Hildegard M. Schuller

Classification of Proliferative Pulmonary Lesions of the Mouse Recommendations of the Mouse Models of Human Cancers Consortium

Rapid advances in generating new mouse genetic models for lung neoplasia provide a continuous challenge for pathologists and investigators. Frequently, phenotypes of new models either have no precedents or are arbitrarily attributed according to incongruent human and mouse classifications. Thus, comparative characterization and validation of novel models can be difficult. To address these issues, a series of discussions was initiated by a panel of human, veterinary, and experimental pathologists during the Mouse Models of Human Cancers Consortium (NIH/National Cancer Institute) workshop on mouse models of lung cancer held in Boston on June 20–22, 2001. The panel performed a comparative evaluation of 78 cases of mouse and human lung proliferative lesions, and recommended development of a new practical classification scheme that would (a) allow easier comparison between human and mouse lung neoplasms, (b) accommodate newly emerging mouse neoplasms, and (c) address the interpretation of benign and preinvasive lesions of the mouse lung. Subsequent discussions with additional experts in pulmonary pathology resulted in the current proposal of a new classification. It is anticipated that this classification, as well as the complementary digital atlas of virtual histological slides, will help investigators and pathologists in their characterization of new mouse models, as well as stimulate further research aimed at a better understanding of proliferative lesions of the lung.

Is cancer triggered by altered signalling of nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) are the central regulators of stimulatory and inhibitory neurotransmitters that control the synthesis and release of growth, angiogenic and neurotrophic factors in cancer cells, the cancer microenvironment and distant organs. Data discussed in this Review suggests that smoking and possibly other environmental and lifestyle factors increase the function of nAChRs that stimulate cancer cells and reduce the function of nAChRs that inhibit cancer cells. This novel paradigm necessitates the development of marker-guided cancer intervention strategies that aim to restore the balance between nAChR-mediated stimulatory and inhibitory neurotransmitters and their downstream effectors.

Mechanisms of smoking-related lung and pancreatic adenocarcinoma development

Adenocarcinoma of the lungs and pancreas are among the most common and most deadly smoking-associated cancers. Cigarette smoke contains various toxic chemicals, including a carcinogenic nitrosamine, nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). One of the most well-known features of NNK is the ability of its metabolites to bind to DNA and induce activating point mutations in the RAS gene. But NNK is also a β-adrenergic-receptor agonist that stimulates arachidonic acid release, leading to the formation of mitogenic metabolites that stimulate DNA synthesis and cell proliferation. NNK therefore contributes to tobacco-induced carcinogenesis by several mechanisms.

Cell type specific, receptor-mediated modulation of growth kinetics in human lung cancer cell lines by nicotine and tobacco-related nitrosamines

The objective of this study was to investigate a potential involvement of nicotinic cholinergic receptors in the mediation of cell type specific biological effects of nicotine and the two tobacco-related nitrosamines N-nitrosodiethylamine (DEN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on human lung cells. Three well differentiated human lung cancer cell lines that have been reported previously to possess ultrastructural and biochemical features of normal pulmonary neuroendocrine cells, Clara cells and alveolar type II cells, respectively, were used for these experiments. The effects of nicotine, DEN, and NNK on cell proliferation and its modulation by established antagonists of nicotinic and muscarinic cholinergic receptors were studied. In the neuroendocrine cell line, nicotine and the two nitrosamines caused a strong stimulation of cell proliferation that was inhibited by antagonists of nicotinic cholinergic receptors. In the cell lines with features of Clara cells and alveolar type II cells, nicotine did not stimulate cell proliferation. Both nitrosamines stimulated cell proliferation in the cell line with Clara cell features. This effect was not changed by pre-exposure to cholinergic antagonists. The data suggest a selective uptake of nicotine and the two nitrosamines via nicotinic cholinergic receptors in pulmonary neuroendocrine cells.

Nicotinic receptor-mediated activation by the tobacco-specific nitrosamine NNK of a Raf-1/MAP kinase pathway, resulting in phosphorylation of c-myc in human small cell lung carcinoma cells and pulmonary neuroendocrine cells.

