The p75NTR intracellular domain generated by neurotrophin-induced receptor cleavage potentiates Trk signaling

The p75 neurotrophin receptor (p75NTR) potentiates Trk signaling, but the underlying mechanisms remain uncertain. Here, we examine the relationship between p75NTR cleavage and Trk signaling. We found that, in PC12 cells, nerve growth factor (NGF) induces rapid and robust alpha-secretase-and gamma-secretase-dependent cleavage of p75NTR, releasing the resulting intracellular domain into the cytosol. Brain-derived neurotrophic factor similarly induces p75NTR cleavage in primary cerebellar granule neurons. p75NTR cleavage occurs by means of Trk-dependent activation of MEK-Erk signaling and induction of alpha-secretase activity, and is independent of ligand binding to p75NTR. Neurons and PC12 cells lacking p75NTR display defects in neurotrophin-dependent Akt activation. Normal Akt activation is rescued using full-length p75NTR or the p75 intracellular domain, but not cleavage-resistant p75NTR. We then demonstrate that NGF-dependent growth arrest of PC12 cells requires p75NTR cleavage and generation of the intracellular domain. We conclude that generation of the soluble p75NTR intracellular domain by Trk-induced cleavage plays a fundamental role in Trk-dependent signaling events.