Neurotensin increases colonic motility

Dietary carbohydrate influences the colocalization pattern of Glucagon-like Peptide-1 with neurotensin in the chicken ileum

Glucagon-like peptide (GLP)-1 colocalizes with neurotensin (NT) in the same enteroendocrine cells (EECs) of the chicken ileum. The present study was designed to clarify the influence of dietary carbohydrate (CHO) on the colocalization pattern of GLP-1 with NT in the chicken distal ileum. Male White Leghorn chickens at 6 weeks of age (n = 15) were divided into three groups, a control and two experimental (low-CHO and CHO-free), with five chickens in each, and fed control or experimental diets for 7 d. Distal ileum was collected from each bird as a tissue sample and subjected to double immunofluorescence staining to detect GLP-1 and NT. Three types of EEC, GLP-1+/NT+, GLP-1+/NT- and GLP-1-/NT+, were demonstrated in the chicken ileum. GLP-1+/NT+ cells in the control group had a spindle-like shape with a long cytoplasmic process, but those in the experimental groups were round and lacked a cytoplasmic process. The ratio of GLP-1+/NT+ cells was significantly decreased in the two experimental groups compared with that in the control group. The ratio of GLP-1+/NT+ cells was significantly lower than those of GLP-1+/NT- and GLP-1-/NT+ cells in the two experimental groups. Most cells that were immunoreactive for GLP-1 and NT antisera lacked signals of proglucagon (PG) and NT precursor (NTP) mRNA in the experimental groups. The number of EECs expressing PG and NTP mRNA signals showed tendencies for decreases with a reduction of dietary CHO level. These findings suggest that dietary CHO could be a significant regulator of the pattern of colocalization pattern of GLP-1 with NT in the chicken ileum.

Potential use of radiolabelled neurotensin in PET imaging and therapy of patients with pancreatic cancer

Pancreatic cancer is the fourth leading cause of cancer-related death in both men and women. Neurotensin receptors are overexpressed in different malignancies, above all pancreatic cancer. On the other hand, neurotensin receptor expression in inflammation is quite low. This fact can probably solve the most important problem of F-FDG PET imaging - distinguishing malignant and inflammatory processes. The first therapeutic injection of radiolabelled neurotensin in human with pancreatic cancer has been successfully performed. Animal experiments are also very close to the first in human injection of radiolabelled neurotensin for diagnostic purposes. The purpose of this article is to provide an overview of radiolabelled neurotensin analogues that can be used in imaging and therapy in patients with pancreatic ductal adenocarcinoma.

Dietary Protein Level Influences on Neurotensin-immunoreactive Cells in the Chicken Ileum

Neurotensin is secreted from intestinal N cells in response to the food ingestion. Influences of different dietary protein levels on neurotensin-immunoreactive cells in the chicken ileum were examined by using immunohistochemical and morphometrical techniques. The results showed that dietary protein had an obvious influence on neurotensin-immunoreactive cells in the chicken ileum. Four experimental groups were used, with dietary crude protein (CP) levels of 18% (control), 9%, 4.5% and 0%. Enteroendocrine cells showing neurotensin-immunoreactivity were located in crypts and villous epithelium in all groups. Most of the neurotensin-immunoreactive cells in the villous epithelium showed pyramidal or spindle-like shape with a long cytoplasmic process reaching the intestinal lumen, but cells with round or oval shape were found in the CP4.5% and 0% groups. Frequencies of occurrence of neurotensin-immunoreactive cells in the CP18%, 9%, 4.5% and 0% groups were 42.4±3.3, 36.6±2.2, 30.8±2.6 and 25.4±3.8 (cell count per mucosal area: cells/mm², mean±SD), respectively. There were significant differences in neurotensin-immunoreactive cell frequency between the control and lower CP level, 4.5% and 0%, groups. A significant correlation was found between frequency of occurrence of neurotensin-immunoreactive cells and daily protein intake. These results indicate that ingested protein is likely to be a potential signal for neurotensin production and secretion of N cells in the chicken ileum.

The role of Neurotensin and its receptors in non-gastrointestinal cancers: a review

Background

Neurotensin, originally isolated in 1973 has both endocrine and neuromodulator activity and acts through its three main receptors. Their role in promoting tumour cell proliferation, migration, DNA synthesis has been studied in a wide range of cancers. Expression of Neurotensin and its receptors has also been correlated to prognosis and prediction to treatment.

Main body

The effects of NT are mediated through mitogen-activated protein kinases, epidermal growth factor receptors and phosphatidylinositol-3 kinases amongst others. This review is a comprehensive summary of the molecular pathways by which Neurotensin and its receptors act in cancer cells.

Conclusion

Identifying the role of Neurotensin in the underlying molecular mechanisms in various cancers can give way to developing new agnostic drugs and personalizing treatment according to the genomic structure of various cancers.

Serum Neurotensin in Human Pancreatic Cancer

The role of neurotensin as a physiologic regulator of exocrine pancreatic secretion is known, but the hormone has only recently been recognized as important mitogen in vitro for human cancer cells. The aim of this study was to evaluate the variations of serum levels of neurotensin in pancreatic cancer. We studied 58 patients: 13 control subjects, 20 pancreatic cancer patients, 11 chronic pancreatitis patients, and 14 cases of extrapancreatic disease. No differences were found between serum values of neurotensin in pancreatic cancer and control subjects or extrapancreatic disease. Significantly higher values were detected in chronic pancreatitis than in pancreatic cancer patients ( P <0.04). In chronic pancreatitis patients, the serum levels of neurotensin were correlated with serum amylase ( r = 0.95, P <0.01). Lower levels of neurotensin were found in stage IV pancreatic cancer than in stages I-II ( t = 1.82, P <0.04) and in grade II than in grade I ( t = 2.21, P <0.02). Significant correlations were found between serum levels of neurotensin and two indices of nutrition: albumin ( r = 0.60, P <0.05) and the percentage reduction in body weight (Z = 2.20, P <0.02). No correlations were found between serum levels of the hormone and size of the neoplasm or the survival of patients. We can conclude that the serum variations of neurotensin do not seem to be related to the progression of human pancreatic cancer. The variation of serum levels of the hormone may be linked to a poor nutritional status of the patient.

Glucagon-like peptide-1 is co-localized with neurotensin in the chicken ileum

Glucagon-like peptide (GLP)-1 and neurotensin (NT) are distributed throughout the chicken ileum. Here, we attempt to determine if GLP-1 and NT co-localize in the chicken ileum by using immunofluorescence, immunocytochemistry and in situ hybridization techniques. Three types of enteroendocrine cells, GLP-1⁺/NT⁺, GLP-1⁺/NT^- and GLP-1^-/NT⁺ cells, were detected in the mucosal epithelium by the double immunofluorescence method. The ratio of GLP-1⁺/NT⁺ cells at the crypts in the distal ileum was significantly higher than that in the proximal ileum. The ratios of the three cell types were similar along the crypt-villous axis in the proximal ileum but the percentage of GLP-1⁺/NT⁺ cells significantly decreased at the middle part of villi relative to crypts and the bottom part of villi in the distal ileum. Enteroendocrine cells that were immunoreactive to both GLP-1 and NT peptides and showed both proglucagon and NT precursor mRNA signals were found in the crypts of the distal ileum but not in the villous epithelium. The results from performing an immunocytochemical method with colloidal gold indicated that the GLP-1 content within GLP-1⁺/NT⁺ cell secretory granules decreased stepwise from the crypt to the middle part of the villus but the NT content in these granules increased in this direction. These findings reveal that the cells producing both GLP-1 and NT are mainly localized in the crypts of the chicken ileum but these endocrine cells specialize in NT-producing cells at the villous epithelium of the distal ileum.

