Lm. Tolbert et J. Lameh, ANTIBODY TO EPITOPE TAG INDUCES INTERNALIZATION OF HUMAN MUSCARINIC SUBTYPE-1 RECEPTOR, Journal of neurochemistry, 70(1), 1998, pp. 113-119
We have studied the effect of an antibody against the epitope EYMPME o
n the internalization of the human muscarinic cholinergic receptor hm1
tagged with the epitope at the amino terminus. The antibody to the ta
g induces internalization of the hm1 receptor within minutes after exp
osure of human embryonic kidney 293 cells transfected with the tagged
receptor. This antibody-induced internalization is reversible followin
g removal of the antibody. In contrast to hm1 internalization induced
by the agonist carbachol, internalization induced by antibody is not b
locked by the muscarinic antagonist atropine. The mechanism of antibod
y-mediated internalization does not appear to involve receptor dimeriz
ation by the antibody, as Fab fragments derived from the antibody also
induce internalization. The pathway of antibody-induced internalizati
on, similar to the agonist-induced process, is mediated by clathrin-co
ated vesicles. Furthermore, antibody treatment does not result in any
second messenger production, as measured by phosphoinositide accumulat
ion. Our data show that internalization of a G protein-coupled recepto
r can be triggered by interaction of the amino terminus of the recepto
r with an exogenous ligand and can occur independently of second messe
nger production, This result suggests that the receptor can exist in m
ultiple conformations, each mediating distinct downstream events.