U. Zimmermann et al., COEXISTENCE OF NOVEL AMYLIN-BINDING SITES WITH CALCITONIN RECEPTORS IN HUMAN BREAST-CARCINOMA MCF-7 CELLS, Journal of Endocrinology, 155(3), 1997, pp. 423-431
Amylin, calcitonin (CT) and calcitonin gene-related peptide (CGRP) sha
re limited structural homology including amino-terminal ring structure
s linked by a disulfide bridge and amidated carboxy-termini. Here, we
have compared [I-125]Bolton-Hunter-[Lys(1)] rat amylin ([I-125]amylin)
binding and the stimulation of cyclic AMP accumulation by human (h) a
mylin, hCT and hCGRP-I in the human breast carcinoma cell lines MCF-7
and T47D, which predominantly express hCT(1a) and hCT(1b) receptor iso
forms (hCTR(1a), hCTR(1b)) at a similar total number of hCT-binding si
tes. In MCF-7 cells, half-maximal inhibition (IC50) of [I-125]amylin b
inding by human amylin was observed at 3.6 +/- 0.8 nM (n=6). hCT and h
CGRP-I displaced [I-125]amylin binding with 22 and 66 times higher IC5
0. [I-125]hCT binding was inhibited by hCT with an IC50 of 8.1 +/- 1.9
nM (n=5), and human amylin and hCGRP-I were over 100 times less poten
t. In T47D cells, on the other hand, specific binding of [I-125]amylin
was not observed, but hCT inhibited [I-125]hCT binding with an IC50 o
f 3.2 +/- 0.4 nM (n=3), and human amylin and hCGRP-I had over 200 time
s higher IC50. In MCF-7 cells, half-maximal stimulation (EC50) of cycl
ic AMP accumulation by human amylin, hCT and hCGRP-I occurred at 1.4 /- 0.2, 1.7 +/- 0.4 and 6.3 +/- 1.3 nM respectively. In T47D cells, th
e EC50 of hCT was C.32 +/- 0.02 nM (n=3), and 30- and 1900-fold higher
with human amylin and hCGRP-I. In conclusion, the expression of hCTR(
1a) and hCTR(1b) and [I-125]hCT binding were indistinguishable in MCF-
7 and T47D cells. Yet, [I-125]amylin binding was only recognized in MC
F-7 cells, consistent with a distinct amylin receptor.