The autocrine function of vasoactive intestinal peptide on human neuroblastoma cell growth and differentiation

Uncommon reasons of the digestive tract-related paraneoplastic syndromes in children with neuroblastic tumors: three case reports

Aim of the study

presentation of the uncommon paraneoplastic syndromes related to the gastrointestinal tract that may occur in children with neuroblastic tumors and their impact on the disease course.

Material and methods

Retrospective analysis of three cases of patients mainly with digestive tract-related symptoms, who were originally admitted to the gastroenterology department from 2013 to 2016 and were finally diagnosed with neuroblastic tumors.

Results

The clinical data analysis showed that the symptoms from gastrointestinal tract were dominant in analyzed subjects. The first case is a girl with weight loss, bloating and severe diarrhea, admitted to the hospital in a state of dehydration. The laboratory tests revealed severe hypokalemia. Finally, vasoactive intestinal peptide (VIP) secreting ganglioneuroblastoma was diagnosed and effective surgery was performed. The second case was also a girl who suffered from the incidents of watery diarrhea and flatulence. The tumor was detected by computerized tomography scan. The 3^rd stage of ganglioneuroblastoma was diagnosed. The patient required chemotherapy, radiotherapy and surgery treatment. The third child was a boy, hospitalized due to abdominal pain, constipation and weakness. During the diagnostic process, the 4^th stage of neuroblastoma was recognized. The chemotherapy, surgery, radiotherapy and immunotherapy were applied.

Conclusions

In children with common abdominal symptoms as chronic flatulence, diarrhea or severe constipation of unknown etiology, the neuroblastic tumors should be considered.

The vasoactive intestinal peptide-receptor system is involved in human glioblastoma cell migration

Glioblastoma multiforme (GBM) is the most aggressive form of brain tumor in adults. This cancer has an infiltrative nature and the median survival of patients is about one year. Vasoactive intestinal peptide (VIP) belongs to a structurally related family of polypeptides and is a major regulatory factor in the central and peripheral nervous systems. VIP regulates proliferation of astrocytes and of numerous cancer cell lines and modulates migration in prostatic and colonic cancer cell lines. Little is known about the involvement of VIP and its receptors (VIP-receptor system) in proliferation or migration of GBM cells. The effects of VIP, PACAP and of synthetic VIP antagonists were tested in two human GBM cell lines, M059K and M059J, established from two different parts of a single tumor. In these cells, the data revealed that the VIP-receptor system did not affect proliferation but controlled cell migration. Indeed, in M059K cells which express components of the VIP receptor system, the VIP receptor antagonists and a PACAP antibody enhanced migration. The VIP receptor antagonists increased generation of typical migration-associated processes: filopodia and lamellipodia, and activation of Rac1 and Cdc42 GTPases. Reciprocally, in M059J cells which poorly express the VIP-receptor system, treatments with the agonists VIP and PACAP resulted in decreased cell migration. Furthermore, the peptides appeared to act through a subclass of binding sites displaying an uncommon very high affinity for these ligands. Taken together, these observations suggest that components of the VIP-receptor system negatively regulate cell migration, thus showing potential anti-oncogenic properties.

Characterization of novel splice variants of the PAC1 receptor in human neuroblastoma cells: consequences for signaling by VIP and PACAP

