Regulation of nerve growth factor receptor gene expression by nerve growth factor in the developing peripheral nervous system.

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Abstract
Nerve growth factor (NGF) is a target-derived neurotrophic protein that promotes the survival and growth of developing sympathetic and sensory neurons. We have examined NGF receptor gene expression in these neurons after NGF administration. Northern blot and in situ hybridization analyses demonstrated that NGF given systemically to neonatal rats increased levels of NGF receptor mRNA in sympathetic neurons within the superior cervical ganglion. This increase was accompanied by a differential regulation of genes associated with neurotransmitter phenotype; tyrosine hydroxylase mRNA was increased, but neuropeptide Y mRNA was not. NGF receptor mRNA levels were also increased in L4-L5 dorsal root ganglia, although this mRNA was not expressed uniformly in sensory neurons of control or NGF-treated animals. Levels of T alpha 1 alpha-tubulin mRNA, a marker of neuronal growth, also increased. In contrast to developing neurons, systemic NGF did not increase NGF receptor mRNA in nonneuronal cells of the sciatic nerve. To determine if NGF regulated NGF receptor gene expression at the transcriptional level, we examined PC12 cells. NGF treatment for 6 h increased NGF receptor mRNA fourfold; this increase was inhibited by cycloheximide. Nuclear run-off transcription assays demonstrated that the increase in steady-state NGF receptor mRNA levels was mediated at the transcriptional level. In contrast, although NGF treatment increased steady-state tyrosine hydroxylase mRNA levels, this effect was not blocked by cycloheximide, and was not due to increased transcription. These data raise the possibility that transcriptional regulation of NGF receptor gene expression by target-derived NGF could be a molecular mechanism for potentiating NGF's effects on neurons during developmental periods of neuronal competition and cell death.