Epigenetic silencing of NTSR1 is associated with lateral and noninvasive growth of colorectal tumors

Our aim was to identify DNA methylation changes associated with the growth pattern and invasiveness of colorectal cancers (CRCs). Comparison of the methylation statuses of large (≥20 mm in diameter along the colonic surface) noninvasive tumors (NTs) and small (<20 mm in diameter along the colonic surface) invasive tumors (ITs) using CpG island microarray analysis showed neurotensin receptor 1 (NTSR1) to be hypermethylated in large NTs. Quantitative bisulfite pyrosequencing revealed that NTSR1 is frequently methylated in colorectal tumors, with large NTs exhibiting the highest methylation levels. The higher NTSR1 methylation levels were associated with better prognoses. By contrast, NTSR1 copy number gains were most frequent among small ITs. Methylation of NTSR1 was associated with the gene's silencing in CRC cell lines, whereas ectopic expression of NTSR1 promoted proliferation and invasion by CRC cells. Analysis of primary tumors composed of adenomatous and malignant portions revealed that NTSR1 is frequently methylated in the adenomatous portion, while methylation levels are generally lower in the cancerous portions. These results suggest that NTSR1 methylation is associated with lateral and noninvasive growth of colorectal tumors, while low levels of methylation may contribute to the malignant potential through activation of NTSR1. Our data also indicate that NTSR1 methylation may be a prognostic biomarker in CRC.

Neurotensin Changes Propulsive Activity into a Segmental Motor Pattern in the Rat Colon

BACKGROUND/AIMS

Neurotensin is a gut-brain peptide with both inhibitory and excitatory actions on the colonic musculature; our objective was to understand the implications of this for motor patterns occurring in the intact colon of the rat.

METHODS

The effects of neurotensin with concentrations ranging from 0.1-100 nM were studied in the intact rat colon in vitro, by investigating spatio-temporal maps created from video recordings of colonic motility before and after neurotensin.

RESULTS

Low concentration of neurotensin (0.1-1 nM) inhibited propagating long distance contractions and rhythmic propagating motor complexes; in its place a slow propagating rhythmic segmental motor pattern developed. The neurotensin receptor 1 antagonist SR-48692 prevented the development of the segmental motor pattern. Higher concentrations of neurotensin (10 nM and 100 nM) were capable of restoring long distance contraction activity and inhibiting the segmental activity. The slow propagating segmental contraction showed a rhythmic contraction-- relaxation cycle at the slow wave frequency originating from the interstitial cells of Cajal associated with the myenteric plexus pacemaker. High concentrations given without prior additions of low concentrations did not evoke the segmental motor pattern. These actions occurred when neurotensin was given in the bath solution or intraluminally. The segmental motor pattern evoked by neurotensin was inhibited by the neural conduction blocker lidocaine.

CONCLUSIONS

Neurotensin (0.1-1 nM) inhibits the dominant propulsive motor patterns of the colon and a distinct motor pattern of rhythmic slow propagating segmental contractions develops. This motor pattern has the hallmarks of haustral boundary contractions.

Sexually dimorphic characteristics of the small intestine and colon of prepubescent C57BL/6 mice

BACKGROUND

There is increasing appreciation for sexually dimorphic effects, but the molecular mechanisms underlying these effects are only partially understood. In the present study, we explored transcriptomics and epigenetic differences in the small intestine and colon of prepubescent male and female mice. In addition, the microbiota composition of the colonic luminal content has been examined.

METHODS

At postnatal day 14, male and female C57BL/6 mice were sacrificed and the small intestine, colon and content of luminal colon were isolated. Gene expression of both segments of the intestine was analysed by microarray analysis. DNA methylation of the promoter regions of selected sexually dimorphic genes was examined by pyrosequencing. Composition of the microbiota was explored by deep sequencing.

RESULTS

Sexually dimorphic genes were observed in both segments of the intestine of 2-week-old mouse pups, with a stronger effect in the small intestine. Amongst the total of 349 genes displaying a sexually dimorphic effect in the small intestine and/or colon, several candidates exhibited a previously established function in the intestine (i.e. Nts, Nucb2, Alox5ap and Retnlγ). In addition, differential expression of genes linked to intestinal bowel disease (i.e. Ccr3, Ccl11 and Tnfr) and colorectal cancer development (i.e. Wt1 and Mmp25) was observed between males and females. Amongst the genes displaying significant sexually dimorphic expression, nine genes were histone-modifying enzymes, suggesting that epigenetic mechanisms might be a potential underlying regulatory mechanism. However, our results reveal no significant changes in DNA methylation of analysed CpGs within the selected differentially expressed genes. With respect to the bacterial community composition in the colon, a dominant effect of litter origin was found but no significant sex effect was detected. However, a sex effect on the dominance of specific taxa was observed.

CONCLUSIONS

This study reveals molecular dissimilarities between males and females in the small intestine and colon of prepubescent mice, which might underlie differences in physiological functioning and in disease predisposition in the two sexes.

Molecular characterization of structure and tissue distribution of chicken neurotensin receptor

Neurotensin, a tridecapeptide, is distributed in a wide range of tissues and exhibits multiple functions through its receptors. Hitherto molecular characterization of the neurotensin receptor has been reported in mammalian, amphibian, and fish species but not in avian species. In this study, we cloned the cDNA encoding chicken neurotensin receptor from the duodenum and characterized its primary structure, biological activity and distribution in the gastrointestinal tract. The cDNA encoded a protein consisting of 399 amino acids that had significant overall sequence homology to other vertebrate neurotensin receptor 1 with higher extent in the seven transmembrane domains. Chicken neurotensin increased intracellular Ca(2+) concentrations in human embryonic kidney 293 cells transiently expressing the chicken neurotensin receptor 1. Real-time PCR analysis showed that chicken neurotensin receptor 1 mRNA is expressed throughout the gastrointestinal tract with markedly higher level in the colon/rectum. These results indicate that the chicken neurotensin receptor 1 is involved in gastrointestinal functions through an intracellular signaling pathway accompanied by an increase in Ca(2+) levels.

Insulin-like growth factor-1 receptor transactivation modulates the inflammatory and proliferative responses of neurotensin in human colonic epithelial cells

Neurotensin (NT) is a gastrointestinal neuropeptide that modulates intestinal inflammation and healing by binding to its high-affinity receptor NTR1. The dual role of NT in inflammation and healing is demonstrated in models of colitis induced by Clostridium difficile toxin A and dextran sulfate sodium, respectively, and involves NF-κB-dependent IL-8 expression and EGF receptor-mediated MAPK activation in human colonocytes. However, the detailed signaling pathways involved in these responses remain to be elucidated. We report here that NT/NTR1 coupling in human colonic epithelial NCM460 cells activates tyrosine phosphorylation of the insulin-like growth factor-1 receptor (IGF-1R) in a time- and dose-dependent manner. NT also rapidly induces Src tyrosine phosphorylation, whereas pretreatment of cells with the Src inhibitor PP2 before NT exposure decreases NT-induced IGF-1R phosphorylation. In addition, inhibition of IGF-1R activation by either its specific antagonist AG1024 or siRNA against IGF-1 significantly reduces NT-induced IL-8 expression and NF-κB-dependent reporter gene expression. Pretreatment with AG1024 also inhibits Akt activation and apoptosis induced by NT. Silencing of Akt expression by siRNA also substantially attenuates NT-induced IL-8 promoter activity and NF-κB-dependent reporter gene expression. This is the first report to indicate that NT transactivates IGF-1R and that this response is linked to Akt phosphorylation and NF-κB activation, contributing to both pro-inflammatory and tissue repair signaling pathways in response to NT in colonic epithelial cells. We propose that IGF-1R activation represents a previously unrecognized key pathway involved in the mechanisms by which NT and NTR1 modulate colonic inflammation and inflammatory bowel disease.

Characterization of promoter elements regulating the expression of the human neurotensin/neuromedin N gene

Expression of the gene encoding neurotensin/neuromedin N (NT/N) is mostly limited to the brain and specialized enteroendocrine N cells in the distal small intestine. We have identified key regulatory elements in the promoter region that are involved in human NT/N (hNT/N) gene expression in the novel human endocrine cell line, BON, which resembles intestinal N cells in several important aspects including NT/N precursor protein processing, ratios of different NT/N mRNA isoforms, and high levels of constitutive expression of the NT/N gene. In this study, we demonstrated multiple cis-regulatory elements including a proximal region containing a cAMP-responsive element (CRE)/AP-1-like element that binds both the AP-1 and CRE-binding protein (CREB)/ATF proteins (c-Jun, ATF-1, ATF-2, JunD, and CREB). Similar to the rat NT/N gene, this region is critical for constitutive hNT/N gene expression. Moreover, we identified a novel region that binds the orphan hormone receptor, NR2F2. We have demonstrated that the C terminus of NR2F2 strongly represses hNT/N transcription, whereas an N-terminal domain antagonizes this repressive effect. Regulation of NT/N expression by NR2F2 may have important consequences for lipid metabolism. We speculate that a complex interplay between the proximal CRE/AP-1-like motif and NR2F2 binding region exists to regulate hNT/N expression, which is critical for the high level of constitutive expression of NT/N in enteroendocrine cells. Finally, the BON cell line provides a unique model to characterize the factors regulating expression of the hNT/N gene and to better understand the mechanisms responsible for terminal differentiation of the N cell lineage in the gut.

