The tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone stimulates proliferation of immortalized human pancreatic duct epithelia through beta-adrenergic transactivation of EGF receptors

Pancreatic cancer cells and normal pancreatic duct epithelial cells express an autocrine catecholamine loop that is activated by nicotinic acetylcholine receptors α3, α5, and α7

Pancreatic cancer is the fourth leading cause of cancer deaths in developed countries. Smoking is an established risk factor for this malignancy but the underlying mechanisms are poorly understood. Previous reports have provided evidence that nicotinic acetylcholine receptors (nAChR) and beta adrenergic receptors (β-AR) stimulate the growth and migration of pancreatic cancer cells. However, a potential cooperation of these two receptor families in the regulation of pancreatic cancer has not been studied to date. Using two pancreatic cancer cell lines and immortalized pancreatic duct epithelia in vitro, our current data show that all three cell lines synthesized and released the catecholamine neurotransmitters noradrenaline and adrenaline upon exposure to nicotine and that this activity was regulated by α3, α5, and α7-nAChRs. In accordance with the established function of these catecholamines as β-AR agonists, nicotine-induced cell proliferation was blocked by the β-AR antagonist propranolol. Nicotine-induced proliferation was also abolished by the α7-nAChR antagonist α-bungarotoxin, whereas catecholamine production in response to nicotine was blocked by gene knockdown of the α3, α5, and α7-nAChRs. The nicotinic agonists acetylcholine, nicotine, and its nitrosated carcinogenic derivative NNK induced the phosphorylation of CREB, ERK, Src, and AKT and these responses were inhibited by propranolol. Our findings identify this hitherto unknown autocrine catecholamine loop as an important regulatory cascade in pancreatic cancer that may prove a promising new target for cancer intervention.

Regulation of pancreatic cancer by neuropsychological stress responses: a novel target for intervention

Pancreatic cancer has a poor prognosis and is associated with high levels of psychological stress that may adversely affect clinical outcomes. However, the potential influence of neuropsychological factors on pancreatic cancer has not been investigated to date. Using a mouse model of social stress, we have tested the hypothesis that psychological stress promotes the progression of pancreatic cancer xenografts via neurotransmitter-induced activation of multiple pathways and that the inhibitory neurotransmitter γ-aminobutiric acid (GABA) inhibits these responses. Sytemic and xenograft levels of noradrenalin, adrenalin, GABA, cortisol, vascular endothelial growth factor (VEGF) and cyclic adenosine 3', 5'-monophosphate (cAMP) were measured by immunoassays. Xenograft expression of nicotinic acetylcholine receptors (nAChRs) α3, α4, α5, α6 and α7 and β-adrenergic receptors 1 and 2 were assessed by real-time PCR and western blots. Expression of glutamate decarboxylases GAD65 and GAD67 and phosphorylated and unphosphorylated signaling proteins of relevance to pancreatic cancer were determined in tumor tissue by western blots. Psychological stress significantly promoted xenograft growth and increased systemic and tumor levels of noradrenalin, adrenalin, cortisol, VEGF and cAMP while GABA and GAD were suppressed. Stress upregulated nAChR proteins but not RNAs and induced phosphorylated ERK, CREB, Src and AKT in xenografts. Reduction of cAMP by treatment with GABA prevented tumor progression and activation of signaling proteins. Our findings suggest that neurotransmitter responses to psychological stress negatively impact clinical outcomes of pancreatic cancer via the activation of multiple pathways and that replacement of the suppressed inhibitory neurotransmitter GABA prevents these effects.

Epidemiology and potential mechanisms of tobacco smoking and heavy alcohol consumption in pancreatic cancer

Tobacco smoking represents an important known cause of ductal pancreatic adenocarcinoma. Recent data from pooled analyses in consortia involving multiple case-control and cohort studies suggest that heavy (but not moderate or light) alcohol consumption also may increase pancreatic cancer risk. Animal and human evidence indicate that tobacco carcinogens and metabolites may act in concert and have both genetic and epigenetic effects at early and later stages in pancreatic tumorigenesis. One of the more important tobacco-related carcinogens, NNK, probably acts via multiple pathways. Heavy alcohol consumption may increase pancreatic cancer risk by potentiating the effects of other risk factors such as tobacco smoking, poor nutrition, and inflammatory pathways related to chronic pancreatitis, but also may have independent genetic and epigenetic effects. Animal and human studies of tobacco- and alcohol-related pancreatic carcinogenesis suggest multi-modal, overlapping mechanistic pathways. Tobacco smoking and heavy alcohol consumption are preventable exposures, and their avoidance would substantially decrease the burden of pancreatic cancer worldwide.

β2-adrenoceptor blockage induces G1/S phase arrest and apoptosis in pancreatic cancer cells via Ras/Akt/NFκB pathway

Background

Smoking and stress, pancreatic cancer (PanCa) risk factors, stimulate nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and catecholamines production respectively. NNK and catecholamine bind the β-adrenoceptors and induce PanCa cell proliferation; and we have previously suggested that β-adrenergic antagonists may suppress proliferation and invasion and stimulate apoptosis in PanCa. To clarify the mechanism of apoptosis induced by β₂-adrenergic antagonist, we hypothesize that blockage of the β₂-adrenoceptor could induce G₁/S phase arrest and apoptosis and Ras may be a key player in PanCa cells.