Abstract. Objective: Small cell lung carcinoma (SCLC) expresses phenotypic features of pulmonary neuroendocrine cells and demonstrates a strong etiologic association with smoking. SCLC cell lines express a Raf-1-dependent mitogenic signal transduction pathway, which is thought to transduce the mitogenic signals initiated by neuropeptide autocrine growth factors. Recent studies have identified the tobacco-specific carcinogenic nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) as a site-selective high-affinity agonist for the α7 nicotinic acetylcholine receptor (α7 nAChR), which regulates the growth of a significant subset of SCLC in vitro by stimulating the release of the autocrine growth factor serotonin. The purpose of this study was to identify signaling events initiated by binding of NNK to the α7 nAChR. Design: We have used a human SCLC cell line and fetal hamster pulmonary neuroendocrine cells with in vitro kinase activation assays and western blots to assess the levels of expression and activation of Raf-1, MAPK and c-myc to address this issue. Results: Our data show that NNK activates the Raf-1/MAP kinase pathway, resulting in phosphorylation of c-myc. The activation of this signal transduction pathway by NNK was inhibited by the site-selective antagonist for the α7 nAChR α-bungarotoxin (α-BTX) or by the serotonin reuptake inhibitor imipramine, suggesting that the responses to NNK were mediated by nicotinic receptor-initiated release of serotonin. Accordingly, NNK-induced 5-HT release was blocked by α-BTX while NNK-induced DNA synthesis was inhibited by α-BTX, imipramine, the PKC inhibitor sphingosine or the MEK inhibitor PD98059. SCLC cells demonstrated high basal levels of 5-HT release, DNA synthesis, and over-expressed Raf-1 and MAPK protein suggesting the constitutive activation of an upstream regulator such as the α7 nAChR. Conclusion: Our findings link, for the first time, the stimulation of a nicotinic acetylcholine receptor by a cancer-causing agent with the activation of a Raf-1/MAPK/c-myc signaling pathway. Furthermore, our data suggest that serotonin uptake inhibitors may protect against the development or be useful in the clinical management of SCLC.

Interaction of tobacco-specific toxicants with the neuronal α7 nicotinic acetylcholine receptor and its associated mitogenic signal transduction pathway: potential role in lung carcinogenesis and pediatric lung disorders

Pulmonary neuroendocrine cells function as hypoxia-sensitive chemoreceptors, and they release peptides and biogenic amines that are important mediators of pulmonary neonatal adaptation. Some of these products additionally act as autocrine growth factors. Increased numbers of pulmonary neuroendocrine cells have been observed in several smoking-associated pediatric lung disorders such as bronchopulmonary dysplasia, cystic fibrosis, sudden infant death syndrome, and asthma. Disturbed pulmonary neuroendocrine function has been implicated in the etiology of this disease complex. One of the most common smoking-associated lung cancer types, small cell lung carcinoma, expresses phenotypic and functional features of pulmonary neuroendocrine cells. We, as well as others, have shown that the release of the autocrine growth factors 5-hydroxytryptamine (5-HT, serotonin) and mammalian bombesin/gastrin releasing peptide (MB/GRP) by cell lines derived from human small cell lung carcinoma or fetal hamster pulmonary neuroendocrine cells are regulated by a neuronal nicotinic acetylcholine receptor comprised of alpha(7) subunits. In radio-receptor assays, nicotine and the nicotine-derived carcinogenic nitrosamines NNNN. Binding of nicotine or NNK to the alpha(7) receptor resulted in calcium influx and overexpression and activation of the serine-threonine protein kinase Raf-1. In turn, this event lead to overexpression and activation of the mitogen activated (MAP) kinases extracellular signal regulated kinase 1 (ERK1) and extracellular signal regulated kinase 2 (ERK2) and stimulation of DNA synthesis accompanied by an increase in cell numbers in fetal pulmonary neuroendocrine cells and small cell carcinoma cells. Exposure of fetal pulmonary neuroendocrine cells for 6 days to NNK caused a prominant up-regulation of Raf-1. Our findings suggest that chronic exposure to nicotine and NNK in pregnant women who smoke may up-regulate the alpha(7) nicotinic receptor as well as components of its associated mitogenic signal transduction pathway, thus increasing the susceptibilities of the infants for the development of pediatric lung disorders. Similarly, up-regulation of one or several components of this nicotinic receptor pathway in smokers may be an important factor for the development of small cell lung carcinoma.

Beta-adrenergic modulation of NNK-induced lung carcinogenesis in hamsters

Objective: Lung cancer is the leading cause of cancer death in industrialized countries. Pulmonary adenocarcinoma (PAC) is the most common histologic type of lung cancer, and it is reproducibly induced by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in laboratory rodents. We have recently shown that the growth of cell lines derived from human PACs is controlled by β-adrenergic receptors, and that NNK is a high affinity agonist for this receptor family. Design: In the current study, we have tested the relevance of these in in vitro findings for in vivo NNK-induced lung tumorigenesis, using a well-established hamster model of NNK-induced PAC. Results: Our experiments demonstrate a significant increase in NNK-induced PAC multiplicity in animals chronically exposed to the β-adrenergic agonist epinephrine or theophylline which causes intracellular accumulation of the β-adrenergic second messenger cAMP. On the other hand, our data show that administration of the β-adrenergic antagonist propranolol prior to each NNK injection significantly inhibited the development of PACs. Discussion: Our findings support the hypothesis that the development of tobacco-associated PAC may be modulated by β-adrenergic agents, and that the interaction of NNK with β-adrenergic receptors contributes to the genesis of this histologic lung cancer type.

