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Cigarette smoking is an important risk factor for esophageal squamous-cell carcinoma. Recent evidences suggested that β-adrenoceptors and cyclooxygenase-2 (COX-2) are involved in regulating the growth of pulmonary, pancreatic, and colon carcinoma cell invoked by cigarette smoking. The molecular and cellular events underlying the pathogenesis of smoking-related esophageal squamous-cell carcinoma, however, were undefined. In the present study, the proliferative response of esophageal squamous carcinoma EC109 cells to cigarette smoke extracts and the involvement of β-adrenoceptors and COX-2 in this action were investigated. Smoke extracts were prepared by dissolving cigarette smoke in ethanol and chloroform solvents. Cell proliferation was assessed as DNA synthesis. The expression levels of β-adrenoceptors and COX-2 were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. Intracellular cyclic adenosine monophosphate (cAMP) level after stimulation with cigarette smoke extracts was measured by enzyme immunoassay. The constitutive expressions of β1- and β2- adrenoceptors were detected in EC109 cells. Results also revealed that both chloroform- and ethanol-extracts of cigarette smoke increased EC109 cell proliferation in a dose-dependent manner. The stimulatory action of cigarette smoke extracts was mediated through β-adrenoceptors and COX-2 because the effects were abolished by atenolol and ICI 118,551, a β1- and β2-selective antagonist respectively, or by nimesulide, a COX-2 inhibitor. Both extracts of cigarette smoke also elevated intracellular cAMP levels and COX-2 expression. The induction of COX-2 expression by cigarette smoke extracts was also reversed by atenolol and ICI 118,551, implicating that COX-2 expression was under the control of β-adrenoceptors. Cigarette smoke extracts, in addition, upregulated β1- and β2-adrenoceptors transcript and protein expression. In conclusion, cigarette smoke extracts not only directly stimulate esophageal squamous-cell carcinoma growth through a mechanism that involves β-adrenoceptors and COX-2 pathway but may also sensitize the cells to such stimulation by upregulating the expression levels of the receptors. These novel findings partly delineate the carcinogenic actions of cigarette smoke and provide new insights into the novel regulatory roles of cigarette smoking on β-adrenoceptors expression in the development of esophageal cancer.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]