Islet amyloid polypeptide stimulates cyclic AMP accumulation via the porcine calcitonin receptor

CHO-cells stably transfected with an expression vector for the porcine calcitonin receptor were exposed to various concentrations of IAPP, CGRP or calcitonin from different species. In these, but not in untransfected cells, rat IAPP mediated cAMP accumulation at concentrations above 25 nM. This potency was three orders of magnitude lower than that of porcine calcitonin and two and four orders of magnitude lower than those of human and salmon calcitonin, respectively. Human beta-CGRP had an effect similar to rat IAPP whereas human alpha-CGRP was at least one order of magnitude less potent than rat IAPP. COS cells expressing recombinant porcine calcitonin receptors transiently or stably showed a different pattern of responses to calcitonin, IAPP and the CGRPs. In these cells, rat IAPP was as potent an inducer of cAMP as was salmon or porcine calcitonin and more potent than human calcitonin or the CGRPs. The dissociation constants for salmon calcitonin binding to the porcine calcitonin receptors on CHO and COS cells were 0.2 nM and 2.0 nM and the corresponding number of binding sites per cell were approximately 7 x 10(4) and 2 x 10(6), respectively. These results demonstrate that IAPP and CGRP can mediate signal transduction via the porcine calcitonin receptor and provide a possible explanation for the calcitonin-like effects of pharmacological levels of IAPP and CGRP administrated in vivo. The difference between CHO and COS cells in their relative response to the various ligands may relate to the difference in receptor number, post-transcriptional processing, or to dissimilarities in the signal transduction pathways between the two cell types.