Zuo Xiangsheng, Shen Lanlan, Issa Jean-Pierre, Moy Ofir, Morris Jeffrey S, Lippman Scott M, Shureiqi Imad
Department of Clinical Cancer Prevention, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030-4009, USA.
FASEB J. 2008 Jun;22(6):1981-92. doi: 10.1096/fj.07-098301. Epub 2008 Jan 15.
Methylation of promoter DNA contributes to transcriptional silencing of various tumor-suppressor genes in cancer. Transcriptional silencing of 15-lipoxygenase-1 (15-LOX-1) promotes tumorigenesis. Methylation of 15-LOX-1 promoter DNA occurs in some cancers, but its mechanistic role in 15-LOX-1 transcriptional silencing is unclear. We examined the mechanistic role of 15-LOX-1 promoter DNA methylation in 15-LOX-1 transcriptional regulation in human colorectal cancers. 15-LOX-1 promoter methylation occurred in colorectal cancer cells in vitro, in 36% of tumor tissue samples of colorectal cancer patients, and in virtually no normal colonic mucosa samples of 50 human subjects with no history of colorectal cancer or polyps. 15-LOX-1 promoter DNA methylation levels, however, did not correlate with 15-LOX-1 expression levels (Spearman's r=0.21; P=0.38). We employed siRNA knockdown and genetic disruption models of DNA methyltransferases (DNMTs) to study the effects of this methylation on 15-LOX-1 expression in colon cancer cells. 15-LOX-1 promoter demethylation was insufficient to reestablish 15-LOX-1 expression. 15-LOX-1 transcription was activated by the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) only after DNMT-1 dissociation from the 15-LOX-1 promoter and without altering 15-LOX-1 promoter DNA methylation. DNMT-1 protein hypomorphism impaired DNMT-1 recruitment to the 15-LOX-1 promoter, which allowed 15-LOX-1 transcription activation by SAHA. DNMT-1 has a direct suppressive role in 15-LOX-1 transcriptional silencing that is independent of 15-LOX-1 promoter DNA methylation.
启动子DNA的甲基化导致癌症中各种肿瘤抑制基因的转录沉默。15-脂氧合酶-1（15-LOX-1）的转录沉默促进肿瘤发生。15-LOX-1启动子DNA的甲基化在某些癌症中出现，但其在15-LOX-1转录沉默中的机制作用尚不清楚。我们研究了15-LOX-1启动子DNA甲基化在人类结直肠癌15-LOX-1转录调控中的机制作用。15-LOX-1启动子甲基化在体外结肠癌细胞、36%的结直肠癌患者肿瘤组织样本中出现，而在50名无结直肠癌或息肉病史的人类受试者的正常结肠黏膜样本中几乎未出现。然而，15-LOX-1启动子DNA甲基化水平与15-LOX-1表达水平不相关（Spearman相关系数r = 0.21；P = 0.38）。我们采用DNA甲基转移酶（DNMTs）的小干扰RNA敲低和基因破坏模型来研究这种甲基化对结肠癌细胞中15-LOX-1表达的影响。15-LOX-1启动子去甲基化不足以重新建立15-LOX-1表达。仅在DNMT-1从15-LOX-1启动子解离后，组蛋白去乙酰化酶抑制剂辛二酰苯胺异羟肟酸（SAHA）激活了15-LOX-1转录，且未改变15-LOX-1启动子DNA甲基化。DNMT-1蛋白低表达削弱了DNMT-1募集至15-LOX-1启动子，这使得SAHA能够激活15-LOX-1转录。DNMT-1在15-LOX-1转录沉默中具有直接抑制作用，且该作用独立于15-LOX-1启动子DNA甲基化。
