High conservation of upstream regulatory sequences on the human and mouse vasoactive intestinal peptide (VIP) genes

Targeting vasoactive intestinal peptide-mediated signaling enhances response to immune checkpoint therapy in pancreatic ductal adenocarcinoma

A paucity of effector T cells within tumors renders pancreatic ductal adenocarcinoma (PDAC) resistant to immune checkpoint therapies. While several under-development approaches target immune-suppressive cells in the tumor microenvironment, there is less focus on improving T cell function. Here we show that inhibiting vasoactive intestinal peptide receptor (VIP-R) signaling enhances anti-tumor immunity in murine PDAC models. In silico data mining and immunohistochemistry analysis of primary tumors indicate overexpression of the neuropeptide vasoactive intestinal peptide (VIP) in human PDAC tumors. Elevated VIP levels are also present in PDAC patient plasma and supernatants of cultured PDAC cells. Furthermore, T cells up-regulate VIP receptors after activation, identifying the VIP signaling pathway as a potential target to enhance T cell function. In mouse PDAC models, VIP-R antagonist peptides synergize with anti-PD-1 antibody treatment in improving T cell recruitment into the tumors, activation of tumor-antigen-specific T cells, and inhibition of T cell exhaustion. In contrast to the limited single-agent activity of anti-PD1 antibodies or VIP-R antagonist peptides, combining both therapies eliminate tumors in up to 40% of animals. Furthermore, tumor-free mice resist tumor re-challenge, indicating anti-cancer immunological memory generation. VIP-R signaling thus represents a tumor-protective immune-modulatory pathway that is targetable in PDAC.

VIPhyb, an antagonist of vasoactive intestinal peptide receptor, enhances cellular antiviral immunity in murine cytomegalovirus infected mice

Vasoactive intestinal peptide (VIP) is a neuropeptide hormone that suppresses Th1-mediated cellular immunity. We previously reported that VIP-knockout (VIP-KO) mice have enhanced cellular immune responses and increased survival following murine cytomegalovirus (mCMV) infection in C57BL/6 mice. In this study, we tested whether treatment with a VIP receptor antagonistic peptide protects C57BL/6 and BALB/c mice from mCMV-infection. One week of daily subcutaneous injections of VIPhyb was non-toxic and did not alter frequencies of immune cell subsets in non-infected mice. VIPhyb administration to mCMV-infected C57BL/6 and BALB/c mice markedly enhanced survival, viral clearance, and reduced liver and lung pathology compared with saline-treated controls. The numbers of effector/memory CD8+ T-cells and mature NK cells were increased in VIPhyb-treated mice compared with PBS-treated groups. Pharmacological blockade of VIP-receptor binding or genetic blockade of VIP-signaling prevented the up-regulation of PD-L1 and PD-1 expression on DC and activated CD8⁺ T-cells, respectively, in mCMV-infected mice, and enhanced CD80, CD86, and MHC-II expression on conventional and plasmacytoid DC. VIPhyb-treatment increased type-I IFN synthesis, numbers of IFN-γ- and TNF-α-expressing NK cells and T-cells, and the numbers of mCMV-M45 epitope-peptide-MHC-I tetramer CD8⁺ T-cells following mCMV infection. VIP-treatment lowered the percentage of Treg cells in spleens compared with PBS-treated WT mice following mCMV infection, while significantly decreasing levels of serum VEGF induced by mCMV-infection. The mice in all treated groups exhibited similar levels of anti-mCMV antibody titers. Short-term administration of a VIP-receptor antagonist represents a novel approach to enhance innate and adaptive cellular immunity in a murine model of CMV infection.

