Protein kinase C is a common component of CGRP receptor desensitization induced by distinct agonists

Abstract

The calcitonin gene-related peptide (CGRP) is a neuropeptide involved in vasodilation and other physiological functions throughout the body. The receptor for CGRP has been cloned and well studied, but the mechanism of CGRP receptor desensitization has not been fully elucidated. In the present study, we evaluated the kinetics for agonist-mediated desensitization of the adenylate cyclase response in human neuroblastoma SK-N-MC cells. Distinct CGRP receptor agonists were used, including alpha and beta isoforms of CGRP, the linearized derivative cys(Et)2,7 alphaCGRP, adrenomedullin, and adrenomedullin 2. betaCGRP was 4-600 times more potent at desensitizing the cAMP production as compared to the other receptor-activating ligands, and all of the desensitization effects were blocked by a CGRP receptor antagonist. Although the different agonists vary in their ability to induce functional desensitization, a pretreatment/washout sequence with each peptide was able to reduce the activation potency of the other members of the calcitonin/CGRP peptide family. Next we tested whether the desensitizing effects of the distinct peptides involve protein kinase C (PKC) or protein kinase A (PKA). A PKC inhibitor, Ro 31-8220, concentration-dependently reduced the desensitization induced by the 5 CGRP receptor agonists, while having little effect on their desensitization potencies. PKA inhibitors KT-5720 and H-89, on the other hand, showed little effect on the induced level of desensitization. The findings indicate that functional desensitization is produced by distinct peptides acting through the active site of CGRP receptors, and involves the activation of PKC as a common component necessary to achieve maximal desensitization of receptor signaling.