Submitted on November 16, 2006
Accepted on August 24, 2007
Overexpression of Human Hsp27 Inhibits Serum Induced Proliferation in Airway Smooth Muscle Myocytes and Confers Resistance to Hydrogen Peroxide Cytotoxicity
Sonemany Salinthone1, Mariam Ba1, Lisa J Hanson1, Jody L Martin2, Andrew John Halayko3, and William T. Gerthoffer4*
1 Department of Pharmacology, Univ. of Nevada School of Medicine, Reno, Nevada, United States
2 Cardiovascular Institute, Loyola University Medical Center, Maywood, Illinois, United States
3 Department of Physiology, Univ. of Manitoba, Winnipeg, Canada
4 Department of Pharmacology, University of Nevada School of Medicine, Reno, United States
* To whom correspondence should be addressed. E-mail: wgerthoffer{at}usouthal.edu.
Airway smooth muscle (ASM) hypertrophy and hyperplasia are characteristics of asthma that lead to thickening of the airway wall and obstruction of airflow. Very little is known about mechanisms underlying ASM remodeling, but in vascular smooth muscle it is known that progression of atherosclerosis depends on the balance of myocyte proliferation and cell death. Small heat shock protein 27 (Hsp27) is antiapoptotic in nonmuscle cells, but its role in ASM cell survival is unknown. Our hypothesis was that phosphorylation of Hsp27 may regulate airway remodeling by modifying proliferation, cell survival or both. To test this hypothesis, adenoviral vectors were used to overexpress human Hsp27 in ASM cells. Cells were infected with empty vector (Ad5) or wild-type Hsp27 (AdHsp27 WT) and proliferation and death was assessed. Overexpressing Hsp27WT caused a 50% reduction in serum-induced proliferation and increased cell survival after exposure to 100 µM hydrogen peroxide (H2O2) compared to mock-infected controls. Overexpression studies utilizing an S15A, S78A and S82A non-phosphorylation mutant (AdHsp27 3A) and S15D, S78D and S82D pseudophosphorylated mutant showed phosphorylation of Hsp27 was necessary for regulation of ASM proliferation, but not survival. Hsp27 provided protection against H2O2 induced cytotoxicity by up-regulating cellular glutathione levels and preventing necrotic cell death, but not apoptotic cell death. The results support the notion that ASM cells can be stimulated to undergo proliferation and death and that Hsp27 may regulate these processes, thereby contributing to airway remodeling in asthmatics.
