Analysis of epigenetic mechanisms of nuclear receptor expression in prostatic carcinogenesis

表观遗传机制包括DNA甲基化和组蛋白去乙酰化被认为在基因转录失活中起重要作用。我们已经报道了包括CpG甲基化和组蛋白乙酰化在内的表观遗传调控在AR调控中的重要性。此外，这些结果表明甲基化参与核受体的表达。视黄酸受体(RAR) β基因是位于染色体3p24上的推定肿瘤抑制基因，在许多类型的肿瘤中检测到高发生率的杂合性缺失。前列腺癌（PCas）中RARβ mRNA和蛋白的选择性缺失或下调已被报道，尽管其机制尚不清楚。我们研究了表观遗传修饰在RARβ2基因沉默中的作用。在14例原发性前列腺癌中有11例（79%），10例激素难治性前列腺癌中有9例（90%），4例前列腺癌细胞系中有2例（50%）检测到异常甲基化，但在任何正常前列腺样本中均未检测到异常甲基化。染色质免疫沉淀实验显示，所有rar β2阴性细胞（LNCaP、PC3和DU145）在组蛋白H3和H4上都发生了低乙酰化。在RARβ2阴性细胞中，经5-aza-2'-脱氧胞苷处理后，曲古霉素A和全反式维甲酸诱导部分去甲基化，乙酰化组蛋白积累增加，RARβ2表达明显恢复。这些结果提示RARβ2基因可能是PCa中常见的表观遗传修饰沉默基因之一。此外，我们发现CD44的甲基化与前列腺癌的进展有关。我们的数据显示，表观遗传机制可能参与了癌症相关基因的表达。

Epigenetic mechanisms including DNA methylation and histone deacetylation are thought to play important roles in gene transcriptional inactivation. We have reported the importance of that epigenetic regulations including CpG methylation and histone acetylation in the regulation of the AR. In addition, these results suggested involvement of methylation in expression of nuclear receptors. The retinoic acid receptor (RAR) β gene is a putative tumor suppressor gene on chromosome 3p24, where a high incidence of loss of heterozygosity is detected in many types of tumors. Selective loss or down-regulation of RARβ mRNA and protein has been reported in prostate cancers (PCas), although the mechanisms remain unclear. We investigated the role of epigenetic modification in RARβ2 gene silencing. Aberrant methylation was detected in 11 of 14 (79%) primary PCas, 9 of 10 (90%) hormone-refractory PCas, and 2 of 4 (50%) PCa cell lines, but not in any normal prostate samples. Chromatin immunoprecipitation assay showed that all RARβ2-negative cells (LNCaP, PC3, and DU145) were hypoacetylated at both histones H3 and H4. After exposure to 5-aza-2'-deoxycytidine treatment, Trichostatin A and all-trans retinoic acid induced partial demethylation, increased accumulation of acetylated histones, and markedly restored the expression of RARβ2 in RARβ2-negative cells. These results suggest that the RARβ2 gene may be one of the frequently silenced genes by epigenetic modifications in PCa. In addition, we found that methylation of the CD44 was related with prostate cancer progression. Our data shows that epigenetic mechanisms may be involved in expression of cancer-related genes.