title: Gangliosides activate Trk receptors by inducing the release of neurotrophins.
abstract: We used NIH-3T3 fibroblasts expressing the different Trk receptors to examine whether GM1 ganglioside and its semisynthetic derivative LIGA20 activate various neurotrophin receptors. GM1 induced autophosphorylation of TrkC more potently than TrkA or TrkB receptors. In contrast, LIGA20 activated TrkB tyrosine phosphorylation only. Therefore, Scatchard analysis was performed to determine whether GM1 binds to TrkC. GM1 failed to displace neurotrophin-3 binding, suggesting that this ganglioside does not act as a ligand for Trk receptors. In addition, GM1 failed to induce autophosphorylation of a chimeric receptor consisting of the extracellular domain of the tumor necrosis factor receptor and the intracellular domain of TrkA, suggesting that GM1 does not affect the tyrosine kinase domain. We next determined whether GM1 induces the release of neurotrophins from fibroblast cells. GM1 induced a rapid and significant increase in the amount of neurotrophin-3, but not other neurotrophins. This effect was independent of the presence of Trk because K252a did not prevent GM1-mediated release of neurotrophin-3. Moreover, GM1-mediated TrkC autophosphorylation was blocked by TrkC-IgG (but not TrkB-IgG) receptor bodies, further suggesting that GM1 activates TrkC by inducing the release of neurotrophin-3. This hypothesis was also tested in cultured cerebellar granule cells. GM1 induced neurotrophin-3 (but not brain-derived neurotrophic factor or nerve growth factor) release. In contrast, LIGA20 increased the secretion of brain-derived neurotrophic factor. Our data show that gangliosides may activate different Trk receptors by differentially affecting the release of neurotrophins.
authors.affiliation: Department of Neuroscience, Georgetown University Medical Center, Washington, D. C. 20057, USA.
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Rabin
authors.forename: Alessia
authors.initials: A
authors.lastname: Bachis
authors.forename: Italo
authors.initials: I
authors.lastname: Mocchetti
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002227:Carbazoles / Q000494:pharmacology; D002470:Cell Survival; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D005677:G(M1) Ganglioside / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D005732:Gangliosides / Q000378:metabolism*; D007074:Immunoglobulin G / Q000378:metabolism; D026121:Indole Alkaloids; D051379:Mice; D009414:Nerve Growth Factors / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D020917:Receptor, trkA / Q000378:metabolism*; D015398:Signal Transduction; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism
chemical_list: D002227:Carbazoles; D005732:Gangliosides; D007074:Immunoglobulin G; D026121:Indole Alkaloids; D009414:Nerve Growth Factors; C086919:LIGA 20; D005677:G(M1) Ganglioside; D014443:Tyrosine; C049985:staurosporine aglycone; D020917:Receptor, trkA; D013110:Sphingosine