Intracellular Localization of Steroid Hormone Receptors: Immunocytochemical Analysis

Abstract

The development of antibodies to steroid hormone receptors consecutively to their purification, represents an important improvement to label and localize receptor molecules inside the target cells. Antibodies recognize various small epitopes on the large receptor molecules, and therefore receptors can be detected independently of the occupancy of the binding site by the hormonal ligand. Unlike radioactive ligands, antibodies reveal hormone-free as well as occupied receptors, thus providing the first direct specific means to localize unoccupied receptor molecules. Although other techniques were proposed in the past, based on the binding of a label to the receptor molecule (1,2), none of them met the criteria necessary to conclude to the specific detection of steroid hormone receptors as defined by their well established physicochemical characteristics (3). Morphological techniques are particularly well suited to address the question of the intracellular distribution of the receptors. They imply no disruption of the cells and little disturbance of the two major cellular compartments: cytoplasm and nuclei. However, although less dramatic to the cell integrity than tissue homogenization, histological procedures may induce alterations and movements of the intracellular material which must not be ignored in the interpretation of the observations.