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

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 alpha7 nicotinic acetylcholine receptor (alpha7 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 alpha7 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 alpha7 nAChR alpha-bungarotoxin (alpha-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 alpha-BTX while NNK-induced DNA synthesis was inhibited by alpha-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 alpha7 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.     

尼古丁对人A549细胞增殖、侵袭和迁移能力的影响

目的 观察烟草烟雾中的主要有害成分尼古丁对人A549细胞增殖、迁移与侵袭能力的影响,探讨尼古丁致病的可能机制.方法 以一定浓度尼古丁刺激体外培养的人A549细胞,应用CCK-8法、Transwell法和细胞划痕实验分别检测A549细胞的增殖、侵袭及迁移能力.Western blot检测α7烟碱型乙酰胆碱受体(α7 nAChR)、血管内皮生长因子(VEGF)和基质金属蛋白酶2(MMP-2)蛋白的表达.结果 与空白对照组比较,10-6 mol/L尼古丁处理A549细胞后,促进人A549细胞增殖(t=7.920,P<0.05);使穿过基质胶的细胞数增多,侵袭能力增强(t=5.298,P<0.05);使细胞迁移率增加,迁移能力增强(P<0.05).与空白对照组比较,10-6 M尼古丁处理A549细胞24 h后,α7 nAChR、VEGF和MMP-2蛋白表达上调,差异有统计学意义(t值分别为5.800、4.074、6.851,P值均<0.05).结论 尼古丁通过其特异性受体α7 nAChR可增强人A549细胞的增殖、侵袭和迁移能力,其机制可能与VEGF和MMP-2蛋白表达上调有关.     

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.     

尼古丁通过下调Akt蛋白水平导致心肌细胞的凋亡

目的研究尼古丁对心肌细胞H9C2的影响及其机制。方法将培养的H9C2细胞分为4组即对照组、尼古丁组(10μmol/L)、对照+丝苏氨酸蛋白激酶(Akt)过表达组、尼古丁(10μmol/L)+Akt过表达组。孵育48 h后用细胞增殖与毒性检测试剂盒(CCK-8)检测细胞活性率;Caspase活性检测试剂盒检测凋亡率;Western blot法检测Akt蛋白表达水平。结果与对照组相比,尼古丁组细胞活性明显降低(P0.05),细胞凋亡显著升高(P0.01),Akt蛋白水平显著下调(P0.01)。Akt过表达可有效改善尼古丁引起的细胞活性的降低(P0.01)减少细胞凋亡。结论尼古丁通过下调Akt蛋白表达水平引起心肌细胞的凋亡。     

Intracellular complexes of the beta2 subunit of the nicotinic acetylcholine receptor in brain identified by proteomics

Nicotine acetylcholine receptors (nAChRs) comprise a family of ligand-gated channels widely expressed in the mammalian brain. The beta2 subunit is an abundant protein subunit critically involved in the cognitive and behavioral properties of nicotine as well as in the mechanisms of nicotine addiction. In this work, we used matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-TOF MS/MS) to uncover protein interactions of the intracellular loop of the beta2 subunit and components of immunoprecipitated beta2-nAChR complexes from mouse brain. Using the beta2-knockout mouse to exclude nonspecific binding to the beta2 antibody, we identify 21 nAChR-interacting proteins (NIPs) expressed in brain. Western blot analysis confirmed the association between the beta2 subunit and candidate NIPs. Based on their functional profiles, the hypothesis is suggested that the identified NIPs can regulate the trafficking and signaling of the beta2-nAChR. Interactions of the beta2 subunit with NIPs such as G protein alpha, G protein-regulated inducer of neurite outgrowth 1, and G protein-activated K(+) channel 1 suggest a link between nAChRs and cellular G protein pathways. These findings reveal intracellular interactions of the beta2 subunit and may contribute to the understanding of the mechanisms of nAChR signaling and trafficking in neurons.     

Mechanism for nicotine-induced up-regulation of Wnt signaling in human alveolar interstitial fibroblasts

