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Mol. Cell. Biol., 08 1996, 4465-4477, Vol 16, No. 8
SW Kim, IM Ahn and PR Larsen
We studied the effects of thyroid hormone (T3) on nuclear protein-DNA
interactions by using dimethyl sulfate (DMS) and DNase I ligation- mediated
PCR footprinting. We examined an endogenous gene the growth hormone (GH)
gene, and a stably transfected plasmid containing the chicken lysozyme
silencer (F2) T3 response element (TRE) gene, F2-TRE- TK-CAT, both in
pituitary tumor (GC) cells. The 235-1 cell line, which expresses prolactin
(PRL) and Pit-1, but not the T3 receptor (TR) or GH, was used as a control.
DMS and DNase I footprinting identified protected G residues in the Pit-1,
Sp1, and Zn-15 binding sites of the GH gene in GC, but not in 235-1, cells.
There was no specific protection of the tripartite GH TRE at -180 bp
against either DMS or DNase I in the absence or presence of T3 in either
cell line. However, T3 increased protection of the Pit-1 and Sp1 binding
sites against DMS in GC cells. In GC cells stably transfected with a
plasmid containing F2-TRE-TK-CAT or TRalpha, chloramphenicol
acetyltransferase expression was T3 inducible and DMS footprinting revealed
both F2 TRE TR-binding half sites in a pattern suggesting the binding of TR
homodimers before and during T3 exposure. We conclude that the GH gene is
accessible to specific nuclear proteins in GC, but not in 235-1, cells and
that T3 enhances this interaction, although there is no evidence of TR
binding to the low-affinity rat GH TRE. The presence of TR binding to the
high- affinity F2 TRE before and during T3 exposure suggests that
reversible interaction of T3 with DNA-bound TRs, rather than transient
T3-TR contact with TREs, determines the level of T3-stimulated
transcriptional activation.
Copyright © 1996, American Society for Microbiology
In vivo genomic footprinting of thyroid hormone-responsive genes in pituitary tumor cell lines
Thyroid Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
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