Nuclear progesterone-binding protein in the guinea pig adrenal cortex: distinction from the classical progesterone receptor |
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Authors: | T Demura W J Driscoll C A Strott |
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Institution: | Section on Adrenal Cell Biology, National Institute of Child Health and Human Development, Bethesda, Maryland 20892. |
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Abstract: | Nuclei purified from the guinea pig adrenal cortex contain a specific progesterone-binding activity which, based on enzyme degradation studies, appears to be proteinaceous. Saturation analysis revealed a Kd of about 15 nM and a binding capacity of about 33 pmol/mg DNA. The activity of the nuclear binding protein was specific essentially for progestational steroids; the two most potent progesterone competitors were 5 alpha-pregnane-3,20-dione and medroxyprogesterone (17 alpha-hydroxy-6 alpha-methylprogesterone), while 17 beta-estradiol, testosterone, cortisol, and other related steroids were poor competitors. The adrenocortical nuclear progesterone-binding protein was present to an equal extent in both male and female guinea pigs. The adrenocortical nuclear progesterone-binding protein differed from the classical progesterone receptor in that 1) the affinity of the adrenocortical binding protein for progesterone is an order of magnitude lower; 2) the potent synthetic progestin R5020 binds less tightly to the adrenocortical progesterone-binding protein; 3) the adrenocortical progesterone-binding protein is not modulated by estrogenic activity; 4) the adrenocortical progesterone-binding protein is more stable at 37 C; 5) the adrenocortical nuclear progesterone-binding protein is not salt extractable; and 6) Western blot analysis has revealed that an antiprogesterone receptor monoclonal antibody, which recognizes the guinea pig uterine classical nuclear progesterone receptor, does not recognize the adrenocortical nuclear progesterone-binding protein. Thus, the guinea pig adrenocortical nucleus contains a type of progesterone-binding protein that appears to be clearly different from the classical progesterone receptor. |
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