The neuropeptide head activator induces activation and translocation of the growth-factor-regulated Ca²⁺-permeable channel GRC

The neuropeptide head activator stimulates cell proliferation of neuronal precursor and neuroendocrine cells. The mitogenic signaling cascade requires Ca²⁺ influx for which, as we show in this paper, the growth-factor-regulated Ca²⁺-permeable cation channel, GRC, is responsible. GRC is a member of the transient receptor potential channel family. In uninduced cells only low amounts of GRC are present on the plasma membrane but, upon stimulation with head activator, GRC translocates from an intracellular compartment to the cell surface. Head activator functions as an inducer of GRC translocation in neuronal and neuroendocrine cells, which express GRC endogenously, and also in COS-7 cells after transfection with GRC. Head activator is no direct ligand for GRC, but its action requires the presence of a receptor coupled to a pertussis-toxin inhibitable G-protein. Heterologously expressed GRC becomes activated by head activator, which results in opening of the channel and Ca²⁺ influx. SK&F 96365, an inhibitor specific for TRP-like channels, blocks Ca²⁺ entry and, consequently, translocation of GRC is prevented. Head activator-induced GRC activation and translocation are also inhibited by wortmannin and KN-93, blockers of the phosphatidylinositol 3-kinase and of the Ca²⁺/calmodulin-dependent kinase, respectively, which implies a role for both kinases in head-activator signaling to GRC.