M3 muscarinic receptor antagonists inhibit small cell lung carcinoma growth and mitogen-activated protein kinase phosphorylation induced by acetylcholine secretion

The importance of acetylcholine as a neurotransmitter in the nervous system is well established, but little is yet known about its recently described role as an autocrine and paracrine hormone in a wide variety of nonneuronal cells. Consistent with the expression of acetylcholine in normal lung, small cell lung carcinoma (SCLC) synthesize and secrete acetylcholine, which acts as an autocrine growth factor through both nicotinic and muscarinic cholinergic mechanisms. The purpose of this study was to determine if interruption of autocrine muscarinic cholinergic signaling has potential to inhibit SCLC growth. Muscarinic receptor (mAChR) agonists caused concentration-dependent increases in intracellular calcium and mitogen-activated protein kinase (MAPK) and Akt phosphorylation in SCLC cell lines. The inhibitory potency of mAChR subtype-selective antagonists and small interfering RNAs (siRNAs) on acetylcholine-increased intracellular calcium and MAPK and Akt phosphorylation was consistent with mediation by M3 mAChR (M3R). Consistent with autocrine acetylcholine secretion stimulating MAPK and Akt phosphorylation, M3R antagonists and M3R siRNAs alone also caused a decrease in basal levels of MAPK and Akt phosphorylation in SCLC cell lines. Treatment of SCLC cells with M3R antagonists inhibited cell growth both in vitro and in vivo and also decreased MAPK phosphorylation in tumors in nude mice in vivo. Immunohistochemical staining of SCLC and additional cancer types showed frequent coexpression of acetylcholine and M3R. These findings suggest that M3R antagonists may be useful adjuvants for treatment of SCLC and, potentially, other cancers.

Leveraging human genomic information to identify nonhuman primate sequences for expression array development

Background

Nonhuman primates (NHPs) are essential for biomedical research due to their similarities to humans. The utility of NHPs will be greatly increased by the application of genomics-based approaches such as gene expression profiling. Sequence information from the 3' end of genes is the key resource needed to create oligonucleotide expression arrays.

Results

We have developed the algorithms and procedures necessary to quickly acquire sequence information from the 3' end of nonhuman primate orthologs of human genes. To accomplish this, we identified terminal exons of over 15,000 human genes by aligning mRNA sequences with genomic sequence. We found the mean length of complete last exons to be approximately 1,400 bp, significantly longer than previous estimates. We designed primers to amplify genomic DNA, which included at least 300 bp of the terminal exon. We cloned and sequenced the PCR products representing over 5,500 Macaca mulatta (rhesus monkey) orthologs of human genes. This sequence information has been used to select probes for rhesus gene expression profiling. We have also tested 10 sets of primers with genomic DNA from Macaca fascicularis (Cynomolgus monkey), Papio hamadryas (Baboon), and Chlorocebus aethiops (African green monkey, vervet). The results indicate that the primers developed for this study will be useful for acquiring sequence from the 3' end of genes for other nonhuman primate species.

Conclusion

This study demonstrates that human genomic DNA sequence can be leveraged to obtain sequence from the 3' end of NHP orthologs and that this sequence can then be used to generate NHP oligonucleotide microarrays. Affymetrix and Agilent used sequences obtained with this approach in the design of their rhesus macaque oligonucleotide microarrays.

Expression of lynx1 in developing lung and its modulation by prenatal nicotine exposure

The expression of nicotinic acetylcholine receptors (nAChR) in fetal lung suggests maternal smoking during pregnancy effects newborn lung structure and function by the direct interaction of nicotine with nAChR in the developing lung. The recent identification of the lynx1 nAChR modulator protein in nicotinic neurons in the brain suggests that lynx1 may be similarly expressed in the lung. To study this, cDNAs encoding lynx1 were cloned from rhesus monkey lung. The temporal expression of lynx1 was studied in pre- and postnatal monkey lungs by in situ hybridization, immunohistochemistry, and realtime polymerase chain reaction (PCR). Lynx1 mRNA signal and lynx1 immunohistochemical staining were localized predominantly in airway epithelial cells, submucous glands, and smooth muscle cells, in endothelial and smooth muscle cells in vessel walls, and in alveolar type II cells. The distribution of lynx1 was similar to that of alpha4, beta2, and beta4 nAChR expression as determined by immunohistochemistry. Immunohistochemical staining also co-localized choline acetyltransferase, the enzyme that synthesizes acetylcholine, with lynx1 expression. Lynx1 expression was first observed in 71-day fetal lungs and increased with age. Immunohistochemistry, Western analysis, and realtime PCR analysis showed increased lynx1 expression in lungs following prenatal nicotine exposure. Thus, lynx1 is co-expressed with nAChR in the lung. Alteration of lynx1 levels is a potential new mechanism by which nicotine affects lung development.

