HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 292/6/L1414    most recent 00123.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Osawa, Y. Articles by Emala, C. W. Search for Related Content PubMed PubMed Citation Articles by Osawa, Y. Articles by Emala, C. W.

Raf-1 kinase mediates adenylyl cyclase sensitization by TNF- in human airway smooth muscle cells

¹Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, New York, New York; and ²Pulmonary and Critical Care Division, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania

Submitted 3 April 2006 ; accepted in final form 28 January 2007

Tumor necrosis factor (TNF)- is a potent inflammatory cytokine implicated in the exacerbation of asthma. Chronic exposure to TNF- has been reported to induce G protein-coupled receptor desensitization, but adenylyl cyclase sensitization, in airway smooth muscle cells by an unknown mechanism. Cyclic AMP, which is synthesized by adenylyl cyclases in response to G protein-coupled receptor signals, is an important second messenger involved in the regulation of the airway muscle proliferation, migration, and tone. In other cell types, TNF- receptors transactivate the EGF receptor, which activates raf-1 kinase. Further studies in transfected cells show that raf-1 kinase can phosphorylate and activate some isoforms of adenylyl cyclase. Cultured human airway smooth muscle cells were treated with TNF- in the presence or absence of inhibitors of prostaglandin signaling, protein kinases, or G_i proteins. TNF- caused a significant dose- (1–10 ng/ml) and time-dependent (24 and 48 h) increase in forskolin-stimulated adenylyl cyclase activity, which was abrogated by pretreatment with GW5074 (a raf-1 kinase inhibitor), was partially inhibited by an EGF receptor inhibitor, but was unaffected by pertussis toxin. TNF- also increased phosphorylation of Ser³³⁸ on raf-1 kinase, indicative of activation. IL-1 and EGF sensitization of adenylyl cyclase activity was also sensitive to raf-1 kinase inhibition by GW5074. Taken together, these studies link two signaling pathways not previously characterized in human airway smooth muscle cells: TNF- transactivation of the EGF receptor, with subsequent raf-1 kinase-mediated activation of adenylyl cyclase.

GW5074; mitogen-activated protein kinase; phosphorylation; immunoblot; cell culture