Androgen receptor translocation from cytosol of rat heart muscle, bulbocavernosus/levator ani muscle and prostate into heart muscle nuclei

Abstract

Translocation of cytosolic androgen receptor of heart muscle (HM), bulbocavernosus/levator ani muscle (BCLA) and prostate (PR) into HM nuclei was studied in a cell-free system. Cytosol and nuclei were obtained from 24 h castrated male rats. The cytosolic androgen receptor was prelabelled with tritiated testosterone (T). After incubation with prelabelled cytosol, the highly purified HM nuclei were treated with 0.6 M NaCl and binding in the salt extractable fraction was analyzed by the charcoal adsorption method and by agargel electrophoresis. Furthermore, the receptor bound metabolites in cytosol and nuclei were analyzed by thin layer chromatography. The main results were as follows: 1. Highly purified HM nuclei were obtained, the purification being checked by electron microscopy and biochemical markers. 2. When incubating HM nuclei with T-labelled HM, BCLA or PR cytosol, a nuclear receptor binding was demonstrated by agargel electrophoresis. 3. No nuclear receptor binding was found using labelled plasma instead of organ cytosol. 4. The identity of cytosolic and nuclear receptor binding was indirectly shown by similarities in competition studies with unlabelled T, cyproterone acetate, and cortisol. Moreover, the metabolite pattern of receptor bound radioactivity was identical in cytosolic and nuclear fractions. The number of receptor bound labelled molecules found in HM nuclei by the charcoal adsorption technique after incubation with HM and PR cytosol were on average 49 and 652 per nucleus respectively. Compared to the receptor concentration in HM and PR cytosol, a 14.5- and 15.7-fold accumulation of receptor bound molecules in the incubated HM nuclei were found respectively. This study indicates that cytosolic androgen receptor of HM, BCLA and PR cytosol can be translocated into HM nuclei. The amount of translocated steroid receptor complex is dependent on the cytosolic receptor concentration.