Neural cell adhesion molecule induces intracellular signaling via multiple mechanisms of Ca2+ homeostasis

The neural cell adhesion molecule (NCAM) plays a pivotal role in the development of the nervous system, promoting neuronal differentiation via homophilic (NCAM-NCAM) as well as heterophilic (NCAM-fibroblast growth factor receptor [FGFR]) interactions. NCAM-induced intracellular signaling has been shown to affect and be dependent on the cytoplasmic Ca2+ concentration ([Ca2+](i)). However, the molecular basis of this remains unclear. In this study, we determined [Ca2+](i) regulating mechanisms involved in intracellular signaling induced by NCAM. To mimic the effect of homophilic NCAM interaction on [Ca2+](i) in vitro, we used a peptide derived from a homophilic binding site of NCAM, termed P2, which triggers signaling cascades similar to those activated by NCAM-NCAM interaction. We found that P2 increased [Ca2+](i) in primary hippocampal neurons. This effect depended on two signaling pathways. The first pathway was associated with activation of FGFR, phospholipase C gamma, and production of diacylglycerol, and the second pathway involved Src-family kinases. Moreover, NCAM-mediated Ca2+ entry required activation of nonselective cation and T-type voltage-gated Ca2+ channels. These channels, together with the Src-family kinases, were also involved in neuritogenesis induced by physiological, homophilic NCAM interactions. Thus, unanticipated mechanisms of Ca2+ homeostasis are shown to be activated by NCAM and to contribute to neuronal differentiation.