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Part of the innate defense of bronchial epithelia against bacterial colonization is regulated secretion of salt, water, and mucus as well as defensins and cytokines involving MAP kinase activation and alterations in early gene expression. We tested two different types of immortalized human airway epithelial cells (S9, 16HBE14o-) for activation of Erk-type MAP kinases and for expression of c-Fos on treatment with Staphylococcus aureus culture supernatants from the stationary growth phase [optical density (OD)(540 nm) = 10] or with recombinant S. aureus hemolysins A and B (Hla, Hlb). OD10 supernatants activated Erk-type MAP kinases and c-Fos expression in a concentration-dependent manner. Hla induced Erk-type kinase phosphorylation in S9 but not in 16HBE14o- cells. Hlb induced Erk activation in either cell type. Basal and stimulated levels of Erk-type MAP kinase phosphorylation were sensitive to the Mek1 inhibitor PD-98059, indicating that the bacterial products activated the entire signaling cascade that coregulates IL-8 induction and secretion. While c-Fos expression was enhanced by OD10 supernatants, Hla, and Hlb in S9 cells, 16HBE14o- cells responded to OD10 supernatant and Hlb but not to Hla. In S9 cells, PD-98059 suppressed c-Fos upregulation by OD10 supernatant, Hla, or Hlb, indicating that c-Fos expression requires activation of Erk-type MAP kinases. In 16HBE14o- cells, however, c-Fos expression by OD10 supernatant was sensitive to PD-98059, while that induced by Hlb was not. This indicates that ingredients of OD10 supernatants other than Hla or Hlb are activating Erk-type MAP kinases in 16HBE14o- cells and that other intracellular signaling systems apart from Erk-type MAP kinases contribute to Hlb-mediated regulation of c-Fos. Thus interaction of bacterial factors with airway epithelial cells may be highly cell type specific.

Mechanical clearance of inhaled dust particles and microorganisms is an important part of the innate defense mechanisms of mammalian airways. Airway epithelia are composed of various cell types with different degrees of cell polarity. Serous cells regulate composition and volume of luminal periciliary fluid and mucus. Autocrine, paracrine, or neuronal messengers determine the secretory and reabsorptive rates of electrolytes and water via cAMP-or inositol triphosphate/calcium-mediated intracellular signals. Comparison of the expression of calcium-mobilizing receptor types (G protein-coupled-, growth factor-, and cytokine receptors) in two types of human immortalized airway epithelial cells (S9, 16HBE14o-) revealed that receptor populations were qualitatively and quantitatively different in the two cell types. Sustained calcium signals were elicited by activation of purinergic receptors in 16HBE14o-cells or muscarinic acetylcholine or histamine receptors in S9 cells. These G protein-coupled receptors mobilized calcium from intracellular stores and activated capacitative calcium influx. The experimental cells may represent different types of original airway epithelial cells and seem to be suited as model cells to study cell signaling and protein expression during interaction with pathogens or their secretory products (e.g., virulence factors).

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