Amylin Receptor Phenotypes Derived from Human Calcitonin Receptor/RAMP Coexpression Exhibit Pharmacological Differences Dependent on Receptor Isoform and Host Cell Environment

Receptor activity modifying proteins (RAMPs) constitute a group of three proteins, designated as RAMP1, 2, and 3, which are able to effect functional changes in some members of the G protein-coupled receptor family. Thus, RAMP1 or RAMP3 can modify the calcitonin receptor (CTR) to also function as a...

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Bibliographic Details
Published in:The Journal of pharmacology and experimental therapeutics 2000-07, Vol.294 (1), p.61-72
Main Authors: Tilakaratne, N, Christopoulos, G, Zumpe, E T, Foord, S M, Sexton, P M
Format: Article
Language:English
Subjects:
Amyloid - metabolism
Animals
CHO Cells
COS Cells
Cricetinae
Humans
Intracellular Signaling Peptides and Proteins
Islet Amyloid Polypeptide
Membrane Proteins - physiology
Phenotype
Protein Isoforms - physiology
Receptor Activity-Modifying Protein 1
Receptor Activity-Modifying Protein 3
Receptor Activity-Modifying Proteins
Receptors, Calcitonin - physiology
Receptors, Islet Amyloid Polypeptide
Receptors, Peptide - physiology
Transfection
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Summary:Receptor activity modifying proteins (RAMPs) constitute a group of three proteins, designated as RAMP1, 2, and 3, which are able to effect functional changes in some members of the G protein-coupled receptor family. Thus, RAMP1 or RAMP3 can modify the calcitonin receptor (CTR) to also function as a high-affinity amylin receptor-like phenotype. To examine the RAMP/CTR interaction, individual RAMPs were coexpressed with either of the two human CTR (hCTR) isoforms, the insert negative (hCTR I1− ) or the insert positive (hCTR I1+ ), in Chinese hamster ovary (CHO-P) or African monkey kidney (COS-7) cells. CHO-P cells provide an environment conducive to a low, but significant, level of amylin binding with either hCTR isoform alone, unlike in COS-7, where RAMP coexpression is imperative for amylin binding. Also, in CHO-P, hCTR I1− induced amylin binding with all three RAMPs, in contrast to COS-7, where only RAMP1 or RAMP3 generate an amylin receptor phenotype. hCTR I1+ induced high-affinity amylin binding with any RAMP in either cell line. In COS-7 cells, hCTR I1+ /RAMP-generated receptor displayed high- and low-affinity states, in contrast with the single-state binding seen with hCTR I1− /RAMP-generated receptor, whereas in CHO-P cells a two-affinity state receptor phenotype was evident with both hCTR isoforms. Endogenous RAMP expression is low and similar between cell lines. The results suggest that CTR/RAMP interaction in these cells is complex with other cellular factors such as the levels of different G proteins and/or receptor/RAMP stoichiometry following heterologous coexpression contributing to the ultimate receptor phenotype.
ISSN:0022-3565
1521-0103