Role of Important Hydrophobic Amino Acids in the Interaction between the Glucocorticoid Receptor τ1-Core Activation Domain and Target Factors

In this work, we determined how altered-function mutants affecting hydrophobic residues within the τ1-core activation domain of the human glucocorticoid receptor (GR) influence its physical interaction with different target proteins of the transcriptional machinery. Screening of putative target proteins showed that the τ1-core can interact with the C-terminal part of the CREB-binding protein (CBP). In addition, the previously identified interactions of the τ1-core with the TATA-binding protein (TBP) and the Ada2 adaptor protein were localized to the C- and N-terminal regions of these proteins, respectively. A panel of mutations within the τ1-core that either decrease or increase activation potential was used to probe the interaction of the τ1-core domain with TBP, Ada2, and CBP. We found that the pattern of effects caused by the mutations was similar for each of the interactions and that the effects on binding generally reflected effects on gene activation potential. Thus, the predominant effect of the mutations appears to influence a property of the τ1-core that is common to all three interactions, rather than properties that are differentially required by each of the target factor interactions, individually. Such a property could be the ability of the domain to adopt a folded conformation that is generally necessary for interaction with target factors. We have also shown that TBP, Ada2, and CBP can interact with both the τ1-core and the GR ligand-binding domain, offering a possible mechanism for synergistic interaction between the τ1-core and other receptor activation domains. However, other target proteins (e.g., RIP140, and SRC-1), which interact with the GR C terminus, did not show significant interactions with the τ1-core under our conditions.