A novel role of hippocalcin in bFGF-induced neurite outgrowth of H19-7 cells.

Hippocalcin is a Ca2+-binding protein that is expressed mainly in pyramidal nerve cells of the hippocampus. However, its functions and mechanism in the brain remain unclear. To elucidate the role of hippocalcin, we used a conditionally immortalized hippocampal cell line (H19-7) and showed that bFGF treatment increased the expression of hippocalcin during bFGF-induced neurite outgrowth of H19-7 cells. Overexpression of hippocalcin dramatically elongated neurites and increased the expression of basic helix-loop-helix transcription factor, that is, NeuroD without bFGF stimulation. Treatment of the cells with hippocalcin siRNA completely blocked bFGF-induced neurite outgrowth and NeuroD expression. bFGF stimulation resulted in activation of phospholipase C-gamma (PLC-gamma) and an increased level of intracellular Ca2+. Hippocalcin expression by bFGF stimulation was fully blocked by both the PLC-gamma inhibitor U73122 and BAPTA-AM, a chelator of intracellular Ca2+, suggesting that hippocalcin expression by bFGF is dependent on PLC-gamma and Ca2+. Moreover, both U73122 and BAPTA-AM completely blocked bFGF-induced neurite outgrowth and NeuroD expression. Taken together, these results suggest for the first time that bFGF induces hippocalcin expression in H19-7 cells through PLC-gamma activation, which leads to neurite outgrowth.