Folate and PSMA Interact to Regulate DNA Methylation and Prostate Carcinogenesis

描述（由申请人提供）：叶酸作为一碳循环的一部分，对s -腺苷基蛋氨酸（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，妊娠期叶酸水平的改变会改变基因的表观遗传状态，成年期甲基供体治疗可逆转DNA甲基化变化。考虑到叶酸水平对DNA甲基化的影响，饮食中叶酸水平影响几种癌症的风险就不足为奇了。叶酸也是细胞增殖所必需的。因此，动物研究表明，叶酸摄入的时间可以调节疾病的结果：补充叶酸可以防止肿瘤的发生，而叶酸的消耗可以抑制肿瘤的生长。前列腺对叶酸有很高的需求，而且似乎也容易受到DNA甲基化改变的影响，这表明叶酸也可能在前列腺癌中起作用。我们已经开发了一种体外模型，通过控制叶酸水平，我们可以在前列腺癌的整体低甲基化背景下同时产生肿瘤抑制基因启动子高甲基化。此外，我们已经证明了一种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，可能是叶酸转运蛋白，在前列腺癌和肿瘤新生血管内皮细胞中显著上调。此外，在叶酸水平低的情况下，PSMA的表达增加了细胞侵袭性，这是肿瘤形成和进展的重要活动。我们的假设是：低，然后是前列腺中叶酸的过量水平在很长一段时间内导致致癌。为了验证这一假设，我们将使用以下具体目标：1)在新的体内模型中确定（a) PSMA表达是否调节细胞内叶酸水平，(b)叶酸水平是否调节前列腺组织中的DNA甲基化，2）确定低水平叶酸是否会增加PSMA的侵袭能力，并导致基因组低甲基化、DNA不稳定和随后的致癌，3)确定在前列腺癌发生前补充叶酸是否具有保护作用，以及在前列腺癌发生后补充叶酸是否具有保护作用。叶酸补充剂通过增强PSMA介导的前列腺中系统性叶酸的摄取，以及通过改变表观遗传程序，促进前列腺肿瘤的生长和进展。相关性：最近的报道描述了叶酸补充剂与前列腺癌之间的显著关联。1998年，美国饮食中叶酸的强化使人们从基本上缺乏叶酸转变为叶酸充足。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。我们的研究表明，近200万60岁或以上的男性血清叶酸水平超过足量的5倍。这一事实，再加上临床前前列腺癌在60岁年龄段男性中的高患病率，强调了研究叶酸与前列腺癌之间关系的重要性。

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.