Human 8-oxoguanine DNA glycosylase 1 mRNA expression as an oxidative stress exposure biomarker of cooking oil fumes

Association of Particulate Matter from Cooking Oil Fumes with Heart Rate Variability and Oxidative Stress

Many studies have reported various cardiovascular autonomic responses to ambient particulate matter (PM) pollution, but few have reported such responses to occupational PM exposures. Even fewer have demonstrated a relationship between PM pollution and oxidative stress in humans. This panel study evaluates the association between occupational exposure to PM in cooking oil fumes (COFs), and changes in both heart rate variability (HRV) and oxidative stress responses in 54 male Chinese cooks. Linear mixed-effects regression models were adopted to estimate the strength of the association between PM and HRV. Participants' pre- and post-workshift urine samples were analyzed for 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA). Exposure to PM in COFs from 15 min to 2 h were associated with a decrease in HRV and an increase in heart rate among cooks. The urinary 8-OHdG levels of cooks were significantly elevated after workshift exposure to COFs. The levels of PM2.5, PM1.0, and particulate benzo(a)pyrene in COFs were all positively correlated with cross-workshift urinary 8-OHdG levels. Furthermore, the levels of benzo(a)pyrene in COFs were positively correlated with cross-workshift urinary MDA levels. The effects of COFs on HRV were independent of cross-workshift urinary 8-OHdG levels. Exposure to COFs leads to disturbed autonomic function and an increased risk of oxidative DNA injury among cooks in Chinese restaurants.

Grill Workers Exposure to Polycyclic Aromatic Hydrocarbons: Levels and Excretion Profiles of the Urinary Biomarkers

Grilling activities release large amounts of hazardous pollutants, but information on restaurant grill workers’ exposure to polycyclic aromatic hydrocarbons (PAHs) is almost inexistent. This study assessed the impact of grilling emissions on total workers’ exposure to PAHs by evaluating the concentrations of six urinary biomarkers of exposure (OHPAHs): naphthalene, acenaphthene, fluorene, phenanthrene, pyrene, and benzo(a)pyrene. Individual levels and excretion profiles of urinary OHPAHs were determined during working and nonworking periods. Urinary OHPAHs were quantified by high-performance liquid-chromatography with fluorescence detection. Levels of total OHPAHs (∑OHPAHs) were significantly increased (about nine times; p ≤ 0.001) during working comparatively with nonworking days. Urinary 1-hydroxynaphthalene + 1-hydroxyacenapthene and 2-hydroxyfluorene presented the highest increments (ca. 23- and 6-fold increase, respectively), followed by 1-hydroxyphenanthrene (ca. 2.3 times) and 1-hydroxypyrene (ca. 1.8 times). Additionally, 1-hydroxypyrene levels were higher than the benchmark, 0.5 µmol/mol creatinine, in 5% of exposed workers. Moreover, 3-hydroxybenzo(a)pyrene, biomarker of exposure to carcinogenic PAHs, was detected in 13% of exposed workers. Individual excretion profiles showed a cumulative increase in ∑OHPAHs during consecutive working days. A principal component analysis model partially discriminated workers’ exposure during working and nonworking periods showing the impact of grilling activities. Urinary OHPAHs were increased in grill workers during working days.

Association between prenatal exposure to cooking oil fumes and full-term low birth weight is mediated by placental weight

OBJECTIVE

Evidence regarding the association between prenatal exposure to cooking oil fumes (COF) and full-term low birth weight (FTLBW) is still controversial, and the mechanism remains unclear. This study thus aims to explore the association of prenatal COF exposure with off-spring FT-LBW as well as the mediating role of placenta in their association.

METHODS

A case-control study enrolling 266 pregnant women delivering FTLBW newborns (cases) and 1420 delivering normal birth weight (NBW) newborns (controls) was conducted. Information on prenatal COF exposure, socio-demographics, and obstetric conditions were collected at the Women's and Children's Hospitals of Shenzhen and Foshan in Guangdong, China. Linear and hierarchical logistic regression models were undertaken to explore the associations among COF exposure, placenta and birth weight, as well as the mediation effect of placental weight.

