Submitted on February 19, 2007
Accepted on June 19, 2007
NEUTROPHIL ELASTASE INHIBITION OF CELL CYCLE PROGRESSION IN AIRWAY EPITHELIAL CELLS IN VITRO IS MEDIATED BY p27Kip1
Bernard M Fischer1*, Shuo Zheng1, Rongrong Fan1, and Judith A. Voynow1
1 Pediatrics, Duke University Medical Center, Durham, North Carolina, United States
* To whom correspondence should be addressed. E-mail: fisch005{at}mc.duke.edu.
Neutrophil elastase (NE), a serine protease present in high concentrations in the airways of cystic fibrosis patients, injures the airway epithelium. We examined the epithelial response to NE-mediated proteolytic injury. We have previously reported that NE treatment of airway epithelial cells causes a marked decrease in epithelial DNA synthesis and proliferation. We hypothesized that NE inhibits DNA synthesis by arresting cell cycle progression. Progression through the cell cycle is positively regulated by cyclin complexes and negatively regulated by cyclin dependent kinase inhibitors (CKI). To test whether NE arrests cell cycle progression, we treated normal human bronchial epithelial (NHBE) cells with NE (50 nM) or control vehicle for 24h and assessed the effect of treatment on the cell cycle by flow cytometry. NE treatment resulted in G1 arrest. Arrest in G1 phase may be due to CKI inhibition of cyclin E complex; therefore, we evaluated whether NE upregulated CKI expression and/or affected the interaction of CKIs with the cyclin E complex. Following NE or control vehicle treatment, expression of p27Kip1, a member of the Cip/Kip family was evaluated. NE increased increased p27Kip1 gene and protein expression. NE increased the co-immunoprecipitation of p27Kip1 with cyclin E complex suggesting that p27Kip1 inhibited cyclin E complex activity. Our results demonstrate that p27 is regulated by NE and is critical for NE-induced cell cycle arrest.
