DNA binding by the androgen receptor : a question of specificity
Binding of the AR to selective and non-selective DNA response elements was investigated to determine how this specificity is achieved. The influence of other receptor domains on protein-DNA interactions was examined and structural studies were performed to study conformational changes in the receptor in the presence and absence of specific DNA response elements. It was confirmed that the affinity of the isolated AR DNA binding domain (DBD) was greater for non-selective response elements compared with selective response elements. Interestingly, a decrease in binding affinity for both non-selective and selective sequences was observed in the presence of the N terminal domain (NTD). Furthermore this inhibitory effect required the NTD to be attached to the DBD. There were no differences detected in protein/DNA contacts of the DBD in the absence or presence of the NTD. However modest differences detected in protein/DNA contacts of the DBD in the absence or presence of the NTD. However modest differences in sensitivity to DNA methylation were observed in the 3' flanking sequences of the non-selective C3(1) element. In addition, structural studies detected a change in conformation of the NTD on binding to DNA response elements suggesting a structural role for the NTD in recognition of androgen binding sites. However no dramatic differences in conformation were observed when selective and non-selective response elements were studied. Taken together these studies indicate that there are reciprocal intradomain communications between the AR DBD and the NTD, leading to modulation of receptor DNA-binding activity, and changes in receptor conformation. It is speculated that the latter may modify specific protein-protein interactions and receptor-dependent gene regulation. Therefore, it is clear from these studies that DNA binding is likely to lay a more active role in receptor activity than simply tethering of the protein to promoter or enhancer sequences and that the nature of the DNA response elements needs to be taken into consideration when studying receptor-dependent transactivation.