Estrogen receptors and human bone cells: immunocytochemical studies

In this immunocytochemical study we have probed a number of human bone cell types and bone preparations for the presence of the estrogen receptor (ER) with two distinct monoclonal antibodies. Using a well-validated antibody (H222) that recognizes human ER and standard peroxidase-antiperoxidase methodology, we were unable to demonstrate nuclear staining for ER in cultured primary or transformed human bone-derived cells or in fetal bone sections. Attempts to visualize ER in osteosarcoma cell lines (TE85C and HTB96) using a silver enhancement procedure were also unsuccessful. Additionally, we failed to detect immunocytochemical staining for the progesterone receptor (using monoclonal antibody mPR1) in control or estrogen-treated human bone cell cultures. Estrogen and progesterone receptor staining was readily detectable in MCF7 human breast cancer cells. In contrast, with a monoclonal antibody that recognizes a 29 kDa cytoplasmic component (p29) closely related to human ER, we observed specific staining in all the osteoblastlike cells studied. Cytoplasmic staining for this p29 antigen was most intense in primary cultures of human bone-derived cells. It is possible that the relatively abundant but as yet undefined p29 antigen may act as a sensitive marker for the presence of ER in cells at levels below the detection limit of the anti-ER monoclonal antibody. If so, our results are consistent with the presence of ER in osteoblastlike cells at very low concentrations.