Complex actions of neurotensin in ascending and sigmoid colonic muscle: Involvement of enteric mediators

The brain-gut peptide neurotensin has complex effects on gastrointestinal smooth muscle. Our objective was to elucidate the mechanisms underlying neurotensin contractions in human colon. Discrete concentration response curves to neurotensin were obtained in strips of circular muscle and taenia coli from "normal" ascending and sigmoid colon segments, in the presence and absence of various pharmacological inhibitors. Potency of neurotensin in all regions was similar (pD(2) ~7). Atropine and the selective muscarinic receptor antagonists, methoctramine and darifenacin, had no effect on neurotensin contractions. In ascending colon circular muscle, responses were enhanced by indomethacin (indicating inhibitory prostaglandin mechanisms) and by tetrodotoxin (TTX), hexamethonium and L-NAME, suggesting nicotinic and enteric inhibitory neurotransmission, with involvement of nitric oxide. In sigmoid circular muscle, neurotensin responses were also enhanced by TTX and hexamethonium, but were attenuated in the presence of mepyramine, MEN10627 and CP99994, suggesting inhibitory neuronal mechanisms and involvement of histamine and tachykinins, respectively; L-NAME and the GABA(B) receptor antagonist, CGP36742, were without effect. The transcripts of NTS1 and NTS3 receptors, but not NTS2 receptors, were detected in sigmoid colon circular muscle and taenia coli. No age and gender differences in NTS1 mRNA expression were found. In conclusion, neurotensin contracts circular muscle strips from ascending and sigmoid regions of the human colon via direct (muscle) and indirect (neuronal/non-neuronal mechanisms). The enteric mediators influenced by neurotensin are regionally specific. In taenia coli strips from both ascending and sigmoid colon, neurotensin contractions were unchanged in the presence of inhibitors, suggesting direct actions only.

Role of neuropeptides in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. The mechanisms triggering the initial attack and relapses, however, are not well understood. In the past several years the enteric nervous system (ENS) has been implicated in the pathophysiology of IBD. Both the ENS and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides are defined as any peptide released from the nervous system that serves as an intercellular signaling molecule. Neuropeptides thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. This review focuses on the role of these neuropeptides in the pathophysiology of IBD and discusses the cell types and mechanisms involved in this process. The available evidence that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis will also be discussed.

Neurotensin stimulates expression of early growth response gene-1 and EGF receptor through MAP kinase activation in human colonic epithelial cells

Neurotensin (NT) is a highly expressed gastrointestinal (GI) neuropeptide, which modulates GI motility, secretion and cell growth as well as intestinal inflammation. Since EGF receptor is highly expressed in human colon cancer cells, we sought to examine whether NT stimulation contributes to the EGFR overexpression using nontransformed colonocyte NCM460 cells. The results show that NT treatment caused a significant increase in EGFR protein expression and gene transcription. Pretreatment with MAP kinase pathway inhibitor PD98059 blocked NT-induced EGFR expression. As the EGFR promoter has a functional Egr-1 site, previously shown to mediate its transcription in response to hypoxia, we examined the role of Egr-1 in the NT response. We first show that NT stimulated Egr-1 expression, which can be inhibited by PD98059. We also determined whether NT increases Egr-1 binding to its site within the EGFR promoter. The data indicate that NT enhanced the amount of Egr-1 binding to the EGFR Egr-1 site and that this binding was significantly decreased by PD98059. To verify that Egr-1 mediated NT-induced EGFR transcription, Egr-1 siRNA was used to knock down its expression. The data show that transfection of Egr-1 siRNA significantly inhibited NT-stimulated EGFR transcription. Together, our results suggest that NT can stimulate MAP kinase-mediated Egr-1 and EGFR gene expression in human colonocytes. Our results may be relevant to the mechanisms by which NT participates in the development of colon cancer.

Transient receptor potential channel TRPM8 agonists stimulate calcium influx and neurotensin secretion in neuroendocrine tumor cells

TRPM8 is a member of the melastatin-type transient receptor potential ion channel family. Activation by cold or by agonists (menthol, icilin) induces a transient rise in intracellular free calcium concentration ([Ca(2+)](i)). Our previous study demonstrated that Ca(2+)-permeable cation channels play a role in IGF-1-induced secretion of chromogranin A in human neuroendocrine tumor (NET) cell line BON [Mergler et al.: Neuroendocrinology 2006;82:87-102]. Here, we extend our earlier study by investigating the expression of TRPM8 and characterizing its impact on [Ca(2+)](i) and the secretion of neurotensin (NT). We identified TRPM8 expression in NET BON cells by RT-PCR, Western blotting and immunofluorescence staining. Icilin increased [Ca(2+)](i) in TRPM8-transfected human embryonic kidney cells (HEK293) but not in mock-transfected cells. Icilin and menthol induced Ca(2+) transients in BON cells as well as in primary NET cell cultures of two different pancreatic NETs as detected by single cell fluorescence imaging. Icilin increased non-selective cation channel currents in BON cells as detected by patch-clamp recordings. This activation was associated with increased NT secretion. Taken together, this study demonstrates for the first time the expression TRPM8 in NET cells and its role in regulating [Ca(2+)](i) and NT secretion. The regulation of NT secretion in NETs by TRPM8 may have a potential clinical implication in diagnosis or therapy.

Neurotensin phosphorylates GSK-3alpha/beta through the activation of PKC in human colon cancer cells

Neurotensin (NT), a gastrointestinal hormone, binds its receptor [neurotensin receptor (NTR)] to regulate the growth of normal and neoplastic intestinal cells; molecular mechanisms remain largely undefined. Glycogen synthase kinase-3 (GSK-3) regulates diverse cellular processes, including cell growth and apoptosis. Here, we show that NT induces the phosphorylation of GSK-3alpha/beta in the human colon cancer cell line HT29, HCT116, or SW480, which possesses high-affinity NTR. The effect of NT was blocked by inhibitors of protein kinase C (PKC), but not by inhibitors of MEK1 or phosphatidylinositol-3 kinase, suggesting a predominant role for PKC in GSK-3beta phosphorylation by NT. Pretreatment with Gö6976 (which inhibits PKCalpha and PKCbeta1) or downregulation of endogenous PKCalpha or PKCbeta1 blocked NT-mediated GSK-3beta (but not GSK-3alpha) phosphorylation. Moreover, a selective PKCbeta inhibitor, LY379196, reduced NT-mediated GSK-3beta (but not GSK-3alpha) phosphorylation, suggesting a role for PKCbeta1 in the NT-mediated phosphorylation of GSK-3beta and an undefined kinase in the NT-mediated phosphorylation of GSK-3alpha. Treatment with NT or the GSK-3 inhibitor SB216763 increased the expression of cyclin D1, a downstream effector protein of GSK-3 and a critical protein for the proliferation of various cells. Our results indicate that NT uses PKC-dependent pathways to modulate GSK-3, which may play a role in the NT regulation of intestinal cell growth.

Effects of NT on gastrointestinal motility and secretion, and role in intestinal inflammation

It is well established that interactions of neuropeptides with several cell types at various parts of the intestine are critically involved in intestinal pathophysiology. Among them, neurotensin has been identified as an important mediator in the development and progress of several gastrointestinal functions and disease conditions, exerting its effects by interacting with specific receptors that exert direct and indirect effects on nerves, epithelial cells, and cells of the immune and inflammatory systems. This review summarizes our recent understanding on the participation of neurotensin in the physiology and pathophysiology of the small and large intestine, and discusses various mechanisms that could be involved in these actions.