Nicotine exposure alters normal homeostatic pulmonary epithelial-mesenchymal paracrine signaling pathways, resulting in alveolar interstitial fibroblast (AIF)-to-myofibroblast (MYF) transdifferentiation. Since the AIF versus MYF phenotype is determined by the expression of peroxisome proliferator-activated receptor γ (PPARγ) and Wingless/Int (Wnt) signaling, respectively, the authors hypothesized that nicotine-induced AIF-to-MYF transdifferentiation is characterized by the down-regulation of PPARγ, and the up-regulation of the Wnt signaling pathway. As nicotine is known to activate protein kinase C (PKC) signaling, the authors also hypothesized that in AIFs, nicotine-induced up-regulation of Wnt signaling might be due to PKC activation. Embryonic human lung fibroblasts (WI38 cells) were treated with nicotine (1 × 10(-6) M) for either 30 minutes or 24 hours, with or without 30-minute pretreatment with calphostin C (1 × 10(-7) M), a pan-PKC inhibitor. Then the authors examined the activation of PKC (p-PKC) and Wnt signaling (p-GSK-3β, β-catenin, LEF-1, and fibronectin). Furthermore, activation of nicotinic acetylcholine receptor (nAChR)-α3 and -α7 and whether a PPARγ agonist, rosiglitazone (RGZ), blocks nicotine-mediated Wnt activation were examined. Following nicotine stimulation, there was clear evidence for nAChR-α3 and -α7 up-regulation, accompanied by the activation of PKC and Wnt signaling, which was further accompanied by significant changes in the expression of the downstream targets of Wnt signaling at 24 hours. Nicotine-mediated Wnt activation was almost completely blocked by pretreatment with either calphostin C or RGZ, indicating the central involvement of PKC activation and Wnt/PPARγ interaction in nicotine-induced up-regulation of Wnt signaling, and hence AIF-to-MYF transdifferentiation, providing novel preventive/therapeutic targets for nicotine-induced lung injury.     

非小细胞肺癌中PI3K/Akt信号通路通过Cdh1调控Skp2表达的机制研究

目的探讨非小细胞肺癌（NSCLC）中Cdc20同源蛋白1（Cdh1）参与磷脂酰肌醇三羟基激酶（PI3K）/Akt信号通路对S期激酶相关蛋白2（Skp2）表达调控的机制。方法体外培养NSCLC细胞系A549、LK2和H460,LY294002特异性阻断PI3K/Akt信号通路后,Western blot检测Skp2、Cdh1及p-Akt蛋白表达的变化,免疫荧光（IF）检测Cdh1在NSCLC中的定位变化。结果 LY294002处理后,与对照组相比3种细胞中Skp2蛋白表达和Akt磷酸化水平均降低（P〈0.01）,Cdh1在3种细胞的核内表达均增多。结论 NSCLC中PI3K/Akt信号通路抑制剂LY294002使Skp2蛋白表达下调与Cdh1由细胞质向细胞核转位有关。     

alpha10: a determinant of nicotinic cholinergic receptor function in mammalian vestibular and cochlear mechanosensory hair cells

We report the cloning and characterization of rat alpha10, a previously unidentified member of the nicotinic acetylcholine receptor (nAChR) subunit gene family. The protein encoded by the alpha10 nAChR subunit gene is most similar to the rat alpha9 nAChR, and both alpha9 and alpha10 subunit genes are transcribed in adult rat mechanosensory hair cells. Injection of Xenopus laevis oocytes with alpha10 cRNA alone or in pairwise combinations with either alpha2-alpha6 or beta2-beta4 subunit cRNAs yielded no detectable ACh-gated currents. However, coinjection of alpha9 and alpha10 cRNAs resulted in the appearance of an unusual nAChR subtype. Compared with homomeric alpha9 channels, the alpha9alpha10 nAChR subtype displays faster and more extensive agonist-mediated desensitization, a distinct current-voltage relationship, and a biphasic response to changes in extracellular Ca(2+) ions. The pharmacological profiles of homomeric alpha9 and heteromeric alpha9alpha10 nAChRs are essentially indistinguishable and closely resemble those reported for endogenous cholinergic eceptors found in vertebrate hair cells. Our data suggest that efferent modulation of hair cell function occurs, at least in part, through heteromeric nAChRs assembled from both alpha9 and alpha10 subunits.     

Nicotinic cholinergic and dopaminergic receptor mRNA expression in male and female rats with high or low preference for nicotine

