The Association of Environmental Carcinogen Exposure and Human Papillomavirus Infection with Female Non-smoking

• Main Authors: Cheng Ya-Wen, 鄭雅文
• Other Authors: Huei Lee
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/29066269769768573457

博士 === 中山醫學大學 === 醫學研究所 === 90 === Lung cancer has been the leading and second cause of cancer death of women and men, respectively, in Taiwan since 1982 and is responsible for about 20% of overall cancer death. Similar trend was also observed in western countries and Japan. Prevention of lung cancer incidence is an important study topic in human health not only in Taiwan, but also worldwide. Cigarette smoking has been implied to be the most important etiological factor of lung cancer and up to 90% of lung cancer in the western countries could be explained by cigarette smoking. Intriguingly, in Taiwan, only around 50% of lung cancer incidence could be related to cigarette smoking, particularly, less than 10% of Taiwanese female lung cancer patients are smokers. Thus, it is conceivable that environmental factors other than cigarette smoking may be associated with lung cancer development in Taiwan and the aim of this study, therefore, is to evaluate possible involved environmental factors, including exposure to environmental carcinogen and microbial infections. It has been well known that benzo[a]pyrene (BaP), one polycyclic aromatic hydrocarbon, is converted into a active metabolite, which will attack DNA to form DNA adduct, through biotransformation. The DNA adduct has been shown to result in mutation on tumor suppressor genes or oncogenes and ultimately, lead to formation of tumor. To prove the feasibility of DNA adduct levels in lung tissues being a risk biomarker of lung cancer, we have to firstly evaluate if DNA adduct levels in lung tissues of lung cancer patients are higher than that of normal controls. In this study, 73 lung cancer patients and 33 non-cancer control were recruited and corresponding DNA adduct levels were analyzed by 32P-postlabeling. Our data showed that DNA adduct levels in lung cancer patients’ non-tumor tissues (49.58±33.39 adducts/108nucleotides) were significantly higher than that of non-cancer controls (18.00±15.33 adducts/108nucleotides, P<0.001). And DNA adduct levels in smoking lung cancer patients (49.03±37.21 adducts/ 108nucleotides) were similar to that of non-smoking ones (49.28±30.73 adducts/108nucleotides, P=0.719). The DNA adduct levels were irrelevant to genetic polymorphisms of CYP1A1 and GSTM1, but related to the CYP1A1 protein expression. The data showed that exposure to environmental carcinogens may play an important role in lung cancer formation other than cigarette smoking. Multivariate logistic regression analysis showed that individuals with higher DNA adduct levels (>48.66 adducts/108nucleotides) had an approximate 25-fold risk of lung cancer compared to that of those with low adduct levels (£48.66 adducts/108nucleotides). The other factor such as gender, smoking behavior, or genetic polymorphism of CYP1A1 and GSTM1 all could not be risk biomarkers for lung cancer. From previous reports, women have been mostly believed to be more susceptible to cigarette smoking. To evaluate whether non-smoking female have higher susceptibility to the environmental carcinogen exposure, DNA adduct levels of non-smoking lung cancer patients, including 30 female and 30 male, and 20 non-smoking non cancer controls were analyzed by 32P-postlabeling and ELISA. Our data suggested that lung cancer patients were indeed more susceptible to the environmental carcinogen exposure than non-cancer controls and DNA adduct levels of female lung cancer patients were actually higher than that of male. Furthermore, this difference in DNA adduct levels was not resulted from genetic polymorphism or protein expression of CYP1A1 and GSTM1. Therefore, high susceptibility to DNA damage of females may be partial responsible for the high mortality rate of lung cancer in non-smoking Taiwanese women. Based on the higher DNA adduct levels in female lung cancer patients in Taiwan, it was suspected that mutation frequencies of p53 and k-ras gene were higher in such patients. From our preliminary data, it was showed that only 2 of 52 female have mutations occurred in p53 gene, which yielding a mutation frequency of 3.9% and there was no K-ras mutation in tumor tissues of female lung cancer patients being detected. However, by immunohistochemistry, p53 and Rb protein expression could not been detected in most lung cancer patients. Meanwhile, the inactivation of the P53 and Rb protein could not be explained by their regulated gene such as MDM2, p16 and cyclinD1. From all these, we, therefore suspected that other biological factors may be responsible for the inactivation of p53 and Rb and therefore involved in lung tumorigenesis in Taiwan. Since the p53 and Rb protein could be inactivated by the E6 and E7 oncoproteins encoded by human papillomavirus 16/18 (HPV 16/18) we hypothesized that the HPV may be involved in P53 and Rb protein inactivation in lung tumor tissues. In this study, 141 lung cancer patient and 60 non-cancer control were recruited to evaluate the infection rate of low-risk (HPV 6/11) and high-risk HPV (HPV 16/18) by nested PCR and in situ hybridization, to determine the difference in the infection rate of HPV between lung cancer patients and non-cancer controls. The infection rate of HPV6, 11, 16 and 18 for lung cancer patients was 28.4%, 10.0%, 35.5% and 41.1%, respectively, and the difference in prevalence rates of 6, 16 and 18 between these two study groups were statistically different. Therefore, the infection of HPV 6, 16 and 18 may be involved in lung cancer development. When stratified by gender and smoking behavior, HPV 16/18 infection rate of non-smoking female lung cancer patients (60.0% and 73.0% for HPV 16 and 18, respectively) were significantly higher than that of man (24.0% and 26.0% for HPV 16 and 18, respectively). But for HPV6, the highest infection rate of HPV6 was in smoking male (38.1%) and the lowest was in non-smoking female (11.1%). The result suggested that the different type of HPV might be involved in lung cancer with different gender and smoking behavior while the infection of HPV 16/18 may be involved in female lung cancer formation in Taiwan. It was also found that the infection rates of HPV 6 and HPV 16 were correlated with tumor stage, with the highest frequency being for stage I patients, therefore, HPV infection may contribute in the early stage in lung cancer development. To understand whether the inactivation of P53 and Rb in lung tumor tissues were correlated with HPV16/18 E6/E7, the HPV16/18 E6/E7 mRNA expression in lung tumor tissue were detected by in situ RT-PCR. In the serial tissue sections, the p53 and Rb protein were not detected in 80% of the lung cancer patients with HPV16/18 E6/E7 mRNA positive expression and these patients have the poor prognosis. Because of these, inactivation of p53 and Rb protein by HPV16/18 E6/E7 may be linked in lung tumorigenesis. In conclusion, the concurrence of high DNA damage susceptibility to environmental carcinogen exposure and high HPV16/18 infection may contribute to the higher mortality rate of non-smoking female lung cancer in Taiwan.