Nerve growth factor-induced differentiation in neuroblastoma cells expressing TrkA but lacking p75NGFR

Nerve growth factor (NGF) binds to two distinct cell surface receptors, TrkA, which is a receptor tyrosine kinase, and p75NGFR, whose role in NGF-induced signal transduction remains unclear. We have found that human neuroblastoma IMR-32 cells express TrkA, but p75NGFR expression was not detectable in these cells by northern blot analysis, immunoblotting, or chemical crosslinking experiments. Despite the lack of p75NGFR expression, subnanomolar concentrations of recombinant human NGF induced neurite outgrowth, tyrosine phosphorylation, and immediate early gene expression in these cells. These results strongly suggest that NGF-induced neuronal differentiation in IMR-32 cells is initiated through TrkA in the absence of p75NGFR. Thus, IMR-32 cells may provide a model for studying neurotrophic effects of NGF on adult striatal cholinergic neurons, which also lack p75NGFR expression.