Retinoic acid regulation of the VIP and PACAP autocrine ligand and receptor system in human neuroblastoma cell lines.

Abstract

Neuroendocrine tumors, neuroblastoma in particular, commonly express the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide (PACAP) and their receptors. Retinoic acid (RA) has been shown to induce differentiation of neuroblastoma cell lines, possibly by augmenting or interfering with neuropeptide autocrine loops. We sought to determine which receptor gene subtypes are expressed in selected human neuroblastoma cell lines (SH-SY5Y, IMR-32, and LA-N-5), and the effect of RA on the VIP/PACAP ligand/receptor system. Expression of both PACAP1 and VIP1/PACAP2 receptor genes was detected by Northern analysis, which characteristically encode Type I (PACAP-preferring), and Type II (bivalent VIP/PACAP) receptors, respectively. Binding experiments carried out on IMR-32 cells, using 125I VIP and 125I PACAP-27 as tracers, corroborated that both receptor subtypes were expressed. In contrast to RA upregulation of VIP binding (confirmed here in IMR-32 cells), levels of both receptor mRNAs were reduced after RA treatment. VIP mRNA in each cell line was increased by RA, whereas PACAP mRNA, detected in IMR-32 cells only, was reduced. The studies indicate that several components of the VIP/PACAP autocrine system are regulated in neuroblastoma cell lines during RA differentiation.