CHARACTERIZATION OF PROGESTERONE-BINDING MOIETIES IN THE LITTLE SKATERAJA-ERINACEA

In this study we report evidence of a [H-3]progesterone-binding moiety in the liver and oviduct of the little skate Raja erinacea. It is cha racterized by high affinity, low capacity, and DNA-cellulose-binding a ctivity. Furthermore Western blot analysis revealed that monoclonal an tibodies against the chicken progesterone receptor (PR) subunits A and B cross-reacted with a 110-kDa band in the liver and a 80-kDa band in the oviduct. When analyzed by DEAE-Sepharose ion-exchange column chro matography, [H-3]progesterone-binding molecules resolved into two peak s, one nonadherent and one adherent to the column. The liver adherent peak eluted in a linear gradient at a NaCl concentration of about 0.07 M and resolved on Western blot as a single band of a 110 kDa. The ovi duct adherent peak eluted at about 0.14 M NaCl and resolved on Western blot as a single band of 80 kDa. Competition studies showed that the progesterone-binding moiety in the cytosol was specific for progestero ne. On the contrary, the nuclear component is not specific for progest erone; it also binds testosterone and estradiol 17 beta in the oviduct , and progesterone, testosterone, dihydrotestosterone, estradiol 17 be ta, mibolerone, and R5020 in the liver. The [H-3] progesterone-binding activity was monitored in both liver and oviduct of females in differ ent reproductive stages. Females were separated into three groups: lay ing, nonlaying, and immature. [H-3]Progesterone-binding activity level s were higher in the liver of immature than of nonlaying skates, and i t was undetectable in laying skates. [H-3]Progesterone binding was hig her in the oviduct of laying and nonlaying skates than of immature ska tes. This PR-binding moiety has many characteristics of a true recepto r: high affinity, low capacity binds to DNA, and cross-reacts with ant ibodies against chicken PR. However, while the cytosolic form of this progesterone-binding component was quite specific for P, nuclear extra cted material was nonspecific. If these progesterone-binding component s are homologous with the PR A and PR B forms of other vertebrates, as we believe, it is clear that there are species differences that proba bly relate to phylogenetic level and physiology of the organism. (C) 1 998 Academic Press.