Expression of Progesterone Receptor B in canine mammary gland tissue; an attempt to detect PRB testing two new PRB-specific antibodies

Abstract

In the female dog, the mammary gland tumor is the most prevalent tumor. The Progesterone Receptor exists in two independently regulated functional isoforms, Progesterone Receptor A (PRA) and Progesterone Receptor B (PRB). Dogs are known to have a different sequence and function of an important regulatory function element of PRB, compared to other species. This may be a causative factor in the very high prevalence of canine mammary gland tumors. So far, PRB expression has never been identified in dogs. The main goal of this 3 month research was thus to detect the PRB isoform in canine mammary gland tissue using immunohistochemistry and Western Blot. For PRB detection, 2 new PRB-specific antibodies were tested, the results of which were compared to an antibody that is known to detect both PRA and PRB. Using the two new antibodies did result in staining of the slides, and we continued our research with the one that we thought was best. For this antibody we found mild to moderate staining of the nucleus as well as the cytoplasm of epithelial cells. Staining of the stromal compartment was also found, but very infrequent. Testing of the specificity of this antibody for Progesterone Receptor B then followed. At present, we are unable to prove that the results obtained in immunohistochemistry were the result of specific binding of the investigated primary antibody to Progesterone Receptor B, but do have some reasons not to conclude it’s definitely not caused by specific binding either. The advice would be to continue on after this project with the antibody used, with some adjustments in order to be able to test our hypothesis.