Results

The β₁ and β₂-adrenoceptor proteins were detected on the cell surface of PanCa cells from pancreatic carcinoma specimen samples by immunohistochemistry. The β₂-adrenergic antagonist ICI118,551 significantly induced G₁/S phase arrest and apoptosis compared with the β₁-adrenergic antagonist metoprolol, which was determined by the flow cytometry assay. β₂-adrenergic antagonist therapy significantly suppressed the expression of extracellular signal-regulated kinase, Akt, Bcl-2, cyclin D1, and cyclin E and induced the activation of caspase-3, caspase-9 and Bax by Western blotting. Additionally, the β₂-adrenergic antagonist reduced the activation of NFκB in vitro cultured PanCa cells.

Conclusions

The blockage of β₂-adrenoceptor markedly induced PanCa cells to arrest at G₁/S phase and consequently resulted in cell death, which is possibly due to that the blockage of β₂-adrenoceptor inhibited NFκB, extracellular signal-regulated kinase, and Akt pathways. Therefore, their upstream molecule Ras may be a key factor in the β₂-adrenoceptor antagonist induced G₁/S phase arrest and apoptosis in PanCa cells. The new pathway discovered in this study may provide an effective therapeutic strategy for PanCa.

GABA (γ-aminobutyric acid), a non-protein amino acid counters the β-adrenergic cascade-activated oncogenic signaling in pancreatic cancer: a review of experimental evidence

GABA is a bioactive constituent of fruits, vegetables, cereals and is believed to play a role in defense against stress in plants. In animals, it acts as an inhibitory neurotransmitter in brain while also expressed in non-neuronal cells. Studies have implicated the regulator of fight or flight stress responses, β-AR signaling cascade, as mediators of cancer growth and progression in in vitro and in vivo models of pancreatic malignancies. Pancreatic cancer is the fourth leading cause of cancer mortality in western countries. This malignancy is generally unresponsive to conventional radio- and chemotherapy, resulting in mortality rate near 100% within 6 months of diagnosis. We review a series of experiments from our laboratory and those of others examining the contribution of this signaling network to pancreatic and other human malignancies. Stimulation of the β-adrenergic receptor by lifestyle and environmental factors, as well as a pre-existing risk of neoplasm, activates downstream effector molecules that lead to pro-oncogenic signaling and thereby aid cancer growth. GABAergic signaling mediated by the serpentine receptor GABA(B) acts as an antagonist to β-adrenergic cascade by intercepting adenylyl cyclase. These evidences enhance the pharmacological value of human diets rich in GABA for use as an adjuvant to standard therapies.

Epigenetic effects and molecular mechanisms of tumorigenesis induced by cigarette smoke: an overview

Cigarette smoking is one of the major causes of carcinogenesis. Direct genotoxicity induced by cigarette smoke leads to initiation of carcinogenesis. Nongenotoxic (epigenetic) effects of cigarette smoke also act as modulators altering cellular functions. These two effects underlie the mechanisms of tumor promotion and progression. While there is no lack of general reviews on the genotoxic and carcinogenic potentials of cigarette smoke in lung carcinogenesis, updated review on the epigenetic effects and molecular mechanisms of cigarette smoke and carcinogenesis, not limited to lung, is lacking. We are presenting a comprehensive review of recent investigations on cigarette smoke, with special attentions to nicotine, NNK, and PAHs. The current understanding on their molecular mechanisms include (1) receptors, (2) cell cycle regulators, (3) signaling pathways, (4) apoptosis mediators, (5) angiogenic factors, and (6) invasive and metastasis mediators. This review highlighted the complexity biological responses to cigarette smoke components and their involvements in tumorigenesis.

Stress hormones increase cell proliferation and regulates interleukin-6 secretion in human oral squamous cell carcinoma cells

Patients with oral cancer can have high psychological distress levels, but the effects of stress-related hormones on oral cancer cells and possible mechanisms underlying these relationships are unknown. In this study, we have investigated the effects of stress-related hormones on interleukin-6 (IL-6) secretion and proliferation of oral squamous cell carcinoma (OSCC) cells. The effects of norepinephrine (NE), and cortisol were studied in SCC9, SCC15, and SCC25 cells and effects of isoproterenol in SCC9 and SCC25 cells. Real-time PCR studies revealed constitutive β1- and β2-adrenergic receptors (β-ARs) expression in the SCC9, SCC15, and SCC25 cells. The results showed that NE and isoproterenol significantly enhanced IL-6 mRNA expression and protein production in supernatants of SCC9 and SCC25 cells. Physiological stress levels of NE and isoproterenol (10 μM) at 1 h elicited the most robust IL-6 increase. Regarding IL-6 secretion, 10 μM NE induced a 5-fold increase at 1 h, 3.7-fold increase at 6 h, and 3.2-fold at 24 h in SCC9 cells. These effects were blocked by the β-adrenergic antagonist propranolol, supporting a role for β-ARs in IL-6 secretion. The effects of cortisol varied according to the hormone concentration. Pharmacological concentrations of cortisol (1000 nM) inhibited IL-6 production by SCC9 and SCC25 cells. Cortisol dose that simulates stress conditions (10 nM) tended to increase IL-6 expression in SCC9 cells. Hormonal doses that simulate stress conditions (10 μM NE, at 6 h in SCC9 and SCC15 cells and 10 nM cortisol, at 48 h in SCC15 cells) stimulated increased cell proliferation. Treatment of SCC9 cells with IL-6 neutralizing ab (10 μg/mL) partially inhibited NE-induced proliferation. Finally, 20 OSCC biopsies were shown to express β1- and β2-ARs. These findings suggest that stress hormones can affect oral cancer cells behavior.