Vitamin C prevents the effects of prenatal nicotine on pulmonary function in newborn monkeys

Smoking during pregnancy leads to decreased pulmonary function and increased respiratory illness in offspring. Our laboratory has previously demonstrated that many effects of smoking during pregnancy are mediated by nicotine. We now report that vitamin C supplementation can prevent some of the effects of maternal nicotine exposure on pulmonary function of offspring. Timed-pregnant rhesus monkeys were treated with 2 mg/kg/day nicotine bitartrate from Gestation Days 26 to 160. On Gestation Day 160 (term, 165 days) fetuses were delivered by C-section and subjected to pulmonary function testing the following day. Nicotine exposure significantly reduced forced expiratory flows, but supplementation of mothers with 250 mg vitamin C per day prevented the effects of nicotine on expiratory flows. Vitamin C supplementation also prevented the nicotine-induced increases in surfactant apoprotein-B protein. Neither nicotine nor nicotine plus vitamin C significantly affected levels of cortisol or cytokines, which have been shown to affect lung development and surfactant expression. Prenatal nicotine exposure significantly decreased levels of elastin content in the lungs of offspring, and these effects were slightly attenuated by vitamin C. These findings suggest that vitamin C supplementation may potentially be clinically useful to limit the deleterious effects of maternal smoking during pregnancy on offspring's lung function.

Effects of prenatal nicotine exposure on primate brain development and attempted amelioration with supplemental choline or vitamin C: neurotransmitter receptors, cell signaling and cell development biomarkers in fetal brain regions of rhesus monkeys

Studies in developing rodents indicate that nicotine is a neuroteratogen that disrupts brain development by stimulating nicotinic acetylcholine receptors (nAChRs) that control neural cell replication and differentiation. We administered nicotine to pregnant Rhesus monkeys from gestational day 30 through 160 by continuous infusion, achieving maternal plasma levels comparable to those in smokers (30 ng/ml). Fetal brain regions and peripheral tissues were examined for nAChR subtypes, other neurotransmitter receptors, and indices of cell signaling and cell damage. Nicotine evoked nAChR upregulation, but with distinct regional disparities indicative of selective stimulatory responses. Similarly, indices of cell loss (reduced DNA), cell size and neuritic outgrowth (protein/DNA and membrane/total protein ratios) were distinct for each region and did not necessarily follow the rank order of nAChR upregulation, suggesting the involvement of additional mechanisms such as oxidative stress. We then attempted to offset the adverse effects of nicotine with standard dietary supplements known to interact with nicotine. By itself, choline elicited nicotine-like actions commensurate with its promotion of cholinergic neurotransmission. When given in combination with nicotine, choline protected some regions from damage but worsened nicotine's effects in other regions. Similarly, Vitamin C supplementation had mixed effects, increasing nAChR responses while providing protection from cell damage in the caudate, the brain region most susceptible to oxidative stress. Our results indicate that nicotine elicits neurodevelopmental damage that is highly selective for different brain regions, and that dietary supplements ordinarily thought to be neuroprotectant may actually worsen some of the adverse effects of nicotine on the fetal brain.

Prenatal nicotine exposure increases connective tissue expression in foetal monkey pulmonary vessels

Among the many deleterious effects of maternal smoking during pregnancy on foetal development, is a higher incidence of persistent pulmonary hypertension. The recent identification of nicotinic acetylcholine receptors (nAChR) on cells of the pulmonary vessel walls suggests that maternal smoking during pregnancy may produce morphological alterations in foetal pulmonary vasculature. Timed-pregnant rhesus monkeys were treated with nicotine (1 mg x kg(-1) x day(-1)) delivered by subcutaneous osmotic mini-pumps from days 26-134 of gestation (term: 165 days). Lung sections from 134-day foetal monkeys were used for morphometric analysis, in situ hybridisation and immunohistochemical staining. Following nicotine treatment, total wall and tunica adventitia thickness of airway associated vessels (AAV) increased significantly. Nicotine exposure significantly increased collagen I and III mRNA and protein in tunica adventitia in all AAV but not in tunica media. By contrast, levels of elastin protein were significantly decreased. alpha7 nAChR were detected in AAV fibroblasts that expressed collagen mRNA. Choline acetyltransferase, the enzyme which synthesises acetylcholine, the ligand for alpha7 nAChR was also detected in endothelium and fibroblasts. These findings suggest that with smoking during pregnancy, nicotine is transported across the placenta and directly interacts with nicotinic acetylcholine receptors in pulmonary vessels to alter connective tissue expression and therefore produce vascular structural alterations.

