Nuclear progestin receptors in human uterus

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• The human uterine progestin receptor facilitates the action of progestins.
• Understanding receptor translocation is crucial for comprehending progestin-mediated effects.

Purpose of the Study:

• To characterize the translocation of human uterine progestin receptors from cytosol to nucleus.
• To evaluate different progestins as tags for studying receptor dynamics.

Main Methods:

• A cell-free system was employed using radiolabeled progesterone ([3H]P), norethindrone ([3H]NET), and norethindrone acetate ([3H]NETA).
• Cytosol treatments (warming, salt concentration, protein dilution) were used to assess their effect on nuclear translocation.
• Physicochemical properties of nuclear-bound receptors were analyzed via gel chromatography, sedimentation, and isoelectric focusing.

Main Results:

• Nuclear binding required uterine cytosol; cytosol treatments enhanced receptor affinity for the nucleus.
• Nuclear receptors exhibited common physicochemical properties (mol wt 72,000, 4.2S, pI 5.3–5.6).
• Binding site concentrations were higher in proliferative (3780–4480 molecules/cell) versus secretory phase tissues (1790–1920 molecules/cell).
• High-affinity binding was observed (NET Kd ~0.7–0.8 nM, P Kd ~0.9–1.2 nM, NETA Kd ~6.7–7.1 nM).
• NET and NETA showed slower dissociation rates than P and did not bind corticosteroid-binding globulin.

Conclusions:

• Progestins act via a common receptor that translocates from cytosol to nucleus.
• Norethindrone (NET) is a suitable progestin receptor tag due to its distinct binding characteristics and advantages.