The significance of vasoactive intestinal peptide in immunomodulation

First identified by Said and Mutt some 30 years ago, the vasoactive intestinal peptide (VIP) was originally isolated as a vasodilator peptide. Subsequently, its biochemistry was elucidated, and within the 1st decade, their signature features as a neuropeptide became consolidated. It did not take long for these insights to permeate the field of immunology, out of which surprising new attributes for VIP were found in the last years. VIP is rapidly transforming into something more than a mere hormone. In evolving scientifically from a hormone to a novel agent for modifying immune function and possibly a cytokine-like molecule, VIP research has engaged many physiologists, molecular biologists, biochemists, endocrinologists, and pharmacologists and it is a paradigm to explore mutual interactions between neural and neuroendocrine links in health and disease. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as exciting new candidates for therapeutic intervention and drug development.

Calcium signal-mediated expression of the vasoactive intestinal polypeptide gene and its small contribution to activity-dependent survival of mouse cerebellar granule cells

We have demonstrated previously in primary cultures of mouse cerebellar granule cells (CGCs) that endogenously synthesized pituitary adenylate cyclase-activating polypeptide (PACAP) contributes at least in part to the activity-dependent survival of CGCs (Tabuchi et al. [2001] Neurosci. Res. 39:85-93). In this study, we have demonstrated that expression of vasoactive intestinal polypeptide (VIP), a member of the same VIP/secretin/glucagon family as PACAP, was activated markedly by Ca(2+) influx through L-type voltage-dependent Ca(2+) channels (L-VDCCs), which could be induced under the depolarizing condition induced by high concentration of potassium (K(+)) in the medium. The activation of VIP mRNA expression, different from that of PACAP, was dependent partly on de novo protein synthesis. On the other hand, mRNA expression of secretin and PACAP/VIP receptors (PAC(1), VPAC(1), and VPAC(2)) was not activated by the Ca(2+) influx; rather, PAC(1) mRNA expression was reduced. Exogenously added VIP prevented apoptosis of CGCs under nondepolarizing conditions, the effect of which was mediated specifically through the VPAC(1) receptor. Furthermore, the survival of CGCs under depolarizing conditions could be mediated partly through VPAC(1), the contribution of which was much less than that of PAC(1). These findings indicate that PACAP and VIP genes are coordinately activated by the Ca(2+) signals in CGCs, but the contribution of VIP to the activity-dependent survival of CGCs is quite small.

Disrupted circadian rhythms in VIP- and PHI-deficient mice

The related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) are expressed at high levels in the neurons of the suprachiasmatic nucleus (SCN), but their function in the regulation of circadian rhythms is unknown. To study the role of these peptides on the circadian system in vivo, a new mouse model was developed in which both VIP and PHI genes were disrupted by homologous recombination. In a light-dark cycle, these mice exhibited diurnal rhythms in activity which were largely indistinguishable from wild-type controls. In constant darkness, the VIP/PHI-deficient mice exhibited pronounced abnormalities in their circadian system. The activity patterns started approximately 8 h earlier than predicted by the previous light cycle. In addition, lack of VIP/PHI led to a shortened free-running period and a loss of the coherence and precision of the circadian locomotor activity rhythm. In about one-quarter of VIP/PHI mice examined, the wheel-running rhythm became arrhythmic after several weeks in constant darkness. Another striking example of these deficits is seen in the split-activity patterns expressed by the mutant mice when they were exposed to a skeleton photoperiod. In addition, the VIP/PHI-deficient mice exhibited deficits in the response of their circadian system to light. Electrophysiological analysis indicates that VIP enhances inhibitory synaptic transmission within the SCN of wild-type and VIP/PHI-deficient mice. Together, the observations suggest that VIP/PHI peptides are critically involved in both the generation of circadian oscillations as well as the normal synchronization of these rhythms to light.

