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 Macaca nemestrina is shown to exist in cells of tissue involved in reproduction. The localization was demonstrated by immunofluorescence with monospecific antibodies raised against homogeneous human SBP. These antibodies were previously shown to 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 plasma of humans and that of most species tested contain a protein, SBP, which specifically binds 5a-dihydrotestosterone (DHT) and testosterone with high affinity and estradiol-17f with lower affinity depending upon the species. This protein has been purified to homogeneity from the plasma of humans (1-4), rabbits (5), cows (6), and dogs (7). The physicochemical characteristics of the protein isolated from each of these species have been described (3-9).Various reports have appeared suggesting that, in humans, SBP may enter interstitial fluid and tissues and, therefore, may not be exclusively localized in the plasma (10-13). Others, however, have suggested that this observed presence of SBP in cell extracts is due to plasma contamination when the tissues are homogenized. Although the nature of the experimental evidence gathered from those studies does not allow us to distinguish between these two possibilities, it becomes imperative to establish whether or not SBP exists inside cells of target tissues. The consequence of tissue localization of this protein will undoubtedly affect our thoughts and future experimentation with regards to the physiological role of SBP in relation to sex steroid hormone action.We have been able to prepare monospecific antibodies against homogeneous human SBP (14). These antibodies also crossreact with nonhuman primate SBP, such as that present in the plasma of the monkey (Macaca nemestrina) and the The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 5678 baboon (Papio cynocephalus) (14). The antibodies, however, do not crossreact with the plasma of any other animals tested, including rabbits, dogs, cats, sheep, goats, cows, and calves (14). Using the monkey model, we have presented preliminary evidence for the existence of SBP within tissue cells.t In this report, we formally describe our results in detail and discuss the possible implication of these findings in relation to already existing information. METHODSSBP was purified from human serum essentially as described (1) except for a modified affinity chromatographic procedure (2). In some cases, the purified protein was passed through an antitransferrin-agarose column to remove traces of transferrin. This immunoadsorbent was synthesized as follows: 12 ml of Affigel-10 (Bio-Rad) was washed rapidly with cold distilled water on a small fritte...

Sex Hormone-binding Globulin in the Human Prostate Is Locally Synthesized and May Act as an Autocrine/Paracrine Effector

“…That SHBG, or an SHBG-like antigen, exists in human prostate has been documented in a number of laboratories both by biochemical (34 -36) and immunocytochemical techniques (16,18). However, the uniform interpretation of these results has been that the origin of the protein was from the plasma.…”

“…Because there is a substantial concentration of SHBG in plasma, the staining seen in sections of human prostate could result from simple diffusion of SHBG from plasma with subsequent cellular uptake. Indeed, that is the inference from early observations in both monkey (16) and man (17), and there is no subsequent literature that takes issue with this conjecture. To address this issue, we examined sections, adjacent to those used for SHBG expression, by in situ hybridization.…”

Biochemistry, pharmacology and physiological role of sex hormone binding globulin

“…Η ερμηνεία των παραπάνω όμως είναι δύ σκολη για διάφορους λόγους. Προπον, αν και τα αντισώ ματα για τη SBP δεν αντιδρούν με τους υποδοχείς πον στε-ροειδοη' ορμονών 37 , αντιδρούν με την ΑΒΡ (androgen binding protein), μία παρόμοια πρωτεΐνη με την SBP, η ο ποία εκφράζεται στον όρχι : ", αλλά m-RNA γι' αυτήν έχει ανιχνευθεί και στον προστάτη 41 . Έτσι στα παραπάνοο πει ράματα, εάν η ΑΒΡ εκφράζεται και σε άλλους ιστούς, τό τε είναι πιθανό ο ανοσοφθορισμός να σημαίνει παρουσία της ΑΒΡ και όχι της SBP.…”

Identification of sex hormone binding globulin-interacting proteins in the brain using phage display screening

“…Pope and Lee (27) identified another protein called SNARE associated protein which is also a component of the SNARE complex (53). SHBG internalization was observed in a number of tissues (7,8,10,11,13,54) including the brain (15), so it is possible that some of the proteins we identified here, in particular SNAP-25, are involved in that internalization process.…”

“…SHBG internalization has been demonstrated in multiple tissues (7)(8)(9)(11)(12)(13)54) including the brain (15) suggesting that SHBG along with associated steroids are selectively brought into cells, where cytosolic proteins may bind the SHBG. This work may have identified proteins that are candidates for an intracellular SHBGbinding complex.…”