Immunocytochemical localization of the sex steroid-binding protein of plasma in tissues of the adult monkey Macaca nemestrina.

Abstract

The sex steroid-binding protein (SBP) present in the serum of the monkey M. nemestrina exists in cells of tissue involved in reproduction. The localization was demonstrated by immunofluorescence with monospecific antibodies raised against homogeneous human SBP. These antibodies crossreact with monkey SBP. The protein appears to be located in the cytoplasm of epithelial cells lining the prostate alveoli, the ducti of the epididymis and the seminiferous tubula of the testes of the monkey. The protein is also present in the cytoplasm of parenchymal cells of the liver, where SBP is believed to be synthesized, and in cells of the adrenal cortex, where steroids are synthesized. Controls appear dark and illustrate specificity of the immunofluorescence, ruling out both tissue autofluorescence and other nonspecific interactions. In all cases, the relative intensity of fluorescence appears minimal in the nuclei of cells. Experiments performed with cultured [human breast carcinoma] MCF-7 cells indicate that SBP can cross the plasma membrane and enter into the cytoplasm but not into the nucleus. Monospecific antibodies do not crossreact with the monkey prostate androgen receptor, as shown by ultracentrifugation in sucrose density gradients. The physiological significance of these observations is not known; the existence of this protein in cells of target tissues for sex steroids introduces a new dimension in the thinking about the role of this protein in androgen action.