Differential effects of neurotrophic factors on neurotransmitter development in the IMR-32 human neuroblastoma cell line

The human neuroblastoma cell line IMR-32 exhibits both cholinergic and adrenergic properties. We have used IMR-32 cells to study the effects of CDF (CAT development factor) and bFGF (basic fibroblast growth factor) on the development of neurotransmitter properties. CDF treatment increases CAT activity in a dose-dependent manner, independent of cell density. Time course studies show that there is a threefold increase in the specific CAT activity in IMR-32 cells treated with CDF for 6 d. CDF does not, however, affect the level of tyrosine hydroxylase (TH) activity, or the rate of cell proliferation. bFGF, on the other hand, induces TH activity and decreases CAT activity in a dose-dependent manner. bFGF's effect on TH is enhanced by increasing cell density, while its reduction of specific CAT activity is independent of cell density. Time course studies show a 30-fold increase in TH activity per cell and a threefold decrease in CAT activity per cell, after treatment with bFGF for 6 d. In contrast to the effects of CDF, bFGF enhances cell proliferation in IMR-32 cells. Double-labeled immunofluorescence studies showed that 95% of the cells stain for CAT and 65% stain for TH following treatment with CDF and bFGF, respectively. When these factors are combined, approximately 75% of the cells express both CAT and TH, demonstrating that IMR-32 cells are bipotential with regard to neurotransmitter-associated enzyme expression. We also show that insulin-like growth factor I and NGF selectively induce CAT activity and cell proliferation, respectively, whereas epidermal growth factor has no effect. Thus, IMR-32 cells appear to be differentially responsive to distinct neurotrophic factors and also provide a model for studying the specific effects of neurotrophic factors on functional differentiation.