Kim Hanna, Lapointe Jacques, Kaygusuz Gulsah, Ong David E, Li Chunde, van de Rijn Matt, Brooks James D, Pollack Jonathan R
Department of Pathology, Stanford University, Stanford, California 94305-5176, USA.
Cancer Res. 2005 Sep 15;65(18):8118-24. doi: 10.1158/0008-5472.CAN-04-4562.
Prostate cancer is the most common cancer among men in the United States, and aberrant DNA methylation is known to be an early molecular event in its development. Here, we have used expression profiling to identify novel hypermethylated genes whose expression is induced by treatment of prostate cancer cell lines with the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (5-aza-dC). Of the 271 genes that were induced by 5-aza-dC treatment, 25 also displayed reduced expression in primary prostate tumors compared with normal prostate tissue, and the decreased expression of only one gene, aldehyde dehydrogenase 1 family, member A2 (ALDH1a2), was also associated with shorter recurrence-free survival. ALDH1a2 encodes an enzyme responsible for synthesis of retinoic acid (RA), a compound with prodifferentiation properties. By immunohistochemistry, we observed that ALDH1a2 was expressed in epithelia from normal prostate but not prostate cancer. Using bisulfite sequencing, we determined that the ALDH1a2 promoter region was significantly hypermethylated in primary prostate tumors compared with normal prostate specimens (P = 0.01). Finally, transfection-mediated reexpression of wild-type ALDH1a2 (but not a presumptive catalytically dead mutant) in the prostate cancer cell line DU145 resulted in decreased colony growth (P < 0.0001), comparable with treatment with either 5-aza-dC or RA. Taken together, our findings implicate ALDH1a2 as a candidate tumor suppressor gene in prostate cancer and further support a role of retinoids in the prevention or treatment of prostate cancer.
前列腺癌是美国男性中最常见的癌症，已知异常的DNA甲基化是其发展过程中的早期分子事件。在此，我们利用表达谱分析来鉴定新型高甲基化基因，这些基因的表达可通过用DNA甲基转移酶抑制剂5-氮杂-2'-脱氧胞苷（5-aza-dC）处理前列腺癌细胞系来诱导。在经5-aza-dC处理后诱导表达的271个基因中，有25个基因在原发性前列腺肿瘤中的表达也较正常前列腺组织降低，并且只有一个基因醛脱氢酶1家族成员A2（ALDH1a2）的表达降低也与无复发生存期缩短相关。ALDH1a2编码一种负责视黄酸（RA）合成的酶，RA是一种具有促分化特性的化合物。通过免疫组织化学，我们观察到ALDH1a2在正常前列腺上皮中表达，但在前列腺癌中不表达。利用亚硫酸氢盐测序，我们确定与正常前列腺标本相比，原发性前列腺肿瘤中ALDH1a2启动子区域显著高甲基化（P = 0.01）。最后，在前列腺癌细胞系DU145中转染介导的野生型ALDH1a2（而非推定的催化失活突变体）的重新表达导致集落生长减少（P < 0.0001），与用5-aza-dC或RA处理相当。综上所述，我们的研究结果表明ALDH1a2是前列腺癌中的一个候选肿瘤抑制基因，并进一步支持视黄酸在前列腺癌预防或治疗中的作用。