Neurotensin and growth of normal and neoplastic tissues

Neurotensin (NT) is a brain-gut tridecapeptide that functions as a neurotransmitter/neuromodulator in the central nervous system (CNS) and as an endocrine agent in the periphery. NT has numerous physiologic effects on multiple organs. This review will focus on the effects of NT as a trophic factor for normal and neoplastic tissues. In this regard, NT may act as an endocrine agent or, in some instances, in a paracrine and/or autocrine fashion. These effects appear to be mediated predominantly through the G protein-coupled high-affinity NT receptor. However, some of the trophic effects may also be through the other two receptor subtypes, particularly the NT receptor type 3, which belongs to a recently identified family of sorting receptors. The signaling pathways mediating the effects of NT are multiple but most appear to activate the ERK signaling pathway, which then activates downstream transcription factors, ultimately leading to proliferation. NT may be a useful agent to enhance the growth of normal tissues such as the small bowel mucosa during periods of gut disuse or disease and, finally, the selective targeting of NT receptor subtypes on certain cancers may offer a novel strategy in the armamentarium of cancer chemotherapeutics.

Neurotensin enhances nitric oxide generation via the JAK2-STAT1 pathway in murine macrophage Raw264.7 cells during costimulation with LPS and IFNgamma

Neurotensin has been known to be implicated in immune function, but its molecular mechanisms remain largely unclear. In this study, we report that neurotensin increased the intracellular calcium levels of murine macrophage Raw264.7 cells, and that this calcium increase disappeared in the presence of either U73122, a PLC inhibitor, or SR48692, a neurotensin receptor antagonist. Also, the production of nitric oxide (NO) during costimulation with lipopolysaccharide (LPS) and interferon gamma (IFNgamma) was potentiated by exposure to neurotensin, whereas neurotensin itself had no ability to induce NO generation. The up-regulation of NO generation was correlated with the induction of inducible NO synthase (iNOS). In addition, the activities of janus activated kinase 2 (JAK2)-signal transducer and activated transcription 1 (STAT1) and the migration capacity of macrophage were increased as the result of costimulation of neurotensin with LPS and IFNgamma, and pretreatment of either U73122 or SR48692 attenuated these phenomenon. Moreover, the neurotensin-mediated enhancement of NO generation and migration were observed in the wild-type JAK2 transfected cells, but not in the dominant negative JAK2 transfected cells. Together, these results demonstrate that neurotensin can effect enhancement in LPS/IFNgamma-induced NO generation and migration capacity, via the JAK2-STAT1 pathway.

Neurotensin stimulates interleukin-8 expression through modulation of I kappa B alpha phosphorylation and p65 transcriptional activity: involvement of protein kinase C alpha

Neurotensin (NT) is released in the gastrointestinal tract and participates in the pathophysiology of colonic inflammation. We have shown that NT mediates acute intestinal inflammation in vivo and stimulates nuclear factor-kappaB-dependent interleukin (IL)-8 expression in nontransformed human colonocytes in vitro. However, the exact mechanisms by which NT induces IL-8 expression have not been elucidated. In this study, we first show that NT stimulates IkappaBalpha phosphorylation and degradation and p65 phosphorylation and transcriptional activity. Inhibition of protein kinase C (PKC) activation significantly attenuates NT-induced IL-8 expression. This effect seems to be mediated through inhibition of IkappaBalpha phosphorylation and degradation and by p65 phosphorylation and transcriptional activity. We also show that intracellular calcium mobilization is necessary for NT-induced phosphorylation of IkappaBalpha and p65, suggesting that a conventional PKC is involved. Furthermore, transfection of a dominant-negative form of PKCalpha significantly reduces NT-induced IL-8 promoter activity. These results indicate that the conventional PKCalpha is an important mediator in the proinflammatory signaling pathway elicited by NT at the colonocyte level.

Myristoylated Alanine-rich C Kinase Substrate-mediated Neurotensin Release via Protein Kinase C-δ Downstream of the Rho/ROK Pathway

Myristoylated alanine-rich protein kinase C substrate (MARCKS) is a cellular substrate for protein kinase C (PKC). Recently, we have shown that PKC isoforms-alpha and -delta, as well as the Rho/Rho kinase (ROK) pathway, play a role in phorbol 12-myristate 13-acetate (PMA)-mediated secretion of the gut peptide neurotensin (NT) in the BON human endocrine cell line. Here, we demonstrate that activation of MARCKS protein is important for PMA- and bombesin (BBS)-mediated NT secretion in BON cells. Small interfering RNA (siRNA) to MARCKS significantly inhibited, whereas overexpression of wild-type MARCKS significantly increased PMA-mediated NT secretion. Endogenous MARCKS and green fluorescent protein-tagged wild-type MARCKS were translocated from membrane to cytosol upon PMA treatment, further confirming MARCKS activation. MARCKS phosphorylation was inhibited by PKC-delta siRNA, ROKalpha siRNA, and C3 toxin (a Rho protein inhibitor), suggesting that the PKC-delta and the Rho/ROK pathways are necessary for MARCKS activation. The phosphorylation of PKC-delta was inhibited by C3 toxin, demonstrating that the role of MARCKS in NT secretion was regulated by PKC-delta downstream of the Rho/ROK pathway. BON cell clones stably transfected with the receptor for gastrin releasing peptide, a physiologic stimulant of NT, and treated with BBS, the amphibian equivalent of gastrin releasing peptide, demonstrated a similar MARCKS phosphorylation as noted with PMA. BBS-mediated NT secretion was attenuated by MARCKS siRNA. Collectively, these findings provide evidence for novel signaling pathways, including the sequential regulation of MARCKS activity by Rho/ROK and PKC-delta proteins, in stimulated gut peptide secretion.

Inhibition of mitochondrial gene transcription suppresses neurotensin secretion in the human carcinoid cell line BON

Mitochondria, organelles essential for ATP production, play a central role in a number of cellular functions, including the regulation of insulin secretion. Neurotensin (NT), an important regulatory intestinal hormone, has been implicated in fatty acid translocation, gut motility and secretion, and intestinal cell growth; however, mechanisms regulating NT secretion have not been entirely defined. The purpose of this study was to determine the effect of inhibition of mitochondrial gene transcription on NT secretion. BON cells, a novel human carcinoid cell line that produces and secretes NT peptide and expresses the gene encoding NT (designated NT/N), were treated with ethidium bromide (EB; 0.05, 0.1, and 0.4 microg/ml), an inhibitor of DNA and RNA synthesis, or vehicle over a time course (1-4 days). Cells were then stimulated with either ACh (100 microM) or phorbol 12 myristate,13-acetate (PMA, 10 nM) for 30 min. Media and cells were extracted, and NT peptide measured by RIA. Treatment with EB had no effect on BON cell viability or cell cycle distribution over the 4-day course. In contrast, EB treatment produced a dose-dependent reduction of mitochondrial gene expression; however, NT/N gene expression was not altered. Mitochondrial inhibition by EB treatment suppressed NT secretion induced by ACh and PMA, both in a dose-dependent manner. EB-mediated inhibition of NT secretion and mitochondrial gene expression was reversed with removal of EB. Our results demonstrate that inhibition of mitochondrial gene transcription suppresses both ACh- and PMA-stimulated NT release. These findings are the first to demonstrate that mitochondrial function is important for agonist-mediated NT secretion.

Metalloproteinase-dependent transforming growth factor-alpha release mediates neurotensin-stimulated MAP kinase activation in human colonic epithelial cells

Expression of the neuropeptide neurotensin (NT) and its high affinity receptor (NTR1) is increased during the course of Clostridium difficile toxin A-induced acute colitis, and NTR1 antagonism attenuates the severity of toxin A-induced inflammation. We recently demonstrated in non-transformed human colonic epithelial NCM460 cells that NT treatment caused activation of a Ras-mediated MAP kinase pathway that significantly contributes to NT-induced interleukin-8 (IL-8) secretion. Here we used NCM460 cells, which normally express low levels of NTR1, and NCM460 cells stably transfected with NTR1 to identify the upstream signaling molecules involved in NT-NTR1-mediated MAP kinase activation. We found that inhibition of the epidermal growth factor receptor (EGFR) by either an EGFR neutralizing antibody or by its specific inhibitor AG1478 (0.2 microm) blocked NT-induced MAP kinase activation. Moreover, NT stimulated tyrosine phosphorylation of the EGFR, and pretreatment with a broad spectrum metalloproteinase inhibitor batimastat reduced NT-induced MAP kinase activation. Using neutralizing antibodies against the EGFR ligands EGF, heparin-binding-EGF, transforming growth factor-alpha (TGFalpha), or amphiregulin we have shown that only the anti-TGFalpha antibody significantly decreases NT-induced phosphorylation of EGFR and MAP kinases. Furthermore, inhibition of the EGF receptor by AG1478 significantly reduced NT-induced IL-8 promoter activity and IL-8 secretion. This is the first report demonstrating that NT binding to NTR1 transactivates the EGFR and that this response is linked to NT-mediated proinflammatory signaling. Our findings indicate that matrix metalloproteinase-mediated release of TGFalpha and subsequent EGFR transactivation triggers a NT-mediated MAP kinase pathway that leads to IL-8 gene expression in human colonic epithelial cells.

