Schwartz B, Melnikova V O, Tellez C, Mourad-Zeidan A, Blehm K, Zhao Y-J, McCarty M, Adam L, Bar-Eli M
Department of Cancer Biology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Oncogene. 2007 Jun 14;26(28):4049-58. doi: 10.1038/sj.onc.1210193. Epub 2007 Jan 15.
Activator protein-2 (AP-2) is a transcription factor that regulates proliferation and differentiation in mammalian cells and has been implicated in the acquisition of the metastatic phenotype in several types of cancer. Herein, we examine the role of AP-2alpha in colon cancer progression. We provide evidence for the lack of AP-2alpha expression in the late stages of colon cancer cells. Re-expression of the AP-2alpha gene in the AP-2alpha-negative SW480 colon cancer cells suppressed their tumorigenicity following orthotopic injection into the cecal wall of nude mice. The inhibition of tumor growth could be attributed to the increased expression of E-cadherin and decreased expression and activity of matrix-metalloproteinase-9 (MMP-9) in the transfected cells, as well as a substantial loss of their in vitro invasive properties. Conversely, targeting constitutive expression of AP-2alpha in AP-2-positive KM12C colon cancer cells with small interfering RNA resulted in an increase in their invasive potential, downregulation of E-cadherin and increased expression of MMP-9. In SW480 cells, re-expression of AP-2alpha resulted in a fourfold increase in the activity of E-cadherin promoter, and a 5-14-fold decrease in the activity of MMP-9 promoter, indicating transcriptional regulation of these genes by AP-2alpha. Chromatin immunoprecipitation assay showed that re-expressed AP-2alpha directly binds to the promoter of E-cadherin, where it has been previously reported to act as a transcriptional activator. Furthermore, chromatin immunoprecipitation assay revealed AP-2alpha binding to the MMP-9 promoter, which ensued by decreased binding of transcription factor Sp-1 and changes in the recruitment of transcription factors to a distal AP-1 element, thus, contributing to the overall downregulation of MMP-9 promoter activity. Collectively, our data provide evidence that AP-2alpha acts as a tumor suppressor gene in colon cancer..
激活蛋白-2（AP-2）是一种转录因子，可调节哺乳动物细胞的增殖和分化，并与多种癌症转移表型的获得有关。在此，我们研究了AP-2α在结肠癌进展中的作用。我们提供证据表明，在结肠癌细胞的晚期阶段缺乏AP-2α表达。在AP-2α阴性的SW480结肠癌细胞中重新表达AP-2α基因，可抑制其原位注射到裸鼠盲肠壁后的致瘤性。肿瘤生长的抑制可能归因于转染细胞中E-钙黏蛋白表达增加、基质金属蛋白酶-9（MMP-9）表达和活性降低，以及其体外侵袭特性的显著丧失。相反，用小干扰RNA靶向AP-2阳性的KM12C结肠癌细胞中AP-2α的组成型表达，导致其侵袭潜力增加、E-钙黏蛋白下调和MMP-9表达增加。在SW480细胞中，AP-2α的重新表达导致E-钙黏蛋白启动子活性增加四倍，MMP-9启动子活性降低5至14倍，表明AP-2α对这些基因的转录调控。染色质免疫沉淀分析表明，重新表达的AP-2α直接与E-钙黏蛋白的启动子结合，此前有报道称它在该启动子处作为转录激活因子发挥作用。此外，染色质免疫沉淀分析显示AP-2α与MMP-9启动子结合，随后转录因子Sp-1的结合减少，转录因子向远端AP-1元件的募集发生变化，从而导致MMP-9启动子活性整体下调。总体而言，我们的数据提供了证据，表明AP-2α在结肠癌中作为肿瘤抑制基因发挥作用。
