Nerve growth factor-induced increase in biopterin level of pheochromocytoma PC12.

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Nerve growth factor (NGF) is a protein required for the survival and development of various neurons. In culture system, NGF induces differentiation of pheochromocytoma PC12 into sympathetic neuron-like cells from chromaffin cell-like phenotype. In this study, tetrahydrobiopterin (BPH4) in PC12 cells are found to be transiently increased by NGF. Then the mechanism of this NGF action and the biological meaning of the phenomenon are investigated.1. Mechanism of action: (1) NGF-induced increase in BPH4 was blocked by actinomycin D (AD) and cycloheximide (CH). (2) The activity of GTP cyclohydrolase (GTPCH), which is thought to be a regulatory enzyme in BPH4 biosynthesis, was also transiently increased by NGF. The GTPCH activity and BPH4 level showed quite similar responses to NGF in the time course and dose dependence experiments. The NGF effect on GTPCH was also blocked by AD and 'CH. These results suggest that NGF increase BPH4 level by increasing the amount of GTPCH via synthesis of RNA and of protein. (3) Protein kinase inhibitors, H-7 and H-8, of the concentrations around K_i values for protein kinase A, protein kinase G and protein kinase C did not affect the NGF action. (4) Dibutyryl cyclic AMP (dBcAMP) also increased the GTPCH activity and BPH4 level, but the action mechanism of NGF seems to be different from that of dBcAMP.2. Biological meaning: Effect of an analog of BPH4, tetrahydro-6-methylpterin (MPH4), on the phosphorylation of a nuclear protein named SMP, of which phosphorylation is stimulated by NGF, was examined. MPH4 inhibited the NGF-stimulated phosphorylation of SMP, suggesting a possible function of BPH4 as a modulator of NGF action. Further study, however, should be needed to clarify the biological role of transient increase in BPH4 induced by NGF.