TY - JOUR
T1 - Structure/function relationships of calcitonin analogues as agonists, antagonists, or inverse agonists in a constitutively activated receptor cell system
AU - Pozvek, Gordana
AU - Hilton, Joanne M.
AU - Quiza, Maribel
AU - Houssami, Souheir
AU - Sexton, Patrick M.
PY - 1997/1/1
Y1 - 1997/1/1
N2 -
The structure/function relationship of salmon calcitonin (sCT) analogues was investigated in heterologous calcitonin receptor (CTR) expression systems. sCT analogues with progressive amino-terminal truncations intermediate of sCT-(1-32) to sCT-(8-32) were examined for their ability to act as agonists, antagonists, or inverse agonists. Two CTR cell clones, B8- H10 and G12-E12, which express ~5 million and 25,000 C1b receptors/cell, respectively, were used for this study. The B8-H10 clone has an ~80-fold increase in basal levels of intracellular cAMP due to constitutive activation of the overexpressed receptor. In whole-cell competition binding studies, sCT-(1-32) was more potent than any of its amino-terminally truncated analogues in competition for
125
I-sCT binding. In cAMP accumulation studies, sCT-(1-32) and modified analogues sCT-(2-32) and sCT-(3-32) had agonist activities. SDZ-216-710, with an amino-terminal truncation of four amino acids, behaved as a partial agonist/antagonist, whereas amino-terminal truncations of six or seven amino acid residues produced a 16-fold reduction in basal cAMP levels and attenuated the response to the agonist sCT-(1-32) in the constitutively active CTR system. This inverse agonist effect was insensitive to pertussis toxin inhibition. In contrast, the inverse agonist activity of these peptides was not observed in the nonconstitutively active CTR system, in which sCT analogues with amino-terminal truncations of four or more amino acids behaved as neutral competitive antagonists. These results suggest that the inverse agonist activity is mediated by stabilization of the inactive state of the receptor, which does not couple to G protein, and attenuates basal signaling initiated by ligand-independent activation of the effector adenylyl cyclase.
AB -
The structure/function relationship of salmon calcitonin (sCT) analogues was investigated in heterologous calcitonin receptor (CTR) expression systems. sCT analogues with progressive amino-terminal truncations intermediate of sCT-(1-32) to sCT-(8-32) were examined for their ability to act as agonists, antagonists, or inverse agonists. Two CTR cell clones, B8- H10 and G12-E12, which express ~5 million and 25,000 C1b receptors/cell, respectively, were used for this study. The B8-H10 clone has an ~80-fold increase in basal levels of intracellular cAMP due to constitutive activation of the overexpressed receptor. In whole-cell competition binding studies, sCT-(1-32) was more potent than any of its amino-terminally truncated analogues in competition for
125
I-sCT binding. In cAMP accumulation studies, sCT-(1-32) and modified analogues sCT-(2-32) and sCT-(3-32) had agonist activities. SDZ-216-710, with an amino-terminal truncation of four amino acids, behaved as a partial agonist/antagonist, whereas amino-terminal truncations of six or seven amino acid residues produced a 16-fold reduction in basal cAMP levels and attenuated the response to the agonist sCT-(1-32) in the constitutively active CTR system. This inverse agonist effect was insensitive to pertussis toxin inhibition. In contrast, the inverse agonist activity of these peptides was not observed in the nonconstitutively active CTR system, in which sCT analogues with amino-terminal truncations of four or more amino acids behaved as neutral competitive antagonists. These results suggest that the inverse agonist activity is mediated by stabilization of the inactive state of the receptor, which does not couple to G protein, and attenuates basal signaling initiated by ligand-independent activation of the effector adenylyl cyclase.
UR - http://www.scopus.com/inward/record.url?scp=0031002114&partnerID=8YFLogxK
U2 - 10.1124/mol.51.4.658
DO - 10.1124/mol.51.4.658
M3 - Article
C2 - 9106632
AN - SCOPUS:0031002114
VL - 51
SP - 658
EP - 665
JO - Molecular Pharmacology
JF - Molecular Pharmacology
SN - 1521-0111
IS - 4
ER -