RESULTS

After controlling for potential confounders, prenatal COF exposure was significantly associated with the higher risk of FT-LBW (OR = 1.31, 95% CI= 1.06-1.63) and the lower placental weight (ß = -0.12, 95% CI= -0.23 ~ -0.005). Compared with mothers who never cooked, those cooking sometimes (OR= 2.99, 95% CI= 1.48-6.04) or often (OR= 3.41, 95% CI= 1.40-8.34) showed a higher risk of FT-LBW, and likewise, those cooking for less than half an hour (OR= 2.08, 95% CI= 1.14-3.79) or cooking between half to an hour (OR= 2.48, 95% CI= 1.44-4.29) were also more likely to exhibit FT-LBW. Different cooking methods including pan-frying (OR= 2.24, 95% CI= 1.30-3.85) or deep-frying (OR= 1.78, 95% CI= 1.12-2.85) during pregnancy were associated with increased FT-LBW risks as well. The further mediation analysis illustrated that placental weight mediated 15.96% (95% CI: 12.81~28.80%) and 15.90% (95% CI= 14.62%~16.66%) of the associations of cooking during pregnancy and frequency of prenatal COF exposure, respectively, with FT-LBW.

Exposure to cooking oil fumes and chronic bronchitis in nonsmoking women aged 40 years and over: a health-care based study

Background

Little is known about the effect of exposure to cooking oil fumes (COFs) on the development of non-malignant respiratory diseases in nonsmoking women. This study investigated the relationship between exposure to COFs and chronic bronchitis in female Taiwanese non-smokers.

Methods

Searching the 1999 claims and registration records maintained by Taiwan’s National Health Insurance Program, we identified 1846 women aged 40 years or older diagnosed as having chronic bronchitis (ICD-9 code: 491) at least twice in 1999 as potential study cases and 4624 women who had no diagnosis of chronic bronchitis the same year as potential study controls. We visited randomly selected women from each group in their homes, interviewed to collect related data including cooking habits and kitchen characteristics, and them a spirometry to collect FEV1 and FVC data between 2000 and 2009.

Results

After the exclusion of thirty smokers, the women were classified those with chronic bronchitis (n = 53), probable chronic bronchitis (n = 285), and no pulmonary disease (n = 306) based on physician diagnosis and American Thoracic Society criteria. Women who had cooked ≥ 21 times per week between the ages of 20 and 40 years old had a 4.73-fold higher risk of chronic bronchitis than those cooking < 14 times per week (95% CI = 1.65–13.53). Perceived kitchen smokiness was significantly associated with decreased FEV1 (− 137 ml, p = 0.021) and FEV1/FVC ratio (− 7.67%, p = 0.008).

Conclusions

Exposure to COF may exacerbate the progression of chronic bronchitis in nonsmoking women.

Electronic supplementary material

The online version of this article (10.1186/s12889-018-5146-x) contains supplementary material, which is available to authorized users.

Feasibility of 8-OHdG formation and hOGG1 induction in PBMCs for assessing oxidative DNA damage in the lung of COPD patients

BACKGROUND AND OBJECTIVE

Oxidative stress has long been recognized to play a role in chronic obstructive pulmonary disease (COPD); however, approaches for assessing oxidative stress are lacking. The objective of this study was to address the feasibility of measuring 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-OHdG) formation and human 8-oxoguanine DNA glycosylase (hOGG1) induction in peripheral blood mononuclear cell (PBMC) to assess oxidative deoxyribonucleic acid (DNA) damage in the lung of smoking COPD patients.

METHODS

PBMC were obtained from 412 participants including 129 smokers with COPD, 143 healthy smokers and 140 healthy non-smokers. Lung tissue specimens and PBMC were obtained from smoker COPD (n = 12), healthy smokers (n = 12) and healthy non-smokers (n = 10). 8-OHdG and hOGG1 were detected, and correlation analysis was conducted for assessing the feasibility.

RESULTS

Oxidative DNA damage (8-OHdG formation) along with impaired induction of hOGG1 expression in the lung was a prominent feature for smokers COPD patients. PBMC originated from smokers COPD patients also displayed similar features to that of lung tissues. Correlation analysis suggests that PBMC could be used as a surrogate for oxidative DNA damage in lung of smokers COPD patients. Indeed, 8-OHdG levels in PBMC DNA were negatively correlated with lung function, while hOGG1 induction in PBMC was associated with improved lung function in smokers COPD patients.

CONCLUSIONS

COPD patients manifest oxidative DNA damage of 8-OHdG along with impaired hOGG1 expression in the lung, whereas 8-OHdG formation and hOGG1 induction in PBMC could be a biomarker of oxidative DNA damage in the lung.