Acetylcholine is an autocrine or paracrine hormone synthesized and secreted by airway bronchial epithelial cells

The role of acetylcholine (ACh) as a key neurotransmitter in the central and peripheral nervous system is well established. However, the role of ACh may be broader because ACh may also function as an autocrine or paracrine signaling molecule in a variety of nonneuronal tissues. To begin to establish ACh of nonneuronal origin as a paracrine hormone in lung, we have examined neonatal and adult monkey bronchial epithelium for the components involved in nicotinic cholinergic signaling. Using immunohistochemistry and RT-PCR, we have demonstrated in lung bronchial epithelial cells (BECs) expression of choline acetyltransferase, the vesicular ACh transporter, the choline high-affinity transporter, alpha7, alpha4, and beta2 nicotinic ACh receptor (nAChR) subunits, and the nAChR accessory protein lynx1. Confocal microscopy demonstrates that these factors are expressed in epithelial cells and are clearly distinct from neighboring nerve fibers. Confirmation of RNA identity has been confirmed by partial sequence analysis of PCR products and by cDNA cloning. Primary culture of BECs confirms the synthesis and secretion of ACh and the activity of cholinesterases. Thus, ACh meets all the criteria for an autocrine/paracrine hormone in lung bronchial epithelium. The nonneuronal cholinergic signaling pathway in lung provides a potentially important target for cholinergic drugs. This pathway may also explain some of the effects of nicotine on fetal development and also provides additional mechanisms by which smoking affects lung cancer growth and development.

Synthesis of acetylcholine by lung cancer

The role of autocrine growth factors in the stimulation of lung cancer growth is well established. Nicotine is an agonist for acetylcholine receptors and stimulates lung cancer growth. This suggests that if lung cancers synthesize acetylcholine (ACh), then ACh may be an autocrine growth factor for lung cancer. Analysis of normal lung demonstrated that the cells of origin of lung cancers express the proteins necessary for non-neuronal ACh storage and synthesis. Analysis of mRNA from squamous cell lung carcinoma, small cell lung carcinoma (SCLC) and adenocarcinoma showed synthesis of choline acetyltransferase (ChAT) and nicotinic receptors. Immunohistochemical analysis of a retrospective series of SCLC and adenocarcinomas showed that more than 50% of the lung cancers screened expressed ChAT and nicotinic receptors. To study the effect of endogenous ACh synthesis on growth, SCLC cell lines were studied. SCLC cell lines were found to express ChAT mRNA and to secrete ACh into the medium as measured by HPLC separation and enzymatically-coupled electrochemical detection. The SCLC cell line NCI-H82 synthesized highest levels of ACh. Showing that the endogenously synthesized ACh interacted with its receptors to stimulate cell growth, addition of muscarinic and nicotinic antagonists slowed H82 cell proliferation. These findings demonstrate that lung cancer cell lines synthesize and secrete ACh to act as an autocrine growth factor. The existence of a cholinergic autocrine loop in lung cancer provides a basis for understanding the effects of nicotine in cigarette smoke on lung cancer growth and provides a new pathway to investigate for potential therapeutic approaches to lung cancer.

Acetylcholine is synthesized by and acts as an autocrine growth factor for small cell lung carcinoma

It is well established that small cell lung carcinomas (SCLCs) express receptors for acetylcholine (ACh) and that stimulation of these receptors by nicotine or other cholinergic agonists stimulates cell growth via activation of nicotinic cholinergic receptors (nAChRs) and/or muscarinic cholinergic receptors (mAChRs). The aim of this study was to determine whether SCLC cells synthesize and secrete ACh and respond to endogenous ACh to create a functioning cholinergic autocrine loop. Reverse transcription-PCR was used to screen a panel of SCLC cell lines for components of cholinergic signaling. Choline acetyltransferase (ChAT) and the vesicular ACh transporter (VAChT), as well as alpha3, alpha5, alpha7, beta2, and beta4, nAChR subunits and M3 and M5 mAChRs, were found to be present in most of the SCLC cell lines tested. Real-time PCR showed that mRNA levels for ChAT, VAChT, and alpha7 and beta2 nAChR subunits varied significantly among different SCLC cell lines tested. The H82 cell line was found to express the highest levels of ChAT, and that cell line was chosen for additional studies of ACh release and cell proliferation. ACh was easily detectable in H82 cell culture media, and levels of ACh were increased by the acetylcholinesterase inhibitor neostigmine. Vesamicol, an inhibitor of VAChT, and hemicholinium-3, an inhibitor of choline transport, both reduced H82 cell ACh basal release in a dose-dependent manner. In parallel with the reductions of ACh release, vesamicol and hemicholinium-3 also decreased H82 cell proliferation. H82 cell proliferation was also inhibited by the muscarinic and nicotinic antagonists atropine and mecamylamine, respectively, in dose- and time-dependent manners. Finally, archival cases of SCLC were screened by immunohistochemistry for expression of ChAT. Thirteen of 26 tumors screened were positive for ChAT. These findings demonstrate that SCLC can synthesize, secrete, and degrade ACh and that released ACh stimulates SCLC cell growth. Identification of this new autocrine loop provides a potential new target for therapeutic intervention.