Lymphocyte regulation of neuropeptide gene expression after neuronal injury

The neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase-activating peptide (PACAP) are induced strongly in neurons after several types of injury, and exhibit neuroprotective actions in vitro and in vivo. It is thought that changes in expression of neuropeptides and other molecules in injured neurons are mediated by new factors produced in Schwann and immune cells at the injury site, a loss of target-derived factors, or a combination of mediators. To begin to determine the role of the inflammatory mediators, we investigated axotomy-induced changes in VIP and PACAP gene expression in the facial motor nucleus in severe combined immunodeficient (SCID) mice, and in mice with targeted mutations in specific cytokine genes. In normal mice, VIP and PACAP mRNA was induced strongly in facial motor neurons 4 days after axotomy. The increase in PACAP mRNA was blocked selectively in SCID mice, indicating that mechanisms responsible for VIP and PACAP gene induction are not identical. The loss of PACAP gene expression in SCID mice after axotomy was fully reversed by an infusion of normal splenocytes, suggesting that PACAP mRNA induction requires inflammatory mediators. PACAP and VIP mRNA inductions, however, were maintained in mice lacking leukemia inhibitory factor (LIF) and interleukin-6 (IL-6), and in mice lacking both receptors for tumor necrosis factor alpha (TNFalpha). The data suggest that an inflammatory response, most likely involving T lymphocytes, is necessary for the axotomy-induced increase in PACAP but not in VIP. LIF, IL-6, and TNFalpha, however, are not required for this response to injury.

Synchronization and phase-resetting by glutamate of an immortalized SCN cell line

SCN 2.2 cultures were stably transfected with luciferase reporter constructs driven by Ca(2+)/cAMP response element, E-box, or vasoactive intestinal peptide promoter to probe the circadian properties of this clock cell line. SCN 2.2 reporter lines displayed approximately 24-h rhythms of transcriptional activation after serum-shock. Serum-shocked cultures pulsed with glutamate exhibited phase-gated induction of phospho-CREB and of VIP, CRE, and E-box promoter activity. Glutamate-induced CRE promoter activity displayed restricted sensitivity to inhibitors of nitric oxide synthase and cGMP-dependent protein kinase. The temporal pattern of these sensitivities paralleled those of the SCN to light and glutamate during the night. Taken together, our data indicate that serum-shock can synchronize the circadian clock of SCN 2.2 cells to a state consistent with the day/night transition and, thus, establishes a temporal context for this cell line.

VIP gene transcription is regulated by far upstream enhancer and repressor elements

SK-N-SH human neuroblastoma subclones differ widely in basal and second messenger induction of the gene encoding the neuropeptide vasoactive intestinal peptide (VIP). These differences were recapitulated by a chimeric gene which consisted of 5.2 kb of the human VIP gene 5' flanking sequence fused to a reporter. Subsequent gene deletion experiments revealed several regulatory regions on the gene, including a 645-bp sequence located approximately 4.0 upstream from the transcription start site. Here we examined this upstream region in detail. Inhibitory sequences were found to be present on each end of the 645-bp fragment. When removed, basal transcription increased more than 50-fold. Subsequent deletion/mutation analysis showed that the 213-bp fragment contained at least two enhancer elements. One of these was localized to an AT-rich 42-bp sequence shown by others to bind Oct proteins in neuroblastoma cells, while the other corresponded to a composite AP-1/ets element. In addition to these enhancers, a 28-bp sequence on the 213-bp fragment with no apparent homology to known silencers inhibited transcription. The studies provide molecular details of a complex regulatory region on the VIP gene that is likely to be used to finely tune the level of gene transcription in vivo.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Identification of a novel gp130-responsive site in the vasoactive intestinal peptide cytokine response element

