Determinants of high-affinity DNA binding by the glucocorticoid receptor: evaluation of receptor domains outside the DNA-binding domain.

In this study, we have investigated the influence of regions outside the DNA-binding domain of the human glucocorticoid receptor on high-affinity DNA binding. We find that the DNA-binding domain shows a 10-fold lower affinity for a palindromic DNA-binding site than the intact receptor. The N-terminal part of the receptor protein does not influence its DNA-binding affinity, while the C-terminal steroid-binding domain increases the DNA-binding affinity of the receptor molecule. It has previously been shown that both the intact glucocorticoid receptor and the glucocorticoid receptor DNA-binding domain bind to a palindromic glucocorticoid response element on DNA as dimers. It is likely that differences in DNA-binding affinity observed result from protein-protein interactions outside the DNA-binding domain between receptor monomers, as has been shown for the estrogen receptor. We have previously identified a segment involved in protein-protein interactions between DNA-binding domains of glucocorticoid receptors. This, in combination with results presented in this study, suggests that there are at least two sites of contact between receptor monomers bound to DNA. We suggest that the interaction between the DNA-binding domains may act primarily to restrict DNA binding to binding sites with appropriate half-site spacing and that additional stability of the receptor dimer is provided by the interactions between the steroid-binding domains.     

Competition for DNA steroid response elements as a possible mechanism for neuroendocrine integration

For the analysis of a simple steroid-dependent mating behavior, careful response definition, complete neural circuit delineation and placement of estrogen-responsive cells within this circuit have been accomplished. Molecular studies of two relevant genes have emphasized DNA/RNA hybridization assays nd DNA binding techniques. For both the rat preproenkephalin gene and the gene for the progesterone receptor, a strong induction by estrogen, tissue specificity of expression and a sex difference in regulation are prominent phenomena. On the rat preproenkephalin promoter, estrogen (ER) and thyroid receptors may compete for a DNA binding site. Likewise, progesterone (PR) and glucocorticoid receptors may compete for the same sites. On the rat PR gene, interactions between ER and AP-1 binding proteins are of special interest. Such interactions could underlay competitions and synergies between steroid hormones and neurally signalled events in the environment.