Abstract
Heterogeneous populations of saturable specific high-affinity binding sites for the biologically active subunit of the 7S nerve growth factor complex purified from mouse submaxillary gland (NGF) are detected on human tumor cells of neural crest origin. Detailed studies of the melanoma cell line MeWo demonstrate two populations of binding sites of high affinity with dissociation equilibrium constants of Kd 4 × 10-11 and 5 × 10-10 m, respectively. Other cell lines of neural crest origin also show high-affinity binding heterogeneity. Exposure of the cell lines to 1 mm theophylline reversibly reduces the number of available NGF binding sites without influencing the affinities of binding. On the MeWo cell line, this is not related to the stages of the cell cycle or to production and release of a NGF-like molecule by the theophylline-exposed cells. These observations complement earlier studies of theophylline-induced alterations in NK cell sensitivity on the MeWo cell line, providing further evidence for cell surface phenotypic changes induced by a compound that promotes differentiation in melanocytes and melanoma cells. Future studies of cell surface phenomena involved in theophylline-induced NGF binding site disappearance may lead to a better understanding of the NGF receptor and its disappearance from certain embryonic cells of neural crest origin during differentiation.
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