Oxidative DNA Damage And Repair In Prostate Cancer

正如我们已经成功地在乳腺癌细胞系的核和线粒体水平上鉴定出氧化损伤修复缺陷一样，我们也必须在前列腺癌中这样做，前列腺癌是一种常见的恶性肿瘤，与乳腺癌有许多共同的特征。两者的年龄调整发病率和死亡率相似，都需要性腺发育，可以通过激素控制治疗，两者都有生殖反应，都有非常相似的生活方式风险因素（高动物脂肪饮食，高红肉饮食，高体重，高出生体重，高乳制品摄入量），并且两者都与年龄显著相关。氧化损伤和修复在疾病模仿、促进或进展中的作用是否与基因组中氧化DNA碱基损伤的频率以及识别和消除这种损伤的生物途径的效率有关？ 前列腺癌的风险和宿主易感性因素知之甚少。文献似乎表明，某些形式的DNA修复（包括氧化损伤修复）的缺陷可能在前列腺癌的发展中至关重要。Grossman实验室也有证据显示前列腺癌患者的紫外线损伤修复缺陷，这表明核苷酸切除修复途径也可能发生改变。对前列腺癌发展的研究表明，慢性和急性炎症在整个生命周期中发生在前列腺中（例如前列腺炎），并与环境，遗传和饮食因素协同作用，导致前列腺上皮损伤。作为对这种损伤的应答，发生细胞增殖（DeMarzo，Coffey，纳尔逊1999）。这种增殖发生在与正在进行的炎症过程相关的氧化应激环境中，这反过来可能导致对DNA的高速率氧化损伤（DeMarzo，Putzi，纳尔逊2001）。如果这个模型是正确的，我们假设有效的碱基切除修复途径可能是维持遗传保真度和最终预防细胞转化的关键。Malins已经显示了DNA人类前列腺癌样本内病变的积累。利用GCMS技术，他和他的小组已经鉴定出恶性和良性前列腺组织中的加合物。 支持氧化性碱基病变（如8-oxo-G）的识别和清除可能在前列腺癌发生中起关键作用这一假设的进一步证据已在工作中提供，该工作表明hOGG 1基因（编码DNA糖基化酶/AP裂解酶，其活性为8-羟基鸟嘌呤的切割）的序列变异可能与前列腺癌易感性相关（Isaacs 2002）。涉及氧化性DNA损伤作用的其他发现包括Oberley的工作，该工作表明前列腺上皮内瘤变和前列腺癌中的SOD 1、SOD 2和过氧化氢酶水平低于良性前列腺上皮（Cancer 2000）。最后，APE /ref-1水平也显示在前列腺癌中显著升高（Kelley 2001）。两者合计，有足够的证据表明，活性氧和可能的氧化DNA损伤在前列腺癌的发生中发挥作用。 我们已经开始评估8-oxoG和其他DNA碱基损伤的氧化DNA损伤修复是否有效地从核和线粒体DNA中去除。使用三个充分研究的前列腺癌细胞系，DU-145，LNCaP和PC-3，我们正在研究从这些细胞系制备的核和线粒体提取物切割各种常见的氧化DNA碱基病变的能力。初步数据表明，未经处理的DU-145和PC-3细胞在8-羟基鸟嘌呤和胸腺嘧啶乙二醇加合物的切割中存在缺陷。进一步的实验将包括其他加合物（尿嘧啶、5-羟基胞嘧啶和AP位点）的测定、所选碱基切除修复酶的蛋白质和mRNA水平的分析以及相关基因的序列分析。

Just as we have been successful in identifying a defect in repair of oxidative damage at the nuclear and mitochondrial levels of breast cancer cell lines, it is imperative that we also do so in prostate cancer, a commonly occurring malignancy that shares many features with breast cancer. Both have an age-adjusted incidence and death that are similar, both require gonads for development and can be treated by hormonal manipulation, both are also hormonally responsive, both have very similar life style risk factors (high animal fat diet, high red meat diet, high body mass, high birth weight, high dairy product intake) and both are significantly age related. Is there a role for oxidative damage and repair in disease imitation, promotion or progression that is tied to the frequency of oxidative DNA bases lesions in the genome and the efficiency of biologic pathways that recognize and remove this damage? The risk and host susceptibility factors involved in prostate cancer are poorly understood. The literature seems to suggest that defects in certain forms of DNA repair including oxidative damage repair may be critical in the development of prostate cancer. There is also evidence from the Grossman laboratory showing defective UV-damage repair in prostate cancer patients suggesting that there may be alterations in the nucleotide excision repair pathway as well. Research on the development of prostate cancer suggests that chronic and acute inflammation occurs in the prostate over the life span (e.g. prostatitis) and acts in synergy with environmental, genetic, and dietary factors to cause injury to prostatic epithelium. In response to this injury, cellular proliferation occurs (DeMarzo, Coffey, Nelson 1999). This proliferation occurs in a setting of oxidative stress related to the ongoing inflammatory process that in turn may result in high rates of oxidative damage to DNA (DeMarzo, Putzi, Nelson 2001). If this model is correct, we hypothesize that efficient base excision repair pathways may be critical for maintenance of genetic fidelity and ultimately prevention of cellular transformation. The accumulation of lesions within the DNA human prostate cancer specimens has been shown by Malins. Using GCMS technology he and his group have identified adducts in malignant and benign prostatic tissue. Further evidence supporting the hypothesis that the recognition and removal of oxidative base lesions (such as 8-oxo-G) may be pivotal in prostate carcinogenesis has been provided in work showing that sequence variation in the hOGG1 gene (that encodes a DNA glycosylase/AP lyase whose activity is the incision of 8-hydroxyguanine) may be associated with prostate cancer susceptibility (Isaacs 2002). Other findings that implicate a role for oxidative DNA damage include work by Oberley that has shown that SOD1, SOD2 and catalase levels were lower in prostate intraepithelial neoplasia and prostate cancer than in benign prostate epithelium (Cancer 2000). Finally, APE /ref-1 levels have also been shown to be dramatically elevated in prostate cancer (Kelley 2001). Taken together there is ample evidence to suggest the reactive oxygen species and perhaps oxidative DNA damage play a role in prostatic carcinogenesis. We have begun to evaluate whether oxidative DNA damage repair of 8-oxoG and other DNA base lesions are efficiently removed from nuclear and mitochondrial DNA. Using three well-studied prostate cancer cell lines, DU-145, LNCaP, and PC-3, we are examining the ability of nuclear and mitochondrial extracts prepared from these cell lines to incise a wide variety of commonly occurring oxidative DNA base lesions. The preliminary data suggest that untreated DU-145 and PC-3 cells have defects in the incision of 8-hydroxyguanine and thymine glycol adducts. Further experiments will include assays of other adducts (uracil, 5 hydroxycytocine, and AP sites), analysis of protein and mRNA levels of selected base excision repair enzymes and sequence analysis of implicated genes.