Maternal nicotine exposure upregulates collagen gene expression in fetal monkey lung. Association with alpha7 nicotinic acetylcholine receptors

The recent identification of nicotinic acetylcholine receptors (nAChR) in pulmonary fibroblasts suggests that in utero nicotine exposure may alter collagen expression by these cells in the developing lung. To test this hypothesis, timed-pregnant rhesus monkeys were administered nicotine (1-1.5 mg/kg/d, subcutaneously) using osmotic minipumps from Days 26-134 or 26-160 of gestation (term = 165 d). In utero nicotine exposure significantly increased airway wall area per unit epithelial basement membrane. Collagen type I and III mRNA expression and immunostaining were significantly increased in the airway and alveolar walls of the nicotine-treated group. Elastin mRNA expression increased, but protein expression in parenchyma remained unchanged. Dual labeling studies colocalized alpha7 nAChR and collagen to the same cells in airway wall cells, and colocalization of alpha7 nAChR and collagen was confirmed in isolated pulmonary fibroblasts. These findings suggest that nicotine may directly interact with alpha7 nAChR to increase collagen accumulation in airway and alveolar walls following in utero nicotine exposure. These data suggest that passage of nicotine across the placenta to increase collagen deposition and therefore increase airway wall dimensions in fetal lung may partially explain the observed alterations in lung mechanics in the infants of mothers who smoke during pregnancy.

Chronic maternal nicotine exposure alters neuronal systems in the arcuate nucleus that regulate feeding behavior in the newborn rhesus macaque

It is well known that maternal smoking during pregnancy can lead to low birth weight and low body fat in human newborns. The purpose of this study was to determine whether chronic maternal nicotine treatment alters levels of known regulators of energy balance in the newborn offspring. Pregnant rhesus monkeys were treated with nicotine tartrate (1.5 mg/kg x d) starting on d 26 of pregnancy and maintained through d 160 of gestation. Nicotine exposure had no significant effect on absolute birth weights of the neonatal monkeys, although there was a 10% reduction in birth weights with nicotine exposure when they were normalized to maternal weight. Postnatal d 1 plasma leptin levels were significantly reduced by about 50% in the nicotine treatment group compared with saline controls, suggesting that the infant monkeys exposed to nicotine may also have lower body fat levels. In situ hybridization studies demonstrated that chronic nicotine exposure resulted in a significant decrease in arcuate NPY mRNA expression in the neonatal monkeys. In addition, there was a 2-fold increase in POMC mRNA in the arcuate nucleus in the nicotine-exposed group. These data suggest that nicotine exposure during pregnancy may increase energy expenditure in the developing fetus through actions on hypothalamic systems, resulting in lower birth weights and body fat levels.

Prenatal nicotine exposure alters pulmonary function in newborn rhesus monkeys

Epidemiological studies have shown that offspring of women who smoke during pregnancy have abnormal lung function and associated higher incidences of lower respiratory disorders. The recent identification of nicotinic acetylcholine receptors (nAChR) in fetal lung suggests that the direct interaction between nicotine and nAChR in fetal lung may underlie the postnatal pulmonary abnormalities seen in such infants. This hypothesis was tested in monkeys to determine if maternal nicotine exposure would produce changes in lung mechanics in newborn monkeys similar to those observed in human infants whose mothers smoked during pregnancy. Timed pregnant rhesus monkeys were infused with either nicotine (1.5 mg/kg/d, n = 7) or saline (n = 7) using subcutaneous osmotic pumps from Day 26 to 160 of gestation. On Day 160 of pregnancy (term = 165 d), fetuses were delivered by C-section, and the following day were subjected to pulmonary function testing. After testing, animals were sacrificed, and lungs weighed and fixed. Lung weight and fixed lung volume decreased (16% and 14%, respectively) significantly following in utero nicotine exposure. Peak tidal expiratory flow, FEV(0.2), mean mid-expiratory flow, forced expiratory volume at peak expiratory flow (FEV(PEF)), and FEV(PEF)/FVC% were significantly lower in newborns exposed to nicotine during gestation. Absolute and specific pulmonary resistance increased significantly whereas absolute and specific dynamic compliance remained unchanged in prenatally nicotine-treated pups. These changes in pulmonary function are strikingly similar to the changes observed in offspring of human smokers. This suggests that the interaction of nicotine with nAChR in developing lung is responsible for the altered pulmonary mechanics observed in human infants whose mothers smoked during pregnancy.