Expression of VPAC and PAC1 receptor isoforms was determined in six neuroblastoma cell lines as well as in human embryonic and adult brain using reverse transcriptase PCR and quantitative PCR. PAC1 receptor splice variants missing a 21 amino acid sequence in the amino terminal domain were found to be the major receptor variants in the neuroblastoma cell lines and also were highly expressed in embryonic brain compared to adult brain. In four of the neuroblastoma cell lines, VIP and PACAP stimulated cyclic AMP production with different potencies and levels of maximal stimulation. High potency and greatest maximal stimulation of cyclic AMP for each peptide were recorded in SH-SY5Y cells, indicating the presence of high affinity VIP and PACAP receptors. Further characterization of specific VPAC and PAC1 receptor isoforms was carried out in the SH-SY5Y cell line, where along with known PAC1 receptor splice variants and the VPAC2 receptor, a number of novel PAC1 receptor splice variants were identified. The comparatively low level expression of the VPAC2 receptor along with the poor responsiveness of SH-SY5Y cells to the VPAC2 receptor-specific agonist Ro 25-1553 indicated that this receptor did not contribute significantly to the observed VIP responses. When the individual PAC1 receptor isoforms were expressed in COS 7 cells, the ability of VIP to activate cyclic AMP production was increased more than 50-fold at the majority of the PAC1 receptor variants lacking the 21 amino acid amino terminal domain sequence compared to those with the complete domain. Smaller changes were seen in the potency of PACAP-38. Similar trends were seen with inositol phosphate responses, where in each case agonist potencies were lower than for cyclic AMP production. The results of this study show that the combination of different amino terminal and intracellular loop 3 splicing variants in the PAC1 receptor dictates the ability of agonists, particularly VIP, to activate signaling pathways. VIP has considerably greater potency at most PAC1 receptors with the short amino terminal domain, and these therefore may mediate physiological effects of both VIP and PACAP. Furthermore, there may be a phenotypic switch in the expression of different PAC1 receptor amino terminal splice variants between embryonic and mature nervous system, indicating that regulation of this event may have an important role in VIP/PACAP function, particularly in the developing nervous system.

Vasoactive intestinal peptide-induced neurite remodeling in human neuroblastoma SH-SY5Y cells implicates the Cdc42 GTPase and is independent of Ras-ERK pathway

Vasoactive intestinal peptide (VIP) is known to regulate proliferation or differentiation in normal and tumoral cells. SH-SY5Y is a differentiated cell subclone derived from the SK-N-SH human neuroblastoma cell line and possess all the components for an autocrine action of VIP. In the present study, we investigated the morphological changes and intracellular signaling pathways occurring upon VIP treatment of SH-SY5Y cells. VIP induced an early remodeling of cell projections: a branched neurite network spread out and prominent varicosities developed along neurites. Although activated by VIP, the Ras/ERK pathway was not required for the remodeling process. In contrast, pull-down experiments revealed a strong Cdc42 activation by VIP while expression of a dominant-negative Cdc42 prevented the VIP-induced neurite changes, suggesting an important role for this small GTPase in the process. These data provide the first evidence for a regulation of the activity of Rho family GTPases by VIP and bring new insights in the signaling pathways implicated in neurite remodeling process induced by VIP in neuroblastoma cells.

The somatostatin analogue octreotide inhibits neuroblastoma growth in vivo

Neuroblastoma, a neural crest-derived childhood tumor of the sympathetic nervous system, may in some cases differentiate to a benign ganglioneuroma or regress due to apoptosis. However, the majority of neuroblastomas are diagnosed as metastatic tumors with a poor prognosis despite intensive multimodal therapy. The neuropeptide somatostatin (SOM) has been shown to inhibit neuroblastoma growth and induce apoptosis in vitro. Therapeutic effects of SOM analogues are dependent on tumor expression of high-affinity receptors. In the present study, human neuroblastoma SH-SY5Y cells were grown as xenografts in nude rats. In vivo SOM receptor expression in the xenografts was identified using scintigraphy with 111In-pentetreotide. Rats were randomized to treatment with the long-acting SOM analogue octreotide (10 microg s.c. every 12 h), 13-cis-retinoic acid (4 mg orally every 24 h), or vasoactive intestinal peptide (40 microg s.c. every 24 h) and compared with controls. Tumor volume was assessed every second day and tumor weight after 10-12 d. Octreotide treatment inhibited neuroblastoma growth significantly with reduced tumor volumes at 10 and 12 d compared with untreated controls (mean 3.56 and 4.24 versus 6.48 and 8.01 mL, respectively; p < 0.01). Also, tumor weights after 10-12 d were reduced in octreotide-treated animals (n = 8, median weight 2.90 g, range 1.67-5.57 g) compared with untreated rats (n = 14, 7.54 g, 1.65-10.82 g, p = 0.005). Serum IGF-I decreased significantly over time both in rats treated with octreotide and in untreated controls. It is concluded that treatment with the SOM analogue octreotide may significantly decrease neuroblastoma tumor growth in vivo. Further studies are warranted to establish the role of SOM analogues in the treatment of children with unfavorable neuroblastoma.

