Neurotensin Precursor Research Articles

Neurotensin accelerates atherosclerosis and increases circulating levels of short-chain and saturated triglycerides

Background and aimsObesity and type 2 diabetes are significant risk factors for atherosclerotic cardiovascular disease (CVD) worldwide, but the underlying pathophysiological links are poorly understood. Neurotensin (NT), a 13-amino-acid hormone peptide, facilitates intestinal fat absorption and contributes to obesity in mice fed a high-fat diet. Elevated levels of pro-NT (a stable NT precursor produced in equimolar amounts relative to NT) are associated with obesity, type 2 diabetes, and CVD in humans. Whether NT is a causative factor in CVD is unknown. MethodsNt+/+ and Nt–/– mice were either injected with adeno-associated virus encoding PCSK9 mutants or crossed with Ldlr–/– mice and fed a Western diet. Atherosclerotic plaques were analyzed by en face analysis, Oil Red O and CD68 staining. In humans, we evaluated the association between baseline pro-NT and growth of carotid bulb thickness after 16.4 years. Lipidomic profiles were analyzed. ResultsAtherosclerotic plaque formation is attenuated in Nt-deficient mice through mechanisms that are independent of reductions in circulating cholesterol and triglycerides but associated with remodeling of the plasma triglyceride pool. An increasing plasma concentration of pro-NT predicts atherosclerotic events in coronary and cerebral arteries independent of all major traditional risk factors, indicating a strong link between NT and atherosclerosis. This plasma lipid profile analysis confirms the association of pro-NT with remodeling of the plasma triglyceride pool in atherosclerotic events. ConclusionsOur findings are the first to directly link NT to increased atherosclerosis and indicate the potential role for NT in preventive and therapeutic strategies for CVD.

Higher circulating levels of proneurotensin are associated with increased risk of incident NAFLD.

Neurotensin (NT), an intestinal peptide able to promote fat absorption, is implicated in the pathogenesis of obesity. Increased levels of pro-NT, a stable NT precursor fragment, have been found in subjects with non-alcoholic fatty liver disease (NAFLD), however whether higher pro-NT levels are associated with an increased NAFLD risk independently of other metabolic risk factors is unsettled. Ultrasound-defined presence of NAFLD was assessed on 303 subjects stratified into tertiles according to fasting pro-NT levels. The longitudinal association between pro-NT levels and NAFLD was explored on the study participants without NAFLD at baseline re-examined after 5 years of follow-up (n = 124). Individuals with higher pro-NT levels exhibited increased adiposity, a worse lipid profile and insulin sensitivity as compared to the lowest tertile of pro-NT. Prevalence of NAFLD was progressively increased in the intermediate and highest pro-NT tertile as compared to the lowest tertile. In a logistic regression analysis adjusted for several confounders, individuals with higher pro-NT levels displayed a raised risk of having NAFLD (OR = 3.43, 95%CI = 1.48-7.97, P = 0.004) than those in the lowest pro-NT tertile. Within the study cohort without NAFLD at baseline, subjects with newly diagnosed NAFLD at follow-up exhibited higher baseline pro-NT levels than those without incident NAFLD. In a cox hazard regression analysis model adjusted for anthropometric and metabolic parameters collected at baseline and follow-up visit, higher baseline pro-NT levels were associated with an increased risk of incident NAFLD (HR = 1.52, 95%CI = 1.017-2.282, P = 0.04). Higher pro-NT levels is a predictor of NAFLD independent of other metabolic risk factors. This article is protected by copyright. All rights reserved.

The Neurotensinergic System: A Target for Cancer Treatment.