The neuropoietic cytokine ciliary neurotrophic factor (CNTF) potently induces transcription of the vasoactive intestinal peptide (VIP) gene through a 180-base pair (bp) cytokine response element (CyRE) in the VIP promoter. We have previously shown that CNTF induction of STAT and AP-1 protein binding within the CyRE is necessary to mediate CNTF induction of VIP gene transcription. We now show that a third, previously uncharacterized site at the 3'-end of the CyRE is also critical to CNTF induction of CyRE transcription. A 4-bp mutation in this 3'-region reduced CNTF-mediated induction of transcription approximately 80%. Whereas mutations in both the STAT and AP-1 sites substantially reduced CNTF induction of transcription, mutations in these sites together with the novel 3'-site completely abolished the ability of CNTF to induce CyRE-mediated transcription. Gel shift analysis indicated that a complex in neuroblastoma cells bound specifically to this 3'-site. This complex was not altered by CNTF treatment. Mutations in an 8-bp sequence (TTACTGGA) eliminated binding of this protein complex and markedly reduced transcriptional activation of the CyRE by CNTF. Thus, we have identified a protein complex binding to a novel DNA sequence that is necessary for full CNTF induction of VIP gene transcription.

Targeting of embryonic and postnatal autonomic and enteric neurons with a vasoactive intestinal peptide transgene

The neuropeptide vasoactive intestinal peptide (VIP) is expressed in several distinct sites in the CNS, in cholinergic and enteric ganglia, and in a small subpopulation of neurons within sympathetic ganglia. Previous studies on the human VIP gene indicate that transcription in neural crest-derived neuroblastoma and pheochromocytoma cell lines is controlled in part by multiple regulatory elements located along 4.5 kb of upstream 5' flanking sequence. In the current studies, transgenic mice were created with a chimeric gene consisting of 16.5 kb of the mouse VIP gene fused to the beta-galactosidase reporter. In situ hybridization analysis in adult mice indicated that reporter gene expression was correctly targeted to neurons in the esophagus, stomach, small intestine, and colon. No expression was observed in the brain, including regions that contain abundant VIP-expressing cells, such as the thalamus, amygdala, cerebral cortex, hippocampus, and suprachiasmatic nucleus. Analysis of transgene expression in neonatal and embryonic day 13.5 mice revealed a near perfect correlation between VIP and beta-galactosidase gene expression in cranial cholinergic ganglia and the superior cervical ganglia, and lack of transgene expression in sensory ganglia and in nonneuronal tissue. Potential ectopic transgene expression was observed in neonates, in the cerebellar external granule layer and in a small subpopulation of neurons in the olfactory epithelium. We conclude that the 16.5 kb of VIP gene used in these studies contains sequences sufficient for directing expression specifically to VIP neurons in the PNS, and that sequences located elsewhere on the gene are required for proper CNS expression. The VIP gene sequences used here should be capable of targeting other gene products to specific populations of embryonic and adult peripheral neurons without causing significant expression in the CNS.

Two separate cis-active elements of the vasoactive intestinal peptide gene mediate constitutive and inducible transcription by binding different sets of AP-1 proteins

Vasoactive intestinal peptide (VIP) gene expression is highly restricted throughout the neuroaxis and regulated by extracellular factors that activate tyrosine- or serine/threonine-directed protein kinase pathways. Cytokine, cyclic AMP, and tissue-specific response elements on the VIP gene have been characterized. Those mediating responsiveness to protein kinase C have not. The endogenous VIP gene and a 5.2-kilobase pair (kb) VIP-luciferase reporter gene, are up-regulated by phorbol 12-myristate 13-acetate (PMA) in SK-N-SH neuroblastoma cells. PMA stimulation was abolished by deletion of sequences at -1.37 to -1.28 or -1.28 to -0.904 kb, but not by removal of the single phorbol ester response element (TRE; TGACTCA) located at -2.25 kb. Mutation of sites at -1.32 or -1.20 that mediate neurotrophin responsiveness of the VIP gene (Symes, A., Lewis, S., Corpus, L., Rajan, P., Hyman, S. E., and Fink, J. S. (1994) Mol. Endocrinol. 8, 1750-1763) each reduced PMA induction in SK-N-SH cells by >50%, and double mutation abolished it. The two mutations also reduced basal VIP reporter gene transcription in SH-EP neuroblastoma cells expressing VIP constitutively. Both cis-active elements bound pre-existing AP-1 proteins in SH-EP- or PMA-stimulated SK-N-SH cell nuclear extracts. The AP-1 complex at both sites contained a Fos-related protein with c-Jun in SH-EP cells and c-Fos with a Jun-related protein in SK-N-SH cells. Recruitment of combinatorially distinct AP-1 complexes to these elements may underlie cell type-specific regulation of the VIP gene.

