Trafficking the NGF signal: implications for normal and degenerating neurons.
Nerve growth factor (NGF) activates TrkA to trigger signaling events that promote the survival, differentiation and maintenance of neurons. The mechanism(s) that controls the retrograde transport of the NGF signal from axon terminals to neuron cell bodies is not known. The 'signaling endosome' hypothesis stipulates that NGF, TrkA and signaling proteins are retrogradely transported on endocytic vesicles. Here, we provide evidence for the existence of signaling endosomes. Following NGF treatment, clathrin-coated vesicles (CCVs) contain NGF bound to TrkA together with activated signaling proteins of the Ras/pErk1/2 pathway. NGF signals from isolated CCVs through the Erk1/2 pathway. Early endosomes appear to represent a second type of signaling endosomes. We found that NGF induced a sustained activation of Rap1, a small monomeric GTP-binding protein of the Ras family, and that this activation occurred in early endosomes that contain key elements of Rap1/pErk1/2 pathway. We discuss the possibility that the failure of retrograde NGF signaling in a mouse model of Down syndrome (Ts65Dn) may be due to the failure to retrograde transport signaling endosomes. It is important to define further the significance of signaling endosomes in the biology of both normal and degenerating neurons.
Delcroix
Jean-Dominique
JD
Department of Neurology and Neurological Sciences and of Pediatrics, Program in Neuroscience, Stanford University, Stanford, CA 94305, USA.
Valletta
Janice
J
Wu
Chenbiao
C
Howe
Charles L
CL
Lai
Chun-Fai
CF
Cooper
John D
JD
Belichenko
Pavel V
PV
Salehi
Ahmad
A
Mobley
William C
WC
D033962:Adaptor Protein Complex 2 / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D001921:Brain / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002103:Cadaverine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002746:Chlorpromazine / Q000494:pharmacology; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D018699:Coated Vesicles / Q000187:drug effects / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D018492:Dopamine Antagonists / Q000494:pharmacology; D011992:Endosomes / Q000378:metabolism; D005455:Fluorescent Antibody Technique / Q000379:methods; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D009410:Nerve Degeneration / Q000378:metabolism*; D020932:Nerve Growth Factor / Q000378:metabolism / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D016716:PC12 Cells; D019000:Phosphotyrosine / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011233:Precipitin Tests / Q000379:methods; D021381:Protein Transport / Q000502:physiology*; D011869:Radioligand Assay; D051381:Rats; D020917:Receptor, trkA; D015398:Signal Transduction / Q000502:physiology*; D013997:Time Factors; D033921:Vesicular Transport Proteins; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
D033962:Adaptor Protein Complex 2; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D002868:Chromosomal Proteins, Non-Histone; D017362:Cyclic AMP Response Element-Binding Protein; D018492:Dopamine Antagonists; D008565:Membrane Proteins; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1; C056608:caltractin; D019000:Phosphotyrosine; D020932:Nerve Growth Factor; D020917:Receptor, trkA; D020827:rap1 GTP-Binding Proteins; C008542:monodansylcadaverine; D002103:Cadaverine; D011188:Potassium; D002746:Chlorpromazine