Pharmacology and cell biology of the bombesin receptor subtype 4 (BB4-R)

Recently, a fourth member of the bombesin (Bn) receptor family (fBB4-R) was isolated from a cDNA library from the brain of the frog, Bombina orientalis. Its pharmacology and cell biology are largely unknown, and no known natural cell lines or tissues possess sufficient numbers of fBB4-R's to allow either of these to be determined. To address these issues, we have used three different strategies. fBB4-R expression in cells widely used for other Bn receptor subtypes was unsuccessful as was expression in two frog cell lines. However, stable fBB4-R cell lines were obtained in CHO-K1 cells which were shown to faithfully demonstrate the correct pharmacology of the related Bn receptor, the GRP receptor, when expressed in these cells. [DPhe6,betaAla11,Phe13,Nle14]Bn(6-14) was found to have high affinity (Ki = 0.4 nM) for the fBB4 receptor and 125I-[DTyr6,betaala11,Phe13,Nle14]Bn(6-14) to be an excellent ligand for this receptor. The fBB4-R had a unique pharmacology for naturally occurring Bn-related agonists, with the presence of a penultimate phenylalanine being critical for high-affinity interaction. It also had a unique profile for six classes of Bn antagonists. The fBB4-R was coupled to phospholipase C with activation increasing [3H]inositol phosphates and mobilizing Ca2+ almost entirely from cellular sources. There was a close correlation between agonist the receptor occupation and the receptor activation. Three of the five classes of Bn receptor antagonists that interacted with higher affinity with the fBB4-R functioned as fBB4-R antagonists and two as partial agonists. fBB4-R activation stimulated increases in phospholipase D (PLD) over the same range of concentrations at which it activated phospholipase C. These results demonstrate that the fBB4 receptor has a unique pharmacology for agonists and antagonists and is coupled to phospholipase C and D. The availability of these cell lines, this novel ligand, and the identification of three classes of antagonists that can be used as lead compounds should facilitate the further investigation of the pharmacology and cell biology of the BB4 receptor.

Molecular cloning and characterization of two putative G protein-coupled receptors which are highly expressed in the central nervous system

We have cloned from a rat hypothalamic cDNA library two closely related G protein-coupled receptors (GPCRs) which we have designated GPCR/CNS1 and GPCR/CNS2. The peptide sequences of these two G protein-coupled receptors shared 42% identity with each other and were next most closely related to the endothelin receptors and the bombesin-like peptide receptors (approximately 25% identity). Northern blot analysis showed that both GPCR/CNS1 and GPCR/CNS2 were very highly expressed in rat brain. In situ hybridization of rat brain demonstrated broad distribution of both receptors throughout the central nervous system. GPCR/CNS1 appeared to be expressed primarily in glial cells of the fiber tracts, while GPCR/CNS2 was expressed primarily in cells of the gray matter. The different distribution patterns of these two receptors in rat brain suggests distinct functional roles for each receptor in the central nervous system. Expression of these two receptors in Xenopus oocytes showed no response to any known endothelin and bombesin-like peptides. Therefore, the endogenous ligands and physiological significance of GPCR/CNS1 and GPCR/CNS2 remain to be elucidated, but may be related to the endothelins or bombesins. The very abundant expression in brain by these two receptors, however, suggests that they play important roles in the central nervous system.

Prenatal nicotine increases pulmonary alpha7 nicotinic receptor expression and alters fetal lung development in monkeys

It is well established that maternal smoking during pregnancy is a leading preventable cause of low birth weight and prematurity. Less appreciated is that maternal smoking during pregnancy is also associated with alterations in pulmonary function at birth and greater incidence of respiratory illnesses after birth. To determine if this is the direct result of nicotine interacting with nicotinic cholinergic receptors (nAChRs) during lung development, rhesus monkeys were treated with 1 mg/kg/day of nicotine from days 26 to 134 of pregnancy. Nicotine administration caused lung hypoplasia and reduced surface complexity of developing alveoli. Immunohistochemistry and in situ alpha-bungarotoxin (alphaBGT) binding showed that alpha7 nAChRs are present in the developing lung in airway epithelial cells, cells surrounding large airways and blood vessels, alveolar type II cells, free alveolar macrophages, and pulmonary neuroendocrine cells (PNEC). As detected both by immunohistochemistry and by alphaBGT binding, nicotine administration markedly increased alpha7 receptor subunit expression and binding in the fetal lung. Correlating with areas of increased alpha7 expression, collagen expression surrounding large airways and vessels was significantly increased. Nicotine also significantly increased numbers of type II cells and neuroendocrine cells in neuroepithelial bodies. These findings demonstrate that nicotine can alter fetal monkey lung development by crossing the placenta to interact directly with nicotinic receptors on non-neuronal cells in the developing lung, and that similar effects likely occur in human infants whose mothers smoke during pregnancy.

