Effects of cigarette smoking and restraint stress on human colon tumor growth in mice.

BACKGROUND: Cigarette smoking is a risk factor for colon cancer. Studies suggest that stress increases the incidence and promotes the development of cancers. Cigarette smoking and stress are closely associated, as people often smoke under stressful conditions and both of them can activate the adrenergic nervous system. AIMS: To investigate the effects of cigarette smoking and restraint stress on colon cancer growth and the possible underlying mechanisms in these pathological processes. METHODS: Nude mice bearing a HT-29 human colon cancer xenograft were either exposed to cigarette smoke and/or restraint stress. Cotinine and epinephrine levels in plasma of nude mice were measured by enzyme immunoassays. Expression of cyclooxygenase-2 (COX-2) and B-cell lymphoma-2 (Bcl-2) in tumor tissues were detected by Western blot. Prostaglandin E(2) (PGE(2)) concentrations were determined by enzyme immunoassay. RESULTS: 4% cigarette smoking together with restraint stress 1 h daily for 33 days promoted tumor growth in nude mice. This was accompanied by the increase of plasma levels of cotinine and epinephrine in these animals. They also enhanced the COX-2, Bcl-2 expressions and PGE(2) levels in tumor tissues. CONCLUSION: These findings are important in understanding the pathogenesis of colon cancer, particularly related to cigarette smoking and stress.

E series of prostaglandin receptor 2-mediated activation of extracellular signal-regulated kinase/activator protein-1 signaling is required for the mitogenic action of prostaglandin E2 in esophageal squamous-cell carcinoma.

The use of nonsteroidal anti-inflammatory drugs is associated with a lower risk for esophageal squamous cell carcinoma, in which overexpression of cyclooxygenase-2 (COX-2) is frequently reported. Prostaglandin E(2) (PGE(2)), a COX-2-derived eicosanoid, is implicated in the promotion of cancer growth. However, the precise role of PGE(2) in the disease development of esophageal squamous cell carcinoma remains elusive. In this study, we investigated the effect of PGE(2) on the proliferation of cultured esophageal squamous cell carcinoma cells (HKESC-1). Results showed that HKESC-1 cells expressed all four series of prostaglandin (EP) receptors, namely, EP1 to EP4 receptors. In this regard, PGE(2) and the EP2 receptor agonist (+/-)-15-deoxy-16S-hydroxy-17-cyclobutyl PGE(1) methyl ester (butaprost) markedly increased HKESC-1 cell proliferation. Moreover, the mitogenic effect of PGE(2) was significantly attenuated by RNA interference-mediated knockdown of the EP2 receptor, indicating that this receptor mediated the mitogenic effect of PGE(2). In this connection, PGE(2) and butaprost induced phosphorylation of extracellular signal-regulated kinases 1/2 (Erk1/2), whose down-regulation by RNA interference significantly attenuated PGE(2)-induced cell proliferation. In addition, PGE(2) and butaprost increased c-Fos expression and activator protein 1 (AP-1) transcriptional activity, which were abolished by the mitogen-activated protein kinase/Erk kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)-butadiene ethanolate (U0126). AP-1-binding inhibitor curcumin also partially reversed the mitogenic effect of PGE(2). Taken together, these data demonstrate for the first time that the EP2 receptor mediates the mitogenic effect of PGE(2) in esophageal squamous cell carcinoma via activation of the Erk/AP-1 pathway. This study supports the growth-promoting action of PGE(2) in esophageal squamous cell carcinoma and the potential application of EP2 receptor antagonists in the treatment of this disease.

Nicotine promotes colon tumor growth and angiogenesis through beta-adrenergic activation.

Cigarette smoking is a putative environmental risk factor for colon cancer. Nicotine, an active alkaloid in tobacco, has been implicated in carcinogenesis. In the present study, we demonstrated that oral nicotine administration (50 or 200 microg/ml) for 25 days stimulated growth of human colon cancer xenograft in nude mice. It also increased vascularization in the tumors and elevated cotinine and adrenaline plasma levels. beta-Adrenoceptors, cyclooxygenase-2 (COX-2), prostaglandin E(2) (PGE(2)), and vascular endothelial growth factor (VEGF) in tumor tissues were also increased by nicotine. I.p. injection of beta(1)-selective antagonist (atenolol, 5 or 10 mg/kg) or beta(2)-selective antagonist (ICI 118,551, 5, or 10 mg/kg) blocked the nicotine-stimulated tumor growth dose dependently, in which beta(2)-selective antagonist produced a more prominent effect. beta-Adrenoceptors blockade also abrogated the stimulatory action of nicotine on microvessel densities as well as cell expression of COX-2, PGE(2), and VEGF, in which beta(2)-selective antagonist produced a significant effect. These findings provide a direct evidence that nicotine can enhance colon tumor growth mediated partly by stimulation of beta-adrenoceptors, preferentially the beta(2)-adrenoceptors. Activation of beta-adrenoceptors and the subsequent stimulation of COX-2, PGE(2), and VEGF expression is perhaps an important mechanism in the tumorigenic action of nicotine on colon tumor growth. These data suggest that beta-adrenoceptors play a modulatory role in the development of colon cancer and partly elucidate the carcinogenic action of cigarette smoke.

Functional role of beta-adrenergic receptors in the mitogenic action of nicotine on gastric cancer cells.

