Neurotrophin binding to the p75 neurotrophin receptor is necessary but not sufficient to mediate NGF-effects on APP secretion in PC-12 cells

Summary

In the present study the pheochromocytoma cell line (PC-12) was used as a model system to determine the role of the two neurotrophin receptors in the regulation of amyloid precursor protein (APP) secretion by nerve growth factor (NGF). To stimulate TrkA and/or p75^NTR signaling in PC-12 cells, we used NGF, brain-derived neurotrophic factor (BDNF), and NGF in the presence of an excess of BDNF or the monoclonal antibody 192IgG, to block p75^NTR binding to NGF. Our results demonstrate that NGF stimulates APP secretion in a dose dependent fashion with maximum effects at 10ng/ml, known to saturate high-affinity NGF binding sites. Treatment of PC-12 cells with varying concentrations of BDNF, l–l,000ng/ml, did not alter APP secretion, suggesting that binding to p75^NTR alone is not sufficient to affect APP secretion. When blocking NGF binding to p75^NTR with BDNF or 192IgG, on the other hand, NGF effects on APP secretion were abolished. These findings suggest that in cells expressing p75^NTR and TrkA receptors, binding of NGF to the p75^NTR is required to mediate NGF effects on APP secretion. Our data are also consistent with a proposed function of the p75^NTR in receptor recruitment and “presentation” of NGF to receptors.