Experimental animal models of pancreatic carcinogenesis for prevention studies and their relevance to human disease

Pancreatic cancer is difficult to cure, so its prevention is very important. For this purpose, animal model studies are necessary to develop effective methods. Injection of N-nitrosobis(2-oxopropyl)amine (BOP) into Syrian golden hamsters is known to induce pancreatic ductal adenocarcinomas, the histology of which is similar to human tumors. Moreover, K-ras activation by point mutations and p16 inactivation by aberrant methylation of 5' CpG islands or by homozygous deletions have been frequently observed in common in both the hamster and humans. Thus, this chemical carcinogenesis model has an advantage of histopathological and genetic similarity to human pancreatic cancer, and it is useful to study promotive and suppressive factors. Syrian golden hamsters are in a hyperlipidemic state even under normal dietary conditions, and a ligand of peroxizome proliferator-activated receptor gamma was found to improve the hyperlipidemia and suppress pancreatic carcinogenesis. Chronic inflammation is a known important risk factor, and selective inhibitors of inducible nitric oxide synthase and cyclooxygenase-2 also have protective effects against pancreatic cancer development. Anti-inflammatory and anti-hyperlipidemic agents can thus be considered candidate chemopreventive agents deserving more attention.

Paxillin regulates androgen- and epidermal growth factor-induced MAPK signaling and cell proliferation in prostate cancer cells

Although transcriptional effects of androgens have been extensively studied, mechanisms regulating transcription-independent (nongenomic) androgen actions are poorly understood. Previously, we have shown that paxillin, a multidomain adaptor protein, is a critical regulator of testosterone-induced MAPK-signaling during Xenopus oocyte maturation. Here we examine the nongenomic effects of dihydrotestosterone (DHT) in prostate cancer cells, focusing on how paxillin mediates Erk signaling and downstream physiologic actions. We show that in LnCAP cells DHT functions as a growth factor that indirectly activates the EGF-receptor (EGFR) via androgen receptor binding and matrix metalloproteinase-mediated release of EGFR ligands. Interestingly, siRNA-mediated knockdown of paxillin expression in androgen-dependent LnCAP cells as well as in androgen-independent PC3 cells abrogates DHT- and/or EGF-induced Erk signaling. Furthermore, EGFR-induced Erk activation requires Src-mediated phosphorylation of paxillin on tyrosines 31/118. In contrast, paxillin is not required for PKC-induced Erk signaling. However, Erk-mediated phosphorylation of paxillin on serines 83/126/130 is still needed for both EGFR and PKC-mediated cellular proliferation. Thus, paxillin serves as a specific upstream regulator of Erk in response to receptor-tyrosine kinase signaling but as a general regulator of downstream Erk actions regardless of agonist. Importantly, Erk-mediated serine phosphorylation of paxillin is also required for DHT-induced prostate-specific antigen mRNA expression in LnCAP cells as well as EGF-induced cyclin D1 mRNA expression in PC3 cells, suggesting that paxillin may regulate prostate cancer proliferation by serving as a liaison between extra-nuclear kinase signaling and intra-nuclear transcriptional signals. Thus, paxillin may prove to be a novel diagnostic or therapeutic target in prostate cancer.

Neurotransmitter receptors as central regulators of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has a near 100% mortality because it is generally detected at an advanced stage and responds poorly to existing therapeutics. This review summarizes current evidence suggesting important roles of neurotransmitter receptors in the regulation of this malignancy. Experimental evidence indicates that the alpha(7)-nicotinic acetylcholine receptor (alpha(7)nAChR) stimulates PDAC via stress neurotransmitter-mediated activation of beta-adrenergic signaling while the alpha(4)beta(2)nAChR inhibits PDAC via GABA-mediated inhibition of adenylyl cyclase activation. In analogy to molecular mechanisms that govern nicotine addiction, chronic exposure to nicotine or its nitrosated derivative nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone render the stimulatory alpha(7)nAChR hyperactive while desensitizing the inhibitory alpha(4)beta(2)nAChR. Accordingly, PDAC intervention strategies should include the diagnosis of unphysiological neurotransmitter levels and aim to restore any imbalance in stimulatory and inhibitory neurotransmitters.

HIF-1alpha links beta-adrenoceptor agonists and pancreatic cancer cells under normoxic condition

AIM

To examine whether beta-adrenoceptor (beta-AR) agonists can induce hypoxia-inducible factor (HIF)-1alpha accumulation which then up-regulate the expression of its target genes in pancreatic cancer cells at normoxia, and to further elucidate the mechanism involved.

