Published ahead of print on May 18, 2005, doi:10.1165/rcmb.2004-0411OC
© 2005 American Thoracic Society DOI: 10.1165/rcmb.2004-0411OC 4E-Binding Protein Phosphorylation and Eukaryotic Initiation Factor-4E Release Are Required for Airway Smooth Muscle HypertrophyDepartment of Pediatrics and Communicable Diseases and Department of Molecular and Integrative Physiology, and Department of Cell and Developmental Biology and Department of Medicine, University of Michigan, Ann Arbor, Michigan; and Department of Pediatrics, University of Chicago, Chicago, Illinois Correspondence and requests for reprints should be addressed to Marc B. Hershenson, M.D., University of Michigan, 1150 W. Medical Center Dr., Room 3570, MSRBII, Box 0688, Ann Arbor, MI 48109-0688. E-mail: mhershen{at}umich.edu The molecular mechanisms of airway smooth muscle hypertrophy, a feature of severe asthma, are poorly understood. We previously established a conditionally immortalized human bronchial smooth muscle cell line with a temperature-sensitive SV40 large T antigen. Temperature shift and loss of large T cause G1-phase cell cycle arrest that is accompanied by increased airway smooth muscle cell size. In the present study, we hypothesized that phosphorylation of eukaryotic initiation factor-4E (eIF4E)-binding protein (4E-BP), which subsequently releases eIF4E and initiates cap-dependent mRNA translation, was required for airway smooth muscle hypertrophy. Treatment of cells with chemical inhibitors of PI 3-kinase and mammalian target of rapamycin blocked protein synthesis and cell growth while decreasing the phosphorylation of 4E-BP and increasing the binding of 4E-BP to eIF4E, consistent with the notion that 4E-BP1 phosphorylation and eIF4E function are required for hypertrophy. To test this directly, we infected cells with a retrovirus encoding a phosphorylation site mutant of 4E-BP1 (AA-4E-BP-1) that dominantly inhibits eIF4E. Upon temperature shift, cells infected with AA-4E-BP-1, but not empty vector, failed to undergo hypertrophic growth. We conclude that phosphorylation of 4E-BP, eIF4E release, and cap-dependent protein synthesis are required for hypertrophy of human airway smooth muscle cells.
Key Words: translation • protein synthesis • phosphatidylinositol 3-kinase • mammalian target of rapamycin This article has been cited by other articles:
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