Pedigo Nancy G, Zhang Hongxing, Bruno Maria E C, Kaetzel Charlotte S, Dugan Amy R, Shanehsaz Piam, Hennigan Robert F, Xing Zhenlan, Koszewski Nicholas J, Kaetzel David M
Department of Molecular and Biomedical Pharmacology, University of Kentucky College of Medicine, Lexington, KY 40536, USA.
Oncogene. 2005 Apr 14;24(16):2654-66. doi: 10.1038/sj.onc.1208336.
Overexpression of platelet-derived growth factor A-chain (PDGF-A) is clearly linked to autocrine and paracrine stimulation of malignant growth in many human cancers. We have shown previously that PDGF-A overexpression in choriocarcinoma, hepatoma and lung carcinoma cell lines is driven by the activity of a 66 bp enhancer element (ACE66) located approximately 7 kb upstream of the PDGF-A transcription start site. In this study, the ACE66 element is shown to be activated in JEG-3 choriocarcinoma cells through synergistic interactions between consensus DNA motifs for binding of vitamin D receptor, AP1 and ELK1. Binding of the vitamin D/retinoid-X receptor (VDR/RXRalpha) heterodimer to the ACE66 element was reconstituted in vitro with recombinant VDR/RXRalpha and with JEG-3 nuclear extract, and was verified in living JEG-3 cells by chromatin immunoprecipitation analysis. Transcriptional activity of the ACE66 element, as well as occupancy of the element by VDR/RXRalpha, was shown to be independent of stimulation with the hormonal VDR ligand, 1,25-dihydroxyvitamin D3. The jun kinase pathway of mitogen-activated protein kinase (MAPK) signaling was shown to activate the ACE66 enhancer, most likely through activation of factors binding to the AP1 element. These results identify a novel mechanism of transcriptional enhancement involving ligand-independent activity of the VDR/RXR heterodimer and MAPK signaling pathways that appears to play an important role in the overexpression of PDGF in many different settings of human malignancy.
血小板衍生生长因子A链（PDGF-A）的过表达与许多人类癌症中恶性生长的自分泌和旁分泌刺激明显相关。我们之前已经表明，绒毛膜癌、肝癌和肺癌细胞系中PDGF-A的过表达是由位于PDGF-A转录起始位点上游约7 kb处的一个66 bp增强子元件（ACE66）的活性驱动的。在本研究中，ACE66元件在JEG-3绒毛膜癌细胞中通过维生素D受体、AP1和ELK1结合的共有DNA基序之间的协同相互作用而被激活。维生素D/视黄酸X受体（VDR/RXRα）异二聚体与ACE66元件的结合在体外通过重组VDR/RXRα和JEG-3核提取物进行了重建，并通过染色质免疫沉淀分析在活的JEG-3细胞中得到了验证。ACE66元件的转录活性以及VDR/RXRα对该元件的占据情况被证明与激素VDR配体1,25-二羟基维生素D3的刺激无关。丝裂原活化蛋白激酶（MAPK）信号传导的jun激酶途径被证明可激活ACE66增强子，最有可能是通过激活与AP1元件结合的因子来实现的。这些结果确定了一种新的转录增强机制，涉及VDR/RXR异二聚体的非配体依赖性活性和MAPK信号通路，这似乎在许多不同类型的人类恶性肿瘤中PDGF的过表达中发挥重要作用。
