Differences in the physicochemical characteristics of androgen-receptor complexes formed in vivo and in vitro

This study compares the physicochemical characteristics of the androgen-receptor hormone complexes formed in vitro by incubation of prostatic cytosol with tritiated 5 alpha-dihydrotestosterone (DHT) and methyltrienolone (R1881; 17 beta-hydroxy-17 alpha-methyl-4,9, 11-estra-trien-3-one) with those of hormone-receptor complexes formed in vivo upon hormone injection. [3H]DHT and [3H]R1881 had similar affinities for the androgen receptor in vitro (Kd = 0.3 nM). Dissociation of DHT at 0 C from the receptor complexes formed in vitro or in vivo was much slower than that of R1881. Furthermore, DHT and R1881 dissociated much more slowly from the cytoplasmic receptor labeled in vivo than in vitro. The sedimentation characteristics of the in vitro and in vivo formed hormone-receptor complexes were similar when analyzed on sucrose density gradients containing 400 mM KCl and 10 mM Na2MoO4. Higher concentrations (50 mM) of Na2MoO4, however, prevented the salt-induced disaggregation of the in vitro formed receptor complexes, which sedimented at 7-8S. In contrast, androgen-receptor complexes formed in vivo sedimented as 5.5S complexes, even in the presence of 50 mM molybdate. These differences were paralleled by the elution patterns from Sephacryl S-200. A further difference was found in the sensitivity of the hormone-receptor complex to the organic mercurial reagent mersalyl acid. This reagent, at 0.2 mM, induced ligand exchange of 80-90% of the in vitro formed hormone-receptor complexes, whereas it was nearly ineffective with complexes formed in vivo. Finally, the prostatic androgen receptor content 1 h after injection of radioactive steroid into castrated rats was 12-14 pmol/mg DNA, while incubation of tissue slices at 37 C yielded only 3-4 pmol receptor/mg DNA.