Estrogen-specific target site identified by progesterone-11 alpha-hemisuccinate-(2-[125I]-iodohistamine) in mouse brain membranes.

Using photoaffinity labeling with the progesterone analogue, progesterone-11 alpha-hemisuccinate-(2-[125I]-iodohistamine) ([125I]-his-PG), we identified and characterized a protein band of MW 29 kDa (p29) in mouse cerebellar membranes whose labeling is markedly inhibited by estrogens. Inhibition of the labeling was specific with respect to steroid structure. Labeling was strongly inhibited by estradiol-17 beta, estradiol-17 alpha, and the anti-estrogen tamoxifen and the synthetic estrogen diethylstilbestrol. Other estrogens (estriol, estrone) were less effective and the steroids, dihydroandrosterone, androsterone and aldosterone were ineffective. Preincubation with estradiol-17 alpha or estradiol-17 beta inhibited the labeling in a dose-dependent manner with IC50 values of 0.3 and 2.0 microM, respectively. The extent of labeling was three times as high in cerebellar membranes from males as from females. In males, labeling of cerebellar membranes was greater than that of cortex or limbic region. The labeling pattern of p29 was also different in membranes prepared from cerebellum, heart and liver. Moreover, PG enhanced the labeling of p29 in liver demonstrating a tissue-specific mode of interaction. The present results characterize p29 as a membrane-bound estrogen target site.