Veeck Jürgen, Geisler Cordelia, Noetzel Erik, Alkaya Sevim, Hartmann Arndt, Knüchel Ruth, Dahl Edgar
Molecular Oncology Group, Institute of Pathology, University Hospital of the RWTH Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany.
Carcinogenesis. 2008 May;29(5):991-8. doi: 10.1093/carcin/bgn076. Epub 2008 Mar 19.
Disruption of the Wnt pathway is thought to be crucial in the development of human cancer. Pathway inhibitory members of the secreted frizzled-related protein (SFRP) family were found to be downregulated due to epigenetic inactivation in various malignancies. To date, only SFRP1 has been studied in human breast cancer and we questioned whether other SFRP genes may be implicated in the pathogenesis of this disease as well. An initial real-time polymerase chain reaction analysis of SFRP5 expression in normal human tissues (n = 9) revealed weak expression in most tissues, including breast. Malignant mammary cell lines showed further SFRP5 expression loss in five of six cases. Consistently, in matched pairs of primary breast tumor/normal breast tissue, this downregulation (>5-fold) could be confirmed (n = 8/13; 62%). We identified promoter methylation as the predominant mechanism of SFRP5 gene silencing since SFRP5 promoter methylation correlated significantly with loss of SFRP5 expression in cell lines (P = 0.040) and primary tumors (P = 0.003). Moreover, cancerous cell lines re-expressed SFRP5 messenger RNA following treatment with DNA-demethylating drugs. Of 168 primary breast carcinomas, 73% harbored a methylated SFRP5 promoter, whereas 27% were unaffected by epigenetic alteration. Most interestingly, SFRP5 methylation was associated with reduced overall survival (OS) (P = 0.045) and was an independent risk factor affecting OS in a multivariate Cox proportional hazard model (hazard ratio): 4.55; 95% confidence interval: 1.01-20.56; P = 0.049). In conclusion, SFRP5 is a target of epigenetic inactivation in human breast cancer, supporting the hypothesis of its role as tumor suppressor gene. SFRP5 methylation may be a novel DNA-based biomarker potentially useful in clinical breast cancer management.
Wnt信号通路的破坏被认为在人类癌症的发展中至关重要。分泌型卷曲相关蛋白（SFRP）家族的通路抑制成员被发现由于表观遗传失活而在各种恶性肿瘤中下调。迄今为止，仅在人类乳腺癌中对SFRP1进行了研究，我们质疑其他SFRP基因是否也可能与该疾病的发病机制有关。对正常人体组织（n = 9）中SFRP5表达的初步实时聚合酶链反应分析显示，包括乳腺在内的大多数组织中表达较弱。恶性乳腺细胞系在6例中有5例显示出进一步的SFRP5表达缺失。同样，在原发性乳腺肿瘤/正常乳腺组织的配对样本中，这种下调（>5倍）可以得到证实（n = 8/13；62%）。我们确定启动子甲基化是SFRP5基因沉默的主要机制，因为SFRP5启动子甲基化与细胞系（P = 0.040）和原发性肿瘤（P = 0.003）中SFRP5表达的丧失显著相关。此外，癌细胞系在用DNA去甲基化药物处理后重新表达了SFRP5信使核糖核酸。在168例原发性乳腺癌中，73%的肿瘤SFRP5启动子发生甲基化，而27%未受表观遗传改变的影响。最有趣的是，SFRP5甲基化与总生存期（OS）降低相关（P = 0.045），并且在多变量Cox比例风险模型中是影响OS的独立危险因素（风险比：4.55；95%置信区间：1.01 - 20.56；P = 0.049）。总之，SFRP5是人类乳腺癌表观遗传失活的靶点，支持其作为肿瘤抑制基因的作用假说。SFRP5甲基化可能是一种新型的基于DNA的生物标志物，在临床乳腺癌管理中可能有用。