Background: Nicotine exerts its central actions through nicotinic acetylcholine receptors (nAChRs), which in turn regulate major neurotransmitter systems including dopamine. Nicotinic and dopaminergic systems play significant roles in physiological functions, neuropsychiatric disorders, and addiction. Objectives: To evaluate possible differences in the expression of nAChR subunit and dopamine receptor (DR) mRNAs following voluntary nicotine intake. Methods: Male and female rats (n = 67) were exposed to long-term free-choice oral nicotine (24 hours/day, 6 weeks); rats with maximum and minimum nicotine preference/intake were selected. The mRNA levels of genes encoding α4,β2,α5, and α7 nAChR subunits and DR Drd1and Drd2 subtypes were evaluated in the striatum (STR), prefrontal cortex (PFC), and hippocampus using quantitative real-time polymerase chain reaction in selected rats (n = 30) and their control groups (n = 15). Results: In addition to baseline differences, expression changes were observed in the mRNA levels of evaluated genes in rats exposed to voluntary oral nicotine in a brain region-, sex-, and preference-related manner. Nicotine intake is correlated negatively with Chrnb2, Chrna7 and positively with Drd1 expression. In the cholinergic system, regional differences in Chnrb2 and Chrna5, sex differences in Chrna4 and Chrna5, and nicotine preference effects in the expression of all subunits except α4 were observed. Chrna5 was lower in maximum than in minimum preferring, and in male than female rats, supporting the inhibitory role of the α5 subunit in nicotine dependence. Nicotine increased Drd2 mRNA expression only in minimum preferring female rats in STR and PFC. Conclusion: Modulation of nAChR and DR gene expression by nicotine may have clinical implications and aid drug development. Pharmaceuticals targeting the nicotinic cholinergic and dopaminergic systems might be expected to have differential efficacy that varies with the patient’s sex or smoking status.     

Functional analysis of the cytoplasmic domain of the integrin {alpha}1 subunit in endothelial cells

Integrin alpha1beta1, the major collagen type IV receptor, is expressed by endothelial cells and plays a role in both physiologic and pathologic angiogenesis. Because the molecular mechanisms whereby this collagen IV receptor mediates endothelial cell functions are poorly understood, truncation and point mutants of the integrin alpha1 subunit cytoplasmic tail (amino acids 1137-1151) were generated and expressed into alpha1-null endothelial cells. We show that alpha1-null endothelial cells expressing the alpha1 subunit, which lacks the entire cytoplasmic tail (mutant alpha1-1136) or expresses all the amino acids up to the highly conserved GFFKR motif (mutant alpha1-1143), have a similar phenotype to parental alpha1-null cells. Pro(1144) and Leu(1145) were shown to be necessary for alpha1beta1-mediated endothelial cell proliferation; Lys(1146) for adhesion, migration, and tubulogenesis and Lys(1147) for tubulogenesis. Integrin alpha1beta1-dependent endothelial cell proliferation is primarily mediated by ERK activation, whereas migration and tubulogenesis require both p38 MAPK and PI3K/Akt activation. Thus, distinct amino acids distal to the GFFKR motif of the alpha1 integrin cytoplasmic tail mediate activation of selective downstream signaling pathways and specific endothelial cell functions.     

Nicotine enhances migration and invasion of human esophageal squamous carcinoma cells which is inhibited by nimesulide

AIM： To study the effect of nicotine on the migration and invasion of human esophageal squamous carcinoma cells and to investigate whether nimesulide can inhibit the effect of nicotine.METHODS： The esophageal squamous carcinoma cell line （TE-13） was treated with different concentrations of nicotine （100 μg/mL and 200 μg/mL） or 200 μg/mL nicotine plus 100 μmol/L nimesulide. Cell migration and invasion were measured using migration and invasion chamber systems. COX-2 expression was determined by Western blotting. Matrix metalloproteinase-2 （MMP-2） was analyzed by zymography and ELISA.RESULTS： Nicotine （100 μg/mL, 200 μg/mL） enhanced TE-13 cells migration and invasion, and increased the protein expression of COX-2 and the activity of MMP-2. Nicotine （200 μ/mL） stimulated TE-13 cells migration and invasion which were partly blocked by nimesulide. This was associated with decreased protein expression of COX-2 and decreased activity and protein expression of MMP-2. CONCLUSION： Nicotine enhances the migration and invasion of the esophageal squamous carcinoma cell line, and nimesulide partly blocks the effect ofnicotine-enhanced esophageal squamous carcinoma cell migration and invasion.     

微RNA-29家族降解PTEN mRNA促进非小细胞肺癌细胞存活与淋巴结侵袭

目的:探索微RNA(microRNA,miRNA/miR)-29家族对淋巴结侵袭性非小细胞肺癌(non-small cell lung cancer,NSCLC)细胞增殖、侵袭的影响及潜在的分子机制.方法:TCGA数据库分析磷酸酶和张力蛋白同源基因(phosphatase and tension homology de...     

Correlation between nicotine-induced inhibition of hematopoiesis and decreased CD44 expression on bone marrow stromal cells.

