Progesterone and Estrogen Receptors in GH3 Cells

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Abstract
GH3 cells are shown to contain cytosolic progesterone receptor in a mean concentration of 270 fmol/mg protein with a dissociation constant (KD) for promegestone of 3 × 10-9M (4°C). Estrogen receptor (KD = 1.8 × 10-10M) is demonstrated in cytosol (121 fmol/mg protein) as well as in 0.4 M KCl extracts (89 fmol/mg protein) of crude nuclear fractions. No progesterone receptor was detectable in the nuclear fraction. Both receptors are characterized by isoelectric focussing and by competition experiments. Addition of 10-8M estradiol to the growth medium increases progesterone receptor levels up to five, suggesting that the progesterone receptor is under estrogenic control.