The scientific interest regarding the involvement of peptides in cancer has increased in the last few years. In tumor cells, the overexpression of peptides and their receptors is known, and new therapeutic targets for the treatment of cancer have been suggested. The overexpression of the neurotensinergic system has been associated with poor prognosis, tumor size, higher tumor aggressiveness, increased relapse risk, and worse sensitivity to chemotherapy agents. The aim of this review is to update the findings regarding the involvement of the neurotensinergic system in cancer to suggest anticancer therapeutic strategies targeting this system. The neurotensin (NT) precursor, NT and its receptors (NTR), and the involvement of the neurotensinergic system in lung, breast, prostate, gastric, colon, liver, and pancreatic cancers, glioblastoma, neuroendocrine tumors, and B-cell leukemia will be mentioned and discussed as well as the signaling pathways mediated by NT. Some research lines to be developed in the future will be suggested, such as molecules regulating the expression of the NT precursor, the influence of the diet in the development of tumors, molecules and signaling pathways activated by NT, and antitumor therapeutic strategies targeting the neurotensinergic system. NT, via the NTR, exerts oncogenic (tumor cell proliferation, invasion, migration, angiogenesis) and antiapoptotic effects, whereas NTR antagonists inhibit these effects. NTR expression can be used as a diagnostic tool/therapeutic target, and the administration of NTR antagonists as antitumor drugs could be a therapeutic strategy to treat tumors overexpressing NTR.

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.

High plasma levels of pro-NT are associated with increased colon cancer risk.

Emerging data supports a potential role of neurotensin (NT) in the development of obesity, obesity-associated comorbidities, and certain cancers. The association of NT with colon cancer risk has not been explicitly explored. We determined plasma levels of pro-NT, a stable NT precursor fragment, in 223 incident colon cancer patients and 223 age-, gender-, BMI-matched population controls participating in a population-based case-control study of colon cancer. On average, the cases have significantly higher levels of pro-NT than the controls (median = 205.6 pmol/L vs 183.1 pmol/L, respectively; P = 0.02). Multivariate logistic regression models, adjusted for age, gender, BMI, family history of colorectal cancer, smoking, diabetes mellitus, alcohol, and non-steroidal anti-inflammatory drugs use, show statistically significant risk associations: for continuous measure of pro-NT, the OR estimate was 1.30 (95% CI =1.03-1.64; P = 0.026) for each increment of 175 pmol/L; for dichotomized measure of pro-NT, the OR estimate was 1.75 (95% CI = 1.12-2.74; P = 0.025) for those in the top quartile comparing to the other participants. Our results support circulating levels of pro-NT as a novel risk biomarker for colon cancer.

Increased Plasma Proneurotensin Levels Identify NAFLD in Adults With and Without Type 2 Diabetes.

Neurotensin (NT), an intestinal peptide released by fat ingestion, promotes lipid absorption; higher circulating NT levels are associated with type 2 diabetes (T2D), obesity, and cardiovascular disease. Whether NT is related to nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) has not been fully investigated. To study the relationship between plasma proneurotensin 1 to 117 (pro-NT), a stable fragment of the NT precursor hormone, and the presence/severity of NAFLD/NASH and to unravel correlates of increased pro-NT levels. For this cross-sectional study, 60 obese individuals undergoing bariatric surgery for clinical purposes were recruited. The association between pro-NT and NAFLD was further investigated in 260 consecutive subjects referred to our outpatient clinics for metabolic evaluations, including liver ultrasonography. The study population underwent complete metabolic characterization; in the obese cohort, liver biopsies were performed during surgery. Plasma pro-NT levels in relation to NAFLD/NASH. Obese subjects with biopsy-proven NAFLD (53%) had significantly higher plasma pro-NT than those without NAFLD (183.6 ± 81.4 vs 86.7 ± 56.8 pmol/L, P < 0.001). Greater pro-NT correlated with NAFLD presence (P < 0.001) and severity (P < 0.001), age, female sex, insulin resistance, and T2D. Higher pro-NT predicted NAFLD with an area under receiver operating characteristic curve of 0.836 [95% confidence interval (CI), 0.73 to 0.94; P < 0.001]. Belonging to the highest pro-NT quartile correlated with increased NAFLD risk (odds ratio, 2.62; 95% CI, 1.08 to 6.40) after adjustment for confounders. The association between higher pro-NT and NAFLD was confirmed in the second cohort independently from confounders. Increased plasma pro-NT levels identify the presence/severity of NAFLD; in dysmetabolic individuals, NT may specifically promote hepatic fat accumulation through mechanisms likely related to increased insulin resistance.