METHODS

Pulse-chase assay, RT-PCR, and Western blot were employed to detect the effects of beta-AR agonists and antagonists, siRNA as well as several inhibitors of signal transduction pathways on MIA PaCa2 and BxPC-3 pancreatic cancer cells.

RESULTS

Treatment of pancreatic cancer cell lines with beta-AR agonists led to accumulation of HIF-1alpha and then up-regulated expression of its target genes independently of oxygen levels. The induction was partly or completely inhibited not only by beta-AR antagonists but also by inhibitors of PKA transduction pathways and by siHIF-1alpha. Both beta1-AR and beta2-AR agonists produced the above-mentioned effects, but beta2-AR agonist was more potent.

CONCLUSION

Activation of beta-AR receptor transactivates epidermal growth factor receptor (EGFR) and then elicits Akt and ERK1/2 in a PKA-dependent manner, which together up-regulate levels of HIF-1alpha and downstream target genes independently of oxygen level. Our data suggest a novel mechanism in pancreatic cancer cells that links beta-AR and HIF-1alpha signaling under normoxic conditions, with implications for the control of glucose transport, angiogenesis and metastasis.

Desmoplasia of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common form of pancreatic cancer and is characterized by remarkable desmoplasia. The desmoplasia is composed of extracellular matrix (ECM) proteins, myofibroblastic pancreatic stellate cells, and immune cells associated with a multitude of cytokines, growth factors, and ECM metabolizing enzymes. The mechanisms of participation of this complex matrix process in carcinogenesis are only starting to be appreciated. Recent studies showed key roles for stellate cells in the production of ECM proteins as well as cytokines and growth factors that promote the growth of the cancer cells all present in the desmoplastic parts of PDAC. In addition, interactions of ECM proteins and desmoplastic secreted growth factors with the cancer cells of PDAC activate intracellular signals including reactive oxygen species that act to make the cancer cells resistant to dying. These findings suggest that the desmoplasia of PDAC is a key factor in regulating carcinogenesis of PDAC as well as responses to therapies. A better understanding of the biology of desmoplasia in the mechanism of PDAC will likely provide significant opportunities for better treatments for this devastating cancer.

Nicotinic receptor-associated modulation of stimulatory and inhibitory neurotransmitters in NNK-induced adenocarcinoma of the lungs and pancreas

Small airway-derived pulmonary adenocarcinoma (PAC) and pancreatic ductal adenocarcinoma (PDAC) are among the most common human cancers and smoking is a risk factor for both. Emerging research has identified cAMP signalling stimulated by the stress neurotransmitters adrenaline and noradrenaline as an important stimulator of adenocarcinomas, including PAC and PDAC. The nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent mutagen and the most powerful tobacco carcinogen. NNK is also an agonist for nicotinic acetylcholine receptors (nAChRs). Using hamster models of NNK-induced PAC and PDAC, we have tested the hypothesis that in analogy to chronic effects of nicotine in the brain, NNK may modulate the alpha(7)- and alpha(4)beta(2)nAChRs, causing an increase in stress neurotransmitters and a decrease in the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Immunoassays showed a significant increase in serum adrenaline/noradrenaline and increased intracellular cAMP in the cellular fraction of blood of NNK-treated hamsters. Western blots on microdissected control small airway epithelia, alveolar epithelia, pancreatic islet and pancreatic duct epithelia, and from NNK-induced PACs and PDACs showed that the GABA-synthesizing enzyme glutamate decarboxylase 65 (GAD65) and GABA were suppressed in NNK-induced PACs and PDACs. In contrast, protein expression of the alpha(7)nAChR, alpha(4)nAChR as well as p-CREB and p-ERK1/2 were up-regulated. These findings suggest that NNK-induced alterations in regulatory nAChRs may contribute to the development of smoking-associated PAC and PDAC by disturbing the balance between cancer-stimulating and -inhibiting neurotransmitters.

Prevention of pancreatic cancer by the beta-blocker propranolol

Pancreatic ductal adenocarcinoma (PDAC) is among the leading causes of cancer deaths and is unresponsive to existing therapy. Smoking and alcohol-induced pancreatitis are among the risk factors for PDAC. We have previously reported that beta-adrenergic receptors (beta-ARs) stimulate the proliferation and migration of human PDAC cells in vitro by cAMP-dependent signaling and that the nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) activates this pathway directly in vitro while additionally stimulating the release of noradrenaline/adrenaline by binding to alpha7 nicotinic acetylcholine receptors (alpha7 nAChR) in hamsters. In this study, we have tested the hypothesis that the beta-AR antagonist propranolol prevents the development of PDAC induced in hamsters with ethanol-induced pancreatitis by NNK. We found that propranolol had strong cancer preventive effects in this animal model. Western blots of pancreatic duct cells and PDAC cells harvested by laser capture microscopy showed significant upregulation of the alpha7 nAChR associated with significant inductions of p-CREB, p-ERK1/2, and increases in epidermal growth factor and vascular endothelial growth factor in PDAC cells of hamsters not treated with propranolol. These effects were reversed by treatment with propranolol. Our data suggest that propranolol may prevent the development of PDAC by blocking cAMP-dependent intracellular signaling, cAMP-dependent release of epidermal growth factor, and PKA-dependent release of vascular endothelial growth factor while additionally downregulating the alpha7 nAChR by inhibiting cAMP-mediated subunit assembly. We conclude that increased cAMP signaling is an important factor that drives the development and progression of PDAC and that the inhibition of cAMP formation is a promising new target for the prevention and adjuvant therapy of PDAC.

