ErbB2 activity is required for airway epithelial repair following neutrophil elastase exposure

In cystic fibrosis and chronic bronchitis, airways are chronically injured by exposure to neutrophil elastase ( NE). We sought to identify factors required for epithelial repair following NE exposure. Normal human bronchial epithelial cells were treated with NE ( 50 nM, 22 h) or control vehicle. Following NE treatment, we found a marked and sustained decrease in epithelial proliferation as detected by Ki67 immunostaining. H-3-thymidine incorporation was also initially depressed but increased over 72 h in NE-treated cells, which suggests that DNA synthesis constitutes an early repair process following NE exposure. We hypothesized that ErbB2 receptor tyrosine kinase, a regulator of cancer cell proliferation, was required for epithelial DNA synthesis following NE exposure. Immediately following NE treatment, by flow cytometry analysis, we found a decrease in ErbB2 surface expression. Protein levels of the full-length 185 kD ErbB2 receptor significantly decreased following NE treatment and smaller ErbB2-positive bands, ranging in size from 23 to 40 kD, appeared, which suggests that NE caused ErbB2 degradation. By real-time RT-PCR analysis, we found no change in ErbB2 mRNA expression following NE treatment, which suggests that changes in ErbB2 protein levels were regulated at the post-translational level. Following NE treatment, full-length 185 kD ErbB2 levels increased to pretreatment levels, correlating with the increase in thymidine incorporation during the same time period. Importantly, inhibition of ErbB2 activity with AG825 ( 5 mu M) or Herceptin (3.1 mu M), an ErbB2-neutralizing antibody, blocked thymidine incorporation only in NE-treated cells. These results suggest ErbB2 is a critical factor for epithelial recovery following NE exposure.