Endocrinology, Vol 128, 2837-2843, Copyright © 1991 by Endocrine Society

ARTICLES

The slow rate of internalization of deglycosylated human chorionic gonadotropin is not due to its inability to stimulate cyclic adenosine monophosphate accumulation

SR Hoelscher, MR Sairam and M Ascoli
Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242.

Using a clonal strain of cultured Leydig tumor cells (designated MA- 10), we have compared the internalization and degradation of human CG (hCG) and deglycosylated hCG. Deglycosylated hCG is a derivative of hCG which retains the ability to bind to the LH/CG receptor, but is unable to activate adenylyl cyclase and thus stimulate cAMP production. A comparison of the fates of the receptor-bound hormones during a single round of endocytosis showed that deglycosylated hCG is internalized slower than hCG. It was also noted that the rate of degradation of the internalized deglycosylated hCG is slower than that of hCG. Two sets of experiments were performed which led to the conclusion that the slower internalization of deglycosylated hCG is not due to its inability to stimulate cAMP production. First, the rate of internalization of deglycosylated hCG in MA-10 cells is not increased in the presence of a cAMP analog. Second, there is little or no difference in the rate of internalization of hCG in a subclone of MA-10 cells [designated MA- 10(K3)] that express a cAMP-resistant phenotype.

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