Calmodulin interacts with PAC1 and VPAC2 receptors and regulates PACAP-induced FOS expression in human neuroblastoma cells.

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) mediates its physiological functions through activation of PAC1, VPAC1 and VPAC2 receptors, and the ubiquitous Ca(2+)-sensor calmodulin has been implicated in PACAP-induced signaling. The immediate early response gene FOS is a well-known marker of neuronal activation, so we used a human neuroblastoma cell line NB-1 to explore the role of calmodulin in PACAP-induced FOS gene expression. We observed both short-term and prolonged altered PACAP-mediated activation of the FOS gene in the presence of the calmodulin-antagonist W-7. NB-1 cells were shown to express PAC1 and VPAC2 receptors, and immunoprecipitation of both receptors displayed a co-association with calmodulin in the absence of Ca(2+). Our findings indicate a novel mechanism of calmodulin in regulating PACAP signaling by possible interaction with the inactive state of PAC1 and VPAC2 receptors.