T3 receptor suppression of Sp1-dependent transcription from the epidermal growth factor receptor promoter via overlapping DNA-binding sites

• Published in: The Journal of biological chemistry Vol. 268; no. 21; pp. 16065 - 16073
• Main Authors: JUN XU, THOMPSON, K. L, SHEPHARD, L. B, HUDSON, L. G, GILL, G. N
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 25.07.1993
• Subjects: Animals; Base Sequence; Binding, Competitive; Biological and medical sciences; Cells, Cultured; DNA - metabolism; Drosophila; ErbB Receptors - genetics; Fundamental and applied biological sciences. Psychology; HeLa Cells; Humans; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Nuclear Proteins - metabolism; Promoter Regions, Genetic; Receptors, Cell Surface - metabolism; Receptors, Retinoic Acid; Receptors, Thyroid Hormone - metabolism; Retinoid X Receptors; Sp1 Transcription Factor - metabolism; Transcription Factors; Transcription, Genetic; Transcription. Transcription factor. Splicing. Rna processing; Human; Epidermal growth factor; Transcription; Triiodothyronine; Growth factor; Biological receptor; Hormonal receptor
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)82358-4

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.