Regulation of nuclear Ca2+ signaling by translocation of the Ca2+ messenger synthesizing enzyme ADP-ribosyl cyclase during neuronal depolarization

In neurons, voltage-gated Ca2+ channels and nuclear Ca2+ signaling play important roles, such as in the regulation of gene expression. However, the link between electrical activity and biochemical cascade activation involved in the generation of the nuclear Ca2+ signaling is poorly understood. Here we show that depolarization of Aplysia neurons induces the translocation of ADP-ribosyl cyclase, a Ca2+ messenger synthesizing enzyme, from the cytosol into the nucleus. The translocation is dependent on Ca2+ influx mainly through the voltage-dependent L-type Ca2+ channels. We report also that specific nucleoplasmic Ca2+ signals can be induced by three different calcium messengers, cyclic ADP-ribose, nicotinic acid adenine dinucleotide phosphate (NAADP), both produced by the ADP-ribosyl cyclase, and inositol 1,4,5-trisphosphate (IP3). Moreover, our pharmacological data show that NAADP acts on its own receptor, which cooperates with the IP3 and the ryanodine receptors to generate nucleoplasmic Ca2+ oscillations. We propose a new model where voltage-dependent L-type Ca2+ channel-induced nuclear translocation of the cytosolic cyclase is a crucial step in the fine tuning of nuclear Ca2+ signals in neurons.