Promoter -dependent interactions of the androgen receptor with the POU transcription factor Oct -1 and other nuclear proteins on the <italic>Slp</italic> enhancer.

Abstract

Androgen-specific activation of the mouse sex-limited protein (<italic> Slp</italic>) gene is mediated through protein interactions of the androgen receptor (AR) with other nuclear factors. A critical nonreceptor region, FPIV, has been identified and shown to bind the octamer transcription factor-1 (Oct-1). To determine how Oct-1 is involved in the androgen response, interaction of Oct-1 with AR and the glucocorticoid receptor (GR) was compared. Results demonstrated that AR interacts with Oct-1 more efficiently when DNA-bound, while GR-Oct-1 interaction is DNA-independent. DNA-dependent AROct-1 interaction was shown to facilitate recruitment of the steroid receptor coactivator-1 (SRC-1) into an apparent multiprotein complex. The antiandrogens Casodex (CDX) and hydroxyflutamide (OH-F) were used to induce alternative AR conformations to determine their influence in AR protein interactions with other proteins. Binding to antagonists promoted AR interactions with the corepressor N-CoR while abrogated recruitment of SRC-1. However, AR-Oct-1 association was not affected by the antiandrogens. OH-F-AR showed a residual interaction with SRC-1 that correlates with a moderate agonist activity in transfection. In the presence of androgens, CDX was an incomplete antagonist. This seems to be due to the interaction between CDX and DHT-bound ARs that obviate the effects of antagonist in AR-SRC-1 association. Results obtained support the importance of AR conformation in receptor interactions with other nuclear proteins and showed that antiandrogens can acquire agonism in distinct manners. Finally, AR interactions with Oct-1 and Brain-1 (Brn-1), another POU protein, were compared. In transfection, Brn-1 repressed AR activation of the <italic>Slp</italic> enhancer, while cooperated with AR when bound to consensus octamer sequences. Brn-1 repression involved the POU-domain but its cooperativity with AR required additional domains. Unlike Oct-1, Brn-1 interacted with AR in a DNA-independent fashion. These differences in DNA-dependence in Oct-1 and Brn-1 interactions with AR were due to variations in their POU-domain. Thus, the octamer binding sequence can influence the functional interaction of POU factors with AR. Although interaction of AR, Oct-1, and SRC-1 from within a complex remains to be demonstrated <italic>in vivo</italic>, this study shows that AR differential protein interactions with nonreceptor factors, rather than their stringent and exclusive specificity, can confer and modulate the hormonal response.