Gamma-aminobutyric acid, a potential tumor suppressor for small airway-derived lung adenocarcinoma.

Pulmonary adenocarcinoma (PAC) is the leading type of lung cancer in smokers and non-smokers that arises in most cases from small airway epithelial cells. PAC has a high mortality due to its aggressive behavior and resistance to cancer therapeutics. We have shown previously that the proliferation of human PAC cells NCI-H322 and immortalized human small airway epithelial cells HPL1D is stimulated by cyclic adenosine monophosphate (cAMP)/protein kinase A-dependent phosphorylation of cyclic adenosine monophosphate response element-binding (CREB) protein and transactivation of the epidermal growth factor receptor and that this pathway is activated by beta-1-adrenoreceptors (beta(1)-ARs) and the non-genomic estrogen receptor beta. Our current in vitro studies with HPL1D and NCI-H322 cells showed that signaling via the gamma-amino butyric acid receptor (GABA(B)R) strongly inhibited base level and isoproterenol-induced cAMP, p-CREB, cyclic adenosine monophosphate response element-luciferase activity and p-extracellular regulated kinase-1 (ERK1)/2 and effectively blocked DNA synthesis and cell migration. The inhibitory effects of gamma-amino butyric acid (GABA) were disinhibited by the GABA(B)R antagonist CGP-35348 or GABA(B)R knockdown. Immunohistochemical investigation of hamster lungs showed significant underexpression of GABA in animals with small airway-derived PACs induced by the nicotine-derived carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). These findings suggest that GABA may have tumor suppressor function in small airway epithelia and the PACs derived from them and that downregulation of GABA by NNK may contribute to the development of this cancer in smokers. Our findings suggest that marker-guided treatment with GABA or a GABA(B)R agonist of individuals with downregulated pulmonary GABA may provide a novel targeted approach for the prevention of PAC in smokers.

GABAB receptor is a novel drug target for pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer death. Smoking, diabetes, and pancreatitis are risk factors. It has been shown that the growth of PDAC and pancreatic duct epithelial cells is regulated by beta‐adrenoreceptors (β‐ARs). The activity of β‐ARs in the central nervous system is counteracted by γ‐aminobutyric acid (GABA) via GABAB receptor‐mediated inhibition of adenylyl cyclase. The aim of the study was to investigate if GABABR inhibits β‐AR signaling in PDAC and pancreatic duct epithelial cells, thus blocking driving forces of cancer progression, such as cell proliferation and cell migration.

Expression of the α7 nicotinic acetylcholine receptor in human lung cells

BackgroundWe and others have shown that one of the mechanisms of growth regulation of small cell lung cancer cell lines and cultured pulmonary neuroendocrine cells is by the binding of agonists to the α7 neuronal nicotinic acetylcholine receptor. In addition, we have shown that the nicotine-derived carcinogenic nitrosamine, 4(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is a high affinity agonist for the α7 nicotinic acetylcholine receptor. In the present study, our goal was to determine the extent of α7 mRNA and protein expression in the human lung.MethodsExperiments were done using reverse transcription polymerase chain reaction (RT-PCR), a nuclease protection assay and western blotting using membrane proteins.ResultsWe detected mRNA for the neuronal nicotinic acetylcholine receptor α7 receptor in seven small cell lung cancer (SCLC) cell lines, in two pulmonary adenocarcinoma cell lines, in cultured normal human small airway epithelial cells (SAEC), one carcinoid cell line, three squamous cell lines and tissue samples from nine patients with various types of lung cancer. A nuclease protection assay showed prominent levels of α7 in the NCI-H82 SCLC cell line while α7 was not detected in SAEC, suggesting that α7 mRNA levels may be higher in SCLC compared to normal cells. Using a specific antibody to the α7 nicotinic receptor, protein expression of α7 was determined. All SCLC cell lines except NCI-H187 expressed protein for the α7 receptor. In the non-SCLC cells and normal cells that express the α7 nAChR mRNA, only in SAEC, A549 and NCI-H226 was expression of the α7 nicotinic receptor protein shown. When NCI-H69 SCLC cell line was exposed to 100 pm NNK, protein expression of the α7 receptor was increased at 60 and 150 min.ConclusionExpression of mRNA for the neuronal nicotinic acetylcholine receptor α7 seems to be ubiquitously expressed in all human lung cancer cell lines tested (except for NCI-H441) as well as normal lung cells. The α7 nicotinic receptor protein is expressed in fewer cell lines, and the tobacco carcinogen NNK increases α7 nicotinic receptor protein levels.