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Specific sex steroid hormone binding sites have been identified in a discrete nuclear subfraction that is chromatin-depleted and salt-insoluble. This structure, referred to as the nuclear matrix, contains a residual pore complex-lamina, remnants of an internal network, and a residual nucleolus. The nuclear matrix of an estrogen-responsive tissue (chicken liver) and of an androgen target tissue (rat ventral prostate) contains binding sites for estradiol and dihydrotestosterone, respectively. The binding of steroids to these sites is saturable, high affinity (Kd approximately 10(-9) M), steroid-specific (liver binds estrogens, prostate binds androgens), and heat- and pronase-sensitive. The levels of these matrix-associated steroid binding sites change in response to manipulation of the hormonal status of the animal. Thus, the liver nuclear matrix of laying hens contains a significant number of estradiol binding sites, whereas that of untreated chicks or roosters contains very few sites. Treatment of chicks or roosters with a dose of estrogen that stimulates the liver to synthesize vitellogenin leads to a marked increase in the number of estradiol binding sites associated with the liver nuclear matrix. In the rat ventral prostate, the nuclear matrix-associated binding sites for dihydrotestosterone that are present in intact adults essentially disappear within 24 h after castration. Androgen replacement therapy restores, within 1 h, the number of matrix binding sites for dihydrotestosterone to normal levels. Inhibitors of proteolysis (phenylmethylsulfonyl fluoride) are essential for the protection of these androgen binding sites. Conditions that lead to the solubilization of the internal network material of the nuclear matrix also result in the extraction of 70 to 85% of the specific dihydrotestosterone binding sites from the matrix; a limited number of binding sites still remain associated with the peripheral lamina.
Barrack et al. (Fri,) studied this question.