Cis-regulatory elements controlling basal and inducible VIP gene transcription

The cis-acting elements of the VIP gene important for basal and stimulated transcription have been studied by transfection of VIP-reporter gene constructs into distinct human neuroblastoma cell lines in which VIP transcription is constitutively high, or can be induced to high levels by protein kinase stimulation. The 5.2 kb flanking sequence of the VIP gene conferring correct basal and inducible VIP gene expression onto a reporter gene in these cell lines was systematically deleted to define its minimal components. A 425-bp fragment (-4656 to -4231) fused to the proximal 1.55 kb of the VIP promoter-enhancer was absolutely required for cell-specific basal and inducible transcription. Four additional components of the VIP gene were required for full cell-specific expression driven by the 425 bp TSE (region A). Sequences from -1.55 to -1.37 (region B), -1.37 to -1.28 (region C), -1.28 to -.094 (region D), and the CRE-containing proximal 94 bp (region E) were deleted in various combinations to demonstrate the specific contributions of each region to correct basal and inducible VIP gene expression. Deletion of region B, or mutational inactivation of the CRE in region E, resulted in constructs with low transcriptional activity in VIP-expressing cell lines. Deletion of regions B and C together resulted in a gain of transcriptional activity, but without cell specificity. All five domains of the VIP gene were also required for cell-specific induction of VIP gene expression with phorbol ester. Gelshift analysis of putative regulatory sequences in regions A-D suggests that both ubiquitous and neuron-specific trans-acting proteins participate in VIP gene regulation.

Five discrete cis-active domains direct cell type-specific transcription of the vasoactive intestinal peptide (VIP) gene

Vasoactive intestinal peptide (VIP) is a neuromodulator expressed with great anatomical specificity throughout the nervous system. Cell-specific expression of the VIP gene is mediated by a tissue specifier element (TSE) located within a 2.7-kilobase (kb) region between -5.2 and -2.5 kb upstream from the transcription start site, and requires an intact promoter proximal VIP-CRE (cyclic AMP-responsive element) (Hahm, S. H., and Eiden, L. E. (1997) J. Neurochem. 67, 1872-1881). We now report that the TSE comprises a 425-base pair domain located between -4.7 and -4.2 kb containing two AT-rich octamer-like sequences. The 425-base pair TSE is sufficient to provide full cell-specific regulation of the VIP gene, when fused to the 5' proximal 1.55 kb of the VIP gene. Mutational analysis and gel shift assays of these octamer-like sequences indicate that the binding of proteins related to the ubiquitously expressed POU-homeodomain proteins Oct-1 and/or Oct-2 to these octamer-like sequences plays a central role for the function of the TSE. The TSE interacts with three additional discrete domains besides the cAMP response element, which are located within the proximal 1.55 kb of the VIP gene, to provide cell-specific expression. An upstream domain from -1.55 to -1.37 kb contains E-boxes and MEF2-like motifs, and deletion of this domain results in complete abrogation of cell-specific transcriptional activity. The region from -1.37 to -1. 28 kb contains a STAT motif, and further removal of this domain allows the upstream TSE to act as an enhancer in both SH-EP and HeLa cells. The sequence from -1.28 to -0.9 kb containing a non-canonical AP-1 binding sequence (Symes, A., Gearan, T., Eby, J., and Fink, J. S. (1997) J. Biol. Chem. 272, 9648-9654), is absolutely required for TSE-dependent cellspecific expression of the VIP gene. Thus, five discrete domains of the VIP gene provide a combination of enhancer and repressor activities, each completely contingent on VIP gene context, that together result in cell-specific transcription of the VIP gene.

