Howard K. Plummer

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.

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.

Expression of inwardly rectifying potassium channels (GIRKs) and beta-adrenergic regulation of breast cancer cell lines

BackgroundPrevious research has indicated that at various organ sites there is a subset of adenocarcinomas that is regulated by beta-adrenergic and arachidonic acid-mediated signal transduction pathways. We wished to determine if this regulation exists in breast adenocarcinomas. Expression of mRNA that encodes a G-protein coupled inwardly rectifying potassium channel (GIRK1) has been shown in tissue samples from approximately 40% of primary human breast cancers. Previously, GIRK channels have been associated with beta-adrenergic signaling.MethodsBreast cancer cell lines were screened for GIRK channels by RT-PCR. Cell cultures of breast cancer cells were treated with beta-adrenergic agonists and antagonists, and changes in gene expression were determined by both relative competitive and real time PCR. Potassium flux was determined by flow cytometry and cell signaling was determined by western blotting.ResultsBreast cancer cell lines MCF-7, MDA-MB-361 MDA-MB 453, and ZR-75-1 expressed mRNA for the GIRK1 channel, while MDA-MB-468 and MDA-MB-435S did not. GIRK4 was expressed in all six breast cancer cell lines, and GIRK2 was expressed in all but ZR-75-1 and MDA-MB-435. Exposure of MDA-MB-453 cells for 6 days to the beta-blocker propranolol (1 μM) increased the GIRK1 mRNA levels and decreased beta2-adrenergic mRNA levels, while treatment for 30 minutes daily for 7 days had no effect. Exposure to a beta-adrenergic agonist and antagonist for 24 hours had no effect on gene expression. The beta adrenergic agonist, formoterol hemifumarate, led to increases in K+ flux into MDA-MB-453 cells, and this increase was inhibited by the GIRK channel inhibitor clozapine. The tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a high affinity agonist for beta-adrenergic receptors stimulated activation of Erk 1/2 in MDA-MB-453 cells.ConclusionsOur data suggests β-adrenergic receptors and GIRK channels may play a role in breast cancer.

Social stress promotes and γ-aminobutyric acid inhibits tumor growth in mouse models of non small cell lung cancer

Psychologic distress is associated with increased lung cancer incidence and mortality. We have shown that non–small cell lung cancer (NSCLC) cells in vitro are stimulated by the cyclic AMP (cAMP)-dependent activation of cAMP-responsive element binding protein (CREB) and extracellular signal–regulated kinase (ERK) downstream of β-adrenergic receptors and that this pathway is inhibited by the neurotransmitter γ-aminobutyric acid (GABA). Because the stress neurotransmitters noradrenalin and adrenalin are β-adrenergic agonists, the current study has tested the hypothesis that social stress stimulates NSCLC growth in vivo and that GABA inhibits this effect. Social stress was induced in mice carrying xenografts from two NSCLC cell lines in the presence and absence of treatment with GABA. Xenograft sizes were measured after 30 days. Noradrenalin, adrenalin, cortisol, GABA, and cAMP were measured in blood and tumor tissues by immunoassays. Expression of nicotinic receptors in the xenografts was assessed by real-time PCR and Western blotting. Protein expression of phospho (p)-CREB, CREB, phospho (p)-ERK, ERK, and glutamate decarboxylase (GAD) 65 and 67 were determined by Western blotting. Xenograft sizes in stress-exposed mice were significantly increased. Nicotinic acetylcholine receptor (nAChR) subunits α3, α4, α5, and α7 in xenograft tissues showed posttranscriptional induction. Noradrenalin, adrenalin, and cortisol were elevated in serum and xenograft tissue whereas GABA was suppressed. Levels of cAMP, p-CREB, and p-ERK were increased whereas GAD65 and GAD67 were suppressed in tumor tissue. Treatment with GABA reversed the effects of stress. Our findings suggest that social stress stimulates NSCLC by increasing nAChR-mediated stress neurotransmitter signaling and that GABA is a promising novel agent for NSCLC intervention. Cancer Prev Res; 5(2); 189–96. ©2011 AACR.

