A Novel Endocytic Recycling Signal Distinguishes Biological Responses of Trk Neurotrophin Receptors

Abstract

Endocytic trafficking of signaling receptors to alternate intracellular pathways has been shown to lead to diverse biological consequences. In this study, we report that two neurotrophin receptors (tropomyosin-related kinase TrkA and TrkB) traverse divergent endocytic pathways after binding to their respective ligands (nerve growth factor and brain-derived neurotrophic factor). We provide evidence that TrkA receptors in neurosecretory cells and neurons predominantly recycle back to the cell surface in a ligand-dependent manner. We have identified a specific sequence in the TrkA juxtamembrane region, which is distinct from that in TrkB receptors, and is both necessary and sufficient for rapid recycling of internalized receptors. Conversely, TrkB receptors are predominantly sorted to the degradative pathway. Transplantation of the TrkA recycling sequence into TrkB receptors reroutes the TrkB receptor to the recycling pathway. Finally, we link these divergent trafficking pathways to alternate biological responses. On prolonged neurotrophin treatment, TrkA receptors produce prolonged activation of phosphatidylinositol 3-kinase/Akt signaling as well as survival responses, compared with TrkB receptors. These results indicate that TrkA receptors, which predominantly recycle in signal-dependent manner, have unique biological properties dictated by its specific endocytic trafficking itinerary.

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

“…The authors of this study determined that a juxtamembrane region (amino acids 473-493) of the TrkA, not present in the corresponding TrkB sequence, is necessary and sufficient for receptor recycling. Furthermore, the introduction of this sequence into TrkB leads to receptor recycling and an increase in neuronal survival (Chen et al 2005). Interestingly, the recycling domain of TrkA also is absent in the corresponding sequence of TrkC (Fig.…”

“…In primary sympathetic neurons, BDNF-stimulated TrkB is targeted for degradation, whereas NGF-stimulated TrkA is targeted for recycling to the plasma membrane, leading to prolonged PI-3K/Akt pathway activation and cell survival (Chen et al 2005). The authors of this study determined that a juxtamembrane region (amino acids 473-493) of the TrkA, not present in the corresponding TrkB sequence, is necessary and sufficient for receptor recycling.…”

Inhibition of Abl tyrosine kinase enhances nerve growth factor-mediated signaling in Bcr–Abl transformed cells via the alteration of signaling complex and the receptor turnover

“…In the absence of imatinib, only 16% (P ¼ 0.05) of the molecules disappeared from the cell surface within 15 min ( Figure 6). In the presence of Monensin, a potent inhibitor of receptor recycling (Saxena et al, 2005), the level of surface expression of TrkA decreases more than 40% within 15 min in the presence or absence of imatinib, suggesting that Abl tyrosine kinase suppresses receptor internalization and/or enhances receptor recycling (Chen et al, 2005 NGF treatment induces cell survival of TrkA expressing CML cell lines in the presence of imatinib To examine whether NGF-TrkA signaling may rescue cells from imatinib-mediated cell death, we incubated K562, Meg-01, HMC-1 and U937 cells with or without NGF in the presence of imatinib for 4 days and the number of living cells was then counted. After treatment with 0.5 or 5 mM imatinib, more than 50% of all K562 cells died within 4 days.…”

Syntaxin 8 Modulates the Post-synthetic Trafficking of the TrkA Receptor and Inflammatory Pain Transmission*

“…Rat pheochromocytoma cell line 12 (PC12) cells were maintained in DMEM containing 5% FBS, 10% horse serum supplemented with 100 units/ml penicillin/ streptomycin, and 2 mM L-glutamine. The 615 cell line was PC12 cells stably expressing the TrkA receptor cultured as described previously (15). DRG neurons were dissected from embryonic day 18 (E18) Wistar rats and grown in Neurobasal medium containing 2% B27 supplement (Invitrogen), 0.5 mM L-glutamine, 100 units/ml penicillin/streptomycin, and 50 ng/ml NGF at 37°C, 5% CO 2 , and 95% humidity.…”

“…Next, the cells were homogenized on ice using ϳ30 strokes of a glass Dounce homogenizer in 0.5 ml of buffer (320 mM sucrose, 10 mM Hepes, pH 7.2, with protease inhibitors) and centrifuged at 500 ϫ g for 2 min. The post-nuclear supernatant was then subjected to fractionation by centrifugation at 105,000 ϫ g for 120 min in an SW60 Ti rotor (Beckman Instruments) and layered on a discontinuous sucrose density gradient (15,30,40, and 55%). Fractions of 0.4 ml were collected from the top (designated fraction number 1 (top) to 13 (bottom)).…”