Chang Lydia, Schwarzenbach Heidi, Meyer-Staeckling Sönke, Brandt Burkard, Mayr Georg W, Weitzel Joachim M, Windhorst Sabine
Universitätsklinikum Hamburg-Eppendorf, Hamburg; and 3Leibniz-Institut für Nutztierbiologie, Dummerstorf, Dummerstorf, Mecklenburg-Vorpommern, Germany.
Mol Cancer Res. 2011 Apr;9(4):497-506. doi: 10.1158/1541-7786.MCR-10-0556. Epub 2011 Apr 1.
Under physiologic conditions, the inositol-1,4,5-trisphosphate (InsP(3))-metabolizing, F-actin-bundling InsP(3)-kinase-A (ITPKA) is expressed only in neurons. Tumor cells that have gained the ability to express ITPKA show an increased metastatic potential due to the migration-promoting properties of ITPKA. Here we investigated the mechanism how tumor cells have gained the ability to reexpress ITPKA by using a breast cancer cell line (T47D) with no expression and a lung carcinoma cell line (H1299) with ectopic ITPKA expression. Cloning of a 1,250-bp ITPKA promoter fragment revealed that methylation of CpG islands was reduced in H1299 as compared with T47D cells, but DNA demethylation did not alter the expression of ITPKA. Instead, we showed that the repressor-element-1-silencing transcription factor (REST)/neuron-restrictive silencer factor (NRSF), which suppresses expression of neuronal genes in nonneuronal tissues, regulates expression of ITPKA. Knockdown of REST/NRSF induced expression of ITPKA in T47D cells, whereas its overexpression in H1299 cells strongly reduced the level of ITPKA. In T47D cells, REST/NRSF was bound to the RE-1 site of the ITPKA promoter and strongly reduced its activity. In H1299 cells, in contrast, expressing comparable REST/NRSF levels as T47D cells, REST/NRSF only slightly reduced ITPKA promoter activity. This reduced suppressor activity most likely results from expression of a dominant-negative isoform of REST/NRSF, REST4, which impairs binding of REST/NRSF to the RE-1 site. Thus, ITPKA may belong to the neuronal metastasis-promoting proteins whose ectopic reexpression in tumor cells is associated with impaired REST/NRSF activity. Mol Cancer Res; 9(4); 1-10. ©2011 AACR.
在生理条件下，代谢肌醇 - 1,4,5 - 三磷酸（InsP(3)）、捆绑F - 肌动蛋白的InsP(3)激酶 - A（ITPKA）仅在神经元中表达。获得ITPKA表达能力的肿瘤细胞由于ITPKA的促迁移特性而显示出增加的转移潜能。在此，我们使用无表达的乳腺癌细胞系（T47D）和异位表达ITPKA的肺癌细胞系（H1299），研究了肿瘤细胞如何获得重新表达ITPKA的能力。一个1250 bp的ITPKA启动子片段的克隆显示，与T47D细胞相比，H1299细胞中CpG岛的甲基化减少，但DNA去甲基化并未改变ITPKA的表达。相反，我们发现抑制元件 - 1 - 沉默转录因子（REST）/神经元限制性沉默因子（NRSF），其在非神经元组织中抑制神经元基因的表达，调节ITPKA的表达。敲低REST/NRSF可诱导T47D细胞中ITPKA的表达，而其在H1299细胞中的过表达则强烈降低ITPKA的水平。在T47D细胞中，REST/NRSF与ITPKA启动子的RE - 1位点结合并强烈降低其活性。相比之下，在H1299细胞中，REST/NRSF水平与T47D细胞相当，但其仅轻微降低ITPKA启动子活性。这种降低的抑制活性很可能是由于REST/NRSF的显性负性异构体REST4的表达，其损害了REST/NRSF与RE - １位点的结合。因此，ITPKA可能属于神经元转移促进蛋白，其在肿瘤细胞中的异位重新表达与REST/NRSF活性受损有关。分子癌症研究；9(4)；1 - 10。©2011美国癌症研究协会。