Transformation of non-cancerous human breast epithelial cell line MCF10A by the tobacco-specific carcinogen NNK.

Repeated treatments of non-cancerous human breast epithelial cells MCF10A with a low dose of the tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induced the development of cancerous cells. NNK-transformed MCF10A cells acquired cancerous properties including anchorage-independent cell growth and increased cell motility. Cellular transformation of MCF10A cells was accompanied by a loss of responsiveness to 17β-estradiol and decreased rate of cell proliferation. NNK-transformed MCF10A cells were also tumorigenic in immunodifficient mice. Studies of changes in the regulation of intracellular signaling pathways revealed that the upstream Erk pathway was down-regulated in the NNK-transformed cells. Our data provide the first evidence suggesting that the tobacco carcinogen NNK is competent to induce malignant transformation of non-cancerous human breast epithelial cells. Our findings suggest that the tobacco carcinogen NNK may contribute to early events in human breast carcinogenesis.

Interaction of tobacco-specific toxicants with nicotinic cholinergic regulation of fetal pulmonary neuroendocrine cells : Implications for pediatric lung disease

Pulmonary neuroendocrine cells (PNEC) produce neuropeptides and biogenic amines which regulate pulmonary vasoconstriction and bronchoconstriction. Increased numbers of PNEC along with elevated levels of their products have been consistently observed in a variety of pediatric pulmonary diseases, some of which are etiologically linked with prenatal exposure to cigarette smoke, and all of which are exacerbated by passive smoking. The objective of our studies was to characterize the autonomic regulation of these cells and to explore a potential direct interaction of tobacco-specific toxicants with these regulatory pathways. Using reverse transcription polymerase chain reaction (RT-PCR), radioreceptor assays, flow cytometry, enzyme-linked immunosorbent assay (ELISA), and cell proliferation assays, we found that the release of serotonin from fetal PNEC is regulated by a neuronalalpha7-nicotinic acetylcholine receptor (alpha7-nAChR) via a Ca2+-dependent mechanism. The tobacco-specific toxicants nicotine and 4-(methylnitrosamino)-1-(-3-pyridine)-1-butanone (NNK) bound with high affinity to this receptor, resulting in influx of Ca2+, release of serotonin, and stimulation of DNA synthesis. Chronic stimulation of the alpha7-nAChR in the fetal lungs by prenatal exposure to cigarette smoke may contribute to the development of smoking-related pediatric pulmonary disease, whereas postnatal chronic exposure to environmental smoke may exacerbate these pediatric diseases via direct interaction with this receptor.

Protein expression of G-protein inwardly rectifying potassium channels (GIRK) in breast cancer cells

BackgroundPrevious data from our laboratory has indicated that a functional link exists between the G-protein-coupled inwardly rectifying potassium (GIRK) channel and the beta-adrenergic receptor pathway in breast cancer cell lines, and these pathways were involved in growth regulation of these cells. Alcohol is an established risk factor for breast cancer and has been found to open GIRK. In order to further investigate GIRK channels in breast cancer and possible alteration by ethanol, we identified GIRK channel protein expression in breast cancer cells.ResultsCell pellets were collected and membrane protein was isolated to determine GIRK protein expression. GIRK protein was also analyzed by immuno-precipitation. GIRK protein was over-expressed in cells by transfection of GIRK plasmids. Gene expression studies were done by real-time RT-PCR. GIRK protein expression was identified in breast cancer cell lines. Expression of GIRK1 at the indicated molecular weight (MW) (62 kDa) was seen in cell lines MDA-MB-453 and ZR-75-1. In addition, GIRK1 expression was seen at a lower MW (40–42 kDa) in MDA-MB-361, MDA-MB-468, MCF-7, ZR-75-1, and MDA-MB-453 cell lines. To prove the lower MW protein was GIRK1, MDA-MB-453 cells were immuno-precipitated. GIRK2 expression was seen in MDA-MB-468, MCF-7, and ZR-75-1 and was variable in MDA-MB-453, while GIRK4 protein expression was seen in all six cell lines tested. This is the first report indicating GIRK protein expression in breast cancer cells. To determine functionality, MDA-MB-453 cells were stimulated with ethanol. Decreased GIRK1 protein expression levels were seen after treatment with 0.12% ethanol in MDA-MB-453 breast cancer cells. Serum-free media decreased GIRK protein expression, possibly due to lack of estrogen in the media. Transfection of GIRK1 or GIRK4 plasmids increased GIRK1 protein expression and decreased gene expression in MDA-MB-453 breast cancer cells.ConclusionOur data indicates that functional GIRK channels exist in breast cancer cells that are involved in cellular signaling.