Similar pro-NT and pro-RLX2 levels after preeclampsia and after uncomplicated pregnancy

ObjectiveWomen are at increased risk of developing cardiovascular disease (CVD) after preeclampsia. Proneurotensin 1-117 (pro-NT) and prorelaxin 2 connecting peptide (pro-RLX2) have recently emerged as potential biomarkers for CVD risk in women. We assessed pro-NT and pro-RLX2 levels in women with and without a history of preeclampsia. Study design339 women with a history of early-onset preeclampsia and 327 women with an uncomplicated pregnancy underwent cardiovascular screening 10 years after delivery (the Preeclampsia Risk EValuation in FEMales (PREVFEM) cohort). Main outcome measuresPro-NT, a stable fragment of the neurotensin precursor, was assessed in the whole cohort. Pro-RLX2, the stable connecting peptide of the relaxin 2 prohormone, was assessed in a subset of this cohort, consisting of 27 women with a history of preeclampsia and 23 healthy controls. Associations between biomarker levels and traditional CVD risk factors in the preeclampsia and control group were assessed by Pearson’s correlation coefficient. ResultsWe found no differences in pro-NT and pro-RLX2 levels between the preeclampsia and control group. Pro-NT levels were associated with higher HbA1c levels (r = 0.113, p-value 0.045) and with BMI (r = 0.124, p-value 0.027), but only in the control group. Pro-RLX2 was related to current smoking and triglyceride levels in women with a history of preeclampsia and related to LDL-cholesterol in women with an uncomplicated pregnancy. ConclusionsPro-NT and pro-RLX2 levels were comparable in women 10 years after preeclampsia and women with an uncomplicated pregnancy. The role of pro-NT and pro-RLX2 in CVD development after preeclampsia should be further investigated.

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.

Role of proneurotensin as marker of paediatric coeliac disease.

Neurotensin (NT) is a gut hormone functioning proinflammatory through nuclear factor kappa B (NF-κB) and interleukin (IL)-8 secretion or anti-inflammatory through epidermal growth factor receptors. NT mRNA is down-regulated in duodenal biopsies of children with untreated coeliac disease. The aim of this study was to investigate if plasma pro-NT levels correlated with the degree of intestinal mucosal damage and tissue transglutaminase autoantibody (tTGA) levels in children with coeliac disease. Fasting plasma samples from 96 children with coeliac disease and 89 non-coeliac disease controls were analysed for NT precursor fragment pro-NT 1-117 by a chemiluminometric immunoassay. Pro-NT levels were compared with NT mRNA from duodenal biopsies, assessed previously with quantitative polymerase chain reaction (PCR). Illumina core exome arrays were used for human leucocyte antigen (HLA) typing and the Marsh criteria applied to score mucosal damage. Tissue TGA was measured by radio binding assay. A general linear model compared pro-NT levels with diagnosis of coeliac disease, Marsh score and HLA DQ haplotype. Spearman's rank test was used to compare pro-NT levels with tTGA, age and duodenal NT mRNA levels, respectively. Plasma pro-NT levels were elevated in children with coeliac disease (median 23 pmol/l higher, P = 0·003) and in those with severe intestinal mucosal damage (median 24 pmol/l higher for ≥ Marsh 3b versus not, P = 0·0004). Pro-NT levels correlated further with tTGA (r2 = 0·22, P = 0·002), but not with duodenal NTS mRNA levels (r2 = -0·12, P = 0·14). Pro-NT was not associated with any of the HLA risk-haplotypes. Elevated peripheral pro-NT levels reflect more severe forms of active coeliac disease, indicating a potential role of NT in intestinal inflammation.

Activation of AMPK Stimulates Neurotensin Secretion in Neuroendocrine Cells.