The Role of Protein Kinase D in Neurotensin Secretion Mediated by Protein Kinase C-α/-δ and Rho/Rho Kinase

Neurotensin (NT) is a gut peptide that plays an important role in gastrointestinal (GI) secretion, motility, and growth as well as the proliferation of NT receptor positive cancers. Secretion of NT is regulated by phorbol ester-sensitive protein kinase C (PKC) isoforms-alpha and -delta and may involve protein kinase D (PKD). The purpose of our present study was: (i) to define the role of PKD in NT release from BON endocrine cells and (ii) to delineate the upstream signaling mechanisms mediating this effect. Here, we demonstrate that small interfering RNA (siRNA) targeted against PKD dramatically inhibited both basal and PMA-stimulated NT secretion; NT release is significantly increased by overexpression of PKD. PKC-alpha and -delta siRNA attenuated PKD activity, whereas overexpression of PKC-alpha and -delta enhanced PKD activity. Rho kinase (ROK) siRNA significantly inhibited NT secretion, whereas overexpression of ROKalpha effectively increased NT release. Rho protein inhibitor C3 dramatically inhibited both NT secretion and PKD activity. In conclusion, our results demonstrate that PKD activation plays a central role in NT peptide secretion; upstream regulators of PKD include PKC-alpha and -delta and Rho/ROK. Importantly, our results identify novel signaling pathways, which culminate in gut peptide release.

SR 48692, a specific neurotensin receptor antagonist, has no effect on oesophageal motility in humans

BACKGROUND

The administration of exogenous neurotensin can reduce the lower oesophageal sphincter pressure, but it is unclear whether this effect is pharmacological or physiological.

AIM

A specific neurotensin receptor antagonist (SR 48692) was used to assess the effect of endogenous neurotensin on lower oesophageal sphincter function.

METHODS

Twenty-four healthy male subjects were included in a double-blind, placebo-controlled, randomized, cross-over study designed to determine the effects of two single doses (90 and 300 mg, preceded by a loading dose) of SR 48692 on the resting lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxations, primary oesophageal peristalsis and oesophageal acid exposure. Oesophageal pH and motility recordings were performed during 1 h of fasting and 3 h post-prandially. Plasma neurotensin-like immunoreactivity release was determined by radioimmunoassay.

RESULTS

During fasting, the lower oesophageal sphincter pressure, transient lower oesophageal sphincter relaxation rate and reflux episodes were similar with the two doses of SR 48692 and placebo. Meal ingestion induced a rise in plasma neurotensin-like immunoreactivity, a decrease in lower oesophageal sphincter pressure and an increase in both the transient lower oesophageal sphincter relaxation rate and the number of reflux episodes, which were not significantly modified by SR 48692. SR 48692 did not affect oesophageal primary peristalsis.

CONCLUSION

This study shows that SR 48692, a specific neurotensin 1 receptor antagonist, has no effect on oesophageal motility in humans.

Neurotensin stimulates IL-8 expression in human colonic epithelial cells through Rho GTPase-mediated NF-kappa B pathways

Neurotensin (NT), a neuropeptide highly expressed in the gastrointestinal tract, participates in the pathophysiology of intestinal inflammation. We recently showed that NT stimulates interleukin-8 (IL-8) expression in NCM460 nontransformed human colonic epithelial cells via both mitogen-activating protein kinase (MAPK)- and NF-kappaB-dependent pathways. However, the molecular mechanism by which NT induces expression of proinflammatory cytokines such as IL-8 has not been investigated. In this study we show that inhibition of endogenous Rho family proteins (RhoA, Rac1, and Cdc42) by their respective dominant negative mutants inhibits NT-induced IL-8 protein production and promoter activity. Western blot experiments demonstrated that NT strongly activated RhoA, Rac1, and Cdc42. Overexpression of the dominant negative mutants of RhoA, Rac1, and Cdc42 significantly inhibited NT-induced NF-kappaB-dependent reporter gene expression and NF-kappaB DNA binding activity. NT also stimulated p38 MAPK phosphorylation, and overexpression of dominant negative mutants of RhoA, Rac1, and Cdc42 did not significantly alter p38 and ERK1/2 phosphorylation in response to NT. Together, our findings indicate that NT-stimulated IL-8 expression is mediated via a Rho-dependent NF-kappaB-mediated pathway.

Phorbol ester-mediated neurotensin secretion is dependent on the PKC-alpha and -delta isoforms

Neurotensin (NT) plays an important role in gastrointestinal secretion, motility, and growth. The mechanisms regulating NT secretion are not entirely known. Our purpose was to define the role of the PKC signaling pathway in secretion of NT from BON cells, a human pancreatic carcinoid cell line that produces and secretes NT peptide. We demonstrated expression of all 11 PKC isoforms at varying levels in untreated BON cells. Expression of PKC-alpha, -beta2, -delta, and -mu isoforms was most pronounced. Immunofluorescent staining showed PKC-alpha and -mu expression throughout the cytoplasm and in the membrane. Also, significant fluorescence of PKC-delta was noted in the nucleus and cytoplasm. Treatment with PMA induced translocation of PKC-alpha, -delta, and -mu from cytosol to membrane. Activation of PKC-alpha, -delta, and -mu was further confirmed by kinase assays. Addition of PKC-alpha inhibitor Gö-6976 at a nanomolar concentration, other PKC inhibitors Gö-6983 and GF-109203X, or PKC-delta-specific inhibitor rottlerin significantly inhibited PMA-mediated NT release. Overexpression of either PKC-alpha or -delta increased PMA-mediated NT secretion compared with control cells. We demonstrated that PMA-mediated NT secretion in BON cells is associated with translocation and activation of PKC-alpha, -delta, and -mu. Furthermore, inhibition of PKC-alpha and -delta blocked PMA-stimulated NT secretion, suggesting a critical role for these isoforms in NT release.

Targeted inactivation of the neurotensin type 1 receptor reveals its role in body temperature control and feeding behavior but not in analgesia

Three subtypes of neurotensin receptor have been described, two members of the heptahelical transmembrane domain G protein-coupled receptor superfamily NT-1R and NT-2R, and NT-3R unrelated to this family. We have generated NT-1R deficient (NT-1R(-/-)) mice. NT-1R(-/-) mice were born at the expected Mendelian frequency without obvious abnormalities and they were fertile. The NT-induced analgesia on the writhing induced by phenyl-p-benzoquinone administration remained at wild-type levels in the NT-1R(-/-) mice demonstrating that the NT-1R is not implicated in the analgesic effect of NT in this test. The NT-1R(-/-) mice were hyperthermic; their body temperature was not affected by intracerebroventricular (i.c.v.) administration of NT, contrasting with the hypothermia induced in NT-1R(+/+) mice. NT-1R(-/-) mice showed a small significant increase in body weight compared to the NT-1R(+/+) congeners as early as 10 weeks after birth, correlated with a higher food intake. NT-1R(-/-) mice showed similar spontaneous locomotion to the control littermates, but did not respond to i.c.v. NT-induced hypolocomotion. I.c.v. injection of NT inhibited feeding in fasted wild-type mice, but had no effect on feeding of the NT-1R(-/-) mice. I.c.v. administration of the orexigenic neuropeptide Y (NPY) stimulated feeding to the same extent in both wild-type and NT-1R(-/-) mice. This analysis of NT-1R-deficient mice shows that the NT-1R does not play a role in NT-induced analgesia, but that it is clearly implicated in thermal and feeding regulation, weight control, and NT-induced hypolocomotion.

