This project includes several studies on the regulation of biosynthesis of protein precursors of neuropeptides in the mammalian nervous system. One study concerns the regulation of the gene coding for neuropeptide Y (NPY), an important neurotransmitter in the central and peripheral nervous systems. We have studied the effects of hormones and second-messenger systems on the abundance of NPY precursor mRNA in clonal PC12 rat pheochromocytoma cells. Large increases in NPY mRNA levels were elicited by the synergistic actions of cyclic AMP and phorbol esters, which activate protein kinases A and C, respectively. Furthermore, glucocorticoids and the calcium ionophore A23187 potentiate this effect, resulting in NPY mRNA levels up to 200 times the control. Treatment of PC12 cells for 1-6 days with nerve growth factor (NGF) also elevates NPY mRNA 40-100-fold as a result of both transcriptional activation and increased mRNA stability. The action of NGF is profoundly inhibited by glucocorticoids, illustrating an important antagonism between NGF and glucocorticoids in the regulation of neural gene expression. A second project concerns regulation of transcription of the gene coding for proenkephalin, the precursor of the opioid peptides methionine- and leucine-enkephalin. Glucocorticoids and cAMP synergistically increase the transcription of the proenkephalin gene and the abundance of proenkephalin mRNA in C6 rat glioma cells. Glucocorticoids exert a permissive effect on proenkephalin gene transcription by prolonging the transcriptional stimulation elicited by cAMP elevation. Sequences near and within the rat NPY gene are examined for a glucocorticoid regulation element by the transient expression of fusion genes, but none was found within 2500 bases upstream from the promoter. These studies shed light on the control of biosynthesis of peptides that are important in autonomic regulation, pain perception, and cognitive function.
