Nerve Growth Factor Processing and Trafficking Events Following TrkA-Mediated Endocytosis¹

Abstract

1) TrkA, in the absence of p75, is fully capable of mediating 125I-NGF endocytosis; 2) internalized 125I-NGF is slowly and inefficiently degraded; 3) following internalization, 125I-NGF is retroendocytosed; and 4) the ability of 125I-NGF to remain receptor-associated during acidic conditions may provide a mechanism for its retroendocytosis via recycling TrkA vesicles.

Peptide-Conjugated Quantum Dots Activate Neuronal Receptors and Initiate Downstream Signaling of Neurite Growth

“…These results show that βNGF-QD binds to PC12 cells in a punctate fashion characteristic of receptor labeling. The high levels of βNGF-QD internalization observed compared to that of control strep-QD is consistent with known information concerning the endocytosis of ligand bound-Trk receptor complexes as a natural cell regulatory function , and suggests that βNGF-QDs retain substantial TrkA-specific binding.…”

Quantum Dots Monitor TrkA Receptor Dynamics in the Interior of Neural PC12 Cells

“…Formation of groups of QD-TrkA receptors occurs upon endocytosis and is physiologically consistent with receptor dimerization and integration of receptors into common vesicle sorting endosomes. 30,32,33 We observed active shuttling of TrkA receptor-QD complexes into neurites with net directions and velocities similar to those reported for native TrkA receptors in the same PC12 model cell system. 29,35 Shuttling was also observed for NGF-QD-TrkA complexes.…”

“…These brighter clusters are similar to those observed for TrkA receptor staining and thus may mirror the process of receptor dimerization as well as receptor recombination into larger vesicles. 30,32,33 Because of the increased photostability of QDs, we were able to track QDs for longer periods of time than what was previously possible in live cells. At time points after 18-24 h, we continued to observe QD fluorescent puncta in cells (Figure 2D).…”

“…32 Although the affinity of NGF to TrkA is purported to be very high, the time course over which NGF remains bound to TrkA receptors is controversial and unclear. 31,33 Future work aimed at assaying the biochemical activity of NGF and anti-TrkA QD-TrkA complexes and their association with known endosomal and shuttling proteins will be useful for evaluating the trafficking pathway for QD-TrkA complexes.…”

Identification of Quantum Dot Bioconjugates and Cellular Protein Co-localization by Hybrid Gel Blotting

“…[29][30][31] NGF binds to trkA and is endocytosed into cells as a ligand-receptor complex. [32][33][34][35] We have shown in past work that QDs conjugated with nerve growth factor (NGF) bind specifically to trkA receptors, induce trkA downstream signaling, and are internalized into cell bodies. 16,28 Conventional Western blots of lysates obtained from cells treated with NGF-QDs show that trkA is detectable and that NGF-QDs stimulate a profound increase in trkAs compared to baseline trkA of cells treated with null streptavidin QDs (Supporting Information).…”