Characterization of NCS1-InsP3R1 interaction and its functional significance.

Inositol 1,4,5-trisphosphate receptors (InsP3Rs) are endoplasmic reticulum-localized channels that mediate Ca2+ release from the endoplasmic reticulum into the cytoplasm. We previously reported that an EF-hand Ca2+-binding protein, neuronal calcium sensor 1 (NCS1), binds to the InsP3R and thereby increases channel open probability, an event associated with chemotherapy-induced peripheral neuropathy. However, the exact NCS1-binding site on InsP3R remains unknown. Using protein docking, co-immunoprecipitation, and blocking peptides, we mapped the NCS1-binding site to residues 66-110 on the suppressor domain of InsP3R type 1 (InsP3R1). We also identified Leu-89, a residue in the hydrophobic pocket of NCS1, as being critical for facilitating the NCS1-InsP3R1 interaction. Overexpression of WT NCS1 in MDA-MB231 breast cancer cells increased Ca2+ signaling and survival, whereas overexpression of Leu-89 NCS1 variants decreased Ca2+ signaling and survival, further suggesting the importance of this residue in the NCS1-InsP3R1 interaction. In conclusion, we show that NCS1-InsP3R1 interaction enhances intracellular Ca2+ signaling in cells and can be modulated by altering or occluding the hydrophobic pocket of NCS1. This improved understanding of the NCS1-InsP3R1 interaction may facilitate the development of management strategies for diseases resulting from aberrant NCS1 expression.