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Mol. Cell. Biol., 10 1995, 5346-5354, Vol 15, No. 10
ML Espinas, J Roux, R Pictet and T Grange
The rat tyrosine aminotransferase gene is a model system to study
transcriptional regulation by glucocorticoid hormones. We analyzed
transcription factor binding to the tyrosine aminotransferase gene
glucocorticoid-responsive unit (GRU) at kb -2.5, using in vivo footprinting
studies with both dimethyl sulfate and DNase I. At this GRU, glucocorticoid
activation triggers a disruption of the nucleosomal structure. We show here
that various regulatory pathways affect transcription factor binding to
this GRU. The binding differs in two closely related
glucocorticoid-responsive hepatoma cell lines. In line H4II, glucocorticoid
induction promotes the recruitment of hepatocyte nuclear factor 3 (HNF3),
presumably through the nucleosomal disruption. However, the footprint of
the glucocorticoid receptor (GR) is not visible, even though a regular but
transient interaction of the GR is necessary to maintain HNF3 binding. In
contrast, in line FTO2B, HNF3 binds to the GRU in the absence of
glucocorticoids and nucleosomal disruption, showing that a "closed"
chromatin conformation does not repress the binding of certain
transcription factors in a uniform manner. In FTO2B cells, the footprint of
the GR is detectable, but this requires the activation of protein kinase A.
In addition, protein kinase A stimulation also improves the recruitment of
HNF3 independently of glucocorticoids and enhances the glucocorticoid
response mediated by this GRU in an HNF3-dependent manner. In conclusion,
the differences in the behavior of this regulatory sequence in the two cell
lines show that various regulatory pathways are integrated at this GRU
through modulation of interrelated events: transcription factor binding to
DNA and nucleosomal disruption.
Copyright © 1995, American Society for Microbiology
Glucocorticoids and protein kinase A coordinately modulate transcription factor recruitment at a glucocorticoid-responsive unit
Institut Jacques Monod du Centre National de la Recherche Scientifique, Universite Paris, France.
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