Progesterone and estrogen receptors in GH3 cells

GH3 cells are shown to contain cytosolic progesterone receptor in a mean concentration of 270 fmol/mg protein with a dissociation constant (K(D)) for promegestone of 3 times 10(-9) M (4 degrees C). Estrogen receptor (K(D) = 1.8 times 10(-10) M) 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(-8) M estradiol to the growth medium increases progesterone receptor levels up to five, suggesting that the progesterone receptor is under estrogenic control.