Purified mouse nerve growth factor (NGF)radiolabeled with 125I was tested for its ability to bind to a variety of different cultured cells. NGF binds readily to human and hamster melanoma cells but does not bind to many other cell lines. The three cell lines with the highest number of NGF receptors were derived from metastatic melanomas. One of these lines, A875, was studied in detail and was shown to have approximately 7x10(5) NGF receptors per cell with an association constant of 1.0x10(9) liters/mole. The use of these cells in competition binding assays permits the detection of 0.25 ng of NGF in various biologic fluids. NGF can be shown to increase the survival, but not the division, of melanoma cells maintained in medium depleted of serum growth factors. This effect of NGF as a specific "survival factor" appears analogous to its effect on cultured sympathetic ganglion cells and on other cells derived from the neural crest.
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