Pituitary adenylate cyclase-activating polypeptide stimulates secretoneurin release and secretogranin II gene transcription in bovine adrenochromaffin cells through multiple signaling pathways and increased binding of pre-existing activator protein-1-like-transcription factors

Secretoneurin (SN) is a novel bioactive peptide that derives from the neuro endocrine protein secretogranin II (SgII) by proteolytic processing and par ticipates in neuro-immune communication. The neuropeptide pituitary adenyla te cyclase-activating polypeptide (PACAP-38) dose-dependently stimulates (E C50 similar to 3 nM) SN release (up to 4-fold) and SgII gene expression (up to 60-fold) in cultured bovine adrenochromaffin cells. The effect of PACAP on both SN secretion and SgII mRNA levels is rapid and long lasting. We an alyzed in this neuroendocrine cell model the transduction pathways involved in both SN secretion and SgII gene transcription in response to PACAP. The cytosolic calcium chelator BAPTA-AM and the nonselective calcium channel a ntagonist NiCl2, equally inhibited both secretion of the peptide and transc ription of the SgII gene, indicating a major contribution of calcium influx in PACAP-induced SN biosynthesis and release in chromaffin cells. Inhibiti on of protein kinase A (PKA) or C (PKC) also reduced PACAP-evoked SN releas e but did not alter the stimulatory effect of PACAP on SgII mRNA levels. Co nversely, application of mitogen-activated protein kinase inhibitors suppre ssed PACAP-induced SgII gene expression. The effect of PACAP on SgII mRNA l evels, like the effect of the PKC stimulator 12-O-tetradecanoylphorbol-13-a cetate (TPA), was not affected by cycloheximide, whereas the effects of the PKA stimulator forskolin or cell-depolarization by high K+ were significan tly reduced by the protein synthesis inhibitor. PACAP and TPA both increase d the binding activity of the SgII cAMP response element to trans-acting fa ctors present in chromaffin cell nuclear extracts, which are recognized by antibodies to activator protein-1-related proteins. These data indicate tha t SN biosynthesis is regulated by PACAP in chromaffin cells through complex signaling cascades, suggesting that SN may play a function during trans-sy naptic stimulation of the adrenal medulla.