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Cyclooxygenase 2 (COX-2) expression is induced by physiological and inflammatory stimuli. Regulation of COX-2 expression is stimulus and cell type specific. Exposure to Zn2+ has been associated with activation of multiple intracellular signaling pathways as well as the induction of COX-2 expression. This study aims to elucidate the role of intracellular signaling pathways in Zn2+-induced COX-2 expression in human bronchial epithelial cells. Inhibitors of the phosphatidylinositol 3-kinase (PI3K) potently block Zn2+-induced COX-2 mRNA and protein expression. Overexpression of adenoviral constructs encoding dominant-negative Akt kinase downstream of PI3K or wild-type phosphatase and tensin homolog deleted on chromosome 10, an important PI3K phosphatase, suppresses COX-2 mRNA expression induced by Zn2+. Zn2+ exposure induces phosphorylation of the tyrosine kinases, including Src and EGF receptor (EGFR), and the p38 mitogen-activated protein kinase. Blockage of these kinases results in inhibition of Zn2+-induced Akt phosphorylation as well as COX-2 protein expression. Overexpression of dominant negative p38 constructs suppresses Zn2+-induced increase in COX-2 promoter activity. In contrast, the c-Jun NH2-terminal kinase and the extracellular signal-regulated kinases have minimal effect on Akt phosphorylation and COX-2 expression. Inhibition of p38, Src, and EGFR kinases with pharmacological inhibitors markedly reduces Akt phosphorylation induced by Zn2+. However, the PI3K inhibitors do not show inhibitory effects on p38, Src, and EGFR. These data suggest that p38 and EGFR kinase-mediated Akt activation is required for Zn2+-induced COX-2 expression and that the PI3K/Akt signaling pathway plays a central role in this event.

The distribution of the major surfactant apoprotein (SP-A) in adult rat lung was determined in order to gain insight into its metabolism, including packaging of SP-A into lamellar bodies. The effect of glucocorticoid treatment on surfactant apoprotein was studied to test whether regulation of surfactant apoprotein genes, which has been described for the fetal lung, can be demonstrated in the adult animal. We measured the amounts of immunoreactive SP-A in several lung tissue compartments and lavage fractions from control animals and from the lungs of rats given dexamethasone for 1 wk. Protein and phospholipids were measured, SP-A was quantitated with a noncompetitive enzyme-linked immunoabsorbent assay (ELISA) and SP-A, SP-B, and SP-C mRNAs were estimated by Northern blotting. We found an 85-fold concentration of SP-A in a lamellar body-rich fraction compared with lung tissue homogenate and we calculated that as much as one-half of all the tissue SP-A might be accounted for by a lamellar body pool. After 1 wk of dexamethasone treatment, there was an increase in adult rat lung SP-A, SP-B, and SP-C mRNA and a substantial increase in tissue and lavage fluid immunoreactive SP-A pools. Lamellar body fraction SP-A content per lung was 1.4-fold higher after dexamethasone, and there was a fivefold increase in the lavage SP-A pool, much of which was inseparable from the alveolar macrophages. We conclude that SP-A is concentrated in the lamellar bodies of type II cells, that dexamethasone treatment increased all surfactant mRNAs, and that it increased SP-A content in adult rat lung.