Cooking oil fumes and lung cancer: a review of the literature in the context of the U.S. population

There is growing evidence that exposure to cooking oil fumes (COF) is linked to lung cancer. Existing literature on this risk was reviewed, specifically as it may relate to potentially at-risk populations such as Chinese immigrants and restaurant workers in the United States. Studies were identified by searching the NCBI database with key terms. All studies that examined the significance, prevalence, and/or mechanism(s) of the association between COF exposure and cancer (all types) were included. A majority of epidemiologic studies found associations between lung cancer and COF exposure. All studies that examined the mechanisms underlying the risk found evidence for mutagenic and/or carcinogenic compounds in COF extract and/or molecular mechanisms for COF-induced DNA damage or carcinogenesis. The evidence reviewed underscores the need to thoroughly investigate the association among at-risk groups in the United States, as well as to develop and assess concrete interventions to reduce these risks.

Toxic effect of cooking oil fumes in primary fetal pulmonary type II-like epithelial cells

Epidemiological studies indicated that there is an increased risk of respiratory tract cancer among cooks and bakers. The cooking oil fumes are believed to conduct this risk, and many studies have focused on evaluating the mutagenicity and finding the mutagenic components in oil fumes. COFs contains two major classes of compounds. One class consists of polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]pyrene, benzo[b]fluoranthene, fluoranthene, and benzo[g,h,i]perylene. BaP is a known immunosuppressant. It can also alter cell cycle progression, induce inflammation, and impair DNA repair and apoptotic processes leading to aberrant cellular functioning. This study investigates the effect of toxicity of cooking oil fumes (COFs) in primary ICR mice' fetal lung type II-like epithelium cells (AEC II). The cells were cultured in different concentrations (0, 12.5, 25, 50, 100, and 200μg/ml) of COFs for different time periods. The results showed that cell viability decreased in a dose- and time- dependent manner, which is accompanied by increased malondialdehyde (MDA) level and decreased superoxide dismutase (SOD) and glutathione (GSH) activities. Moreover, comet assay suggested DNA damage, as well as increased production of DNA adducts induced by PAHs. The present study also shows that COFs may disturb cell cycles even at a very low dose. In summary, the present study indicates that COFs may lead to toxicity in AEC II cells.

Occupational exposure to woodsmoke and oxidative stress in wildland firefighters

Experimental studies indicate that exposure to woodsmoke could induce oxidative stress. However studies have not been conducted among the general population and specialized occupational groups despite the existence of elevated woodsmoke exposure situations. Therefore, we investigated whether there were across workshift changes in oxidative stress biomarkers among wildland firefighters who are occupationally exposed to elevated levels of woodsmoke. We collected pre- and post-workshift urine samples from 19 wildland firefighters before and after prescribed burns. We measured malondialdehyde (MDA) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in the samples, and analyzed whether there were cross-shift changes in their levels, and the relationships between the changes and the length of firefighting career, age of firefighter, and quantified workshift exposure to particulate matter. Overall no significant cross-shift change was observed for 8-oxodG or MDA in the urine samples of the firefighters. Changes in both biomarkers were also not associated with PM2.5, which was used as a marker of exposure. However, overall unadjusted geometric mean 8-oxo-dG levels in the samples (31 μg/g creatinine) was relatively higher compared to those measured in healthy individuals in many occupational or general population studies. Additionally, cross-shift changes in 8-oxo-dG excretion were dependent on the length of firefighting career (p=0.01) or age of the subject (p=0.01). Significant increases in 8-oxo-dG level from pre-shift to post-shift were observed for those who had been firefighters for 2 years or less. The results indicate that oxidative stress response measured as cross-shift changes in 8-oxo-dG may depend on age or the length of a firefighter's career. These results suggest the need to investigate the longer term health effects of cumulative exposure of woodsmoke exposure among wildland firefighters, because increased body burden of oxidative stress is a risk factor for many diseases and is theorized to be involved in aging.

