DNA Repair and Tobacco Smoke in Bladder Carcinogenesis

膀胱癌（BC）是在美国发现的第五大常见癌症。在美国，吸烟（TS）是导致BC的主要原因，吸烟者的BC发病率比不吸烟者高5倍。TS含有60多种致癌物；然而，哪些致癌物是导致BC的原因还没有得到很好的确定。芳胺，特别是4-羟基氨基苯（ABP），是职业相关性BC的主要原因，但TS中芳胺的含量很少。事实上，TS含有的丙烯醛（Acr）是ABP的10万倍，而Acr是一种强效的器官特异性致癌物，能够在大鼠模型中诱导BC。我们的实验室长期致力于研究化学致癌物诱导的DNA损伤和修复在肿瘤发生中的作用。我们最近在Acr方面有三个重要发现：(1)Acr通过形成Acr-DNA加合物来破坏DNA，这些加合物具有诱变作用；（ii） Acr通过修饰和加速自噬介导的修饰DNA修复蛋白降解来抑制DNA修复；（iii） Acr-DNA加合物在人类细胞中修复不良。我们提出Acr是一种主要的膀胱致癌物，其致癌性是通过这三种有害作用（假设1）。大多数BC可分为非侵入性（N-lnv）或侵入性（Inv）；N-lnv-BC通常携带H-RAS基因的密码子12（<20%）和FGFRS基因的密码子248、249、372和652（80%）突变，而Inv-BC主要携带p53基因（30-60%）和RB基因突变。我们假设BC中的这些突变热点是膀胱尿路上皮细胞中Acr的优先结合位点（假设2）。我们发现DNA损伤在Inv-BC细胞中诱导的突变比在N-lnv-BC细胞中高得多，并且N-lnv-BC细胞比Inv-BC细胞具有更高的DNA损伤修复能力。我们最近还发现p63基因在N-lnv-BC中高表达，而在Inv-BC细胞中不表达，并且p63基因的引入提高了Inv-BC细胞的DNA修复能力。这些结果使我们假设H- RAS/FGFR3突变激活通过激活p63增强DNA修复能力，而p53突变通过下调p63降低DNA修复能力（假设3）。我们将在培养的人类尿路上皮细胞、人类膀胱肿瘤组织样本和转基因小鼠模型中验证这些假设，以了解DNA修复能力与膀胱癌不同途径之间的关系。

Bladder cancer (BC) is the fifth most frequent cancer found in the United States (US). Tobacco smoke (TS) is the major cause of BC in US, and tobacco smokers have a 5-fold higher BC incidence than nonsmokers. TS contains more than 60 carcinogens; however, which carcinogens are responsible for BC is not well established. Arylamines, 4-hydroxy-aminoblphenyl (ABP) in particular, are the major cause of occupation-related BC, but the amount of arylamines in TS is minute. In fact, TS contains 100,000 fold more acrolein (Acr) than ABP, and Acr is a potent and organ-specific carcinogen capable of Inducing BC in rat models. Our laboratory has a longstanding interest in studying the role of chemical carcinogen induced DNA damage and repair in tumorigenesis. We recently made three important findings regarding Acr: (1) Acr damages DNA by forming Acr-DNA adducts that are mutagenic; (ii) Acr inhibits DNA repair by modifying and accelerating autophagy-mediated degradation of the modified DNA repair proteins; and (iii) Acr-DNA adducts are poorly repaired in human cells. We propose that Acr Is a major bladder carcinogen and its carcinogenicity Is via these three detrimental effects (Hypothesis 1). Most BC can be classified as either noninvasive (N-lnv) or invasive (Inv); while N-lnv-BC often bear mutations in codon 12 ofthe H-RAS (<20%) and codons 248, 249, 372 and 652 ofthe FGFRS gene (80%), Inv-BC mainly carry mutations in the p53 (30-60%) and RB genes. We hypothesize that these mutation hotspots in BC are Acr preferential binding sites in bladder urothelial cells (Hypothesis 2). We found that DNA damage induces much higher mutations in Inv-BC cells than in N-lnv-BC cells and that N-lnv-BC cells have a much higher DNA damage repair capacity than Inv-BC cells. We also recently found that p63 gene is highly expressed in N-lnv-BC but not in Inv-BC cells, and that introduction of p63 gene elevates DNA repair capacity in Inv-BC cells. These results lead us to hypothesize that H- RAS/FGFR3 mutation-activation enhances DNA repair capacity via activation of p63 and that p53 mutations reduce DNA repair capacity via down regulation of p63 (Hypothesis 3). We will test these hypotheses in cultured human urothelial cells, human bladder tumor tissue samples and transgenic mouse models to understand the relationship between DNA repair capacity and divergent pathways of bladder cancer.