A 5'-distal enhanceosome in the PDGF-A gene is activated in choriocarcinoma cells via ligand-independent binding of vitamin D receptor and constitutive jun kinase signaling.
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.
Pedigo
Nancy G
NG
Department of Molecular and Biomedical Pharmacology, University of Kentucky College of Medicine, Lexington, KY 40536, USA.
Zhang
Hongxing
H
Bruno
Maria E C
ME
Kaetzel
Charlotte S
CS
Dugan
Amy R
AR
Shanehsaz
Piam
P
Hennigan
Robert F
RF
Xing
Zhenlan
Z
Koszewski
Nicholas J
NJ
Kaetzel
David M
DM
D024506:5' Flanking Region; D001483:Base Sequence; D002822:Choriocarcinoma / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008024:Ligands; D020935:MAP Kinase Signaling System; D008954:Models, Biological; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000235:genetics; D010982:Platelet-Derived Growth Factor / Q000235:genetics*; D011485:Protein Binding; D018167:Receptors, Calcitriol / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D008024:Ligands; D009838:Oligodeoxyribonucleotides; D010982:Platelet-Derived Growth Factor; D018167:Receptors, Calcitriol; D011994:Recombinant Proteins; C075278:platelet-derived growth factor A; D048031:JNK Mitogen-Activated Protein Kinases