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

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, 1-1,000ng/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.