Signal transduction pathways mediating neurotensin-stimulated interleukin-8 expression in human colonocytes

Neurotensin (NT), a neuropeptide released in the gastrointestinal tract in response to several stimuli, is involved in the pathophysiology of colonic inflammation. However, the molecular mechanism(s) mediating this proinflammatory response remains unclear. We found that NCM460, non-transformed human colonocytes, express a functional high affinity NT receptor that mediates NT-induced Erk activation. By using NCM460 cells stably transfected with NTR1, we show that NTR1 activation leads to interleukin (IL)-8 secretion that is mediated via both NF-kappaB- and Erk-dependent pathways. In addition, NT-stimulated NF-kappaB activation is dependent on intracellular calcium release. NT-stimulated Erk activity requires Ras activation because overexpression of the dominant negative Ras mutant Ras-17N almost completely inhibits the Erk activation. Furthermore, NT directly stimulates Ras-GTP formation as shown by a Ras-GTP pull-down assay. By using reporter gene constructs containing targeted substitutions in the IL-8 promoter, we show that the NF-kappaB, AP-1, and to a lesser degree the C/EBP sites in the IL-8 promoter region are required for IL-8 gene expression induced by NT. In summary, our results demonstrate that NT stimulates calcium-dependent NF-kappaB and Ras-dependent Erk pathways that mediate the release of IL-8 from non-transformed human colonocytes. We speculate that these NT-related proinflammatory pathways are important in the pathophysiology of colonic inflammation.

Site-specific DNA methylation contributes to neurotensin/neuromedin N expression in colon cancers

The neurotensin/neuromedin N (NT/N) gene is expressed in fetal colon, repressed in newborn and adult colon, and reexpressed in approximately 25% of colon cancers. Our purpose was to determine the effect of gene methylation on NT/N silencing in colon cancers. We found that the NT/N gene was expressed in human colon cancer cell line KM12C but not in KM20 colon cancer cells. Bisulfite genomic sequencing demonstrated that all CpG dinucleotides in the region from -373 to +100 of the NT/N promoter, including a CpG site in a distal consensus AP-1 site, were methylated in KM20 but unmethylated in KM12C cells. Treatment of KM20 cells with demethylating agent 5-azacytidine induced NT/N expression, suggesting a role for DNA methylation in silencing of NT/N in colon cancers. To better elucidate the mechanisms responsible for NT/N repression by DNA methylation, we performed gel shift assays using an oligonucleotide probe corresponding to the distal AP-1 consensus sequence of the NT/N promoter. Methylation of the oligonucleotide probe inhibited protein binding to the distal AP-1 site of the NT/N promoter, suggesting a potential mechanism of NT/N gene repression in colon cancers. We show that DNA methylation plays a role in NT/N gene silencing in the human colon cancer KM20 and that NT/N expression in KM12C cells is associated with demethylation of the CpG sites. DNA methylation likely contributes to NT/N gene expression noted in human colon cancers.

Gut peptide receptor expression in human pancreatic cancers

OBJECTIVE

To determine the prevalence of gastrointestinal (GI) peptide receptor expression in pancreatic cancers, and to further assess signaling mechanisms regulating neurotensin (NT)-mediated pancreatic cancer growth.

SUMMARY BACKGROUND DATA

Pancreatic cancer remains one of the leading causes of GI cancer death; novel strategies for the early detection and treatment of these cancers is required. Previously, the authors have shown that NT, an important GI hormone, stimulates the proliferation of an NT receptor (NTR)-positive pancreatic cancer.

METHODS

A total of 26 human pancreatic adenocarcinomas, obtained after resection, and 5 pancreatic cancer xenografts were analyzed for expression of NTR, vasoactive intestinal peptide receptor (VIPR), substance P receptor (SPR), and gastrin-releasing peptide receptor (GRPR). In addition, NTR expression, [Ca2+]i mobilization, and growth in response to NT was determined in L3.6, a metastatic pancreatic cancer cell line.

RESULTS

Neurotensin receptor was expressed in 88% of the surgical specimens examined and all five of the pancreatic cancer xenografts. In contrast, VIPR, SPR, and GRPR expression was detected in 31%, 27%, and 8% of pancreatic cancers examined, respectively. Expression of NTR, functionally coupled to the Ca2+ signaling pathway, was identified in L3.6 cells; treatment with NT (10 micromol/L) stimulated proliferation of these cells.

CONCLUSIONS

The authors demonstrated NTR expression in most of the pancreatic adenocarcinomas examined. In contrast, VIPR, SPR, and GRPR expression was detected in fewer of the pancreatic cancers. The expression of NTR and other peptide receptors suggests the potential role of endocrine manipulation in the treatment of these cancers. Further, the presence of GI receptors may provide for targeted chemotherapy or radiation therapy or in vivo scintigraphy for early detection.

Colonic motility in man: features in normal subjects and in patients with chronic idiopathic constipation

The human colon is still a relatively unknown viscus, especially concerning its motor activity. However, in recent years, techniques have been perfected that allow a better understanding of colonic motility, especially through prolonged recording periods. In this way, it has been demonstrated that the viscus contracts according to a circadian trend, is responsive to physiological stimuli (meals, sleep), and features high amplitude, propulsive contractions that are part of the complex dynamic of the defecatory process. These physiological properties and their alterations in patients with chronic idiopathic constipation are reviewed in this article.

Circulating gastrointestinal hormone abnormalities in patients with severe idiopathic constipation

OBJECTIVE

This study aimed to determine if there is an abnormality of circulating gastrointestinal hormones in patients with severe idiopathic constipation.

METHODS

Twelve patients, all female (median age 34 yr) and 12 healthy controls (eight female, median age 32 yr) were studied. A radioisotope-labeled solid/liquid meal was ingested, and the serum hormone response, as well as the relationship between serum hormones and rates of gastric emptying and small intestinal transit, were studied for 180 min postprandially.

RESULTS

Somatostatin levels were higher in patients with constipation (basal level, controls vs patients, 31 vs 57 pmol/L, p < 0.05, median values; peak level, 48 vs 60, p < 0.05). Patients showed a significantly lower somatostatin integrated incremental meal response (2182 vs 104, p < 0.05). No correlation was found between the somatostatin levels and rates of upper gastrointestinal transit in patients. Pancreatic glucagon was significantly decreased (p=0.04). Enteroglucagon levels were significantly lower (p > 0.05) in patients between 30 and 60 min after the meal. The peak found after the meal in normal subjects was absent. Basal levels of pancreatic glucagon correlated with small bowel transit by two different measures: head of meal (r=0.69, p=0.03) and cecal filling at the time of 50% gastric emptying (r=0.84, p=0.002). No significant differences between the two groups could be found for basal and peak levels at different times and integrated incremental response to the meal for insulin, gastric inhibitory polypeptide (GIP), glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK), gastrin, pancreatic polypeptide (PP), motilin, neurotensin, and peptide tyrosine tyrosine (PYY).

CONCLUSION

Patients with severe idiopathic constipation have specific abnormalities of circulating gut hormones that most likely play a role in gastrointestinal motility and that may be of pathophysiological significance.

Changes in gut neurotensin and modified colonic motility following whole-body irradiation in rat

Exposure to ionizing radiation induces gastrointestinal dysfunction often associated with disorders of intestinal motility. Neurotensin is one of the mediators involved in the control of intestinal muscle activity. The aim of this study was to relate neurotensin tissue content and specific receptor binding with contractile effect of neurotensin in rat colon after irradiation. Rats were exposed to whole-body gamma-irradiation (60Co; 6 Gy). Intestinal (caecum, colon) neurotensin-like immunoreactivity, colonic muscle neurotensin receptor binding and neurotensin-induced contractions in isolated colon were investigated 3 and 7 days after irradiation. Irradiation produced a marked increase in the intestinal muscle content of neurotensin-like immunoreactivity (2.5-fold in caecum, 5-fold in colon) 3 days post-irradiation. At 7 days, the intestinal neurotensin content was close to that of the control values. Three days after irradiation, neurotensin receptors in colonic muscle were characterized by the appearance of a transient second class of sites of low affinity-high capacity. A three-fold increase in the total number of sites was observed. In addition, effects of neurotensin on isolated colon preparations showed an increase (37%) of potency but a decrease (7-fold) of efficacy. Seven days after irradiation, the efficacy was close to the control. Modifications of intestinal neurotensin content and specific receptor characteristics induced by irradiation can influence the colonic contractile activity.

Inhibition of neurotensin-induced pancreatic carcinoma growth by a nonpeptide neurotensin receptor antagonist, SR48692

BACKGROUND

Recently, a nonpeptide neurotensin (NT) receptor antagonist, SR48692, was developed that selectively antagonizes the high affinity, biologically active NT binding site. The effect of SR48692 on NT-mediated growth of a human pancreatic carcinoma, MIA PaCa-2, was determined both in vitro and in vivo.