Oxidatively damaged DNA and its repair in colon carcinogenesis

Inflammation, high fat, high red meat and low fiber consumption have for long been known as the most important etiological factors of sporadic colorectal cancers (CRC). Colon cancer originates from neoplastic transformation in a single layer of epithelial cells occupying colonic crypts, in which migration and apoptosis program becomes disrupted. This results in the formation of polyps and metastatic cancers. Mutational program in sporadic cancers involves APC gene, in which mutations occur most abundantly in the early phase of the process. This is followed by mutations in RAS, TP53, and other genes. Progression of carcinogenic process in the colon is accompanied by augmentation of the oxidative stress, which manifests in the increased level of oxidatively damaged DNA both in the colon epithelium, and in blood leukocytes and urine, already at the earliest stages of disease development. Defence mechanisms are deregulated in CRC patients: (i) antioxidative vitamins level in blood plasma declines with the development of disease; (ii) mRNA level of base excision repair enzymes in blood leukocytes of CRC patients is significantly increased; however, excision rate is regulated separately, being increased for 8-oxoGua, while decreased for lipid peroxidation derived ethenoadducts, ɛAde and ɛCyt; (iii) excision rate of ɛAde and ɛCyt in colon tumors is significantly increased in comparison to asymptomatic colon margin, and ethenoadducts level is decreased. This review highlights mechanisms underlying such deregulation, which is the driving force to colon carcinogenesis.

The precancerous effect of emitted cooking oil fumes on precursor lesions of cervical cancer

Although cooking emission from high-temperature frying has been deemed a Group 2A carcinogen by the International Agency for Research on Cancer, little is known about its impact on cervical tumorigenesis. To investigate the precancerous consequence of cooking oil fumes on cervical intraepithelial neoplasm (CIN), a community-based case-control study, which takes all known risk factors into consideration, was conducted in Taiwan. From 2003 to 2008, in a Pap smear screening and biopsy examination network, 206 pathology-verified women with inflammations/atypical squamous cells of undetermined significance or CIN grade-1 (CIN1) and 73 with CIN2-3 (defined as low-grade squamous intraepithelial lesions (LGSIL) and high-grade squamous intraepithelial lesions (HGSIL), respectively); and 1,200 area-and-age-matched controls with negative cytology were recruited. Multinomial logistic regression was applied in the multivariate analysis to determine the likelihood of contracting LGSIL or HGSIL. The risks of the two lesions increased with the increase of carcinogenic high-risk human papillomavirus DNA load, with a clear dose-response relationship. Chefs were observed to experience a 7.9-fold elevated HGSIL risk. Kitchens with poor fume ventilation during the main cooking life-stage correlated to a 3.7-fold risk of HGSIL, but not for LGSIL. More than 1 hr of daily cooking in kitchens with poor fume conditions appeared to confer an 8.4-fold HGSIL risk, with an 8.3-fold heterogeneously higher odds ratio than that (aOR = 1.0) for LGSIL. Similar risk pattern has been reproduced among never-smoking women. Our findings demonstrate the association between indoor exposure to cooking fumes from heated oil and the late development of cervical precancerous lesions. This final conclusion needs to be verified by future research.

Quercetin inhibits hydrogen peroxide-induced DNA damage and enhances DNA repair in Caco-2 cells

Flavonoids are known to have antioxidant activity that may limit DNA damage and help prevent degenerative diseases, including cancer. However, our knowledge of flavonoids' role in DNA protection/repair mechanism(s) is limited. This study investigated the effects of quercetin on DNA oxidation and DNA repair in Caco-2 cells with or without oxidant (H2O2) challenge. Quercetin (1, 100 microM) significantly reduced oxidative DNA damage, as measured by the number of single-strand breaks identified by single cell gel electrophoresis. Quercetin treatment also caused a measurable increase in the mRNA expression of human 8-oxoguanine DNA glycosylase (hOGG1) at 0 and 4h after H2O2 treatment (measured using RT-PCR). In addition, the highest level of quercetin tested (100 microM) maintained hOGG1 expression at basal levels or higher for up to 12h after H2O2 treatment, while oxidant treatment alone resulted in significant reduction of hOGG1 at 8h. Our study indicates that quercetin could protect DNA both by reducing oxidative DNA damage and by enhancing DNA repair through modulation of DNA repair enzyme expression.

Urinary 1-hydroxypyrene and malondialdehyde in male workers in Chinese restaurants

OBJECTIVES

To assess internal dose and oxidative stress in male restaurant workers exposed to polycyclic aromatic hydrocarbons (PAHs) from cooking oil fumes (COFs) in Chinese restaurants.

