%0 Journal Article %A Nanda Tilakaratne %A George Christopoulos %A Emma T. Zumpe %A Steven M. Foord %A Patrick M. Sexton %T Amylin Receptor Phenotypes Derived from Human Calcitonin Receptor/RAMP Coexpression Exhibit Pharmacological Differences Dependent on Receptor Isoform and Host Cell Environment %D 2000 %J Journal of Pharmacology and Experimental Therapeutics %P 61-72 %V 294 %N 1 %X 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 (hCTRI1−) or the insert positive (hCTRI1+), 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, hCTRI1− induced amylin binding with all three RAMPs, in contrast to COS-7, where only RAMP1 or RAMP3 generate an amylin receptor phenotype. hCTRI1+ induced high-affinity amylin binding with any RAMP in either cell line. In COS-7 cells, hCTRI1+/RAMP-generated receptor displayed high- and low-affinity states, in contrast with the single-state binding seen with hCTRI1−/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. The American Society for Pharmacology and Experimental Therapeutics %U https://jpet.aspetjournals.org/content/jpet/294/1/61.full.pdf