透過您的圖書館登入
IP:44.222.92.134
  • 學位論文

抽煙和乙醯轉移酶第二型基因多形性對臺灣結直腸癌之p53基因突變之可能影響

The impact of cigarette smoking and NAT2 genetic polymorphism on p53 mutation in Taiwanese colorectal cancer

指導教授 : 李輝

摘要


大腸直腸癌是台灣及全世界高發生率及高死亡率的疾病,已躍居台灣癌症死因的第三位。許多研究發現抽菸會增加罹患肺癌、頭頸癌、胰腺癌、膀胱癌、大腸直腸癌等十幾種癌症的危險性。香菸煙霧中含有多種致癌物,已有許多研究著重於香菸與各種癌症的基因層次上研究。流行病學之研究發現抽菸和攝取多量的高溫烹調的紅肉可能與罹患大腸直腸癌有關。動物實驗証實香菸與高溫烹調之肉類食物中之異環胺類化合物 (hetercyclic aromatic hydrocarbons, HCAs) 可能與大腸直腸癌之腫瘤形成有關。NAT2 (N-acetyltransferase 2) 是主要參與 HCAs 代謝之酵素,將 HCAs 代謝為攻擊 DNA 之活性代謝物,造成 DNA 鍵結物 和 p53 基因的突變,而 p53 突變是主要引起大腸直腸癌的致癌路徑。本研究擬探討抽菸或飲食中之致癌物是否會產生特別之 p53 突變型態的產生,以提出分子層次之證據,來支持流行病學之發現--抽菸與大腸直腸癌之發生有關。過去許多研究在探討NAT2之基因多型性與大腸直腸之相關性,但並沒有得ㄧ致之結果,因此本研究擬探討台灣人 NAT2 基因多形性是否會增加大腸直腸癌罹患之危險性?本研究首先收集 153 個大腸直腸癌之腫瘤組織進行 p53 基因直接定序,以了解 p53 基因突變是否與抽煙有關。結果發現p53 抑癌基因突變率有 50.3%。抽菸與否並未影響 p53 基因突變率( 抽菸 50.8 vs. 不抽菸 48.9%, P = 0.743)。當分析 p53 基因突變的transition, transversion 和 deletion 型式與抽菸之相關性,結果發現僅有缺失突變 (deletion mutation) 型式與抽菸有關 (P = 0.01),在 8 位發生缺失突變的患者中有 7 位是每天抽一包菸持續十五年以上之重度抽菸者。而台灣大腸直腸癌之缺失突變發生之頻率 ( 8 of 77, 10.4%) 與肺癌之研究結果相似,都遠高於其他歐美國家。因此推測香菸與其他飲食之成分以及與台灣人之 NAT2 易感基因可能特殊之交互作用而導致抽菸之大腸直腸癌患者發生高頻率之 p53 基因缺失突變。為了解NAT2基因型是否與大腸直腸癌之發生是否有關,本研究選取年齡、性別和抽菸習慣相似的病例組與健康者之對照組配對研究。利用聚合酵素鏈鎖反應 (PCR) 與限制片段長度多型性 (RFLP)來判定個體 NAT2 基因型,結果發現NAT2 W/W homozygous genotype 快速代謝基因型發生大腸直腸癌的危險性是 NAT2 慢速代謝基因型 Mx/Mx的1.63 倍 (0.8-2.3)。但在 W/Mx NAT2慢速代謝基因型與Mx/W+W/W快代謝基因型則無差異。若將性別分開分析時發現,女性具有NAT2 W/W homozygous 或 Mx/W+W/W快速代謝基因型發生大腸直腸癌的危險性是Mx/Mx慢速代謝基因型的2.47倍及2.13倍,但在男性則沒有觀察到 NAT2 基因型與大腸直腸癌的相關性。總之,NAT2之基因多型性之分析結果發現,台灣人具有NAT2 快速代謝基因型者較容易罹患大腸直腸癌。並可推測異環胺類(heterocyclic amines, HCAs)之暴露可能參與臺灣大腸直腸癌之形成,特別是臺灣婦女族群。

