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Receptor‐mediated tobacco toxicity: acceleration of sequential expression of α5 and α7 nicotinic receptor subunits in oral keratinocytes exposed to cigarette smoke
Author(s) -
Arredondo Juan,
Chernyavsky Alexander I.,
Jolkovsky David L.,
Pinkerton Kent E.,
Grando Sergei A.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fj.07-9965.com
Subject(s) - mecamylamine , nicotine , chemistry , nicotinic acetylcholine receptor , nicotinic agonist , transcription factor , microbiology and biotechnology , receptor , pharmacology , biology , biochemistry , gene , neuroscience
Tobacco products and nicotine alter the cell cycle and lead to squamatization of oral keratinocytes (KCs) and squamous cell carcinoma. Activation of nicotinic acetylcholine receptors (nAChRs) elicits Ca 2+ influx that varies in magnitude between different nAChR subtypes. Normal differentiation of KCs is associated with sequential expression of the nAChR subtypes with increasing Ca 2+ permeability, such as α5‐containing α3 nAChR and α7 nAChR. Exposure to environmental tobacco smoke (ETS) or an equivalent concentration of nicotine accelerated by severalfold the α5 and α 7 expression in KCs, which could be abolished by mecamylamine and α‐bungarotoxin with different efficacies, suggesting the following sequence of auto regulation of the expression of nAChR subtypes: α3(β2/β4) > α3(β2/β4)α5 > α7 > α7. This conjecture was corroborated by results of quantitative assays of subunit mRNA and protein levels, using nAChR‐ specific pharmacologic antagonists and small interfering RNAs. The genomic effects of ETS and nicotine involved the transcription factor GATA‐2 that showed a multifold increase in quantity and activity in exposed KCs. Using protein kinase inhibitors and dominant negative and constitutively active constructs, we charac terized the principal signaling cascades mediating a switch in the nAChR subtype. Cumulative results indi cated that the α3(β2/β4) to α3(β2/α4)α5 nAChR tran sition predominantly involved protein kinase C, α3(β2/ β4)α5 to α7 nAChR transition—Ca 2+ /calmodulin‐ dependent protein kinase II and p38 MAPK, and α7 self‐up‐regulatio—the p38 MAPK/Akt pathway, and JAK‐2. These results provide a mechanistic insight into the genomic effects of ETS and nicotine on KCs and characterize signaling pathways mediating autoregulation of stepwise overexpression of nAChR subtypes with increasing Ca 2+ permeability in exposed cells. These observations have salient clinical implications, because a switch in the nAChR subunit composition can bring about a corresponding switch in receptor function, leading to profound pathobiologic effects ob served in KCs exposed to tobacco products.—Arredondo, J., Chernyavsky, A. I., Jolkovsky, D. L., Pinkerton, K. E., Grando, S. A. Receptor‐mediated tobacco toxicity: acceleration of sequential expression of α5 and α7 nicotinic receptor subunits in oral keratinocytes exposed to cigarette smoke. FASEB J . 22, 1356–1368 (2008)