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.

Nicotine stimulates pancreatic cancer xenografts by systemic increase in stress neurotransmitters and suppression of the inhibitory neurotransmitter gamma-aminobutyric acid

Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer mortality in Western countries. We have shown previously that four representative human PDAC cell lines were regulated by beta-adrenoreceptors via cyclic adenosine 3',5'-monophosphate (cAMP)-dependent signaling. In the current study, we have tested the hypothesis that nicotine stimulates the growth of PDAC xenografts in nude mice by increasing the systemic levels of the stress neurotransmitters adrenaline and noradrenaline, which are the physiological agonists for beta-adrenoreceptors and that inhibition by gamma-aminobutyric acid (GABA) of the adenylyl cyclase-dependent pathway downstream of adrenoreceptors blocks this effect. The size of xenografts from PDAC cell line Panc-1 was determined 30 days after inoculation of the cancer cells. Stress neurotransmitters in serum as well as cAMP in the cellular fraction of blood and in tumor tissue were assessed by immunoassays. Levels of GABA, its synthesizing enzymes GAD65 and GAD67 and beta-adrenergic signaling proteins in the tumor tissue were determined by western blotting. Nicotine significantly increased the systemic levels of adrenaline, noradrenaline and cAMP while increasing xenograft size and protein levels of cAMP, cyclic AMP response element-binding protein and p-extracellular signal-regulated kinase 1/2 in the tumor tissue. Nicotine additionally reduced the protein levels of both GAD isozymes and GABA in tumor tissue. Treatment with GABA abolished these responses to nicotine and blocked the development of xenografts in mice not exposed to nicotine. These findings suggest that the development and progression of PDAC is subject to significant modulation by stimulatory stress neurotransmitters and inhibitory GABA and that treatment with GABA may be useful for marker-guided cancer intervention of PDAC.

Inhibition of pancreatic cancer cell proliferation by propranolol occurs through apoptosis induction: the study of beta-adrenoceptor antagonist's anticancer effect in pancreatic cancer cell

OBJECTIVES

Propranolol inhibited pancreatic cancer cell proliferation by blocking signaling through the beta-adrenoceptor. We hypothesized that propranolol may suppress pancreatic cancer cell growth through induction of apoptosis.

METHODS

The beta-adrenoceptor antagonist propranolol, beta1-adrenoceptor antagonist metoprolol, and beta2-adrenoceptor antagonist butoxamine were used to induce apoptosis in PC-2 cells. The mRNA and protein expression of beta1- and beta2-adrenoceptors was analyzed using reverse transcriptase-polymerase chain reaction and Western blot. The apoptotic index was determined using Hoechst 33342 fluorescent staining, TUNEL, and annexin V and fluorescein isothiocyanate/propidium iodide flow cytometry assay. The expression of caspase 3, caspase 9, and caspase 8 was analyzed using Western blotting.

RESULTS

PC-2 cell line expressed mRNA and protein for both of beta1- and beta2-adrenoceptors. The Hoechst staining, TUNEL, and flow cytometry assay documented that the 3 drugs increased the number of apoptotic cells; the rate of apoptosis was the highest using butoxamine followed by propranolol, whereas the least was using metoprolol. beta-Adrenoceptor antagonists therapy affected caspase 3 and caspase 9 expression.

CONCLUSIONS

The rate of apoptosis in PC-2 cells was higher after treatment with butoxamine than propranolol, suggesting that propranolol induces apoptosis in PC-2 cells via the beta2-adrenoceptors principally. Our data could be useful for developing beta-adrenoceptor antagonists for inducing apoptosis in pancreatic cancer cells.

Epinephrine stimulates esophageal squamous-cell carcinoma cell proliferation via beta-adrenoceptor-dependent transactivation of extracellular signal-regulated kinase/cyclooxygenase-2 pathway

Esophageal cancer is the sixth leading causes of cancer-related death in the world. It is suggested that beta-adrenoceptor is involved in the control of cell proliferation, but its role in the pathogenesis of esophageal cancer remains unknown. We therefore studied the role of beta-adrenergic signaling in the regulation of growth of an esophageal squamous-cell carcinoma cell line HKESC-1. Results showed that both beta(1)- and beta(2)-adrenoceptors were expressed in HKESC-1 cells. Stimulation of beta-adrenoceptors with epinephrine significantly increased HKESC-1 cell proliferation accompanied by elevation of intracellular cyclic AMP levels, which were abolished by beta(1)- or beta(2)-selective antagonists. Epinephrine also increased extracellular signal-regulated kinase-1/2 (ERK1/2) phosphorylation as well as cyclooxygenase-2 (COX-2) and cytosolic phospholipase A(2) expression, which were blocked by beta(1)- or beta(2)-selective antagonists. Moreover, epinephrine increased cyclin D(1), cyclin E(2), cyclin-dependent kinase (CDK)-4, CDK-6, and E(2)F-1 expression and retinoblastoma protein phosphorylation at Ser807/811, all of which were abrogated by beta(1)-adrenoceptor antagonist. Furthermore, epinephrine increased the expression of vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR)-1 and -2 in a beta(2)-adrenoceptor-, mitogen-activated protein kinase/ERK kinase (MEK)-, and COX-2-dependent manner. MEK or COX-2 inhibitor also significantly inhibited HKESC-1 cell proliferation induced by epinephrine. Collectively, we demonstrate that epinephrine stimulates esophageal squamous-cell carcinoma cell proliferation via beta-adrenoceptor-dependent transactivation of ERK/COX-2 pathway. Stimulation of beta(1)- and beta(2)-adrenoceptors also elicits a differential response on the expression of cell cycle regulators. These novel findings may shed new light on the understanding of beta-adrenergic signaling in the control of esophageal cancer cell growth.