Differential effects of peptide histidine isoleucine (PHI) and related peptides on stimulation and suppression of neuroblastoma cell proliferation. A novel VIP-independent action of PHI via MAP kinase

The growth rate of rodent embryonic neuroblasts and human neuroblastoma cell lines is regulated in part by autocrine or paracrine actions of neuropeptides of the family that includes vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), and pituitary adenylate cyclase-activating peptide (PACAP). These peptides act via seven transmembrane G-protein-linked receptors coupled to cAMP elevation, phospholipase C activation, intracellular Ca2+ release, and/or of mitogen-activated protein (MAP) kinase activation. Here we investigated the action of these peptides on the mouse neuroblastoma cell line Neuro2a. PHI and VIP inhibited proliferation at concentrations as low as 10(-13) M and 10(-10) M, respectively. In contrast, PACAP action was biphasic, with stimulation occurring at subnanomolar doses and inhibition at higher doses. Peptide actions were studied further by measuring cAMP and ERK1/2 MAP kinase activity and by assessing 3H-thymidine incorporation in conjunction with a panel of signal transduction pathways inhibitors. The data obtained indicated that the PHI-inhibitory and PACAP-stimulatory activities were mediated by corresponding changes in activity of the MAP kinase pathway and independent of protein kinase A (PKA) or protein kinase C (PKC). In contrast, the inhibitory actions of VIP and PACAP were specifically blocked by antagonists of PKA. Northern blot analysis revealed gene expression for only the PACAP-preferring (PAC1) receptor. However, binding experiments using 125I-labeled PACAP27, PHI, and VIP, demonstrated the presence of PACAP-preferring sites, bivalent VIP/PACAP sites, and PHI-binding sites that did not interact with VIP. The studies demonstrate potent regulatory actions of PACAP, PHI, and VIP on neuroblastoma cell proliferation which appear to be mediated by multiple subsets of receptors which differentially couple to MAP kinase and PKA signaling pathways.

Differential expression and function of PACAP and VIP receptors in four human colonic adenocarcinoma cell lines

Human colonic adenocarcinoma cell lines have conserved several features of the native tissue. Among these is the expression of cell surface receptors for hormones and neurotransmitters that may be involved in the regulation of proliferation and differentiation processes in these cancer cells. Here, we confirm that high-affinity binding sites for the Vasoactive Intestinal Polypeptide (VIP) and for the VIP analogue Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP), were expressed in 4 human colonic adenocarcinoma cell lines, HT29, SW403, DLD-1 and Caco-2, that spontaneously displayed variable phenotypic properties in culture. We demonstrated that after long-term treatments, VIP and PACAP significantly reduced cell proliferation in the 4 cell lines and modulated intracellular cAMP and cGMP levels. Furthermore, conspicuous differences were observed from one cell type to another concerning expression of the receptor subsets or the effects of the neuropeptides on cell growth and on cyclic nucleotides production.

