Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P56851 (epididymal)
 11,273 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The binding of [3H] delta 6-testosterone photoaffinity-labelled rat androgen-binding protein (rABP) has been studied in an enriched fraction of plasma membranes of epithelial epididymal cells in immature (15 days) and adult rats (40 days). The binding was maximal in less than 30 min and more rapid at 4 degrees C than at 34 degrees C. It was calcium and pH dependent. Scatchard plots of the binding data gave curvilinear plots with two types of binding sites corresponding to a K(ass1) of 18.2 nM-1 and K(ass2) of 1.6 nM-1 (2.2 x 10(11) sites/mg protein and 5.4 x 10(11) sites/mg protein, respectively). In adult rats, only one type of binding site was found, with a K(ass) of 3.7 nM-1 (4.5 x 10(11) sites/mg protein). The number of receptors was 5-fold lower in the cauda than in the caput of the epididymis. The pretreatment of the isolated intact cells with streptozotocin induced a 45% reduction of the binding. Only unlabelled rABP and hSBP (human sex steroid-binding protein) but not other proteins (lactotransferrin, serotransferrin, asialofetuine, fetuine and bovine serum albumin) competed with the labelled ligand to bind plasma membranes. The membrane fraction was solubilized by triton X-100. Its incubation with labelled rABP and hSBP provoked the elution of the tracer as an aggregate into the void volume fraction of superose 6B mini-gel filtration columns. Structural homology between hSBP and rABP could be responsible for the common behaviour of the steroid-carrier molecules for the ABP receptor of rat epididymal epithelial cells.
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PMID:The plasma membrane of epididymal epithelial cells has a specific receptor which binds to androgen-binding protein and sex steroid-binding protein. 131 34

We investigate in this study the hypothesis of human sex steroid-binding protein hSBP internalization into germ cells in a primate model. Human SBP was purified from late-pregnancy serum and labeled either with colloidal gold particles (18 nm) or with [3H]delta 6-testosterone by photoaffinity treatment. The germ cells were isolated from sexually mature monkey testis or caput epididymis (Macaca fascicularis) by mechanical means and cell suspensions (4 x 10(6) per 100 microliters culture medium) were incubated in presence of hSBP-gold complex (60 ng/100 microliters) or hSBP-[3H]delta 6-testosterone complex (66 ng/100 microliters, 20,000 cpm) for 2, 5, 15, 45, and 60 min. The samples were processed for electron microscopy followed by autoradiographic treatment for the radiolabeled samples. Localization of the label occurred over the whole germ cell lineage whichever tracer was used. Spermatogonia, spermatocytes, spermatids, testicular and epididymal spermatozoa exhibited specific binding sites over the plasma membrane associated with clathrin-like coated pits and vesicles. At 34 degrees C, intracellular localization of the labeled ligand was found within coated vesicles, in early and late endosomes. In addition, in early spermatogenic cells, labeled ligand was detected in the nuclei and/or associated with the nuclear envelope whereas in late spermatids and residual bodies, the labeling was accumulated in multivesicular, prelysosomal structures. Quantitative analysis of the "labeled cells/total cells" ratio exhibited a negative correlation to the maturation steps, epididymal spermatozoa being the least labeled. The cellular distribution is similar with one or the other protein in the same spermatogenic cells. Unlabeled hSBP treatment prior to labeled hSBP reduced significantly the internalization. Lowering the temperature to 4 degrees C prevented endocytosis and enhanced membrane binding. EDTA pretreatment strongly decreased hSBP internalization and modified the early endocytic steps, namely, the pinching off of the coated vesicles. It is concluded that monkey germ cells are able to internalize the human sex steroid-binding protein through specific endocytic organelles. This endocytosis leads to the labeling of the nuclei in the early spermatogenic cells and of the multivesicular bodies in the late germ cells. This strongly suggests that steroid-binding proteins may be required for spermatogenesis in acting at the germ cell lineage level either by themselves or by serving as steroid transmembrane carriers.
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PMID:Endocytosis of human sex steroid-binding protein in monkey germ cells. 178 75

The acrosome is a peculiar vacuole that at fertilization undergoes the acrosome reaction (AR), an event unique in the sperm life. Contents released promote sperm penetration through oocyte's investments; membranous components are involved in sperm-egg interaction/fusion. Therefore, both constituents play a role in fertilization. The biogenesis of this vacuole, however, has not been clarified yet; recently, it has been proposed as a novel lysosome-related organelle (LRO). Our research focuses on the involvement of the endosomal pathway in acrosomogenesis starting from the early phases. The trafficking sorted by USP8/UBPy, an endosomal regulator recently described as a compelling candidate for male fertility gene, was investigated in comparison to that of SP56, a marker of the biosynthetic pathway. Mouse spermatids were double/triple immunolabeled and examined by confocal microscopy. The contribution of the vesicular traffic assisted by the cortical microtubule array was also evaluated in nocodazole-treated spermatids. USP8/UBPy-sorted cargo contributes early to acrosomogenesis and its trafficking is microtubule mediated. It was identified, through co-immunoprecipitation/co-immunolocalization assays, that the membrane receptor MET, described herein for the first time in spermatids, as an USP8/UBPy-target substrate is delivered to the acrosome. MET and USP8/UBPy still colocalize in epididymal spermatozoa. Following the AR, MET and USP8/UBPy show a distinct fate. MET, in particular, translocates at the PAS, the post acrosomal segment known to harbor sperm-borne factors involved in oocyte activation. Overall, our results support the concept of the acrosome as a LRO and provide evidence for the identification of MET as a tyrosine kinase receptor that may play a role in fertilization.
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PMID:USP8/UBPy-regulated sorting and the development of sperm acrosome: the recruitment of MET. 2574 85