Changes in expression of 15-lipoxygenase and prostaglandin-H synthase during differentiation of human tracheobronchial epithelial cells.

The purpose of our studies was to examine differentiation-dependent expression of 15-lipoxygenase (15-LO) and prostaglandin H synthase (PGHS) isoforms in cultured normal human tracheobronchial epithelial cells. In the presence of retinoic acid (RA) the cultures differentiated into a mucociliary epithelium. When cultured in RA-depleted media, the cultures differentiated into a squamous epithelium. In the absence of RA the cultures did not express 15-LO or either of the PGHS isoforms. The PGHS-1 isoform was not expressed in RA-sufficient cultures, but both PGHS-2 messenger RNA (mRNA) and protein were strongly expressed, and prostaglandin E2 (PGE2) was produced during the predifferentiation phase. No PGHS-2 expression or PGE2 could be detected in fully differentiated mucociliary cultures. 15-LO showed the opposite expression pattern: neither mRNA nor protein were detected during the predifferentiation stage, but both were strongly expressed once mucous differentiation had occurred. Cytosolic phospholipase A2 protein was expressed throughout all stages of growth and differentiation. The cultures generated no 15-LO metabolites when incubated with 10 microM to 50 microM arachidonic acid (AA) and stimulated with ionophore. However, lysates prepared from such cultures generated 15-hydroxyeicosatetraenoic acid (15-HETE) and 12-HETE from AA, indicating that the cells contained active enzyme. When cultures expressing 15-LO protein were incubated with 10 microM linoleic acid (LA) instead of AA, and were stimulated with ionophore, they generated 13-hydroxy-9,11-octadecadienoic acid. LA rather than AA appeared to be the preferred substrate for the 15-LO enzyme. Our studies indicated that the expression of 15-LO and PGHS-2 is differentiation dependent in airway epithelial cells.