Somatostatin in neuroblastoma and ganglioneuroma

Neuroblastoma, a childhood tumour of the sympathetic nervous system, may in some cases differentiate to a benign ganglioneuroma or regress due to apoptosis. Somatostatin may inhibit neuroblastoma growth and induce apoptosis in vitro and was therefore investigated. Using a radioimmunoassay, we found that all ganglioneuromas contained high somatostatin concentrations (> 16 pmol/g), significantly higher than neuroblastomas (n = 117, median 2.8 pmol/g), healthy adrenals, Wilms' tumours, phaeochromocytomas and other neuroendocrine tumours (P < 0.001). Neuroblastomas contained more somatostatin than control tumours (P < 0.001-0.05). Neuroblastomas amplified for the MYCN oncogene contained less somatostatin than non-amplified tumours (1.2 pmol/g versus 4.0 pmol/g, respectively; P = 0.026). In a clinically unfavourable neuroblastoma subset (age > 12 months, stage 3 or 4) 16 children with high concentrations of somatostatin in primary tumours had a better prognosis than 23 with low somatostatin (46.7% versus 0% survival at 5 years, P < 0.005). Scintigraphy using 111In-pentetreotide identified tumours expressing high-affinity somatostatin receptors in vivo. However, no significant correlation was found between somatostatin receptor expression and peptide content in 15 tumours. Similarly, human SH-SY5Y neuroblastoma xenografts grown in nude rats showed low somatostatin concentrations, but were positive for somatostatin receptor scintigraphy. Treatment of these rats with the somatostatin analogue octreotide seemed to upregulate in vivo receptor expression of somatostatin and vasoactive intestinal peptide more effectively than 13-cis retinoic acid. In conclusion, somatostatin in neuroblastoma is associated with differentiation to benign ganglioneuromas in vivo and favourable outcome in advanced tumours. Furthermore, somatostatin receptor scintigraphy may identify tumours with high-affinity receptors in children that might benefit from targeted therapy using synthetic somatostatin analogues.

Proadrenomedullin N-terminal 20 peptide (PAMP) inhibits proliferation of human neuroblastoma TGW cells

We investigated the effects of proadrenomedullin N-terminal 20 peptide (PAMP) and adrenomedullin (AM) on the growth of human neuroblastoma TGW cells. Both PAMP and AM inhibited growth and DNA synthesis in neuroblastoma cells. Calcitonin gene-related peptide (CGRP)(8-37), an antagonist to CGRP, abolished the inhibitory effect of AM on growth and DNA synthesis of neuroblastoma cells but did not affect that of PAMP. AM(22-52), an antagonist to AM, also reversed the effect of AM. On the other hand, pertussis toxin (PTX) and omega-conotoxin GIVA blocked the effect of PAMP alone. Thus, PAMP inhibits the growth of neuroblastoma cells by inhibiting N-type Ca2+ channels through PTX-sensitive G protein-coupled receptors, which is different mechanism of AM-induced inhibition of the cell growth.

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

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.

Vasoactive intestinal polypeptide-secreting tumours: biology and therapy

VIP-secreting tumours are rare, but they produce a dramatic clinical picture, the most prominent feature being profuse, watery diarrhoea and hypokalaemia. VIPomas are malignant and require sophisticated diagnostic and localization techniques in order to identify their presence. Delays in diagnosis are the rule rather than the exception. Improvements in the diagnosis of VIPomas appear to result in an increase in resectability rates. A definitive diagnosis is aided by the determination of plasma VIP concentrations through the use of sensitive radioimmunoassays. With heightened awareness of this syndrome, increasing numbers of patients can be identified and more effective treatments developed for the refractory and recurrent tumours.

Differential expression of VIP/PACAP receptor genes in breast, intestinal, and pancreatic cell lines

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) are structurally-related neuropeptides that function as trophic factors in addition to their more classical roles as neurotransmitters. Binding and molecular cloning studies have shown that their actions are mediated by receptors encoded by at least three different genes. VIP binding has been demonstrated on many tumor types, and radiolabeled VIP has recently been used as a novel method to localize intestinal tumors in humans and their sites of metastasis. To determine the receptor subtype and level of gene expression, we screened breast, intestinal, and pancreatic, cell lines by Northern blot analysis. Breast lines expressed VIP/PACAP1 receptor mRNA levels comparable to intestinal lines, in agreement with the studies showing particularly high VIP binding in these tumors and their derived cell lines. Pancreatic cell lines expressed mRNA for several receptor types. This extends the potential utility of VIP and PACAP in the localization of tumors, and because VIP and PACAP may regulate the growth rate of some tumors by autocrine or other mechanisms, the identification of receptor subtypes on these lines sets the stage for studies in which the activity of these individual receptors in growth and other processes can be investigated.

