title: Fates of neurotrophins after retrograde axonal transport: phosphorylation of p75NTR is a sorting signal for delayed degradation.
abstract: Neurotrophins can mediate survival or death of neurons. Opposing functions of neurotrophins are based on binding of these ligands to two distinct types of receptors: trk receptors and p75NTR. Previous work showed that target-derived NGF induces cell death, whereas BDNF and NT-3 enhance survival of neurons in the isthmo-optic nucleus of avian embryos. To determine the fate of retrogradely transported neurotrophins and test whether their sorting differs between neurotrophins mediating survival- or death-signaling pathways, we traced receptor-binding, sorting, and degradation kinetics of target-applied radiolabeled neurotrophins that bind in this system to trk receptors (BDNF, NT-3) or only to p75NTR (NGF). At the ultrastructural level, the p75NTR-bound NGF accumulates with a significant delay in multivesicular bodies and organelles of the degradation pathway on arrival in the cell body when compared with trk-bound BDNF or NT-3. This delayed lysosomal accumulation was restricted to target-derived NGF, but was not seen when NGF was supplied to the soma in vitro. The kinase inhibitors K252a and Gö6976 alter the kinetics of organelle accumulation: phosphorylation of p75NTR is a sorting signal for delayed sequestering of p75NTR-bound NGF in multivesicular bodies and delayed degradation in lysosomes when compared with trk-bound neurotrophins. Mutagenesis and mass spectrometry studies indicate that p75NTR is phosphorylated by conventional protein kinase C on serine 266. We conclude that, in addition to the known phosphorylation of trks, the phosphorylation of p75NTR can also significantly affect neuronal survival in vivo by changing the intracellular sorting and degradation kinetics of its ligands and thus signaling duration.
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
authors.forename: Rafal
authors.initials: R
authors.lastname: Butowt
authors.forename: Christopher S
authors.initials: CS
authors.lastname: von Bartheld
mesh_terms: D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D002227:Carbazoles / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects; D002642:Chick Embryo; D055032:Electron Microscope Tomography / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D047468:Immunoprecipitation / Q000379:methods; D026121:Indole Alkaloids / Q000494:pharmacology; D007457:Iodine Radioisotopes / Q000378:metabolism; D013058:Mass Spectrometry; D009414:Nerve Growth Factors / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D016716:PC12 Cells; D010766:Phosphorylation / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D020800:Receptor, Nerve Growth Factor / Q000378:metabolism*; D020813:Receptor, trkB / Q000378:metabolism; D020812:Receptor, trkC / Q000378:metabolism; D012160:Retina / Q000166:cytology; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014162:Transfection
chemical_list: D002227:Carbazoles; D004791:Enzyme Inhibitors; D026121:Indole Alkaloids; D007457:Iodine Radioisotopes; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D020800:Receptor, Nerve Growth Factor; C081021:Go 6976; D012694:Serine; C049985:staurosporine aglycone; D020813:Receptor, trkB; D020812:Receptor, trkC; D011493:Protein Kinase C