Properties of the glucocorticoid modulatory element binding proteins GMEB-1 and-2: Potential new modifiers of glucocorticoid receptor transactivationand members of the family of KDWK proteins

An important component of glucocorticoid steroid induction of tyrosine amin otransferase (TAT) gene expression is the glucocorticoid modulatory element (GME), which is located at -3.6 kb of the rat TAT gene. The GME both media tes a greater sensitivity to hormone, due to a left shift in the dose-respo nse curve of agonists, and increases the partial agonist activity of antigl ucocorticoids. These properties of the GME are intimately related to the bi nding of a heteromeric complex of two proteins (GMEB-1 and -2). We previous ly cloned the rat GMEB-2 as a 67-kDa protein. We now report the cloning of the other member of the GME binding complex, the 88-kDa human GMEB-1, and v arious properties of both proteins. GMEB-1 and -2 each possess an intrinsic transactivation activity in mammalian one-hybrid assays, consistent with o ur proposed model in which they modify glucocorticoid receptor (GR)-regulat ed gene induction. This hypothesis is supported by interactions between GR and both GMEB-1 and -2 in mammalian two-hybrid and in pull-down assays. Fur thermore, overexpression of GMEB-1 and -2, either alone or in combination, results in a reversible right shift in the dose-response curve, and decreas ed agonist activity of antisteroids, as expected from the squelching of oth er limiting factors. Additional mechanistic details that are compatible wit h the model of GME action are suggested by the interactions in a two-hybrid assay of both GMEBs with CREB-binding protein (CBP) and the absence of his tone acetyl transferase (HAT) activity in both proteins. GMEB-1 and -2 shar e a sequence of 90 amino acids that is 80% identical. This region also disp lays homology to several other proteins containing a core sequence of KDWK. Thus, the GMEBs may be members of a new family of factors with interesting transcriptional properties.