METHODS

The study participants included 288 male restaurant workers (171 kitchen and 117 service staff) in Chinese restaurants in Taiwan. Airborne particulate PAHs were measured over 12 h on each of two consecutive work days and then identified using high performance liquid chromatography. Urinary 1-hydroxypyrene (1-OHP) measurements were used to indicate COF exposure, and urinary malondialdehyde (MDA) was adopted as an oxidative stress marker. Multiple regression models were used to assess the relationship between MDA and 1-OHP levels after adjusting for key personal covariates.

RESULTS

Summed particulate PAH levels in kitchens (median 23.9 ng/m(3)) were significantly higher than those in dining areas (median 4.9 ng/m(3)). For non-smoking kitchen staff, mean MDA and 1-OHP levels were 344.2 (SD 243.7) and 6.0 (SD 8.0) mumol/mol creatinine, respectively. These levels were significantly higher than those for non-smoking service staff, which were 244.2 (SD 164.4) and 2.4 (SD 4.3) mumol/mol creatinine, respectively. Urinary 1-OHP levels were significantly associated with work in kitchens (p<0.05). Furthermore, urinary MDA levels were significantly associated with urinary 1-OHP levels (p<0.001) and working hours per day (p<0.05).

CONCLUSIONS

These findings indicate that urinary 1-OHP and MDA levels reflect occupational exposure to PAHs from COFs and oxidative stress in workers in Chinese restaurants.

Enhanced sensitivity to DNA damage induced by cooking oil fumes in human OGG1 deficient cells

Cooking oil fumes (COFs) have been implicated as an important nonsmoking risk factor of lung cancer in Chinese women. However, the molecular mechanism of COFs-induced carcinogenicity remains unknown. To understand the molecular basis underlying COFs-induced cytotoxicity and genotoxicity as well as the roles of hOGG1 in the repair of COFs-induced DNA damage, a human lung cancer cell line with hOGG1 deficiency, A549-R was established by using a ribozyme gene targeting technique that specifically knockdowned hOGG1 in A549 lung adenocarcinoma cells. MTT and comet assays were employed to examine cell viability and DNA damage/repair, respectively, in A549-R and A549 cell lines treated with COF condensate (COFC). RT-PCR and Western blot results showed that the expression of hOGG1 in A549-R cell line was significantly decreased compared with that in A549 cell line. The concentration of COFC that inhibited cell growth by 50% (the IC50) in the A549-R cell line was much lower than that in the A549 cell line, and more COFC-induced DNA damage was detected in the A549-R cell line. The time course study of DNA repair demonstrated delayed repair kinetics in the A549-R cell line, suggesting a decreased cellular damage repair capacity. Our results showed that hOGG1 deficiency enhanced cellular sensitivity to DNA damage caused by COFC. The results further indicate that hOGG1 plays an important role in repairing COF-induced DNA damage. Our study suggests that COFs may lead to DNA damage that is subjected to hOGG1-mediated repair pathways, and oxidative DNA damage may be involved in COF-induced carcinogenesis.

Oxidative DNA damage and human cancer: need for cohort studies

Research of the role of oxidative DNA damage is well established in experimental carcinogenesis. A large number of human studies on biomarkers of oxidative DNA damage, in particular related to guanine oxidation, have been published. The level of oxidative DNA damage and repair activity can be quite different between tumor and normal tissues; case-control studies have shown increased levels of oxidative DNA damage and decreased repair capacity in leukocytes from cases. Similarly, the urinary biomarkers of oxidative DNA damage may be elevated in patients with cancer. However, such studies are likely to be associated with reverse causality. Case-control studies of genetic polymorphisms in DNA repair enzymes suggest that the common variant Ser326Cys in OGG1 may be a risk factor for lung cancer, whereas a rare variant in OGG1 and germ line mutations in the corresponding mismatch repair gene MYH are risk factors for hereditary colon cancer. Cohort studies are required to provide evidence that a high level of oxidative DNA damage implies a high risk of cancer. However, this represents a real challenge considering the large number of subjects and long followup time required with likely spurious oxidation of DNA during collection, assay and/or storage of samples.

