Immunological detection of cat uterine proteins in ferrets, dogs and baboons

In the cat, a high molecular weight (greater than 320 kDa) estrogen (E2)-dependent protein (CUPED) and a group of low molecular weight (28 kDa, 36 kDa, 41 kDa) progesterone (P)-dependent proteins (PDP) are synthesized by the epithelial cells of the deep uterine glands and secreted into the lumen. The present study was designed to investigate the possibility that other species synthesize proteins similar to CUPED and PDP in response to steroids. Uterine flushings and media from cultured endometrial explants obtained from E2 or P dominated animals were analyzed on Western blots for the presence of proteins which cross-react with antibodies raised against CUPED and PDP. CUPED antibody immunoreacted with a protein band at approximately the same molecular weight as CUPED in the media and flushings from E2-treated ferret, dog and baboon, but not from rat, mouse or hamster. In the cat, ferret and dog, specific immunocytochemical staining was observed in the apical portion of the secretory cells. In the baboon, staining was observed in both the basal and apical areas of the epithelial cells. The presence of CUPED in the uterine lumen during the E2-dominated phase of the reproductive cycle in several species suggests that CUPED may play a general role in providing the necessary biochemical milieu for reproductive success. The PDP antibody did not cross-react with proteins in the media of species other than cat, and therefore may be unique to the cat.