S. Abdalla et al., Involvement of the amino terminus of the B-2 receptor in agonist-induced receptor dimerization, J BIOL CHEM, 274(37), 1999, pp. 26079-26084
The mechanisms and the functional importance of G-protein-coupled receptor
dimerization are poorly understood. We therefore analyzed dimerization of t
he bradykinin B-2, receptor. The binding of the agonist bradykinin to the B
-2, receptor endogenously expressed on PC-12 cells led to the formation of
receptor dimers, whereas the B-2, antagonist HOE140 did not induce dimeriza
tion, suggesting that B-2 receptor dimerization was linked to receptor acti
vation. Addition of a peptide corresponding to the amino terminus of the re
ceptor reduced the amount of detected B-2 receptor dimers, whereas peptides
derived from the extracellular loops had no effect. To further analyze the
role of the amino terminus of the receptor in receptor dimerization, we cr
eated two different rat B-2 receptor variants with truncated amino termini,
B-2(53) and B-2(65) Starting at amino acids 53 and 65, In contrast to the
wild-type B-2 receptor and to B-2(53) bradykinin did not induce dimerizatio
n of the B-2(65) receptor. Both receptor variants were similar to the wild-
type B-2 receptor with respect to agonist binding and signal generation. Ho
wever, B-2(65) Was not phosphorylated, did not desensitize, and was not dow
nregulated upon bradykinin stimulation. Likewise, antibodies directed to th
e amino terminus of the receptor partially reduced internalization of [H-3]
bradykinin on PC-12 cells. These findings suggest that the amino terminus o
f the B-2 receptor is necessary for triggering agonist-induced B-2 receptor
dimerization, and receptor dimers are involved in receptor-mediated signal
attenuation.