Discovery of a high affinity radioligand for the human orphan receptor, bombesin receptor subtype 3, which demonstrates that it has a unique pharmacology compared with other mammalian bombesin receptors

An orphan receptor discovered in 1993 was called bombesin receptor subtype 3 (BRS-3) because of 47-51% amino acid identity with bombesin (Bn) receptors. Its pharmacology is unknown, because no naturally occurring tissues have sufficient receptors to allow studies. We made two cell lines stably expressing the human BRS-3 (hBRS-3). hBRS-3 was overexpressed in the human non-small cell lung cancer cells, NCI-H1299, and the other was made in Balb 3T3 cells, which lack endogenous BRS-3. [D-Phe6,beta-Ala11,Phe13, Nle14]Bn-(6-14) (where Nle represents norleucine) was discovered to have high potency for stimulating inositol phosphate formation in both cell lines. [125I-D-Tyr6,beta-Ala11,Phe13, Nle14]Bn-(6-14) bound to both cell lines with high affinity. Neither Bn nor 14 other naturally occurring Bn peptides bound to hBRS-3 with a Kd <1000 nM. Twenty-six synthetic peptides that are high affinity agonists or antagonists at other bombesin receptors had an affinity >1000 nM. Guanosine 5'-(beta,gamma-imido)triphosphate inhibited binding to both cells due to a change in receptor affinity. These results demonstrate hBRS-3 has a unique pharmacology. It does not interact with high affinity with any known natural agonist or high affinity antagonist of the Bn receptor family, suggesting the natural ligand is either an undiscovered member of the Bn peptide family or an unrelated peptide. The availability of these cell lines and the hBRS-3 ligand should facilitate identification of the natural ligand for BRS-3, its pharmacology, and cell biology.

Gastrin-releasing peptide-like immunoreactivity is present in human maternal and fetal placental membranes

Extracts of human term amnion, placenta, and chorion/decidual tissue (n = 5) contained gastrin-releasing peptide-like immunoreactivity (GRPLI) in amounts of 4.7 +/- 2.9 (pmol/g wet wt; mean +/- SEM), 3.6 +/- 1.1 and 2.9 +/- 1.5, respectively. Using C-terminally directed antisera and gel filtration chromatography and reverse-phase high-performance liquid chromatography (HPLC), each tissue contained molecular forms consistent with the presence of GRP1-27 and GRP18-27 but also contained larger amounts of two GRPLI peaks, which apparently are novel GRP-like peptides. In contrast, tissue extracts of human fetal lung contained only GRP1-27, GRP14-27, and GRP18-27. Using RT-PCR and specific GRP primers and probes, messenger RNA encoding for GRP was readily demonstrable from 6-weeks gestation throughout pregnancy to term in full-thickness membranes, placental villi, and decidua. Positive immunohistochemical staining for GRP occurred in extravillous trophoblasts in decidual septa and fetal membranes, cytotrophoblasts, syncytiotrophoblast, and certain stromal cells in placental villi and amniotic epithelium. GRPLI and GRP messenger RNA were present from the earliest dates examined (6-9 weeks) throughout pregnancy to term. Given the proven trophic nature of GRP and related peptides, these peptides may play important roles in maternal, placental, and fetal development during human pregnancy.

There are three distinct forms of bombesin. Identification of [Leu13]bombesin, [Phe13]bombesin, and [Ser3,Arg10,Phe13]bombesin in the frog Bombina orientalis

