Department of Veterinary Pathobiology, University of Missouri, Columbia, Missouri 65211.
Department of Veterinary Pathobiology, University of Missouri, Columbia, Missouri 65211.
J Biol Chem. 2013 Sep 20;288(38):27232-27242. doi: 10.1074/jbc.M113.481184. Epub 2013 Aug 6.
Vascular endothelial growth factor (VEGF) is recognized as an important angiogenic factor that promotes angiogenesis in a series of pathological conditions, including cancer, inflammation, and ischemic disorders. We have recently shown that the inflammatory transcription factor SAF-1 is, at least in part, responsible for the marked increase of VEGF levels in breast cancer. Here, we show that SAF-1-mediated induction of VEGF is repressed by KLF-4 transcription factor. KLF-4 is abundantly present in normal breast epithelial cells, but its level is considerably reduced in breast cancer cells and clinical cancer tissues. In the human VEGF promoter, SAF-1- and KLF-4-binding elements are overlapping, whereas SAF-1 induces and KLF-4 suppresses VEGF expression. Ectopic overexpression of KLF-4 and RNAi-mediated inhibition of endogenous KLF-4 supported the role of KLF-4 as a transcriptional repressor of VEGF and an inhibitor of angiogenesis in breast cancer cells. We show that KLF-4 recruits histone deacetylases (HDACs) -2 and -3 at the VEGF promoter. Chronological ChIP assays demonstrated the occupancy of KLF-4, HDAC2, and HDAC3 in the VEGF promoter in normal MCF-10A cells but not in MDA-MB-231 cancer cells. Co-transfection of KLF-4 and HDAC expression plasmids in breast cancer cells results in synergistic repression of VEGF expression and inhibition of angiogenic potential of these carcinoma cells. Together these results identify a new mechanism of VEGF up-regulation in cancer that involves concomitant loss of KLF-4-HDAC-mediated transcriptional repression and active recruitment of SAF-1-mediated transcriptional activation.
血管内皮生长因子 (VEGF) 被认为是一种重要的血管生成因子,可促进一系列病理条件下的血管生成,包括癌症、炎症和缺血性疾病。我们最近表明,炎症转录因子 SAF-1 在至少部分程度上负责乳腺癌中 VEGF 水平的显著增加。在这里,我们表明 SAF-1 介导的 VEGF 诱导受到 KLF-4 转录因子的抑制。KLF-4 在正常乳腺上皮细胞中大量存在,但在乳腺癌细胞和临床癌组织中的水平显著降低。在人类 VEGF 启动子中,SAF-1 和 KLF-4 结合元件重叠,而 SAF-1 诱导和 KLF-4 抑制 VEGF 表达。KLF-4 的异位过表达和内源性 KLF-4 的 RNAi 介导抑制支持 KLF-4 作为 VEGF 的转录抑制剂和乳腺癌细胞中血管生成的抑制剂的作用。我们表明 KLF-4 在 VEGF 启动子处募集组蛋白去乙酰化酶 (HDACs)-2 和 -3。时程 ChIP 测定表明,KLF-4、HDAC2 和 HDAC3 在正常 MCF-10A 细胞中的 VEGF 启动子中占据,但在 MDA-MB-231 癌细胞中不占据。在乳腺癌细胞中共同转染 KLF-4 和 HDAC 表达质粒会导致 VEGF 表达的协同抑制和这些癌细胞血管生成潜力的抑制。这些结果共同确定了癌症中 VEGF 上调的新机制,涉及 KLF-4-HDAC 介导的转录抑制的同时丧失和 SAF-1 介导的转录激活的主动募集。