G-Protein Inwardly Rectifying Potassium Channel 1 (GIRK1) Knockdown Decreases Beta-Adrenergic, MAP Kinase and Akt Signaling in the MDA-MB-453 Breast Cancer Cell Line.

Previous data from our laboratory have indicated that there is a functional link between the beta-adrenergic receptor signaling pathway and the G-protein inwardly rectifying potassium channel (GIRK1) in breast cancer cell lines and that these pathways are involved in growth regulation of these cells. To determine functionality, MDA-MB-453 breast cancer cells were stimulated with ethanol, known to open GIRK channels. Decreased GIRK1 protein levels were seen after treatment with 0.12% ethanol. In addition, serum-free media completely inhibited GIRK1 protein expression. This data indicates that there are functional GIRK channels in breast cancer cells and that these channels are involved in cellular signaling. In the present research, to further define the signaling pathways involved, we performed RNA interference (siRNA) studies. Three stealth siRNA constructs were made starting at bases 1104, 1315, and 1490 of the GIRK1 sequence. These constructs were transfected into MDA-MB-453 cells, and both RNA and protein were isolated. GIRK1, β2-adrenergic and 18S control levels were determined using real-time PCR 24 hours after transfection. All three constructs decreased GIRK1 mRNA levels. However, β2 mRNA levels were unchanged by the GIRK1 knockdown. GIRK1 protein levels were also reduced by the knockdown, and this knockdown led to decreases in beta-adrenergic, MAP kinase and Akt signaling.

Abstract 1023: Social stress modulates beta-adrenergic and potassium channel-mediated signaling in lung adenocarcinoma

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Small airway epithelial cell-derived adenocarcinoma is the most common human lung cancer. Previous research from our laboratory has indicated the importance of stress neurotransmitters in cancer signaling in these cells in vitro. In the current study, we have assessed the potential modulation of cancer progression by social stress in xenograph models. The adenocarcinoma cell lines NCI-H322 (with activating point mutations in K-ras) and NCI-H441 (without ras mutations) were injected into nude mice 4 weeks after induction of social stress. The social stress continued for an additional 4 weeks when the tumors were removed. RNA was isolated, and PCR microarrays were used to identify genes that could be affected by stress. Using real-time PCR, we investigated some of these genes. We saw significant decreases in β1-adrenergic (0.49 fold), β2-adrenergic (0.55 fold) and calmodulin (0.16 fold) gene expression in the NCI-H322 xenographs. In the NCI-H441 xenographs, only calmodulin was changed (1.59 fold increase). The immortalized normal human small airway epithelial cell HPL1D was chosen for in-vitro studies. Treatment of HPL1D cells for 7 days with 10 μM acetylcholine led to a significant 0.48 fold decrease in β1-adrenergic gene expression. Previous research from our laboratory has indicated the significance of potassium channels in both lung cancer and breast cancer. Therefore, we determined if a potassium channel could be involved in these stress-induced responses. The voltage-dependent human ether a go-go (EAG) potassium channel has been shown to be important in cellular signaling, cancer progression and calcium signaling/calmodulin binding. After assay by real-time PCR, the NCI-H322 xenographs showed a significant 0.51 fold decrease in EAG gene expression, but there was no change in gene expression in the NCI-H441 xenographs. Treatment of HPL1D cells for 7 days with 10 μM acetylcholine led to a significant 0.36 fold decrease in EAG gene expression. Our data indicate social stress modulates beta-adrenergic and potassium channel-mediated signaling in lung adenocarcinoma. Supported by 1RC1CA144640 with the National Institutes of Health. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1023. doi:10.1158/1538-7445.AM2011-1023