並列摘要


Mortality from colorectal cancer has increased remarkably in Taiwan during the past two decades. Recent epidemiological studies suggest that cigarette smoking is associated with an increase risk of colorectal cancer; there is little molecular evidence explaining this association. To examine the relationship between cigarette smoking and colorectal cancer, we compared p53 mutation patterns in colorectal tumors from smokers and nonsmokers. P53 mutations determined by direct sequencing were detected in 77 of 153 (50.3%) colorectal tumors, and no difference was observed in the p53 mutation frequencies in tumors from smokers and nonsmokers. Immunohistochemistry (IHC) showed that p53 immunoreactive tumors were positive correlated with p63 mutated tumors. (P < 0.0001). G:C to A:T transversion and G:C to T:A transition were the predominate types of mutation detected in the tumor p53 gene. The frequency of deletion mutation in smoker tumors was significantly higher than that in nonsmoker tumors (P = 0.01). Thus, the observation of a higher frequency of p53 deletion mutation in smoker tumors supports the association between cigarette smoking and the development of colorectal cancer. Our previous studies showed that various kinds of HCAs (IQ, MeIQ and MeIQx) in delicious Chinese dishes which were commonly consumed by Taiwanese. We hypothesized that HCAs from Chinese dishes consumed by Taiwanese may contribute to the incidence of colorectal cancer. N-acetyltransferase 2 (NAT2) is the major enzyme in the metabolism of HCAs. The association between NAT2 genetic polymorphism and colorectal cancer has been studied extensively, however, no conclusive results have been found. We conducted a study with 244 primary colorectal cancer cases and 299 cancer-free control subjects to verify the association of NAT2 polymorphisms with the risk of Taiwanese CRC. Our data showed that subjects with the NAT2 W/W homozygous genotype had a 1.63-fold increased risk of CRC compared to those with the Mx/Mx slow acetylator genotype (95% CI 1.03-2.58), but no risk was found in the W/Mx heterozygous and Mx/W+W/W fast acetylator genotypes. Being stratified by gender factors, the CRC risk in females with homozygous W/W or Mx/W+W/W fast acetylators increased 2.47- and 2.13-fold compared to those with the Mx/Mx slow acetylator genotype (95% CI 1.27-4.82 for W/W genotype; 95% CI 1.17-3.89 for Mx/W+W/W genotype), however, the risk of the NAT2 genotype and CRC was not observed in males. Collectively, subjects with the NAT2 fast acetylator genotype were more prone to CRC and reflected the possibility that exposure to HCAs may contribute to CRC development in Taiwan, especially in Taiwanese women.

並列關鍵字

colorectal cancer HCA p53 NAT2 genetic polymorphism

參考文獻


Yeh CC, Hsieh LL, Tang R, Chang-Chieh CR, Sung FC.(2003). Risk factors for colorectal cancer in Taiwan: A hospital-based-control study. J Formos Med Assoc 102:305–312.
Le Marchand, L, Hankin JH, Pierce LM, Sinha R, Nerurkar PV, Franke AA, Wilkens LR, Kolonel LN, Donlon T, Seifried A, Custer LJ, Lum-Jones A, Chang W.(2002). Well-done red meat, metabolic phenotypes and colorectal cancer in Hawaii. Mutation Res. 506-507: 205-214.
Barrett JH, Smith G, Waxman R, GooderHam N, Lighfoot T, Garner RC, Augustsson K, Wolf CR, Bishop DT, Forman D, Colorectal Cancer Study Group.(2003). Investigation of interaction between N-acetyltransferase 2 and heterocyclic amines as potential risk factors for colorectal cancer. Carcinogenesis 24:275-82.
Bell DA, Taylor JA , Butler MA, Stephens EA, Wiest J, Brubaker LH, Kadlubar FF, Lucier GW.(1993). Genotype/phenotype discordance for human arylamine N-acetyltransferase (NAT2) reveals a new slow-acetylator allele common in African-Americans. Carcinogenesis 14:1689-92.
Brockton N, Little J, Sharp L, Cotton SC.(2000). N-acetyltransferase polymorphisms and colorectal cancer: a HuGE review. Am. J. Epidemiol. 151:846-61.

延伸閱讀