We previously reported that nicotine promoted gastric cancer cell growth via upregulation of cyclooxygenase 2 (COX-2). In the present study, we further investigated whether beta-adrenoceptors, protein kinase C (PKC), and extracellular signal-regulated kinase-1/2 (ERK1/2) were involved in the modulation of COX-2 expression and cell proliferation by nicotine in AGS, a human gastric adenocarcinoma cell line. Results showed that nicotine dose dependently increased the phosphorylation of EKR1/2 and the expression of AP-1 subunits c-fos and c-jun. In this connection, the ERK1/2 inhibitor U0126 abrogated the upregulation of AP-1 and COX-2 as well as cell proliferation induced by nicotine. Moreover, nicotine induced the translocation of PKC-betaI from cytosol to membrane and increased the total levels of PKC expression. Inhibition of PKC by staurosporine attenuated nicotine-induced ERK1/2 phosphorylation and COX-2 expression. Furthermore, atenolol and ICI 118,551, a beta1- and beta2-adrenoceptor antagonist, respectively, reversed the stimulatory action of nicotine on the expression of PKC, ERK1/2 phosphorylation, and COX-2 together with cell proliferation. Collectively, these results suggest that nicotine stimulates gastric cancer cell growth through the activation of beta-adrenoceptors and the downstream PKC-betaI/ERK1/2/COX-2 pathway.

Nicotine promotes cell proliferation via alpha7-nicotinic acetylcholine receptor and catecholamine-synthesizing enzymes-mediated pathway in human colon adenocarcinoma HT-29 cells.

Cigarette smoking has been implicated in colon cancer. Nicotine is a major alkaloid in cigarette smoke. In the present study, we showed that nicotine stimulated HT-29 cell proliferation and adrenaline production in a dose-dependent manner. The stimulatory action of nicotine was reversed by atenolol and ICI 118,551, a beta(1)- and beta(2)-selective antagonist, respectively, suggesting the role of beta-adrenoceptors in mediating the action. Nicotine also significantly upregulated the expression of the catecholamine-synthesizing enzymes [tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DbetaH) and phenylethanolamine N-methyltransferase]. Inhibitor of TH, a rate-limiting enzyme in the catecholamine-biosynthesis pathway, reduced the actions of nicotine on cell proliferation and adrenaline production. Expression of alpha7-nicotinic acetylcholine receptor (alpha7-nAChR) was demonstrated in HT-29 cells. Methyllycaconitine, an alpha7-nAChR antagonist, reversed the stimulatory actions of nicotine on cell proliferation, TH and DbetaH expression as well as adrenaline production. Taken together, through the action on alpha7-nAChR nicotine stimulates HT-29 cell proliferation via the upregulation of the catecholamine-synthesis pathway and ultimately adrenaline production and beta-adrenergic activation. These data reveal the contributory role alpha7-nAChR and beta-adrenoceptors in the tumorigenesis of colon cancer cells and partly elucidate the carcinogenic action of cigarette smoke on colon cancer.

Shift of homeostasis from parenchymal regeneration to fibroblast proliferation induced by lipopolysaccharide-activated macrophages in gastric mucosal healing in vitro.

Wound healing in the gastrointestinal tract is an orderly process involving orchestrated responses of various cell types. Lipopolysaccharides (LPS) are major components of the outer membrane of Gram-negative bacteria, which are known to impair gastric ulcer healing in animals. The influence of LPS on intercellular communication in wound healing, however, is unknown. We examined the effects of LPS-induced macrophage activation on the proliferative response in cultured rat gastric epithelial cells (RGM-1) and fibroblasts JHU-25. Rat peritoneal resident macrophages were activated with increasing doses of LPS. The supernatant from the activated macrophage preparation, designated as macrophage-conditioned medium, was then used to treat RGM-1 or JHU-25 cells. Cell proliferation and migration were determined by [(3)H]-thymidine incorporation and a monolayer wound-healing assay, respectively. Macrophage-conditioned medium significantly suppressed RGM-1 cell proliferation but had no effect on cell migration. The same medium, however, increased JHU-25 cell proliferation. LPS treatment alone suppressed JHU-25 cell proliferation while it had no effect on RGM-1 cell proliferation, indicating that the differential effects of the macrophage-conditioned medium on cell proliferation were elicited by the factors derived from macrophages. In this regard, tumor necrosis factor (TNF)-alpha stimulated while interleukin (IL)-1beta suppressed RGM-1 cell proliferation, suggesting that IL-1beta but not TNF-alpha may play a part in the mediation of the antiproliferative effect of macrophage-conditioned medium on gastric epithelial cells. In contrast, IL-1beta suppressed while TNF-alpha had no effect on JHU-25 cell proliferation. Collectively, LPS-activated macrophages delay gastric mucosal regeneration but promote fibroblast proliferation in vitro. Such changes may partly elucidate the detrimental effect of bacterial infection on tissue repair in the stomach.

Involvement of Kv1.1 and Nav1.5 in proliferation of gastric epithelial cells.

In the present study, patch clamp experiments demonstrated the expression of multiple ionic currents, including a Ba2+-sensitive inward rectifier K+ current (IKir), a 4-aminopyridine- (4-AP) sensitive delayed rectifier K+ current (IKDR), and a nifedipine-sensitive, tetrodotoxin-resistant inward Na+ current (INa.TTXR) in the non-transformed rat gastric epithelial cell line RGM-1. RT-PCR revealed molecular identities of mRNAs for the functional ionic currents, including Kir1.2 for IKir, Kv1.1, Kv1.6, and Kv2.1 for IKDR, and Nav1.5 for INa.TTXR. Pharmacologic blockade of Kv and Nav, but not Kir, suppressed RGM-1 cell proliferation. To further elucidate which subtypes of the ion channels were involved in cell proliferation, RNA interference was employed to knockdown specific gene expression. Downregulation of Kv1.1 or Nav1.5 by RNA interference suppressed RGM-1 cell proliferation. To conclude, our study is the first to delineate the expression of ion channels and their functions as growth modulators in gastric epithelial cells.