Amphibian bombesin is the prototypic peptide that defines the bombesin-like peptide family. In this paper we show that in the frog Bombina orientalis, there are actually 3 distinct forms of bombesin, and each of these peptides is an agonist with differing affinities for the known bombesin receptors. Oligonucleotides complementary to the 5'- and 3'-untranslated regions of the bombesin mRNA were used to amplify bombesin-related cDNAs from the skin, brain, and gut of B. orientalis. Three classes of cDNAs were found. One class encoded the previously characterized form of bombesin which has a Leu at position 13 ([Leu13]bombesin). The other two classes, respectively, encoded new bombesin-like peptides which we have designated as [Phe13]bombesin and [Ser3,Arg10,Phe13]bombesin ([SAP]bombesin). The existence of [SAP]bombesin in skin was confirmed by tandem mass spectrometry. Polymerase chain reaction analysis of genomic DNA showed the mRNAs for [Leu13]bombesin, [Phe13]bombesin, and [SAP]bombesin most likely arise from separate genes. Polymerase chain reaction analysis showed different patterns of tissue-specific expression for each form. [Leu13]Bombesin and [SAP]bombesin were predominantly expressed in skin, brain, and gut; [Phe13]bombesin was expressed only in brain, and [Leu13]bombesin predominated in oocytes. [SAP]Bombesin contained a cleavage site between residues 4 and 5, which if used would yield the peptide [SAP]bombesin(5-14) which has the sequence [Gln3,Arg6]neuromedin B. Thus a frog homolog of NMB could derive from the [SAP]bombesin prohormone. [Phe13]Bombesin, [SAP]bombesin, and [SAP]bombesin(5-14) were synthesized and their affinities for the mammalian bombesin-like peptide (GRP and NMB) receptors determined. These peptides acted as agonists for the GRP and NMB receptors, with relative potencies for the GRP receptor of [Leu13]bombesin > [Phe13]bombesin > [SAP]bombesin(5-14) > [SAP]bombesin and for the NMB receptor of [Phe13]bombesin > [SAP]bombesin(5-14) > [Leu13]bombesin > [SAP]bombesin. None of these peptides demonstrated high affinity binding for the BRS-3 receptor. The different receptor affinities and tissue distribution of these peptides suggests distinct physiologic roles and raises the possibility of as yet uncharacterized mammalian homologs of these new amphibian peptides.

Locations and molecular forms of gastrin-releasing peptide-like immunoreactive entities in ovine pregnancy

Large quantities of gastrin-releasing peptide-like immunoreactivity (GRP-LI) are present in ovine pregnancy fluids (allantoic fluid > fetal plasma > esophageal fluid = amniotic fluid = urine > maternal plasma) and in term endometrium (60 +/- 29 pmol.g-1) and myometrium (4.5 +/- 1.2 pmol.g-1). The larger molecular size [greater than GRP (1-27)] of this GRP-LI entity is not due to a GRP binding protein nor to a C-terminal extension of GRP. In contrast, ovine fetal colon extracts appear to contain the usual GRP (1-27) and GRP (18-27) forms. Hence, the uterus, not the fetus, is the probable source of this novel GRP-like peptide. It apparently acts as a hormone in ovine pregnancy and may play an important role in fetal-placental development.

Cloning of a receptor for amphibian [Phe13]bombesin distinct from the receptor for gastrin-releasing peptide: identification of a fourth bombesin receptor subtype (BB4)

Bombesin is a tetradecapeptide originally isolated from frog skin and demonstrated to have a wide range of actions in mammals. Based on structural homology and similar biological activities, gastrin-releasing peptide (GRP) has been considered the mammalian equivalent of bombesin. We previously reported that frogs have both GRP and bombesin, which therefore are distinct peptides. We now report the cloning of a bombesin receptor subtype (BB4) that has higher affinity for bombesin than GRP. PCR was used to amplify cDNAs related to the known bombesin receptors from frog brain. Sequence analysis of the amplified cDNAs revealed 3 classes of receptor subtypes. Based on amino acid homology, two classes were clearly the amphibian homologs of the GRP and neuromedin B receptors. The third class was unusual and a full-length clone was isolated from a Bombina orientalis brain cDNA library. Expression of the receptor in Xenopus oocytes demonstrated that the receptor responded to picomolar concentrations of [Phe13]-bombesin, the form of bombesin most prevalent in frog brain. The relative rank potency of bombesin-like peptides for this receptor was [Phe13]bombesin > [Leu13]bombesin > GRP > neuromedin B. In contrast, the rank potency for the GRP receptor is GRP > [Leu13]bombesin > [Phe13]bombesin > neuromedin B. Transient expression in CHOP cells gave a Ki for [Phe13]bombesin of 0.2 nM versus a Ki of 2.1 nM for GRP. Distribution analysis showed that this receptor was expressed only in brain, consistent with the distribution of [Phe13]-bombesin. Thus, based on distribution and affinity, this bombesin receptor is the receptor for [Phe13]bombesin. Phylogenetic analysis suggests that this receptor separated prior to separation of the GRP and neuromedin B receptors; thus, BB4 receptors and their cognate ligands may also exist in mammals.