This study demonstrates that in vivo exposure to cigarette smoke (CS) and in vitro treatment of long-term bone marrow cultures (LTBMCs) with nicotine, a major constituent of CS, result in inhibition of hematopoiesis. Nicotine treatment significantly delayed the onset of hematopoietic foci and reduced their size. Furthermore, the number of long-term culture-initiating cells (LTC-ICs) within an adherent layer of LTBMCs was significantly reduced in cultures treated with nicotine. Although the production of nonadherent mature cells and their progenitors in nicotine-treated LTBMCs was inhibited, this treatment failed to influence the proliferation of committed hematopoietic progenitors when added into methylcellulose cultures. Bone marrow stromal cells are an integral component of the hematopoietic microenvironment and play a critical role in the regulation of hematopoietic stem cell proliferation and self-renewal. Exposure to nicotine decreased CD44 surface expression on primary bone marrow-derived fibroblastlike stromal cells and MS-5 stromal cell line, but not on hematopoietic cells. In addition, mainstream CS altered the trafficking of hematopoietic stem/progenitor cells (HSPC) in vivo. Exposure of mice to CS resulted in the inhibition of HSPC homing into bone marrow. Nicotine and cotinine treatment resulted in reduction of CD44 surface expression on lung microvascular endothelial cell line (LEISVO) and bone marrow-derived (STR-12) endothelial cell line. Nicotine treatment increased E-selectin expression on LEISVO cells, but not on STR-12 cells. These findings demonstrate that nicotine can modulate hematopoiesis by affecting the functions of the hematopoiesis-supportive stromal microenvironment, resulting in the inhibition of bone marrow seeding by LTC-ICs and interfering with stem cell homing by targeting microvascular endothelial cells.     

Early involvement of the phosphatidylinositol 3-kinase/Akt pathway in lung cancer progression

Signaling through the phosphatidylinositol 3-kinase (PI3-kinase) pathway has been associated with lung tumorigenesis. We examined the association between gene copy number of the PI3-kinase catalytic subunit alpha (PIK3CA) and phosphorylated Akt expression in invasive and preinvasive lung cancers. We sought to determine at what stage of tumor development gene copy number increase or phosphorylated Akt overexpression might affect tumor development. We assessed PIK3CA gene copy number by fluorescence in situ hybridization and expression of phosphorylated Akt by immunohistochemistry in 242 invasive and 43 preinvasive lung cancers and correlated our findings with clinical outcome. The PIK3CA was amplified in 70% of squamous carcinomas, 38% of large cell carcinomas, 19% of adenocarcinomas, and 67% of small cell lung cancers. Phosphorylated Akt overexpression was frequently observed, and strongly so in 12 to 17% of lung cancers depending on nuclear or cytoplasmic localization. Neither PIK3CA gene copy number nor phosphorylated Akt protein expression had prognostic significance. In preinvasive lesions, amplification of the PIK3CA and overexpression of phosphorylated Akt were associated with severe dysplasia and each other. These observations suggest frequent and early involvement of the PI3-kinase pathway in lung cancer.     

ErbB-3 mediates phosphoinositide 3-kinase activity in gefitinib-sensitive non-small cell lung cancer cell lines

Therapies that target the EGF receptor (EGFR), such as gefitinib (IRESSA), are effective in a subset of patients with advanced non-small cell lung cancer (NSCLC). The differences in intracellular signaling networks between gefitinib-sensitive and -resistant NSCLCs remain poorly understood. In this study, we observe that gefitinib reduces phospho-Akt levels only in NSCLC cell lines in which it inhibits growth. To elucidate the mechanism underlying this observation, we compared immunoprecipitates of phosphoinositide 3-kinase (PI3K) between gefitinib-sensitive and -resistant NSCLC cell lines. We observe that PI3K associates with ErbB-3 exclusively in gefitinib-sensitive NSCLC cell lines. Gefitinib dissociates this complex, thereby linking EGFR inhibition to decreased Akt activity. In contrast, gefitinib-resistant cells do not use ErbB-3 to activate the PI3K/Akt pathway. In fact, abundant ErbB-3 expression is detected only in gefitinib-sensitive NSCLC cell lines. Two gefitinib-sensitive NSCLC cell lines with endogenous distinct activating EGFR mutations (L858R and Del747-749), frequently observed in NSCLC patients who respond to gefitinib, also use ErbB-3 to couple to PI3K. Down-regulation of ErbB-3 by means of short hairpin RNA leads to decreased phospho-Akt levels in the gefitinib-sensitive NSCLC cell lines, Calu-3 (WT EGFR) and H3255 (L858R EGFR), but has no effect on Akt activation in the gefitinib-resistant cell lines, A549 and H522. We conclude that ErbB-3 is used to couple EGFR to the PI3K/Akt pathway in gefitinib-sensitive NSCLC cell lines harboring WT and mutant EGFRs.