AMP-activated protein kinase (AMPK), a critical fuel-sensing enzyme, regulates the metabolic effects of various hormones. Neurotensin (NT) is a 13-amino acid peptide predominantly localized in enteroendocrine cells of the small bowel and released by fat ingestion. Increased fasting plasma levels of pro-NT (a stable NT precursor fragment produced in equimolar amounts relative to NT) are associated with an increased risk of diabetes, cardiovascular disease, and mortality; however, the mechanisms regulating NT release are not fully defined. We previously reported that inhibition of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) increases NT secretion and gene expression through activation of the MEK/ERK pathway. Here, we show that activation of AMPK increases NT secretion from endocrine cell lines (BON and QGP-1) and isolated mouse crypt cells enriched for NT-positive cells. In addition, plasma levels of NT increase in mice treated with 5-aminoimidazole-4-carboxamide riboside, a pharmacologic AMPK activator. Small interfering RNA-mediated knockdown of AMPKα decrease, whereas overexpression of the subunit significantly enhances, NT secretion from BON cells treated with AMPK activators or oleic acid. Similarly, small interfering RNA knockdown of the upstream AMPK kinases, liver kinase B1 and Ca(2+) calmodulin-dependent protein kinase kinase 2, also attenuate NT release and AMPK phosphorylation. Moreover, AMPK activation increases NT secretion through inhibition of mTORC1 signaling. Together, our findings show that AMPK activation enhances NT release through inhibition of mTORC1 signaling, thus demonstrating an important cross talk regulation for NT secretion.

1C.07

Neurotensin is released from the gut after fat intake and has a role in appetite regulations. Proneurotensin is a stable fragment of the neurotensin precursor hormone and fasting plasma proneurotensin levels have shown to be significantly associated with the development of cardiovascular disease in middle aged participants of the Malmo Diet and Cancer Study. Here, we aimed at replicating the initial findings in an independent second cohort and to extend its validity to an older population.

Changes in expression levels of neurotensin precursor and receptor mRNA in chicken intestinal tissues and liver during late embryonic and early posthatching development

Neurotensin is a tridecapeptide that has multiple functions as a neurotransmitter and as a circulating hormone. Neurotensin and its related peptide, LANT6, have been isolated in the chicken, but the mRNA encoding these peptides has not been identified. In this study, we first cloned the cDNA for the chicken neurotensin precursor mRNA from the duodenum and characterized its primary structure and then investigated tissue expression patterns of neurotensin precursor and receptor mRNA. The cDNA encoded a protein of 495 amino acids that contains the sequences of chicken neurotensin and LANT6 in the C-terminal region. Real-time PCR analysis showed that the neurotensin precursor mRNA is preferentially expressed in intestinal tissues, such as the duodenum, jejunum, ileum, and colon/rectum, with temporal increases during the hatching period. The expression levels of neurotensin receptor 1 mRNA were relatively higher during the late embryonic period compared with the posthatching period in the duodenum and jejunum, whereas the expression levels were higher in the colon/rectum during the posthatching period. In the liver, the expression levels of neurotensin receptor 1 were markedly increased during the early posthatching period. These results suggest that chicken neurotensin is involved in the regulation of gastrointestinal and hepatic functions, especially during the hatching period.

Plasma Proneurotensin and Incidence of Diabetes, Cardiovascular Disease, Breast Cancer, and Mortality

