This project includes several studies on the genetic 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 found that increases in NPY mRNA levels and NPY gene transcription rates in PC12 rat pheochromocytoma cells are elicited by nerve growth factor (NGF) or by synergistic activation of the cyclic AMP and protein kinase C second-messenger systems. The action of NGF is profoundly inhibited by glucocorticoids, illustrating an important antagonism between NGF and glucocorticoids in neural development. We are attempting to identify the sequences near or within the rat NPY gene that are required for these responses and also for appropriate cell type-specific regulation. Other studies concern the regulation of transcription of the gene coding for proenkephalin, the precursor of the enkephalin opioid peptides. The mechanisms of the positive regulation by cyclic AMP, glucocorticoids, and cell type are under investigation in C6 rat glioma cells and other cell lines. The proenkephalin gene was found to be expressed in ONR/D quail retina neuronal cells, a promising model of retinal amacrine neurons. The morphogen retinoic acid was found to increase proenkephalin gene expression in this line. The transactivator protein tax(1) of the human T-cell leukemia virus I (HTLV-l) was found to activate the proenkephalin gene promoter in cultured cell systems. This suggests that proenkephalin biosynthesis may be activated in some cells of patients afflicted with diseases caused by HTLV-I infection, such as tropical spastic paraparesis. The mechanism of this activation is under investigation. These studies will hopefully shed light on the control of biosynthesis of peptides that are important in autonomic regu- lation, pain perception, and cognitive function.