Gastrin-releasing peptide is produced in the pregnant ovine uterus

Our previous finding of appreciable quantities of a gastrin-releasing peptide (GRP)-like immunoreactive (GRPLI) entity in ovine fetal and maternal plasma led us to examine the ovine pregnant uterus as a possible source of this material. At term, intense immunohistochemical staining for GRPLI occurred in the endometrial epithelial cells, and the term ovine uterus also contained abundant GRP messenger RNA (mRNA). In contrast, GRP mRNA was not detected in fetal membranes. GRP mRNA was present in the uterus on gestational day 63; a significant increase in GRP mRNA had occurred by day 100. Thereafter, levels remained elevated until term, but 3 months postpartum, GRP mRNA levels were greatly reduced. As previous studies suggested the GRPLI entity to be of greater molecular size than GRP-(1-27), we deduced the primary structure of ovine uterus GRP by sequencing a complementary DNA clone isolated from a complementary DNA library constructed from term ovine uterus polyadenylated RNA. Ovine uterine GRP is composed of 27 amino acid residues and has a conserved C-terminal region, similar to GRP structures in other species. We conclude that during pregnancy, the ovine uterus produces considerable quantities of GRP, which may play an important but hitherto unrecognized role in utero-placental development and possibly in fetal development after transfer to the fetus.

A rhesus monkey model to characterize the role of gastrin-releasing peptide (GRP) in lung development. Evidence for stimulation of airway growth

Gastrin-releasing peptide (GRP) is developmentally expressed in human fetal lung and is a growth factor for normal and neoplastic lung but its role in normal lung development has yet to be clearly defined. In this study we have characterized the expression of GRP and its receptor in fetal rhesus monkey lung and determined the effects of bombesin on fetal lung development in vitro. By RNA blot analysis, GRP mRNA was first detectable in fetal monkey lung at 63 days gestation, reached highest levels at 80 days gestation, and then declined to near adult levels by 120 days gestation; a pattern closely paralleling GRP expression in human fetal lung. As in human lung, in situ hybridization localized GRP mRNA to neuroendocrine cells though during the canalicular phase of development (between 63-80 days gestation) GRP mRNA was present not only in classic pulmonary neuroendocrine cells, but also in cells of budding airways. Immunohistochemistry showed that bombesin-like immunoreactivity was present in neuroendocrine cells, but not in budding airways, suggesting that in budding airways either the GRP mRNA is not translated, is rapidly secreted, or a related, but different RNA is present. RNase protection analysis using a probe to the monkey GRP receptor demonstrated that the time course of receptor RNA expression closely paralleled the time course of GRP RNA expression. In situ hybridization showed that GRP receptors were primarily expressed in epithelial cells of the developing airways. Thus GRP would appear to be secreted from neuroendocrine cells to act on target cells in developing airways. This hypothesis was confirmed by organ culture of fetal monkey lung in the presence of bombesin and bombesin antagonists. Bombesin treatment at 1 and 10 nM significantly increased DNA synthesis in airway epithelial cells and significantly increased the number and size of airways in cultured fetal lung. In fact, culturing 60 d fetal lung for 5 d with 10 nM bombesin increased airway size and number nearly to that observed in cultured 80 d fetal lung. The effects of bombesin could be blocked by specific GRP receptor antagonists. Thus this study demonstrates that GRP receptors are expressed on airway epithelial cells in developing fetal lung and that the interaction of GRP with the GRP receptor stimulates airway development.

Functional analysis of the 5'-flanking region of the human gastrin-releasing peptide gene in small cell lung carcinoma cell lines

The mammalian bombesin-like peptide, gastrin-releasing peptide (GRP), is expressed by many small cell lung carcinomas (SCLC), stimulates the growth of some SCLC and thus is an autocrine growth factor for a subset of SCLC. The subset of SCLC that expresses GRP typically shows neuroendocrine differentiation and has been designated as "classic" SCLC. To begin to characterize the mechanisms responsible for the expression of GRP in classic SCLC, the 5'-flanking region of the human GRP gene was sequenced and analyzed for cis-acting elements. Constructs containing up to 6.0 kilobases of 5'-flanking region were transiently expressed in SCLC and in control cell lines. Deletion analysis demonstrated that a sequence of 178 bases upstream of the transcriptional start was sufficient for basal expression in SCLC cell lines. A negative regulatory element was located between -5.5 and -2.6 kilobases; a general enhancer element was located between -1409 and -1197 kilobases, and a tissue-specific element was located between -1128 and -793 kilobases. Mobility shift analysis indicated that proteins from nuclear extracts of classic SCLC but not variant SCLC bound to this tissue-specific regulatory element. Thus the regulation of GRP gene expression in SCLC cell lines is a balance between a negative element, a general enhancer, and a tissue-specific element that appears active only in classic SCLC cell lines.