Folate and PSMA Interact to Regulate DNA Methylation and Prostate Carcinogenesis

性状（由申请人提供）：叶酸作为一碳循环的一部分，对于S-腺苷甲硫氨酸（SAM）的从头合成至关重要。SAM反过来为DNA甲基化提供甲基，这是表观遗传调控的关键模式。研究表明，在妊娠期间操纵叶酸水平会改变基因的表观遗传状态，并且在成年期用甲基供体治疗会逆转DNA甲基化变化。考虑到叶酸水平对DNA甲基化的影响，饮食中的叶酸水平影响几种癌症的风险就不足为奇了。叶酸对细胞增殖也是必不可少的。因此，动物研究表明，叶酸摄入的时间调节疾病的结果：补充叶酸可防止肿瘤的发生，而叶酸消耗可抑制肿瘤的生长。前列腺对叶酸的需求很高，而且似乎也容易受到DNA甲基化改变的影响，这表明叶酸可能在前列腺癌中也起作用。我们已经开发了一种体外模型，在这种模型中，我们可以通过操纵叶酸水平，在整体甲基化水平低下的背景下同时产生肿瘤抑制基因启动子高甲基化，这让人联想到前列腺癌。此外，我们已经表明，与细胞内叶酸水平密切相关的蛋白质，前列腺特异性膜抗原（PSMA），有助于前列腺癌的发生。PSMA是一种独特的叶酸水解酶，也可能是叶酸转运蛋白，在前列腺癌和肿瘤新生血管的内皮细胞中经历显著上调。此外，在低水平叶酸的存在下，PSMA表达增加了细胞侵袭性，这是一种对肿瘤形成和进展都很重要的活性。我们的假设是：低，其次是过量水平的可用叶酸在前列腺在很长一段时间内导致致癌作用。为了检验这一假设，我们将使用以下具体目标：1）确定（a）PSMA表达是否调节细胞内叶酸水平，和（B）在新的体内模型中叶酸水平是否调节前列腺组织中的DNA甲基化，2）确定低水平的叶酸是否增加PSMA的侵袭能力，并导致基因组低甲基化、DNA不稳定性和随后的致癌作用，和3）确定，在前列腺癌发生开始之前，补充叶酸是保护性的，并且如果在开始之后，补充叶酸通过增强由PSMA介导的前列腺中的全身叶酸的摄取以及通过改变表观遗传编程来促进前列腺肿瘤生长和进展。相关性：最近的报告描述了叶酸补充剂和前列腺癌之间的显着关联。1998年U.S.diet的叶酸强化已经将人口从叶酸缺乏转变为叶酸充足。研究表明，过量摄入叶酸会增加患乳腺癌、结肠直肠癌和前列腺癌的风险。我们已经证明，近200万60岁或以上的男性血清叶酸水平超过5倍。这一事实，结合临床前前列腺癌在>60岁年龄组男性中的高患病率，强调了研究叶酸与前列腺癌之间关系的重要性。 公共卫生相关性：这些研究有可能产生关于叶酸补充剂对前列腺癌发生和进展的安全性和潜在保护作用的重要信息，并且考虑到最近强制性强化美国饮食中的叶酸，这些研究特别及时。 膳食叶酸摄入量是一个很容易改变的因素;前列腺癌是一种生长缓慢的疾病-即使我们只能通过膳食叶酸摄入量适度增加进展时间，它也可能导致很大的临床影响。 如果我们了解膳食叶酸调控如何改变DNA甲基化模式，以及叶酸的作用如何通过PSMA表达调节，我们可能能够检测并为前列腺癌风险男性提供营养或化疗干预，预防或延迟疾病。

DESCRIPTION (provided by applicant): Folate, as part of the one carbon cycle, is critical for the de novo synthesis of S-adenosyl methionine (SAM). SAM, in turn, provides the methyl group for DNA methylation, a key mode of epigenetic regulation. Studies have shown that manipulation of folate levels during gestation alters the epigenetic status of genes, and that treatment with methyl donors in adulthood reverses DNA methylation changes. Given the effect of folate levels on DNA methylation, it is not surprising that dietary folate status influences the risk for several cancers. Folate is also essential for cell proliferation. Accordingly, animal studies show that the timing of folate intake modulates disease outcome: supplementation protects against tumor initiation while folate depletion inhibits tumor growth. The prostate has a high requirement for folate, and also seems susceptible to alterations in DNA methylation, suggesting that folate might also play a role in prostate cancer. We have developed an in vitro model, in which we can produce simultaneous tumor suppressor gene promoter hypermethylation in an overall context of global hypomethylation reminiscent of prostate cancer, by manipulating folic acid levels. In addition, we have shown that a protein intimately related to intracellular folate levels, Prostate-Specific Membrane Antigen (PSMA), contributes to prostate carcinogenesis. PSMA, a unique folate hydrolase, and possible folate transporter, undergoes significant up-regulation in prostate cancer and in the endothelial cells of tumor neovasculature. Moreover, in the presence of low levels of folate, PSMA expression increases cell invasiveness, an activity important for both tumor formation and progression. Our hypothesis is: Low, followed by excess levels of available folates in the prostate over an extended period of time leads to carcinogenesis. To test this hypothesis we will use the following specific aims; 1) Determine if (a) PSMA expression regulates intracellular folate levels, and (b) if folate levels regulate DNA methylation in prostate tissues in a novel in vivo model, 2) Ascertain if low levels of folates increase the invasive capacity of PSMA, and lead to genomic hypomethylation, DNA instability and subsequently carcinogenesis and 3) Establish if, prior to initiation of prostate carcinogenesis folate supplementation is protective, and if, following initiation, folate supplementation promotes prostate tumor growth and progression by enhanced uptake of systemic folate in the prostate mediated by PSMA, and by altering epigenetic programming. Relevance: Recent reports describe a significant association between folate supplementation and prostate cancer. Folic acid fortification of the U.S.diet in 1998 has converted the population from a largely folate-deficient to folate-replete. Studies have shown that excess folic acid intake increases the risk of breast, colorectal, and now, prostate cancer. We have shown that nearly 2 million men aged 60 or above have serum folate levels greater than 5 fold adequate. This fact, in combination with the high prevalence of preclinical prostate cancer in men of the >60 age group, underscores the importance of investigating the relationship between folate and prostate cancer. PUBLIC HEALTH RELEVANCE: These studies have the potential to yield important information regarding both the safety of, and the potentially protective effects, of folic acid supplementation on prostate carcinogenesis and progression, and are particularly timely given the recent mandatory fortification of the American diet with folic acid. Dietary folate intake is an easily modifiable factor; prostate cancer is a slow growing disease - even if we can effect only a modest increase in time to progression via dietary folate intake, it could result in a large clinical impact. If we understand how dietary folate manipulation can alter DNA methylation patterns, and how the effect of folate may be modulated by PSMA expression, we may be able to detect and provide nutritional or chemo- intervention to men at-risk for prostate cancer, preventing or delaying the disease.