Partial primary sequence of a human endometrial epithelial progesterone dependent protein secreted in vitro

We have recently identified a uterine progesterone-dependent 25 kD protein (protein #27) secreted by endometrial epithelial cells but not stroma. Protein #27 was originally isolated from human luteal phase uterine fluids and partially purified by two-dimensional gel-electrophoresis and electroelution. It could not be detected in serum. We here report the further purification and amino terminal sequence of this protein, obtained from in vitro luteal phase endometrial tissue incubation media. Protein #27 was purified by a one-step method using reverse-phase high performance liquid chromatography. Amino acid compositional analysis confirms a high content of nonpolar and hydrophobic residues (40 mol%) and reveals a preponderance of acidic amino acids, consistent with its isoelectric point (5.9-6.3 pH). The amino terminal sequence obtained from a single individual reveals 85% homology with that of pregnancy-associated alpha 2-globulin from pooled cytosolic fractions from pregnancy endometria. We propose that protein #27, secreted by the endometrial epithelium, is an excellent candidate for a marker to be used to study pathological processes of the endometrium such as endometriosis and invasive carcinoma.