Neurotransmission and cancer: implications for prevention and therapy

Published evidence compiled in this review supports the hypothesis that the development, progression, and responsiveness to prevention and therapy of the most common human cancers is strongly influenced, if not entirely orchestrated, by an imbalance in stimulatory and inhibitory neurotransmission. The neurotransmitters acetylcholine, adrenaline, and noradrenaline of the autonomic nervous system act as powerful upstream regulators that orchestrate numerous cell and tissue functions, by releasing growth factors, angiogenesis factors and metastasis factors, arachidonic acid, proinflammatory cytokines, and local neurotransmitters from cancer cells and their microenvironment. In addition, they modulate proliferation, apoptosis, angiogenesis, and metastasis of cancer directly by intracellular signaling downstream of neurotransmitter receptors. Nicotine and the tobacco-specific nitrosamines have the documented ability to hyperstimulate neurotransmission by both branches of the autonomic nervous system. The expression and function of these neurotransmitter pathways are cell type specific. Lifestyle, diet, diseases, stress, and pharmacological treatments modulate the expression and responsiveness of neurotransmitter pathways. Current preclinical testing systems fail to incorporate the modulating effects of neurotransmission on the responsiveness to anticancer agents and should be amended accordingly. The neurotransmitter gamma-aminobutyric acid has a strong inhibitory function on sympathicus-driven cancers whereas stimulators of cyclic adenosine monophosphate/protein kinase A signaling have strong inhibitory function on parasympathicus-driven cancers. Marker-guided restoration of the physiological balance in stimulatory and inhibitory neurotransmission represents a promising and hitherto neglected strategy for the prevention and therapy of neurotransmitter-responsive cancers.

Epidermal growth factor-induced esophageal cancer cell proliferation requires transactivation of beta-adrenoceptors

Unchecked mitogenic signals due to the overexpression of epidermal growth factor (EGF) and its receptor (EGFR) is implicated in the promotion and progression of cancer. In addition, beta-adrenoceptor is involved in the control of cancer cell proliferation. This study sought to elucidate whether a functional connection exists between these two disparate receptor systems. EGF was used to stimulate HKESC-1 cells, an esophageal squamous cancer cell line, in which beta-adrenoceptor activity was monitored by measuring intracellular cAMP levels in the absence or presence of beta-adrenoceptor antagonists. Results showed that EGF significantly increased cAMP levels and cell proliferation, both of which were attenuated by atenolol [(+)-4-[2-hydroxy-3-[(1-methylethyl)amino]propoxy]benzeneacetamide] or ICI 118,551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol], which are antagonists for the beta-adrenoceptor. Further mechanistic investigation revealed that the cellular release of epinephrine and the expression of its synthesizing enzyme tyrosine hydroxylase were induced by EGF. The expression of beta(1)-adrenoceptor and the downstream signal transducer protein kinase A were also up-regulated. In this connection, AG1478 [4-(3-chloroanilino)-6,7-dimethoxyquinazoline], an EGFR tyrosine kinase inhibitor, abrogated all these EGF-elicited alteration. Collectively, this study demonstrates that beta-adrenergic signaling could be up-regulated at multiple levels upon EGFR activation to mediate the mitogenic signals in esophageal cancer cells. This novel finding not only unveils the sinister liaison between EGFR and beta-adrenoceptors but also sheds new light on the purported therapeutic use of beta-adrenoceptor antagonists in the treatment of esophageal cancer.

GABA B receptor is a novel drug target for pancreatic cancer

BACKGROUND

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 (beta-ARs). The activity of beta-ARs in the central nervous system is counteracted by gamma-aminobutyric acid (GABA) via GABA B receptor-mediated inhibition of adenylyl cyclase. The aim of the study was to investigate if GABA B R inhibits beta-AR signaling in PDAC and pancreatic duct epithelial cells, thus blocking driving forces of cancer progression, such as cell proliferation and cell migration.

