Journal of Neuroscience, Vol 5, 1717-1728, Copyright © 1985 by Society for Neuroscience
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
KH Sonnenfeld and DN Ishii
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.