The Role of Tobacco-Related Chemical Carcinogens and Oxyradicals in Human Cancer

高浓度的一氧化氮(NO)对一氧化氮合酶(NOS)活性的调节对于最小化细胞毒性和遗传毒性氮氧化物物种的影响是必不可少的。我们之前已经证明，在体外，NO诱导的P53蛋白积聚，下调基础和细胞因子调节的诱导型一氧化氮合酶(NOS2)的表达，并且P53基因缺失的小鼠具有较高的NOS2酶活性。我们对原发结肠肿瘤的研究建立了肿瘤中NOS2的存在与CpG二核苷酸G：C到A：T转换频率之间的强烈正相关关系。这些突变在淋巴癌、食道癌、头颈部癌、胃癌、脑癌和乳腺癌中也很常见。在其中四种癌症中，NOS2的表达增加。肿瘤相关的NO产生可以直接修饰DNA，也可以抑制DNA修复活性，例如最近描述的人类胸腺嘧啶-DNA糖基酶，它被证明可以修复CpG二核苷酸的G：T错配。由于NO的产生也会诱导野生型P53的积累，由此产生的生长抑制可以为无功能的突变型P53提供额外的强大选择压力。因此，NO可能是人类结肠癌发生的内源性启动子和促进剂，而最近在动物肿瘤模型中证实的NOS2的特异性抑制物可能在人类结直肠癌中具有重要的化学预防潜力。这些和其他发现表明，NO在肿瘤发生中具有病理生理学作用。为了确定NO在肿瘤进展中的作用，我们建立了结构性产生NO的人类癌细胞系。表达野生型p53的NOS2癌细胞抑制了裸鼠的肿瘤生长，而那些突变的p53癌细胞加速了肿瘤的生长，这与血管内皮生长因子表达增加和新生血管有关。我们的数据表明，肿瘤相关的NO的产生可能通过为带有突变型P53的肿瘤细胞提供选择性生长优势而促进癌症的进展，NOS2的抑制剂可能在这些肿瘤中具有治疗活性。我们也在研究慢性炎症性疾病，例如溃疡性结肠炎，以及遗传性氧自由基过载疾病，例如血色素沉着症和威尔逊病，这些疾病都是癌症的易感性。在这些易患癌症的情况下，p53突变负荷会增加。部分病例NOS2、COX2升高。NOS2的表达受WNT-APC-b-catenin途径的调控。一氧化氮通过丝氨酸激酶的翻译后激活P53。目前，我们正在研究NOS2和COX2通路的相互作用。

High concentrations of nitric oxide (NO) regulation of NO synthase (NOS) activity is essential for minimizing effects of cytotoxic and genotoxic nitrogen oxide species. We have shown previously, that NO-induced p53 protein accumulation, down-regulates basal and cytokine-modulated inducible NOS (NOS2) expression in human cells in vitro, and that p53-null mice have elevated NOS2 enzymatic activity. Our investigation of primary colon tumors establishes a strong positive relationship between the presence of NOS2 in tumors and the frequency of G:C to A:T transitions at CpG dinucleotides. These mutations also are common in lymphoid, esophageal, head and neck, stomach, brain and breast cancers. Increased NOS2 expression has been demonstrated in four of these cancers. Tumor-associated NO production may modify DNA directly, or may inhibit DNA repair activities, such as the recently described human thymine-DNA glycosylase, which has been shown to repair G:T mismatches at CpG dinucleotides. Because NO production also induces the accumulation of wild-type p53, the resulting growth inhibition can provide an additional strong selection pressure for nonfunctional, mutant p53. NO may, therefore, act as both an endogenous initiator and promoter in human colon carcinogenesis, and specific inhibitors of NOS2, as demonstrated recently in an animal tumor model, may have important chemopreventive potential in human colorectal cancer. These and other findings indicate that NO has a pathophysiological role in carcinogenesis. To determine the role of NO in tumor progression, we generated human carcinoma cell lines that produced NO constitutively. Cancer cells expressing NOS2 that had wild-type p53, had reduced tumor growth in athymic nude mice, whereas those with mutated p53 had accelerated tumor growth associated with increased vascular endothelial growth factor expression and neovascularization. Our data indicate that tumor-associated NO production may promote cancer progression by providing a selective growth advantage to tumor cells with mutant p53, and that inhibitors of NOS2 may have therapeutic activity in these tumors. We are also investigating chronic inflammatory diseases, e.g., ulcerative colitis, and genetic oxyradical overload diseases, e.g., hemochromatosis and Wilson Disease, that are cancer prone. p53 mutation load is increased in these cancer-prone conditions. NOS2 and COX2 are increased in a portion of the cases. NOS2 expression can be regulated by the WNT-APC-b-catenin pathway. Nitric oxide activates p53 by its post-translation by serine kinases. Currently, we are investigating the interaction of the NOS2 and COX2 pathways.