Tunicamycin and Neuraminidase Effects on Luteinizing Hormone (LH)-Releasing Hormone Binding and LH Release from Rat Pituitary Cells in Culture*

We have studied the effects of tunicamycin (TM) and neuraminidase on the binding of 125I-labeled Buserelin, a GnRH agonist, and on GnRH-stimulated LH release in cultured rat pituitary cells. Treatment with TM, an antibiotic which inhibits protein glycosylation, abolished the development of elongated cell processes without any effect on cell viability. Concomitantly, TM caused a time- and dose-dependent inhibition of specific binding of Buserelin and of GnRH-stimulated LH release. The inhibition of binding was due to a decrease in the number of GnRH receptors without any significant effect on binding affinity. Protein synthesis was not affected under these experimental conditions, suggesting that the aglycosylated GnRH receptors are probably intracellularly accumulated and are not expressed on the cell surface. Treatment with neuraminidase inhibited only 50% of GnRH agonist binding and did not affect GnRH-stimulated LH release. These results indicate that the oligosaccharide portion is essential for the functional properties of the GnRH receptor.