Progestin receptors from tissues either exhibiting or lacking estrogen response mechanisms : Comparison of conventional and high-performance liquid chromatography methodology

Abstract

Evidence from a variety of target organs has shown that progesterone receptor (PR) is induced by estrogen receptor (ER) in normal and neoplastic tissues. However, approximately 12% of the normal human uterine samples exhibit only PR with no measurable ER, suggesting the expression of both inducible and constitutive receptor isoforms. We investigated several molecular properties of PR from tissues either exhibiting or lacking ER. All studies were conducted in potassium phosphate buffer containing 10 m M sodium molybdate with a synthetic progestin, [ 3H]R5020 as the ligand. Radioinert R5020 was used as competitor to assess nonspecific association. Competition analysis showed that PR from both sources exhibited similar ligand specificities and affinities. Relative affinities were ORG 2058 > R5020 > medroxyprogesterone acetate > progesterone /2>-testosterone K d values ranged from 10 −9 to 10 −10 M; testosterone showed no specific competition). We utilized high-performance liquid chromatography in the size-exclusion (HPSEC) and ion-exchange (HPIC) modes to probe the size and ionic properties of PR. HPSEC profiles showed that the PR isoform from both sources was eluted as a single, sharp peak > 76 Å. HPIEC elution profiles indicated no differences in the surface ionic properties in that PR from both tissue types eluted with ca. 100 m M phosphate. These experiments show no difference between the inducible and the putative constitutive form of PR. Thus, some PR species may not require estrogen for their formation.