Synergistic activation of yeast-expressed rat androgen receptor by modulators of protein kinase-A

We have employed a yeast (Saccharomyces cerevisiae) based rat androgen rece ptor expression system to examine the cross-talk between different signalli ng pathways. We report here the synergistic modulation of androgen regulate d transcriptional activation of P-galactosidase reporter activity by the ac tivators of protein kinase-A, like forskolin and 8-bromo-cyclic AMP. A simi lar ligand-dependent enhancement of reporter activity compared to a DHT tre ated control has been noticed with okadaic acid, which is a potent inhibito r of protein phosphatase. The activation could be blocked by protein kinase -A/C inhibitor, H7. Forskolin treatment neither altered levels of receptor mRNA nor [H-3]R1881 binding to the receptor. Although it promotes binding o f receptor to an androgen response element, forskolin was unable to activat e subsequent interaction with the transcription machinery in the absence of androgen. Additionally, the synergistic actions of these activators were i ndependent of the degree of androgen response element occupancy. Anti-andro gens, cyproterone acetate and flutamide, which failed to exhibit antagonist ic behaviour with yeast expressed receptor, were able to antagonize only th e forskolin mediated augmentation of reporter activity. Finally, analyses o f mutants established, the role of DNA and steroid binding domains of recep tor for this synergism. (C) 1999 Academic Press.