METHODS

(125)I-NT binding and Northern blot analyses were performed for evaluation of the NT receptor in MIA PaCa-2 cells. Intracellular calcium ([Ca2+]i) mobilization and inositol phosphate (IP3) levels were measured. Cell growth studies were performed by counting cell numbers. Athymic nude mice were inoculated with MIA PaCa-2 cells and randomized into four groups to receive either vehicle (NT or SR48692) or NT + SR48692.

RESULTS

MIA PaCa-2 cells possess both a high affinity, SR48692-sensitive and a levocabastine-insensitive NT binding site; Northern blot analysis demonstrated expression of the NT receptor. SR48692 inhibited [Ca2+]i mobilization, IP3 turnover, and MIA PaCa-2 cell growth induced by NT in a dose-dependent fashion. In in vivo experiments, NT significantly increased the size, weight, and DNA and protein content of xenografted MIA PaCa-2 tumors; SR48692 inhibited the effect of NT.

CONCLUSIONS

The novel NT receptor antagonist SR48692 will be a valuable agent to delineate further the cellular mechanisms responsible for peptide-mediated growth of normal and neoplastic gut tissues.

Effects of exogenous neurotensin on intestinal postresectional growth in the suckling rat

BACKGROUND

In the suckling rat, massive bowel resection provokes intestinal malabsorption that leads to diminished growth. The object of this report was to test whether neurotensin, intestinal trophic peptide, enhances postresection intestinal adaptation, improving absorption and reducing the adverse effects of resection on growth.

METHODS

Fifty-seven 15-day-old suckling. Wistar rats were divided into four groups: 41 rats were subjected to resection of 90% of their small bowel, while the rest (n = 16) underwent laparotomy. Half of the animals, resected and laparotomized, were treated with neurotensin for 30 days. The body weight was monitored, and samples of bone and intestinal mucosa were obtained at the end of the study period for analysis. Blood was tested to determine iron, ferritin, folic acid, and vitamin B12 levels.

RESULTS

The resected animals lost body weight regardless of neurotensin administration. In the resected animals, femur weight increased significantly when they received neurotensin. Bowel resection provokes significant increases in the intestinal mucosa (crypts and villi), but after neurotensin administration, significant increases were detected only in the jejunum of the resected animals but not in the ileum of laparotomized rats. In the resected animals, significant decreases in iron, ferritin, folic acid, and vitamin B12 levels were observed. The postresection administration of neurotensin only produced a significant rise in the ferritin concentration.

CONCLUSIONS

In the suckling rat, neurotensin enhances the intestinal proliferative phenomenon but does not improve the course of medium-term postresection growth.

Indirect inhibitory effect of a neurotensin receptor antagonist on human colon cancer (LoVo) growth

The effect of the nonpeptide neurotensin (NT) receptor antagonist SR48692 on NT-mediated growth of xenografted human colon cancers (LoVo) was determined. Sixty-four athymic nude mice, inoculated with LoVo cells at a single site, were randomized into four groups of 16 mice each to receive either vehicle NT (600 microg/kg), SR48692 (2 mg/kg) or NT+SR48692 administered s.c., t.i.d., for 25 days. Treatment with NT significantly stimulated LoVo tumour growth, weight, DNA and protein content; SR48692 blocked this NT-mediated effect but had no effect when administered as a single agent. In addition, normal jejunum and ileum were removed and assessed. Similar to the effects on LoVo tumours, NT stimulated jejunal and ileal growth; SR48692 blocked this NT-mediated effect. In contrast to our in vivo findings, NT had no effect on LoVo cell growth in vitro. Also, Northern blot analysis demonstrated no expression for the NT receptor in either LoVo tumour cells or xenografted tumours. Our findings suggest that the trophic effect of NT on LoVo may be through an indirect effect; one possibility is that administration of NT may stimulate the release of other trophic factors which then stimulate tumour growth. The nonpeptide NT receptor antagonist SR48692 will be a useful agent to delineate the specific effects of NT on neoplastic as well as normal gastrointestinal tissues.

Peripheral neurotensin participates in the modulation of pre- and postprandial intestinal motility in rats

The present study was undertaken to determine whether neurotensin is involved in the regulation of the intestinal postprandial motor response and, if so, whether the regulatory pathway depends upon peripheral or central neurotensin secretion. Neurotensin, injected by the i.v. route (5 micrograms/kg) during the fasting state, induced firstly an increased irregular spiking activity during 30-40 min. This effect was followed by an increase of frequency of the myoelectrical complexes during 60 min. When injected by the i.c.v. route, neurotensin (0.5 microgram/kg) reinforced the fasting motility pattern of the small intestine after a latency of 70 min. Neurotensin was ineffective on the colon. The neurotensin receptor antagonist SR 48692 (200 micrograms/kg i.v.) reduced the duration of the postprandial motor response of the small intestine and blocked the late postprandial phase on the proximal colon while it suppressed the early postprandial phase on the distal colon. When administered i.c.v. (20 micrograms/kg), SR 48692 had no effect. It is concluded that neurotensin modulates intestinal postprandial motility essentially by a peripheral regulatory pathway. Endogenous neurotensin is involved in the maintenance of the postprandial motility pattern on the small intestine and the proximal colon while it is involved in the initiation of this response on the distal colon. This suggests that endogenous neurotensin acts via both endocrine and nervous mechanisms.

Kinetics of neurotensin gene expression in the developing gut

BACKGROUND

Expression of the gene encoding neurotensin (NT/N) is regulated in a strict temporal- and spatial-specific pattern during gut development; the mechanisms (that is, transcriptional versus posttranscriptional) responsible for this expression pattern are not known. The purpose of this study was to determine whether developmental changes in NT/N expression reflect alternations in gene transcription.

METHODS

Sensitive ribonuclease protection assays were performed with a rat NT/N genomic probe containing the entire sequence of both exon 1 and intron 1 hybridized with RNA from fetal (day 19) and postnatal (days 14, 28, and 60) rat jejunum and ileum; signals were quantitated densitometrically.

RESULTS

Mature (exon 1) and precursor (exon 1 + intron 1) NT/N RNA, initially low in the fetus, increased dramatically by postnatal day 14 and attained maximal levels by day 28. NT/N RNA levels remained stable in the ileum of the 60-day-old rat but decreased in the jejunum, consistent with the typical expression pattern in the gut.

CONCLUSIONS

Concomitant changes in expression of precursor and mature NT/N RNA suggest that NT/N gene regulation occurs at the level of transcription in the gut during development. Identifying the factors that regulate NT/N gene transcription is crucial to our understanding of how neurotensin functions in the gut.

Characterization of promoter elements required for cell-specific expression of the neurotensin/neuromedin N gene in a human endocrine cell line

Expression of the gene encoding neurotensin/neuromedin N (NT/N) is mostly limited to the brain and specialized enteroendocrine cells (N cells) of the distal small intestine. We have analyzed the NT/N DNA sequences upstream of the RNA start site that direct cell-specific expression using a novel human endocrine cell line, BON, that resembles intestinal N cells in several important aspects, including NT/N precursor protein processing, ratios of different NT/N mRNA forms, and high levels of constitutive expression of the NT/N gene. Transient transfection assays with plasmids with progressive 5' deletions of the rat NT/N promoter identified the proximal 216 bp of 5' flanking sequences as essential for high-level constitutive NT/N expression in BON cells. In addition, a detailed mutational analysis defined multiple regions within the proximal 216 bp that contribute to cell-specific NT/N expression. These elements include a proximal cyclic AMP response element (CRE)/AP-1-like motif (TGACATCA) that binds c-Jun, JunD, CRE-binding (CREB), and ATF proteins, a near-consensus glucocorticoid response element, and a distal consensus AP-1 site that binds c-Fos, Fra-1, and JunD. In addition, elements contained within two 21-bp imperfect direct repeats play an important role in NT/N expression in BON cells and may bind novel factors that act as positive regulators of NT/N expression. DNase I footprinting and gel shift analyses demonstrate that the sites identified by mutational analysis, and at least one additional site, specifically bind BON cell nuclear proteins in vitro. We speculate that a complex pattern of regulation requiring interaction between a proximal CRE/AP-1-like motif and other upstream control elements play an important role in the high-level constitutive expression of NT/N in the human endocrine cell line BON. In addition, the BON cell line provides a unique model to further characterize the factors regulating cell-specific NT/N expression and to better understand the mechanisms responsible for the terminal differentiation of the N-cell lineage in the gut.

