increases cortisol secretion by normal adrenocortical cells.

Gender difference in DNA adduct levels among nonsmoking lung cancer patients

Lung cancer is the leading cause of cancer mortality in Taiwanese women. Cigarette smoking cannot explain the high lung cancer mortality in this population because less than 10% of women in Taiwan are smokers. Therefore, environmental factors other than smoking may play an important role in lung cancer development in female nonsmokers. The purpose of this study was to elucidate the role of environmental carcinogen exposure in lung cancer development in Taiwanese female nonsmokers, based on DNA adduct formation. We collected nontumorous lung tissues resected from 62 nonsmoking lung cancer patients and 20 noncancer controls to investigate whether differences in susceptibility to DNA adduct formation exist between men and women. (32)P-postlabeling and ELISA (enzyme-linked immunosorbent assay) with polyclonal antibody against BPDE (7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene)-DNA adduct were used to evaluate DNA adduct levels in lung tissues of study subjects. Our data showed that the DNA adduct levels of lung cancer patients determined by both assays were significantly higher than those of noncancer controls (P = 0.0001 for (32)P-postlabeling; P = 0.01 for ELISA). Moreover, DNA adduct levels in females were markedly greater than those in males (P = 0.014 for (32)P-postlabeling; P = 0.001 for ELISA). The difference in DNA adduct levels could not be explained by genetic polymorphisms of cytochrome P-4501A1 (CYP1A1) or glutathione S-transferase (GSTM1), as determined by polymerase chain reaction and restriction fragment length polymorphism. These results demonstrate that lung cancer patients have a higher susceptibility to DNA damage than that of noncancer controls. In addition, differences in susceptibility to DNA damage derived from environmental carcinogen exposure were observed between male and female nonsmokers. In conclusion, high susceptibility to DNA damage in females may partially explain the high mortality rate of lung cancer in nonsmoking Taiwanese women.

Epoxide hydrolases: biochemistry and molecular biology

Epoxides are organic three-membered oxygen compounds that arise from oxidative metabolism of endogenous, as well as xenobiotic compounds via chemical and enzymatic oxidation processes, including the cytochrome P450 monooxygenase system. The resultant epoxides are typically unstable in aqueous environments and chemically reactive. In the case of xenobiotics and certain endogenous substances, epoxide intermediates have been implicated as ultimate mutagenic and carcinogenic initiators Adams et al. (Chem. Biol. Interact. 95 (1995) 57-77) Guengrich (Properties and Metabolic roles 4 (1982) 5-30) Sayer et al. (J. Biol. Chem. 260 (1985) 1630-1640). Therefore, it is of vital importance for the biological organism to regulate levels of these reactive species. The epoxide hydrolases (E.C. 3.3.2. 3) belong to a sub-category of a broad group of hydrolytic enzymes that include esterases, proteases, dehalogenases, and lipases Beetham et al. (DNA Cell Biol. 14 (1995) 61-71). In particular, the epoxide hydrolases are a class of proteins that catalyze the hydration of chemically reactive epoxides to their corresponding dihydrodiol products. Simple epoxides are hydrated to their corresponding vicinal dihydrodiols, and arene oxides to trans-dihydrodiols. In general, this hydration leads to more stable and less reactive intermediates, however exceptions do exist. In mammalian species, there are at least five epoxide hydrolase forms, microsomal cholesterol 5,6-oxide hydrolase, hepoxilin A(3) hydrolase, leukotriene A(4) hydrolase, soluble, and microsomal epoxide hydrolase. Each of these enzymes is distinct chemically and immunologically. Table 1 illustrates some general properties for each of these classes of hydrolases. Fig. 1 provides an overview of selected model substrates for each class of epoxide hydrolase.

DNA adduct level in lung tissue may act as a risk biomarker of lung cancer

Lung cancer is a leading cause of mortality in Taiwan. We hypothesised that high susceptibility to DNA damage in the target organ acts as a risk biomarker for the development of lung cancer. To verify this hypothesis, the aromatic/hydrophobic DNA adduct levels of non-tumorous adjacent lung tissues from 73 primary lung cancer patients and 33 non-cancer controls were evaluated by 32P-postlabelling assay. Wilcoxon rank sum test showed that DNA adduct levels in lung cancer patients (49.58+/-33.39 adducts/10(8) nucleotides) were significantly higher than those in non-cancer controls (18.00+/-15.33 adducts/10(8) nucleotides, P<0.001). The DNA adduct levels among lung cancer and non-cancer samples were not influenced by smoking behaviour and cigarette consumption. Our data also showed that the polymorphisms of cytochrome P4501A1 (CYP1A1) Msp1, glutathione S-transferase M1 (GSTM1) and the combination of both genetic polymorphisms were not related to the DNA adduct levels. Interestingly, positive association between CYP1A1 protein expression and DNA adduct levels was found when CYP1A1 protein expression in lung specimens from lung cancer patients was examined by immunohistochemistry. Multivariate linear regression analysis indicated that the DNA adduct level was not associated with gender, smoking behaviour, or genetic polymorphisms of CYP1A1 and GSTM1. Moreover, multivariate logistic regression analysis showed that persons with high DNA adduct levels (>48.66 adducts/10(8) nucleotides) had an approximately 25-fold risk of lung cancer compared with persons with low DNA adduct levels (</=48.66 adducts/10(8) nucleotides). In conclusion, DNA adduct levels in lung tissue may be a more reliable lung cancer susceptibility biomarker than DNA adduct levels in leucocytes. In addition, higher susceptibility to DNA damage in lung cancer patients may partly play a role in the development of lung cancer.