Cell Surface Trk Receptors Mediate NGF-Induced Survival While Internalized Receptors Regulate NGF-Induced Differentiation

Abstract

Internalization and transport of a ligand-receptor complex are required to initiate cell body responses to target-derived neurotrophin. However, it is not known whether internalized receptors and cell surface receptors initiate the same signaling pathways and biological responses. Here we use a temperature-sensitive mutant of dynamin (G273D) to control the subcellular localization of activated NGF receptors (Trks). We show that dynamin function is required for ligand-dependent endocytosis of Trk receptors. In PC12 cells, nerve growth factor (NGF) stimulation promotes both survival and neuronal differentiation. These distinct biological responses to NGF are controlled by receptors signaling from different locations within the cell. Neuronal differentiation is promoted by catalytically active Trks within endosomes in the cell interior. In contrast, survival responses are initiated by activated receptors at the cell surface where they orchestrate prolonged activation of the kinase Akt. Thus, interactions between Trk receptor tyrosine kinases and intracellular signaling molecules are dictated both by phosphotyrosine motifs within the receptors and by the intracellular location of phosphorylated receptors.

Association of the Atypical Protein Kinase C-interacting Protein p62/ZIP with Nerve Growth Factor Receptor TrkA Regulates Receptor Trafficking and Erk5 Signaling

“…Both pathways are dependent upon TrkA kinase activity, as K252a pretreatment abolishes NGF induced activation of these pathways. However, Erk5 activation is also dependent upon internalization of TrkA (21), and likewise TrkA delivery to the signaling endosome is required for NGFmediated differentiation (11). Because p62 modulated internalization of TrkA (Fig.…”

“…These data shed light on the underlying mechanism whereby p62 can affect NGF-mediated differentiation. Previous studies (11) have shown that internalized TrkA receptors within the signaling endosome are the site of the differentiation signal for NGF/TrkA. The region where p62 binds TrkA lies within amino acids 472-493, and the TrkA juxtamembrane domain has been implicated previously as critical for TrkA-mediated differentiation (30).…”

“…The receptors within signaling vesicles remain catalytically active and phosphorylated because they are less accessible to membrane-associated phosphatases (10). Internalized TrkA receptors induce a higher peak level of mitogen-activated protein kinase (ERK/MAPK) activation thereby regulating cell differentiation (11).…”

Directing traffic in neural cells: determinants of receptor tyrosine kinase localization and cellular responses

“…Blocking internalization of the EGFR expressed in HeLa cells similarly decreases ERK activity but also increases protein kinase C (PKC) activity (Vieira et al 1996). In PC12 cells, nerve growth factor (NGF)-mediated survival is associated with surface localized TrkA via the activation of the PI-3K/Akt pathway, whereas internalized TrkA induces NGF-mediated differentiation via the ERK pathway (Zhang et al 2000). Together, these studies suggest that activation of specific signal transduction pathways may be spatially segregated such that PI-3K and PKC signaling occur at the cell surface and ERK signaling occurs predominantly in internalized endosomal vesicles.…”

“…For example, the inhibition of TrkA internalization in sympathetic neurons leads to a decrease in PI-3K/Akt signaling and cell death (Zhang et al 2000;Ye et al 2003). Wang et al (2004) demonstrated recently that the PDGFR-b activates various signaling pathways within endosomes including PI-3K/Akt in a human hepatocellular carcinoma cell line.…”