Neurotensin regulates both satiety and breast cancer growth in the experimental setting, but little is known about its role in the development of breast cancer or cardiometabolic disease in humans. To test if fasting plasma concentration of a stable 117-amino acid fragment from the neurotensin precursor hormone proneurotensin is associated with development of diabetes mellitus, cardiovascular disease, breast cancer, and mortality. Proneurotensin was measured in plasma from 4632 fasting participants of the population-based Malmö Diet and Cancer Study baseline examination 1991-1994. Multivariate Cox proportional hazards models were used to relate baseline proneurotensin to first events and death during long-term follow-up until January 2009, with median follow-up ranging from 13.2 to 15.7 years depending on the disease. Incident diabetes mellitus, cardiovascular disease, breast cancer, and mortality. Overall, proneurotensin (hazard ratio [HR] per SD increment of log-transformed proneurotensin) was related to risk of incident diabetes (142 events; HR, 1.28; 95% CI, 1.09-1.50; P = .003), cardiovascular disease (519 events; HR, 1.17; 95% CI, 1.07-1.27; P < .001), and cardiovascular mortality (174 events; HR, 1.29; 95% CI, 1.12-1.49; P = .001) with a significant interaction between proneurotensin and sex (P < .001) on risk of cardiovascular disease. Exclusively in women, proneurotensin was related to incident diabetes (74 events; HR, 1.41; 95% CI, 1.12-1.77; P = .003), cardiovascular disease (224 events; HR, 1.33; 95% CI, 1.17-1.51; P < .001), breast cancer (123 events; HR, 1.44; 95% CI, 1.21-1.71; P < .001), total mortality (285 events; HR, 1.13; 95% CI, 1.01-1.27; P = .03), and cardiovascular mortality (75 events; HR, 1.50; 95% CI, 1.20-1.87; P < .001). Fasting proneurotensin was significantly associated with the development of diabetes, cardiovascular disease, breast cancer, and with total and cardiovascular mortality.

HMC-1 human mast cells synthesize neurotensin (NT) precursor, secrete bioactive NT-like peptide(s) and express NT receptor NTS1

To determine if mast cells synthesize the inflammatory peptide, neurotensin (NT), secrete immunoreactive and bioactive NT, and express the NT receptor NTS1. HMC-1 cells, pleural mast cells from Sprague-Dawley rats, LAD2 mast cells, and human cord blood mast cells were used. HMC-1 cells were stimulated with NT, C48/80, mastoparan, or PGE(2). For changes in cutaneous vascular permeability, anesthetized rats were injected intravenously with Evans Blue dye and intradermally with saline, NT, histamine, diphenhydramine, and C48/80. RT-PCR was used to identify RNA transcripts. Histamine was measured by fluorometric assay. In vivo cutaneous vascular permeability assays, radio-immunoassays for NT, Western blotting for the NT precursor protein and NTS1 protein from HMC-1 cells and tissues from rats were used. Immunohistochemistry was used to identify NT precursor-like proteins in HMC-1 mast cells. HMC-1 cells express mRNAs for NT precursor, PC5A processing enzyme and NTS1 receptor. Human cord blood mast cells and LAD2 mast cells express mRNA transcripts for NT precursor and NTS1. Western blotting showed NT precursor and NTS1 receptor in HMC1. Rat tissues with high numbers of mast cells contained NT precursor proteins. NT-like peptides from HMC-1 displayed NT-like bioactivity. HMC-1 mast cells synthesize and secrete immunoreactive and bioactive NT-like peptide(s) and express the NT receptor, suggesting that NT from mast cells might serve autocrine and paracrine roles.

Effect of Gastric Bypass and Gastric Banding on Proneurotensin Levels in Morbidly Obese Patients

