Hypermethylation of a small CpGuanine-rich region correlates with loss of activator protein-2α expression during progression of breast cancer
Hypermethylation of a small CpGuanine-rich region correlates with loss of activator protein-2α expression during progression of breast cancer
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DOI：
10.1158/0008-5472.can-0318-2
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发表时间：
2004-03-01
期刊：
影响因子：
11.2
通讯作者：
Baylin, SB
中科院分区：
文献类型：
--
作者：
Douglas, DB;Akiyama, Y;Baylin, SB
转录因子激活蛋白-2 α（AP-2 α）最近被认为是一种肿瘤抑制蛋白，在肿瘤进展过程中可能会丢失，并且在癌细胞系中过表达时表现出生长抑制特性。我们现在证明，在乳腺癌中，该基因启动子CpG岛内一个离散的5'区域的超甲基化与AP-2 α表达的缺失有关。在乳腺癌演变过程中，岛内的多个CpG位点变得高甲基化。然而，只有最富含CpG的区域（外显子1的3'端的一个小的，类似于300-区域）的高甲基化才能完全区分肿瘤和正常乳腺组织，并与转录沉默相关。在细胞培养中，与外显子1超甲基化相关的沉默的AP-2 α通过5-氮杂-2 '脱氧胞苷重新表达，导致功能性DNA序列特异性结合蛋白的恢复。在体内，如通过非常灵敏的巢式PCR方法检测到的，AP-2 α外显子1区域的离散甲基化不发生在正常乳腺上皮中，并且仅发生在19个导管原位癌（DCIS）病变中的3个（16%）中，但存在于16个浸润性乳腺肿瘤中的12个（75%）中（P < 0.001; DCIS与浸润性癌症）。该区域未甲基化的肿瘤表达AP-2 α蛋白，而高甲基化的肿瘤显示大面积的丢失。我们的研究随后确定，CpG岛的一个小区域的超甲基化与乳腺癌中AP-2 α的沉默相关，并表明该基因的失活可能是DCIS病变进展的一个因素和有用的标志物。
The transcription factor activator protein-2alpha (AP-2alpha) has recently been implicated as a tumor suppressor protein that can be lost during tumor progression and that exhibits growth-inhibitory properties when overexpressed in cancer cell lines. We now demonstrate that hypermethylation of a discrete 5' region within a promoter CpG island of the gene is associated in breast cancer with the loss of AP-2alpha expression. Multiple CpG sites within the island become hypermethylated during breast cancer evolution. However, only hypermethylation of the most CpG-rich region, a small, similar to300-by area at the 3' end of exon 1, fully distinguishes neoplastic from normal breast tissue and correlates with transcriptional silencing. In cell culture, silenced AP-2alpha, associated with exon 1 hypermethylation, is re-expressed by 5-aza-2'deoxycytidine resulting in the restoration of a functional DNA sequence-specific binding protein. In vivo, as detected by a very sensitive nested PCR approach, methylation of the discrete AP-2alpha exon 1 region does not occur in normal breast epithelium and occurs in only 3 (16%) of 19 ductal carcinoma in situ (DCIS) lesions, but is present in 12 (75%) of 16 invasive breast tumors (P < 0.001; DCIS versus invasive cancers). Tumors unmethylated for this region expressed AP-2alpha protein throughout, whereas tumors with hypermethylation showed large areas of loss. Our studies then determine that hypermethylation of a small region of a CpG island correlates with silencing of AP-2alpha in breast cancer and suggest that inactivation of this gene could be a factor in, and a useful marker for, the progression of DCIS lesions.