Upstream sequencing and functional characterization of the human cholinergic gene locus

The 5' flanking region of the human VAChT gene was sequenced to approx 5350 bases upstream of the initiating methionine codon of the VAChT open reading frame (orf). The 5' flanks of the human and rat cholinergic gene loci were compared to identify regions of local sequence conservation, and therefore of potential regulatory importance. Several discrete domains of high homology, including a cluster of far-upstream cis-active consensus motifs, a neuronally restrictive silencer element consensus sequence, and additional conserved sequences within the putative nerve growth factor response domain of the locus, were identified. The probable start of transcription of the VAChT gene was deduced from mapping of sequences of rat and human VAChT cDNAs onto the 5' flanking regions of the human and rat cholinergic gene loci. The actual utilization of a putative 5' VAChT exon in rat central nervous system (CNS) tissue was assessed by in situ hybridization histochemistry. RNA transcripts containing both VAChT and ChAT protein-coding sequences were abundant in spinal cord motoneurons, sympathetic preganglionic cells, basal forebrain, striatum, and cranial motor nuclei. R-exon-containing transcripts could be detected only at low levels in these cell groups, implying that most transcription of VAChT proceeds from a promoter downstream of the R-exon. To assess the structural requirements for expression of the VAChT gene without bias regarding the actual start of transcription, a 5' fragment of the human gene corresponding to approximately 3 kb of sequence extending upstream from within the presumed 5' untranslated region of VAChT itself was fused to a luciferase-encoding reporter and transfected into VAChT-expressing and nonexpressing human and rat cell lines. This portion of the VAChT gene provided strong promoter expression in both cholinergic and noncholinergic cell lines. Deletion of the putative neuronally restrictive silencer element (NRSE) resulted in enhanced transcription in all cell lines. Lack of differential expression of VAChT transcription in VAChT-expressing vs non-VAChT-expressing cell lines suggested that additional enhancer elements controlling cell-specific expression of the VAChT gene exist further upstream in the cholinergic locus 5' flank. Conservation of potential cis-active elements within a 1.4 kb sequence immediately upstream of the NRSE in both rat and human cholinergic gene loci suggests that this domain is required for cholinergic-specific regulation of VAChT and ChAT gene transcription.

Regulation of VIP gene expression in general. Human lung cancer cells in particular

Vasoactive intestinal peptide (VIP) is a neuropeptide of multiple functions affecting development and aging. In cancer, for example, VIP was found to function as an autocrine growth factor in nonsmall cell lung cancer (NSCLC) promotion. Furthermore, a VIP hybrid antagonist (neurotensin(6-11)-VIP(7-28)) was found to inhibit NSCLC growth. In the present study, the expression of VIP mRNA was studied using human lung cancer cells. RNA prepared from 19 cell lines was fractionated by 1% agarose gel electrophoresis followed by blotting onto nitrocellulose membranes and hybridization to a VIP-specific RNA probe. VIP mRNA was detected in about 50% of the cell lines tested with a greater abundance in NSCLC. Cultures of the NSCLC NCI-H727 cell line were treated with forskolin, an activator of cyclic AMP (cAMP), and separately with the tumor promoter phorbol 12-myristate 13-acetate (PMA). Northern blot hybridization analysis showed an increase in VIP mRNA levels after 4 h treatment with 50 microM forskolin. Incubation with PMA also showed a significant increase in the levels of VIP transcripts. Cultures were then incubated with PMA in the presence of actinomycin D, a transcription blocker. Results indicated that PMA treatment may induce both VIP mRNA synthesis as well as VIP mRNA stabilization, and suggested a 4-5 h half-life for the VIP mRNA in the absence of PMA. Thus, lung cancer tumor proliferation may be regulated, in part, at the level of VIP gene expression.