The influence of epidermal growth factor receptor ligands on CD44 and ERM proteins in bronchial epithelial cells

Abstract

Ezrin and moesin were detected in bronchial epithelial cell cultures where under basal conditions they had a cytoplasmic distribution as well as at plasma membrane regions colocalised with CD44. Following treatment with 1nM EGF (15 minutes), enhanced cytoskeletal association along with redistribution of ezrin and moesin to membrane projections resembling lamellipodia and microvilli-like structures was observed and cells appeared to adopt a more migratory phenotype. This EGF stimulated redistribution of ezrin and moesin did not appear to be as a result of activation by phosphorylation on tyrosine residues as determined by immunoprecipitation using anti-phosphotyrosine antibodies followed by Western blotting.

Previously published data showing enhanced repair with EGF were confirmed here in primary bronchial epithelial cells as well as the 16HBE cell line. As EGF stimulated enhanced migration might act in part by modulation of ERM proteins the distribution of ERM proteins and CD44 during repair was observed using double immunofluorescent staining. However at the earlier time points (0-3 hours) cells did not appear to be migrating and ERM proteins were not seen in lamellipodia structures as observed previously. Instead, CD44 and ERM proteins were colocalised in microvilli-like extensions might reflect enhanced adhesion processes following damage. A study of the later phase of repair might confirm an involvement of ERM proteins in migratory processes during repair. In addition to the effects of EGF, the mast cell stabiliser, sodium cromoglycate was shown here to enhance repair of damaged 16HBE 14o-cell monolayers (P<0.03 and <0.02 at 3 and 9 hours respectively) and this was shown to act through an EGFR dependent mechanism as 1mM tyrphostin AG1478 blocked this effect and EGFR receptors phosphorylated on tyrosine residues were detected in anti-phosphotyrosine immunoprecipitates of 16HBE 14o-cells treated with sodium cromoglycate.

In conclusion these data have shown that, ezrin and moesin are associated with the actin cytoskeleton and colocalised with CD44 and can be modulated by EGF in bronchial epithelial cells.

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