Identification and characterization of a response element in the EGFR promoter that mediates transcriptional repression by 1,25-dihydroxyvitamin D3 in breast cancer cells
- Vincent T Lombardi Cancer Center, Department of Biochemistry and Molecular Biology, 3900 Reservoir Road, Georgetown University Medical Center, Washington, DC 20007
- (Requests for offprints should be addressed to K R McGaffin, University of Pittsburgh Medical Center, Scaife Hall S559, 200 Lothrop Street, Pittsburgh, Pennsylvania, Email:krmcgaffin{at}aol.com.)
Abstract
Reduction of epidermal growth factor receptor (EGFR) mRNA and protein by 1,25-dihydroxyvitamin D3 has been documented in MCF7, T47D, and BT549 breast cancer cells. In the present report, functional mapping of the EGFR promoter in BT549 cells has revealed a sequence of DNA between nucleotide positions −536 and −478 that resembles a consensus vitamin D response element (VDRE) and confers a vitamin D response upon both the homologous and a minimal heterologous promoter. In vitro footprinting and gel shift assays demonstrate the presence of an unidentified nuclear factor that is required for strong binding of the vitamin D receptor (VDR) to this putative VDRE. An Sp1 binding site was also identified in close proximity and shown to bind Sp1 from nuclear extract. Mutational analysis and functional studies using a minimal heterologous promoter provide evidence that the VDR in concert with an unknown nuclear partner mediates basal EGFR repression through displacement of Sp1 which is augmented in the presence of a ligand.
- Received 2 May 2005
- Accepted 4 May 2005
- © 2005 Society for Endocrinology
