AJP - Endocrinology and Metabolism, Vol 256, Issue 1 E80-E86, Copyright © 1989 by American Physiological Society
Effects of lectins and tunicamycin on cAMP response to parathyroid hormone
R. Rizzoli and J. P. Bonjour
Department of Medicine, University Hospital of Geneva, Switzerland.
Carbohydrate moieties of cell surface glycoproteins with an external
orientation play a role in hormone recognition and/or transmembrane signal
transmission. We have examined the effect of various lectins, which
interact with specific cell surface glycosyl residues, and of tunicamycin,
an antibiotic that inhibits glycosylation of proteins, on the adenosine
3',5'-cyclic monophosphate (cAMP) response to parathyroid hormone (PTH) in
confluent cultured osteoblast-like rat osteosarcoma cells (UMR-106) and
opossum kidney cells (OK cells). Incubation of both cell lines with wheat
germ lectin (WGL), but not with concanavalin A, succinylated wheat germ,
ricin, or soybean lectins, markedly reduced the PTH-induced cAMP
production, whereas the stimulation obtained with forskolin, a compound
that acts directly on the adenylate cyclase enzyme, was not affected. In
contrast, tunicamycin did not cause any decrease in the cAMP response to
PTH. These results indicate that the masking of sialic acid residue by WGL
considerably blunted PTH-stimulated cAMP production in cultured
osteoblast-like and kidney cells. An 80% inhibition of glycosylation of
cell surface proteins did not appear to affect the response to PTH. Thus
the functional role of this carbohydrate moiety in the PTH receptor remains
to be determined.
