title: Fast and slow nerve growth factor binding sites in human neuroblastoma and rat pheochromocytoma cell lines: relationship of sites to each other and to neurite formation.
abstract: We studied (a) the distribution and properties of fast and slow 125I-nerve growth factor (125I-NGF) binding sites in cultured human neuroblastoma (NB) cell lines that were categorized as responsive (N+) or unresponsive (N-) to NGF by neurite outgrowth, (b) whether fast or slow sites mediate actions of NGF, and (c) whether NGF-mediated conversion of fast to slow sites occurs in human NB and pheochromocytoma PC 12 cells. In human NB SH-SY5Y cells, the slow sites were trypsin resistant and binding was of high affinity. Loss of binding to the slow sites had a half-time of 25 to 30 min at 37 degrees C and was very slow at 4 degrees C. In contrast, the fast sites were trypsin sensitive and binding was of lower affinity; its dissociation half-time was less than 1 min at 4 degrees C and 37 degrees C. The association rate constants of both sites were about 0.8 to 1.2 X 10(7) M-1 sec-1. Some human NB cells had both fast and slow sites. The N+ human NB lines SH-SY5Y and LA-N-5 had only slow sites. Despite the virtual elimination of fast sites by trypsin in NB MC-IXC cells, remaining slow sites could still efficiently bind 125I-NGF. These observations showed that fast sites are not required for slow site binding, neurite outgrowth, or other demonstrated actions of NGF in some NB cells. In PC 12 cells, 125I-NGF initially bound to fast sites was not directly transferred to slow sites as required for NGF-mediated conversion. The association rate constants of fast and slow sites in PC12 cells were both about 2 X 10(7) M-1 sec-1. The association kinetics were consistent with simple bimolecular reactions in both NB and PC12 cells. The combined evidence in NB and PC12 cells did not support the hypothesis of NGF-mediated conversion of fast to slow sites.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009414:Nerve Growth Factors / Q000378:metabolism / Q000502:physiology*; D009447:Neuroblastoma / Q000378:metabolism; D009474:Neurons / Q000254:growth & development* / Q000378:metabolism; D010673:Pheochromocytoma / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000378:metabolism / Q000502:physiology
chemical_list: D009414:Nerve Growth Factors