METHODS

Intracellular cAMP was measured by immunoassays, DNA synthesis by BrdU incorporation assays, activation of ERK1/2 by ERK activation assays, and Western blots and metastatic potential by cell migration assays in the human PDAC cell lines PANC-1 and BXPC-3 and immortalized human pancreatic duct epithelial cells HPDE6-C7. The expression of norepinephrine, PKAR IIalpha, and GABA in PDAC microarrays was assessed by immunohistochemistry. RESULTS.: Stimulation of the GABA B R by GABA or baclofen inhibited isoproterenol-induced cAMP signaling below base levels. ERK1/2 activity in response to isoproterenol was blocked by GABA, an effect enhanced by transient overexpression of the GABA B R and abolished by GABA B R knockdown. DNA synthesis and cell migration were stimulated by isoproterenol, responses blocked by GABA and baclofen. Norepinephrine and PKAR IIalpha were overexpressed while GABA was underexpressed in human PDAC tissue arrays.

CONCLUSIONS

The data suggest the stimulation of GABA B R signaling as a novel target for the treatment and prevention of pancreatic cancer.

Cigarette smoke-induced pancreatic damage: experimental data

BACKGROUND AND AIMS

Epidemiological data clearly indicate that cigarette smoking is associated with an increased risk for developing chronic pancreatitis and pancreatic cancer. Despite of this clear epidemiological correlation, cigarette smoke-induced pancreatic damage has only been investigated in a small number of experimental studies.

METHODS

Experimental studies examining the effect of cigarette smoke or cigarette smoke constituents on the pancreas were reviewed.

RESULTS

Recent data indicate that smoking also induces chronic pancreatic inflammation in rodents within a period of 12 weeks upon exposure with environmental cigarette smoke. Supported by the finding that morphologic pancreatic damage is also induced by nicotine treatment, cigarette smoke-induced pancreatic damage is likely to be caused by a disturbance of regulation of exocrine pancreas. The morphological alterations, however, induced by nicotine, are less pronounced and therefore, other substances and pathophysiologic mechanisms, such as carcinogen action or cigarette smoke-induced reduction of anti-protease activity, are likely to aggravate pancreatic damage upon cigarette smoke inhalation.

CONCLUSION

These data indicate that several constituents of cigarette smoke induce a disturbance of pancreatic function. This multifactorial event induces morphologic pancreatic damage upon cigarette smoke exposure in rodents.

Impact of smoking status on the biological behavior of lung cancer

Cigarette smoking is the most established risk factor for lung carcinogenesis; however, its effects on the progression of lung cancer are still unclear. We reviewed the clinical investigations on this issue, which imply that smoking status is a treatment predictor and prognostic factor for several subtypes of lung cancer. Moreover, gene alterations and various protein expressions of tumor progression were recognized more frequently in the tumor tissues of smokers than in those of the never smokers. A cellular analysis revealed that tobacco-specific chemical compounds cause genetic or epigenetic alterations, modulate expressions of large numbers of genes that include molecules related to proliferation, invasion and metastasis, and deteriorate anti-tumor immunity. Our findings suggest that smoking promotes the progression of lung cancer, and that elucidating the molecular mechanisms may help to clarify the therapeutic targets.

Cigarette smoke components inhibited intercellular communication and differentiation in human pancreatic ductal epithelial cells

Smoking is a well-documented risk factor for the development of pancreatic adenocarcinoma. Although the most abundant polycyclic aromatic hydrocarbons (PAHs) in cigarette smoke are methylated anthracenes and phenanthrenes, the epigenetic toxicity of these compounds has not been extensively studied. We previously showed that methylanthracenes, which possess a bay-like structure, affect epigenetic events such as an induced release of arachidonic acid, inhibition of gap junctional intercellular communication (GJIC) and induction of mitogen-activated protein kinases in a pluripotent rat liver epithelial stem cell line. Anthracenes with no bay-like structures were inactive. These biological effects are all molecular events associated with the promotional phase of cancer. A human immortalized, nontumorigenic pancreatic ductal epithelial cell line, H6c7, was examined to study the epigenetic toxicity of PAHs related to pancreatic cancer by using scrape-loading dye transfer, immunostaining, RT-PCR and telomerase assay methods. H6c7 cells were GJIC-incompetent and exhibited high telomerase activity when grown in growth factor and hormone-supplemented medium. In the presence of the cAMP elevating drugs (forskolin and IBMX) the cells became GJIC competent and expressed connexins. Telomerase activity was also decreased by cAMP elevating drug treatment. After induction of cAMP, 1-methylanthracene with bay-like structures inhibited GJIC, whereas the 2-methylanthracene lacking a bay-like structure had no effect on GJIC. Telomerase activity remained high in 1-methylanthracene treatment but not with 2-methylanthracene. These results indicate that a prominent component of cigarette smoke, namely methylanthracenes with distinct structural configurations, could be a potential etiological agent contributing to the epigenetic events of pancreatic cancer.

