title: A receptor-mediated mechanism of nicotine toxicity in oral keratinocytes.
abstract: Smoking and smokeless tobacco cause morbidity that originates from the epithelium lining of the skin and upper digestive tract. Oral keratinocytes (OKC) express nicotinic acetylcholine receptors (nAChRs) that bind nicotine (Nic). We studied the mechanism of the receptor-mediated toxicity of tobacco products on OKC. Preincubation of normal human OKC with Nic altered the ligand-binding kinetics of their nAChRs, suggesting that the nAChRs underwent structural changes. This hypothesis was confirmed by the finding that exposure of OKC to Nic causes transcriptional and translational changes. Through RT-PCR and immunoblotting, we found a 1.5- to 2.9-fold increase in the mRNA and protein levels of alpha3, alpha5, alpha7, beta2, and beta4 nAChR subunits. Exposure of OKC to Nic also changed the mRNA and protein levels of the cell cycle and cell differentiation markers Ki-67, PCNA, p21, cyclin D1, p53, filaggrin, loricrin, and cytokeratins 1 and 10. The nicotinic antagonist mecamylamine prevented these changes, which indicates that the Nic-induced changes in the expression of both the nAChR and the cell cycle and cell differentiation genes resulted from pharmacologic stimulation of nAChRs with Nic. To establish the relevance of these findings to the pathobiologic effects of tobacco products in vivo, we studied the above parameters in the oral tissue of rats and mice after their exposure for 3 weeks to environmental cigarette smoke or drinking water containing equivalent concentrations of Nic that are pathophysiologically relevant. The changes of the nAChRs and the cell cycle and cell differentiation genes were similar to those found in vitro. The results of indirect immunofluorescence assay of tissue specimens validated these findings. Thus, some pathobiologic effects of tobacco products in oral tissues may stem from Nic-induced alterations of the structure and function of keratinocyte nAChRs responsible for the physiologic regulation of the cell cycle by the cytotransmitter acetylcholine.
authors.affiliation: Department of Dermatology, School of Medicine, University of California, Davis 95817, USA.
authors.forename: J
authors.initials: J
authors.lastname: Arredondo
authors.forename: V T
authors.initials: VT
authors.lastname: Nguyen
authors.forename: A I
authors.initials: AI
authors.lastname: Chernyavsky
authors.forename: D L
authors.initials: DL
authors.lastname: Jolkovsky
authors.forename: K E
authors.initials: KE
authors.lastname: Pinkerton
authors.forename: S A
authors.initials: SA
authors.lastname: Grando
mesh_terms: D000818:Animals; D015415:Biomarkers; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D000091344:Filaggrin Proteins; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D009055:Mouth / Q000166:cytology*; D009538:Nicotine / Q000506:poisoning*; D010936:Plant Extracts / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014028:Tobacco Smoke Pollution; D014030:Tobacco, Smokeless / Q000737:chemistry; D015854:Up-Regulation
chemical_list: D015415:Biomarkers; C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D010936:Plant Extracts; D011978:Receptors, Nicotinic; D014028:Tobacco Smoke Pollution; D009538:Nicotine