T3 receptor suppression of Sp1-dependent transcription from the epidermal growth factor receptor promoter via overlapping DNA-binding sites.
Expression of the human epidermal growth factor receptor (EGFR) gene is inhibited by ligand-activated thyroid hormone receptor (T3R). Binding sites for Sp1 and for the T3R.retinoid X receptor (RXR) complex overlap in a functional core of the EGFR promoter. Sp1 inhibited binding of the T3R complex to this 36-base pair (bp) EGFR element in vitro but did not affect binding of the T3R complex to a positive thyroid hormone response element (TRE). In Drosophila SL2 cells, which lack Sp1 and T3R, function of the EGFR promoter was strongly dependent on Sp1. Sp1-dependent promoter function was inhibited by ligand-activated T3R but not by mutant T3R defective in DNA or T3 binding. RXR increased the extent of inhibition. Sp1 enhanced activity of the 36-bp element placed 5' to a minimal TATA promoter and this enhancement was also repressed by T3R. Mutations in the 36-bp element were unable to separate Sp1 and T3R functions. However, addition of a second half-site 5' to the existing site in an inverted repeat configuration created a positive TRE. In the absence of ligand, T3R inhibited Sp1 stimulation from this altered element; addition of T3 reversed the inhibition. When a dimeric TRE is separated from Sp1-binding sites strong synergism was observed. The nature and location of the TRE thus strongly influence biological responses. A TRE site in the EGFR promoter that overlaps an Sp1-binding site inhibits Sp1 function but is unable to direct positive function.
Xu
J
J
Department of Chemistry, University of California, San Diego, La Jolla 92093.
Thompson
K L
KL
Shephard
L B
LB
Hudson
L G
LG
Gill
G N
GN
D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism*; D004330:Drosophila; D066246:ErbB Receptors / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011956:Receptors, Cell Surface / Q000378:metabolism; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone / Q000378:metabolism*; D047488:Retinoid X Receptors; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic
D009687:Nuclear Proteins; D011956:Receptors, Cell Surface; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D047488:Retinoid X Receptors; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D004247:DNA; D066246:ErbB Receptors