Oxidized guanine lesions and hOgg1 activity in lung cancer

In humans, the oxidatively induced DNA lesion 8-hydroxyguanine (8-oxoG) is removed from DNA by hOgg1, a DNA glycosylase/AP lyase that specifically incises 8-oxoG opposite cytosine. We analysed the expression of hOGG1 mRNA in 18 lung cancer and three normal cell lines. Although hOGG1 was overexpressed in most cell lines, 2/18 (11.1%) showed a lower hOGG1 mRNA and protein expression (approximately 80% decrease) relative to normal cell lines. Liquid chromatography/mass spectrometry analysis showed increased levels of 8-oxoG in the two cell lines with the lowest hOGG1 mRNA expression. We examined the ability of nuclear and mitochondrial extracts to incise 8-oxoG lesion in cell lines H1650 and H226 expressing lower hOGG1 mRNA and H1915 and H1975 with higher than normal hOGG1 mRNA expression. Both nuclear and mitochondrial extracts from H1915 and H1975 cells were proficient in 8-oxoG removal. However, both cell lines with the lowest hOGG1 mRNA expression exhibited a severe reduction in 8-oxoG incision in both nuclear and mitochondrial extracts. Under-expression of hOGG1 mRNA and hOgg1 protein was associated with a decrease in mitochondrial DNA repair in response to oxidative damaging agents. These results provide evidence for defective incision of 8-oxoG in both nuclear and mitochondria of H1650 and H226 lung cancer cell lines. These results may implicate 8-oxoG repair defects in certain lung cancers.

Evaluation of genotoxic risk and oxidative DNA damage in mammalian cells exposed to mycotoxins, patulin and citrinin

Mycotoxins are fungal secondary metabolites with very diversified toxic effects in humans and animals. In the present study, patulin (PAT) and citrinin (CTN), two prevalent mycotoxins, were evaluated for their genotoxic effects and oxidative damage to mammalian cells, including Chinese hamster ovary cells (CHO-K1), human peripheral blood lymphocytes, and human embryonic kidney cells (HEK293). PAT, but not CTN, caused a significant dose-dependent increase in sister chromatid exchange (SCE) frequency in both CHO-K1 and human lymphocytes. PAT also elevated the levels of DNA gap and break in treated CHO-K1. In the single cell gel electrophoresis (SCGE) assay, exposure of HEK293 to concentrations above 15 microM of PAT induced DNA strand breaks; the tail moment values also greatly increased after posttreatment with formamidopyrimidine-DNA glycosylase (Fpg). This suggests that in human cells PAT is a potent clastogen with the ability to cause oxidative damage to DNA. However, no significant change in the tail moment values in CTN-treated cultures was found, suggesting that CTN is not genotoxic to HEK293. Incubation of HEK293 with CTN increased the mRNA level of heat shock protein 70 (HSP70), but not that of human 8-hydroxyguanine DNA glycosylase 1 (hOGG1). PAT treatment did not modulate the expression of either HSP70 or hOGG1 mRNA.

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.

Functional crosstalk between hOgg1 and the helicase domain of Cockayne syndrome group B protein

We have previously reported that the Cockayne syndrome group B gene product (CSB) contributes to base excision repair (BER) of 8-hydroxyguanine (8-OH-Gua) and the importance of motifs V and VI of the putative helicase domains of CSB in BER of 8-OH-Gua. To further elucidate the function of CSB in BER, we investigated its role in the pathway involving human 8-OH-Gua glycosylase/apurinic lyase (hOgg1). Depletion of CSB protein with anti-CSB antibody reduced the 8-OH-Gua incision rate of wild type cell extracts but not of CSB null and motif VI mutant cell extracts, suggesting a direct contribution of CSB to the catalytic process of 8-OH-Gua incision and the importance of its motif VI in this pathway. Introduction of recombinant purified CSB partially complemented the depletion of CSB as shown by the recovery of the incision activity. This complementation could not fully recover the deficiency of the incision activity in WCE from CS-B null and mutant cell lines, suggesting that some additional factor(s) are necessary for the full activity. Electrophoretic mobility shift assays (EMSAs) showed a defect in binding of CSB null and motif VI mutant cell extracts to 8-OH-Gua-containing oligonucleotides. We detected less hOgg1 transcript and protein in the cell extracts from CS-B null and mutant cells, suggesting hOgg1 may be the missing component. Pull-down of hOgg1 by histidine-tagged CSB and co-localization of those two proteins after gamma-radiation indicated their co-existence in vivo, particularly under cellular stress. However, we did not detect any functional and physical interaction between purified CSB and hOgg1 by incision, gel shift and yeast two-hybrid assays, suggesting that even though hOgg1 and CSB might be in a common protein complex, they may not interact directly. We conclude that CSB functions in the catalysis of 8-OH-Gua BER and in the maintenance of efficient hOgg1 expression, and that motif VI of the putative helicase domain of CSB is crucial in these functions.