Neurotensin is produced mainly in the N cells of the ileum and has a role in appetite regulation; levels are decreased in obese subjects and increase after bariatric surgery. Mature neurotensin is very unstable, with a short half-life. The objective of this study was to compare baseline and postoperative levels of the more stable neurotensin precursor, proneurotensin/neuromedin (pro-NT/NMN), in patients after gastric banding, gastric bypass, and nonoperated controls, respectively, during long-term follow-up. This was a prospective observational study in a university hospital. Overnight fasting plasma pro-NT/NMN concentrations were measured with a new sandwich immunoassay in morbidly obese subjects at baseline and 6, 12, and 24 months after gastric banding (n = 8), Roux-en-Y gastric bypass (n = 5), and in nonoperated controls (n = 7). After gastric bypass and banding, body weight decreased by (mean +/- sd) 29.5 +/- 5.5 and 22.8 +/- 5.9 kg, respectively. The decrease after 3 and 6 months was more pronounced after gastric bypass compared with gastric banding (P < 0.05). Plasma pro-NT/NMN levels in patients after gastric bypass increased from 246.3 +/- 174.3 pmol/liter on admission to 748.3 +/- 429.6 pmol/liter after 24 months (P < 0.01). In contrast, in patients with gastric banding, pro-NT/NMN concentrations remained stable (207.3 +/- 60.5 pmol/liter at admission, 226.6 +/- 116.8 pmol/liter after 24 months). Neither body weight nor plasma pro-NT/NMN levels changed in nonoperated controls. Plasma pro-NT/NMN levels show a more pronounced increase after gastric bypass compared with gastric banding, suggesting that specific bariatric surgical procedures result in distinct alterations of gastrointestinal hormone metabolism. The more stable precursor pro-NT/NMN provides a new tool to quantify neurotensin levels in clinical practice.

Corticotropin-releasing hormone induces skin vascular permeability through a neurotensin-dependent process.

Many skin disorders are associated with increased numbers of activated mast cells and are worsened by stress; however, the mechanism underlying these processes is not understood. Corticotropin-releasing hormone (CRH) is secreted under stress from the hypothalamus, but also in the skin, where it induces mast cell activation and vascular permeability. We investigated the effect of CRH in a number of animal models by using i.v. Evans blue extravasation as a marker of vascular permeability. Intradermal CRH is among the most potent peptides at 100 nM, its effect being nearly comparable to that of neurotensin (NT). Pretreatment of skin injection sites with the NT receptor antagonist SR48692 blocks CRH-induced vascular permeability, which is diminished in NT-/- mice, implying that NT is necessary for the effect of CRH. CRH and NT precursor mRNA are shown to be expressed in both dorsal root ganglia and skin, whereas the latter also expresses mRNA for prohormone convertase 5, an enzyme that cleaves pro-NT into its active form. We also show that the effect of both CRH and NT is absent in W/W(v) mast cell-deficient mice; however, only a fraction of skin mast cells express CRH receptors, as shown by FACS analysis of CRH receptor (CRHR) and c-kit double-positive disaggregated mouse skin mast cells. These findings suggest that CRH induces skin vascular permeability through NT acting on mast cells and that both peptides should be considered in the pathogenesis of skin disorders exacerbated by stress.

Neurotensin receptor expression in prostate cancer cell line and growth effect of NT at physiological concentrations.

Neurotensin (NT), a neuroendocrine peptide, exerts trophic effects in vivo and stimulates growth of some tumor cells in vitro. Androgen-sensitive prostate cells derived from lymph node carcinoma of the prostate (LNCaP) secrete NT and exhibit growth responses to NT. This study examines NT secretion, NT receptor and NT-growth responses in androgen-independent prostatic carcinoma (PC3) cells derived from prostate adenocarcinoma metastatic to bone. Binding of 125I-NT to PC3 membranes was studied by filtration. NT was measured by RIA. Reverse transcriptase polymerase chain reaction (RT-PCR) was used for NT and NT receptor mRNA. Growth was measured as 3H-thymidine incorporation into DNA. Scatchard analyses gave two binding components (Kd1 = 40 pM and Kd2 = 300 pM) in equal amounts (15-30 x 10(3) sites/cell). The bioactive region of NT was essential and the specific, non-peptide NT antagonist, SR48692, inhibited (IC50 = 3 nM). GTP analogs, sodium ion and SH-directed alkylating agents also inhibited. Glutaraldehyde crosslinking labeled two substances (M(r) of 23 and 46 kDa). RT-PCR indicated robust expression of authentic NT receptor but little for NT precursor. NT was stable in PC3 cultures but it was not found in cells or conditioned media. Incubated with PC3 cells, NT exhibited a mitogenic effect with bell-shaped dose-response and maximum at 100 pM NT. PC3 cells expressed genuine NT receptors and generated growth responses to physiologic levels of NT which were blocked by SR48692. If NT contributes to the survival of prostate tumor cells upon androgen deprivation therapy, NT antagonists might be useful agents in further treatment.

