Abstract
Recent studies have shown that cAMP analogs can induce expression of prepro (pp) orphanin FA (OFQ)/nociceptin-related gene products in NS20Y mouse neuroblastoma cells (Saito et al. [1996]. J Biol Chem 271, 15615-15622). Additionally, exposure of NS20Y cells to cAMP analogs promoted neurite outgrowth and large dense-core vesicle formation. Even though an OFQ-like precursor (called 27K) was identified in NS20Y cell extracts, no secretion of OFQ-related peptides was detected. We have used reversed-phase high-performance liquid chromatography combined with a specific radioimmunoassay for OFQ1-17 to determine if NS20Y cells secrete ppOFQ-derived peptides when stimulated by the cAMP analog ctp-cAMP. We found that NS20Y cells secreted abundant amounts of OFQ-derived products when stimulated by cAMP analogs. We also have determined that secretion of OFQ peptides was both time and concentration dependent and reversible on removal of cAMP analogs from the culture medium. In addition, the opioid agonist D-Pen2-D-Pen5-enkephalin inhibited forskolin-stimulated OFQ peptide secretion. Further, the synthetic glucocorticoid dexamethasone virtually abolished ctp-cAMP-stimulated OFQ peptide secretion. These results suggest that the biosynthesis, processing, and secretion of the OFQ neuropeptide transmitter system can be modulated through intracellular cAMP levels and that these functions are regulated by opioids and molecules involved in mediating the stress response. The NS20Y cell system will be extremely valuable for studying the regulation of OFQ-derived peptides by a variety of intra-cellular and extracellular signaling pathways.
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