The Glucorticoid Receptor Is Tethered To DNA-bound Oct-1
At The
Mouse GnRH Distal Negative Glucocorticoid Response Element |
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Glucocorticoids act by binding to a cytosolic receptor (GR) which upon translocation to the nucleus acts as a transcription factor. Although most studies have examined transcriptional stimulation by glucorticoids, they produce equivalent levels of transcriptional repression. These studies examined control of a glucocorticoid negatively regulated gene, the Gonadotrophin-releasing Hormone (GnRH) gene. Two negative-regulatory elements (nGREs) are contained within this gene; the focus of this study is on control by the distal element. |
The distal nGRE of the GnRH gene is not directly bound by GRs but is recognized by Oct-1 present in GT1-7 cell nuclear extracts or by purified Oct-1. Rather, purified full length GR interacts directly with Oct-1 bound to the distal nGRE. Mutation of the distal nGRE to an Oct-1 consensus binding site not only increases the affinity of Oct-1 binding, but also alters the conformation of DNA-bound Oct-1 and the pattern of protein-DNA complexes formed in vitro with GT1-7 cell nuclear extracts. In addition, the interaction of purified GR with DNA-bound Oct-1 is altered when Oct-1 is bound to a consensus Oct-1 site. Mutation of the distal GnRH nGRE to a consensus Oct-1 site is also associated with reduced glucocorticoid repression in transfected GT1-7 cells. |
The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), also represses GnRH transcription by utilization of sequences that overlap those of the distal nGRE. Mutation of the distal nGRE to that of a consensus Oct-1 binding site reverses the negative repression by TPA. |
In summary, changes in the assembly of multi-protein complexes at the distal nGRE of the GnRH gene influence the regulation of its transcription. |
