Ling Yaqin, Xu Xiaoying, Hao Jie, Ling Xiaoling, Du Xiaopin, Liu Xin, Zhao Xingxu
College of Veterinary Medicine, Gansu Agricultural University, Lanzhou 730070, Gansu Province, China.
Cancer Genet Cytogenet. 2010 Jan 15;196(2):140-5. doi: 10.1016/j.cancergencyto.2009.09.010.
The thyroid hormone receptors (TR) have three major isoforms, TRalpha1, TRalpha2, and TRbeta1; these are ligand-dependent nuclear transcription factors. THRB, the gene encoding TRbeta1, is considered a potential cancer suppressor. The mechanism of its inactivation is not yet clear. Aberrant silencing of THRB in breast cancer tissue and plasma by promoter hypermethylation was investigated in the present study. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to examine THRB mRNA expression in the breast cancer tissues. Methylation-specific polymerase chain reaction (MSP) combined with nested PCR was used to determine the methylation status of the THRB gene promoter region in 40 cancer tissue and 40 plasma samples from breast cancer patients. Methylation status of MSP product in plasma was also evaluated by direct sequencing. The expression of THRB mRNA in breast cancer tissues was lower than that in the normal tissues; hypermethylation was found in 32 of 40 breast cancer tissues (80%) and in 28 of 40 plasma samples (70%). Loss of THRB gene expression was associated with the CpG island hypermethylation of promoter regions. THRB gene CpG island methylation was not related to clinical pathologic parameters. Sequencing results were identical to agarose gel electrophoresis results. The present results indicate that hypermethylation of THRB as an alternative gene silencing mechanism is highly prevalent in breast cancer. Methylated tumor-specific DNA may serve as a plasma biomarker for prognosis in patients with breast cancer.
甲状腺激素受体（TR）有三种主要亚型，即TRα1、TRα2和TRβ1；它们是配体依赖性核转录因子。THRB是编码TRβ1的基因，被认为是一种潜在的癌症抑制基因。其失活机制尚不清楚。本研究调查了乳腺癌组织和血浆中THRB因启动子高甲基化而出现的异常沉默情况。采用逆转录聚合酶链反应（RT-PCR）检测乳腺癌组织中THRB mRNA的表达。采用甲基化特异性聚合酶链反应（MSP）结合巢式PCR来确定40例乳腺癌患者癌组织和40份血浆样本中THRB基因启动子区域的甲基化状态。还通过直接测序评估血浆中MSP产物的甲基化状态。乳腺癌组织中THRB mRNA的表达低于正常组织；40例乳腺癌组织中有32例（80%）以及40份血浆样本中有28例（70%）发现高甲基化。THRB基因表达缺失与启动子区域的CpG岛高甲基化有关。THRB基因CpG岛甲基化与临床病理参数无关。测序结果与琼脂糖凝胶电泳结果一致。目前的结果表明，THRB高甲基化作为一种替代基因沉默机制在乳腺癌中非常普遍。甲基化的肿瘤特异性DNA可作为乳腺癌患者预后的血浆生物标志物。