Vasoactive intestinal peptide gene expression in the rat pheochromocytoma cell line PC12

Vasoactive intestinal peptide (VIP) gene expression was analyzed in PC12 cells. VIP mRNA was detected in PC12 cells treated with VIP or forskolin whereas no VIP mRNA was detected in the untreated cells. The induction of the VIP mRNA was enhanced by the simultaneous treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). PC12 cells stimulated with forskolin plus TPA released immunoreactive VIP. Sephadex G-50 column chromatography revealed that the immunoreactive VIP secreted from PC12 cells is comprised of multiple forms, one of which was indistinguishable from the authentic VIP. PC12 cells supported an efficient transcription from the human VIP gene promoter in a cell-specific as well as cAMP-dependent manner. These results definitely demonstrated the expression of the VIP gene in PC12 cells. VIP biosynthesis may be positively regulated by VIP in an autocrine fashion in PC12 cells.

Somatostatin and vasoactive intestinal peptide (VIP) in neuroblastoma and ganglioneuroma: chromatographic characterisation and release during surgery

Neuroblastomas and ganglioneuromas frequently produce somatostatin (SOM) and vasoactive intestinal peptide (VIP), and elevated concentrations in tumour tissue are associated with favourable outcome. Both somatostatin and VIP have been shown to have an autocrine effect on tumour growth and differentiation in vitro, and VIP may cause clinical symptoms when released systemically. Using gel-permeation chromatography and specific radioimmunoassays, we further characterised somatostatin-like immunoreactivity (SOM-LI) and VIP-like immunoreactivity (VIP-LI) in neuroblastoma and ganglioneuroma tumour tissue. The major part of SOM-LI and VIP-LI in both neuroblastoma and ganglioneuroma represents the biologically active forms SOM-28, SOM-14 and VIP-2, respectively. 21 children with neuroblastoma and ganglioneuroma were monitored with serial plasma samples during surgery. In 8 children with measurable concentrations of SOM-LI, all showed increased concentrations during tumour manipulation (P = 0.004) that subsequently decreased below preoperative levels in all but one case (P = 0.06). The only child presenting with diarrhoea showed the highest preoperative plasma VIP-LI in the study (54 pmol/l). 2 children with increased concentrations of VIP-LI preoperatively showed a rapid decrease after surgical tumour removal. These findings indicate a systemic release from the tumours. It is concluded that plasma and tumour tissue from children with neuroblastoma and ganglioneuroma contain biologically active molecular forms of somatostatin and vasoactive intestinal peptide. These peptides may bear significance both for specific symptoms in certain patients as well as influencing tumour growth and differentiation in vivo.

A new vasoactive intestinal peptide antagonist discriminates VIP receptors on guinea pig trachea and human neuroblastoma cells

VIP is a widely distributed neuropeptide of 28 amino acids, whose central part is proposed to be an amphiphilic alpha-helix. In order to gain an understanding of the effect of this alpha helix on receptor binding and stimulation, a human VIP analog has been designed in which the residues 12 to 19 were replaced by a spacer of the same length, (gamma-aminobutyryl)2. This peptide altered neither the basal guinea pig tracheal smooth muscle tonus nor the VIP-induced relaxation. Conversely, the VIP analog was found to displace VIP from its binding sites on LA-N-2 human neuroblastoma cells (VIP IC50: 5.4 nM; VIP analog IC50: 52.2 nM) and to inhibit the VIP-induced cyclic AMP production of 58 +/- 15% at 1 microM and 95 +/- 2% at 10 microM. It seems that the alpha helix structure might only play the role of a spacer holding the important residues, at the N- and C-ends, respectively, at an appropriate distance. In the VIP analog structure, the (gamma-aminobutyryl)2 chain introduced in place of the alpha helix plays the role of adequate spacer to bind the LA-N-2 receptors but probably does not induce the active conformation for receptor stimulation. The lack of VIP analog effects on the tracheal receptors related to relaxation argues for a possible heterogeneity of VIP receptors on a pharmacological basis.