Neurotensin and neuromedin N brain levels after fornix transection: evidence for an efficient neurotensin precursor processing in subicular neurons

High levels of neurotensin/neuromedin N precursor mRNA, but few if any NT-positive perikarya have been detected in the dorsal subiculum of the adult rat or human hippocampus. This apparent discrepancy was tentatively ascribed to a lack of precursor mRNA translation or to a poor precursor positranslational processing in neurons of the hippocampus. Another hypothesis is that in long neuronal pathways, maturation of neuropeptide precursors and derived peptides occurs during axonal transport to terminals, a process which accounts for the lack of peptide detection in cell bodies. In order to test this hypothesis, we performed surgical transection of the fornix to interrupt axonal transport of putative NT/NN products arising from the dorsal hippocampus and measured NT and NN levels in different brain regions. In the mamillary bodies, the main projection area of the dorsal subiculum, NN and NT levels were highly reduced 4 or 14 days after the septo-hippocampus transection which was correlated with a slight increase in NN and NT levels in the dorsal hippocampus and the retrosplenial cortex of 4 days lesioned animals. An increase in hypothalamic NN levels was also detected 14 days after the lesion. These data suggest that the peptide precursor processing can take place during the axonal transport, as shown here for neurotensin and neuromedin N from subicular neurons to their efferent brain areas such as the mamillary bodies.

Induction of the neurotensin (NT) gene in PC12 cells gives rise to NT precursor (∼88%), NT(3–13)-like peptide (∼10%), and NT (∼2%)

Neurotensin (NT) is coexpressed with catecholamines in sympathetic neurons and adrenal chromaffin cells. A pheochromocytoma PC12 cell line can also be induced to express the NT gene and produce immunoreactive NT. In the present study, NT mRNA was quantified under various hormonal conditions and NT precursor synthesis rates were determined by pulse labeling and immunoprecipitation. In addition, NT precursor and NT-related products were measured using RIA and were characterized using HPLC and Sephadex chromatography. Neurotensin mRNA, NT precursor synthesis, and NT precursor/product levels were correlated. Surprisingly, NT appeared to be a minor product, both in cells and media: NT precursor (∼88%), NT(3–13)-like peptide (∼10%), and NT(∼2%). Neurotensin added to cultures was not converted to NT(3–13). Treatment of cells with 60 m M KCl or various secretagogues induced Ca 2+-dependent release of NT precursor, NT(3–13), and NT in proportion to their cellular contents. These results suggest a) that NT precursor processing in induced PC12 cells was much slower than NT precursor synthesis, b) that NT(3–13) was a major product and NT a minor one, and c) that NT precursor and its products were stored within secretory vesicles.

Pepsin-mediated processing of synthetic precursor-like sequence yields neurotensin-like peptide

A 15 amino acid synthetic peptide, which spanned the dibasic cleavage site C-terminal to neurotensin (NT), in its 170-residue canine precursor, was synthesized by solid-phase methods. Using this substrate in combination with a radioimmunoassay specific for the C-terminal region of NT, a simple assay was developed to monitor protease-mediated cleavage of the Leu 8-Lys 9 bond in the substrate. Hog pepsin and the related enzymes, rhizopus pepsin, bovine cathepsin D, and mouse renin, were found to be effective in this assay, pepsin cleaving only this bond to liberate the NT-like sequence. The pH dependence of the reaction indicated that pepsin, cathepsin D, and renin exhibited significant activity at pH's characteristic for secretory vesicles (pH 5.5–6.5). In addition, pepsin and cathepsin D were shown to process the native precursor at pH's as high as 5.5. These results, although not proof, are consistent with the idea that endoproteases with pepsin-like specificity may be involved in the processing of the NT precursor in neural/endocrine cells.