Subcellular distribution of androgen binding sites in cultured Sertoli cells before and after exposure to androgens

Abstract

When rat Sertoli cells in culture were exposed to [ 3H]-labeled androgen over 20 min at 34°C, the concentration of [ 3H]-androgen-receptor complex in the cytosol fraction rapidly increased and then declined. Over this same interval, total (i.e. occupied plus unoccupied) receptor levels, measured by an exchange assay, also declined. A substantial proportion of the receptor remaining in the cytosol after 20 min was bound to steroid. Concomitant with these changes, the cytosol/nuclear ratio of specifically bound steroid rapidly declined as label accumulated in the paniculate fraction. By 20 min, nuclear bound label often exceeded cytoplasmic receptor depletion. Some cytosol receptor may adhere to particulate matter and be present in the Triton X-100 washes of the crude nuclear pellet. In cells not exposed to androgen, a substantial number of unoccupied, tightly bound nuclear androgen binding sites of high affinity were measured by incubation of washed pellets with labeled steroid at 0°C. Following exposure to labeled steroid at 34°C, the net number of unoccupied nuclear binding sites declined. These data indicate that while some specifically bound steroid in the Sertoli cell nuclear fraction arises from translocation of cytosol receptor complexes, steroid probably also binds to previously unfilled nuclear binding sites.