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. 1978 Feb;75(2):764–768. doi: 10.1073/pnas.75.2.764

Interaction of human chorionic gonadotropin with membrane components of rat testes

Tadeusz Pacuszka *,†, James C Osborne Jr ‡, Roscoe O Brady *, Peter H Fishman *
PMCID: PMC411337  PMID: 24844

Abstract

Previous studies demonstrating that gangliosides interacted with thyrotropin and human chorionic gonadotropin (hCG) suggested that gangliosides participate in the transduction of the hormonal message across the target cell membrane. As a continuation of these investigations, we examined the effects of down-regulation of hCG receptors on the interaction of hCG with rat testis membrane components. Rat testes contained a complex ganglioside pattern that did not appear to change qualitatively or quantitatively after the injection of hCG into the animals, although testis membranes from hCG-treated rats lost their capacity to bind 125I-labeled hCG (125I-hCG). Gangliosides extracted from the testes of control and treated animals were equally effective inhibitors of 125I-hCG binding to testis membranes. However, inhibition of binding was observed only under conditions (pH 6.0, low ionic strength) such that unlabeled hCG (>2500-fold excess) did not block 125I-hCG binding, and 125I-hCG bound similarly to testis membranes from control and treated rats. Under conditions such that hCG binding was specific (blocked by 250-fold excess of unlabeled hCG), testis gangliosides were noninhibitory. Liposomes containing gangliosides from the testes of control or hCG-treated rats bound similar small amounts of 125I-hCG. These same liposomes bound 50 and 1000 times more thyrotropin and cholera toxin, respectively, than hCG. Oligosaccharides derived from gangliosides did not inhibit 125I-hCG binding to testis membranes nor did they alter the fluorescence of hCG conjugated with fluorescent probes, whereas the gangliosides themselves were inhibitory and enhanced the fluorescence intensity of the hCG derivatives. Exposure of testis membranes from hCG-treated rats to 4 M MgCl2, which displaces bound hCG [Chen, Y.-D. I. & Payne, A. H. (1977) Biochem. Biophys. Res. Commun. 74, 1589-1596], did not restore their ability to bind 125I-hCG. When membranes were solubilized with Triton X-100, a solubilized receptor was detected from testis membranes of control but not hCG-treated rats.

These findings and the absence of demonstrable changes in the composition or quantity of rat testis gangliosides when hCG receptors are down-regulated suggest that gangliosides do not represent the primary binding determinants of hCG receptors.

Keywords: gangliosides, solubilized receptors, receptor regulation, cholera toxin

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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