Distribution of neurotensin-immunoreactive neurons in the digestive tract of the chicken

The origin of the neurotensin-containing nerve fibers in the digestive tract of the chicken has been investigated with the use of colchicine and immunohistochemistry. Neurotensin-immunoreactive nerve fibers were found in the smooth muscle layers from the esophagus to the duodenum. Their density of distribution was very high in the esophagus and crop (maximum mean value: 1315/mm2 of sectional area in the lamina muscularis mucosae of the crop) and decreased progressively to the duodenum. Neurotensin-immunoreactive neuronal cell bodies were observed after colchicine treatment in the submucosal plexuses of the esophagus and crop and in the myenteric plexuses of the esophagus, crop, proventriculus and gizzard, and they extended varicose fibers. The number of neurotensin-immunoreactive cell bodies was high in the myenteric plexus of the gizzard (28.3 +/- 2.7/ganglion) but low in the plexuses of the esophagus, crop and proventriculus. Seven days after cutting the glossopharyngeal nerve and vagus nerve unilaterally, the number and extent of neurotensin-immunostained structures in the smooth muscle layers from the esophagus to the gizzard did not show any significant difference between operated and unoperated sides. These results indicate that in the chicken the great majority of neurotensin-immunoreactive enteric fibers originate in the intramural plexuses of the upper digestive wall and are mainly distributed to smooth muscle cells.

The neurotensin gene is a downstream target for Ras activation

Ras regulates novel patterns of gene expression and the differentiation of various eukaryotic cell types. Stable transfection of Ha-ras into the human colon cancer line CaCo2 results in the morphologic differentiation to a small bowel phenotype. The purpose of our study was to determine whether the Ras regulatory pathway plays a role in the expression of the neurotensin gene (NT/N), a terminally differentiated endocrine product specifically localized in the gastrointestinal tract to the adult small bowel. We found that CaCo2-ras cells, but not parental CaCo2, express high levels of the human NT/N gene and, moreover, that this increase in gene expression is regulated at the level of transcription. Transfection experiments using NT/N-CAT mutation constructs identify the proximal 200 bp of NT/N flanking sequence as sufficient for maximal Ras-mediated NT/N reporter gene induction. Furthermore, a proximal AP-1/CRE motif is crucial for this Ras-mediated NT/N activation. Wild-type Ha-ras induces NT/N gene expression, albeit at lower levels than activated Ras; a dominant-negative Raf blocks this NT/N induction, suggesting that Raf lies down-stream of Ras in this pathway. In addition, postconfluent cultures of CaCo2 cells, which are differentiated to a small bowel phenotype, express the NT/N gene by 6 d after reaching confluency; this increase of NT/N expression is associated with concomitant increases of cellular p21ras protein. We conclude that Ras (both wild-type and activated) enhances expression of the NT/N gene in the gut-derived CaCo2 cell line, suggesting an important role for the Ras signaling pathway in NT/N gene transcription. Our results underscore the possibility that tissue-specific genes (such as NT/N) expressed in distinct subpopulations of the gut may be subject to Ras regulation. Finally, we speculate that the NT/N gene and the CaCo2 and CaCo2-ras cell systems will provide unique models to further define the cellular mechanisms leading to mammalian intestinal differentiation.

Intestinal intraluminal continuity is a prerequisite for the distal bowel motility response to feeding

BACKGROUND

We wanted to elucidate further the regulation of the intestinal motility response to feeding.

METHODS

After intraduodenal administration of an oleate solution, mimicking a meal, the distal bowel motility and the plasma levels of bile acids, cholecystokinin (CCK), and neurotensin were monitored in patients operated on with restorative proctocolectomy (n = 4) or low anterior resection of the rectum (n = 4). Investigations were performed both with and without a diverting loop ileostomy.

RESULTS

Intraduodenal sodium oleate elicited a prompt and significant increase in distal bowel motility. The motility response failed to appear when the luminal flow was diverted by a loop ileostomy. An increase in plasma CCK preceded the motility increase, but CCK was increased also in patients with a loop ileostomy. Whereas plasma bile acid levels were significantly increased after 30-45 min (p < 0.05), both with and without a loop ileostomy, neurotensin levels were not affected.

CONCLUSION

Intestinal continuity is a prerequisite for the distal bowel motility response, indicating that apart from other possible mechanisms, luminal factors are involved in the regulation of intestinal motility.

A role of nitric oxide in Hirschsprung's disease

Nitric oxide (NO) has recently been shown to be a neurotransmitter in the nonadrenergic noncholinergic (NANC) inhibitory nerves in the gastrointestinal tract. To clarify the significance of NO in Hirschsprung's disease (HD), enteric nerve responses in colonic tissue obtained from HD patients were investigated. Colonic tissue specimens were obtained from four patients with HD and from 11 patients without constipation who were used as controls. A mechanograph was used to evaluate in vitro colonic responses to electrical field stimulation (EFS) of the adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, and NG-nitro-L-arginine (L-NNA) and L-arginine with the following results: (1) NANC inhibitory nerves were found to act on normal human colon, but had no effect on aganglionic colon; (2) L-NNA concentration dependently inhibited the relaxation in response to EFS in the normal colon, but had no effect on aganglionic colon; and (3) this inhibitory effect was reversed by L-arginine in the normal colon, but had no effect on the aganglionic colon. Nitric oxide mediates the relaxation reaction of NANC inhibitory nerves in the human colon, but the effect of NO was absent in aganglionic colon. The loss of action by NO may be implicated in the impaired motility observed in aganglionic colon.

Comparative effects of neurotensin and neuromedin N on growth of human pancreatic cancer, MIA PaCa-2

Neurotensin (NT), an important regulatory hormone of the gut, stimulates growth of the human pancreatic cancer cell line MIA PaCa-2 in vitro. The purpose of our study was to compare the stimulatory effects of NT and neuromedin N (NMN), a structurally related hexapeptide, on the growth of MIA PaCa-2. In addition, the effects of NT on the growth of MIA PaCa-2 xenografts and normal GI tissues were assessed in athymic nude mice. MIA PaCa-2 cells, plated in serum-free media, were treated with either NT (10(-12)-10(-6) M) or NMN (10(-11)-10(-7) M) and cells were counted. For the in vivo study, MIA PaCa-2 cells were inoculated sc into 30 athymic nude mice and then randomized to two groups to receive either NT (600 micrograms kg-1, sc, tid) or vehicle. At sacrifice (day 35), the xenografted tumours, as well as normal host pancreas, jejunum and ileum were removed, weighed, and assayed for DNA, RNA and protein. Both NT and NMN stimulated the growth of MIA PaCa-2 cells in vitro with maximal (approximately 30%) increases occurring with dosages of 10(-9) M. In vivo, NT had a transient effect on xenografted MIA PaCa-2 tumour area with increases noted on days 21 and 25 of the study. Conversely, NT significantly stimulated the growth of jejunum and ileum, with a more pronounced effect noted in the jejunum. NT and NMN have similar growth-stimulatory effects on MIA PaCa-2 cells in vitro, which suggests an interaction through the same receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental expression of the neurotensin gene in the rat liver

OBJECTIVE

This study determined whether the neurotensin gene is expressed during early development of the liver.

SUMMARY BACKGROUND DATA

Neurotensin (NT), a gut tridecapeptide localized mainly to the distal small bowel and brain of adults, is an important hormone regulating gut motility, secretion and mucosal growth. Expression of NT peptide and the gene is found in fibrolamellar hepatocarcinomas, a variant of hepatocellular carcinoma, but not in the normal adult liver.

METHODS

Northern and in situ hybridization techniques were used to determine expression of the neurotensin gene (NT/N) in the normal developing liver.

RESULTS

NT/N is expressed in the fetal and early postnatal rat liver, but expression is repressed in the liver of the adult. In situ hybridization confirms the authors' Northern data and demonstrates a random distribution of NT/N expression in the fetal and 3-day postnatal liver.

CONCLUSIONS

The authors conclude from this study that NT/N is expressed during early development of the rat liver with subsequent repression in the adult. NT/N may be reexpressed with malignant transformation of the liver.