Nuclear progestin receptor-like component in human cervical tissue

To study progestin action in human glandular cervix, we extracted the nuclear pellet with 0.5 M KCl and immediately adsorbed a progestin-binding receptor-like component to hydroxylapatite. Binding of 2 nM [3H]R5020 at 4 degrees C for 18 h, in the presence or absence of 100-fold molar excess progesterone and other steroids, was used to measure the total extractable and adsorbed progestin-binding component. With this assay, the amounts of progestin-binding component in the nuclear-rich fraction in specimens from women in the follicular and luteal phases of the ovarian cycle were 930 +/- 143 and 995 +/- 148 fmol/g wet wt (+/- SE), respectively; total cytoplasmic progestin receptor was 2,989 +/- 812 and 1,861 +/- 188 fmol/g wet wt (+/- SE) in the follicular and luteal phases, respectively. The progestin-binding component extracted from the nuclear pellet has a sedimentation velocity coefficient in the 3.5 S region when measured in high salt on 5-20% linear sucrose density gradients that contain 10% glycerol. The progestin binding measured by the hydroxylapatite-exchange assay with [3H]R5020 and radio-insert progesterone is high affinity (Kd 2.6 X 10(-10) M) and heat labile and appears specific for progestins and progesterone target tissues.