The genetics of nicotine dependence: Relationship to pancreatic cancer

Smoking of tobacco products continues to be a major cause of worldwide health problems. Epidemiological studies have shown that tobacco smoking is the greatest risk factor for the development of pancreatic cancer. Smokers who are able to quit smoking can reduce their risk of pancreatic cancer by nearly 50% within two years, however, their risk of developing pancreatic cancer remains higher than that of non-smokers for 10 years. Nicotine is the major psychoactive substance in tobacco, and is responsible for tobacco dependence and addiction. Recent evidence suggests that individuals have genetically based differences in their ability to metabolize nicotine, as well as genetic differences in the psychological reward pathways that may influence individual response to smoking initiation, dependence, addiction and cessation. Numerous associations have been reported between smoking behavior and genetic polymorphisms in genes that are responsible for nicotine metabolism. In addition, polymorphisms in genes that encode neurotransmitters and transporters that function in psychological reward pathways have been implicated in differences in smoking behavior. However, there is a large degree of between-study variability that demonstrates the need for larger, well-controlled case-control studies to identify target genes and deduce mechanisms that account for the genetic basis of inter-individual differences in smoking behavior. Understanding the genetic factors that increase susceptibility to tobacco addiction may result in more effective tobacco cessation programs which will, in turn, reduce the incidence of tobacco related disease, including pancreatic cancer.

Effects of tobacco-specific carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on the activation of ERK1/2 MAP kinases and the proliferation of human mammary epithelial cells

Cigarette smoking is a risk factor in the developing of various cancers including breast tumors. There are more than 60 chemical carcinogens in the cigarette smoke; 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) being one of the strongest tobacco-specific carcinogens. In this study, we demonstrated that NNK rapidly activated ERK1 and ERK2 MAP kinases and stimulated proliferation in human normal mammary epithelial cells. MEK1/2 specific inhibitor UO126 completely blocked NNK-induced ERK1/2 activation and cell proliferation, whereas nicotinic receptor nAchR antagonist mecamylamine partially and the selective α(7)-nAchR antagonist α-bungarotoxin essentially inhibited the NNK-induced ERK1/2 activation and cell proliferation. Surprisingly, receptor tyrosine kinase inhibitor genistein, the selective β(1)-adrenergic antagonist atenolol, and the selective β(2)-adrenergic antagonist ICI118.551 had a strong inhibitory effect on ERK1/2 activation and cell proliferation induced by NNK. These results suggest that there are at least two different routes in activating ERK1/2 by NNK. One is through nicotinic receptor α(7)-nAchR to MEK1/2; the other is from β(1)/β(2)-adrenergic transactivation of tyrosine kinase containing receptor(s) to MEK1/2. In human cancer mammary epithelial cell lines, we found that ERK MAPK signaling pathway was deregulated: (1) ERK1/2 was constitutively activated at various levels; (2) ERK1/2 was further significantly activated in response to NNK induction; (3) UO126 partially or totally failed to inhibit ERK1/2 activation induced by NNK; (4) The expression levels of ERK1/2 in the cancer cell lines were much higher than those in the normal mammary epithelial cells. The tobacco-specific carcinogen NNK showed a strong proliferative effect on human normal and cancer mammary epithelial cells; the proliferation multitudes of these cells are well correlated with the activation levels of ERK1/2 MAP kinases.

Ethanol and the tobacco-specific carcinogen, NNK, contribute to signaling in immortalized human pancreatic duct epithelial cells

OBJECTIVES

Smoking is a well-documented risk factor for pancreatic cancer. The tobacco-specific nitrosamine, NNK (4-[methylnitrosamino]-1-[3-pyridyl]-1-butanone), significantly induces pancreatic ductal adenocarcinomas in laboratory rodents. Recent observations suggest that ethanol enhances the tumorigenic effects of smoking. Ethanol consumption is associated with the development of chronic pancreatitis, also considered a predisposing factor for pancreatic ductal adenocarcinoma. Because the precise role of ethanol in pancreatic carcinogenesis is not known, this study sought to elucidate the cumulative effects of ethanol and NNK on particular signal transduction pathways that might play a role in cell proliferation in immortalized human pancreatic duct epithelial cells.

METHODS

The HPDE6-c7 cells are developed from pancreatic duct epithelial cells, which are the putative cells of origin of pancreatic ductal adenocarcinoma. Cell proliferation assays, Western blot, and cyclic adenosine monophosphate assays were used to demonstrate the effects of ethanol and NNK treatments on these cells.

RESULTS

Ethanol cotreatments enhanced the NNK-induced proliferation of these cells. This response was inhibited by the adenylyl cyclase, protein kinase A, mitogen-activated protein kinase (p42/p44), and epidermal growth factor receptor-specific tyrosine kinase inhibitors. Cotreatments of NNK and ethanol also increased cyclic adenosine monophosphate accumulation, cAMP response element-binding family of proteins and mitogen-activated protein kinase phosphorylation, and protein kinase A activation.

CONCLUSIONS

These findings suggest a potential role for these pathways contributing to the development of smoking- and alcohol-related pancreatic carcinogenesis.

Smoking--a trigger for chronic inflammation and cancer development in the pancreas

Tobacco smoke, with its complexity of constituents, damages the pancreatic organ in multiple ways. Smoke not only affects pancreatic secretion patterns via its nicotine content but induces inflammatory reactions and exerts carcinogenic effects by several other constituents. Smoke enhances ethanol-induced pancreatic injury and accelerates the development and progression of chronic pancreatitis independent of etiology. Through the process of inflammation, smoking contributes to pancreatic carcinogenesis. The experiment of Wittel and colleagues published in this issue of the American Journal of Gastroenterology sheds further light on this topic by reporting in great detail two different kinds of pancreatic damage in rats exposed to high doses of smoke.