Compartmentalization of androgen receptor protein–protein interactions in living cells

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Abstract
Steroid receptors regulate gene expression in a ligand-dependent manner by binding specific DNA sequences. Ligand binding also changes the conformation of the ligand binding domain (LBD), allowing interaction with coregulators via LxxLL motifs. Androgen receptors (ARs) preferentially interact with coregulators containing LxxLL-related FxxLF motifs. The AR is regulated at an extra level by interaction of an FQNLF motif in the N-terminal domain with the C-terminal LBD (N/C interaction). Although it is generally recognized that AR coregulator and N/C interactions are essential for transcription regulation, their spatiotemporal organization is largely unknown. We performed simultaneous fluorescence resonance energy transfer and fluorescence redistribution after photobleaching measurements in living cells expressing ARs double tagged with yellow and cyan fluorescent proteins. We provide evidence that AR N/C interactions occur predominantly when ARs are mobile, possibly to prevent unfavorable or untimely cofactor interactions. N/C interactions are largely lost when AR transiently binds to DNA, predominantly in foci partly overlapping transcription sites. AR coregulator interactions occur preferentially when ARs are bound to DNA.