Mapping of glucocorticoid receptor DNA binding domain surfaces contributing to transrepression of NF-kappa B and induction of apoptosis

Glucocorticoids (GCs) function, in part, through the ability of the glucoco rticoid receptor (GR) to activate gene expression and in part through the t ransrepression of AP-1 and NF-kappaB, Here we characterize the effect of GR DNA binding domain (DBD) mutations, previously analyzed for changes in the ability to activate gene expression or transrepress AP-1. We have identifi ed a GR mutant capable of distinguishing between transrepression of NF-kapp aB and AP-1. Using circular dichroism spectroscopy, we show that this mutat ion does not appreciably alter GR DBD conformation, suggesting that functio nal differences between the mutant and wild type protein are the result of an alteration of a specific interaction surface. These data suggest that tr ansrepression of NF-kappaB and AP-1 occurs through distinct protein-protein interactions and argue against the hypothesis that transrepression occurs through competition for a single coactivator protein. Introduction of these mutations into GC-resistant CEM lymphoblastic T cells restored dexamethaso ne (DEX)-mediated apoptosis as did wild type GR regardless of whether these mutants were transrepression or activation defective. Thus, HEX-mediated a poptosis in transformed T cells is more complex than originally appreciated .