Jj. Buggy et al., ROLE OF THE GLUCAGON RECEPTOR COOH-TERMINAL DOMAIN IN GLUCAGON-MEDIATED SIGNALING AND RECEPTOR INTERNALIZATION, Diabetes, 46(9), 1997, pp. 1400-1405
The binding of glucagon to its hepatic receptor is known to result in
a number of effects, including the intracellular accumulation of cAMP,
the mobilization of intracellular Ca2+, and the endocytosis of glucag
on and its receptor into intracellular vesicles. In this study, are be
gin to define the functional role of the COOH-terminal tail of the hum
an glucagon receptor in glucagon-stimulated signal transduction and re
ceptor internalization. We have created and expressed in Chinese hamst
er ovary (CHO) cells five truncation mutants in which the COOH-termina
l 24, 56, 62, 67, and 73 amino acids have been removed. Cells expressi
ng relevant truncated receptors were assayed for cell surface expressi
on by immunofluorescence, for Ligand-binding properties, for cAMP and
Ca2+-mediated signal transduction properties, and for receptor endocyt
osis. In addition, a mutant receptor containing seven serine-to-alanin
e mutations in the COOH-terminal tail was studied. Our results reveal
the following: 1) a region of the COOH-terminal tail that is required
for proper cell surface expression, 2) the COOH-terminal 62 amino acid
s, which comprise the majority of the tail, are not required for ligan
d binding, cAMP accumulation, or Ca2+ mobilization, and 3) phosphoryla
tion of the COOH-terminal tail is crucial for glucagon-stimulated rece
ptor endocytosis.