Binding of the androgen receptor to the nuclear matrix of human foreskin.
The nuclear matrix (NM) is a salt and nuclease-resistant nuclear substructure. It is associated with active DNA transcription and has been shown to contain acceptor sites for steroid receptors in a number of specific target tissues. We have investigated the presence of acceptor sites for the androgen receptor (AR) in the NM of human newborn foreskin. The NM was prepared from the 800 g pellet by successive treatments with detergent, DNase and high salt extraction. It contained 13 +/- 7% of total proteins and 10 +/- 6% of total DNA. After extensive washing, the NM spheres were incubated in the presence of cytosol and [3H]methyltrienolone +/- 200-fold excess of unlabeled steroid. Maximal binding of the AR to NM was reached in 30 min and decreased slightly thereafter to reach an equilibrium which was maintained for 18 h. Binding was saturable. In the absence of AR, the steroid did not bind to NM. When Scatchard analysis was performed on cytosol previously incubated with NM, cytosolic binding capacity significantly decreased relative to preincubation values (3.6 +/- 1.9 to 1.3 +/- 1.2 fmol/mg protein, P less than 0.05, n = 6). In contrast, apparent binding affinity was not changed. 0.8 mg of NM protein could bind AR from 2.4 mg of cytosol protein. In conclusion, NM from human foreskin binds the AR with high affinity. This binding is rapid and is maintained for at least 18 h. This is consistent with a potential role of NM in the mechanism of action of androgens in their target tissues.