Expression of Xenobiotic-Metabolizing Enzymes in Cultured Rat Tracheal Epithelial Cells

Abstract

Rat tracheal epithelial (RTE) cells were cultured on membrane support with and without retinoic acid (RA). In early (6-day-old) cultures, the epithelium is a monolayer or bilayer of undifferentiated cells and secretes little mucuslike product either in the absence or presence of RA. In late (12- to 15-day-old) cultures, the epithelium differentiates as a mucociliary epithelium in the presence of RA and as a squamous epithelium in the absence of RA. The purpose of our study was to determine whether a number of xenobiotic enzymes are expressed in these cultures and whether their expression depends on the state of differentiation. Enzyme expression was characterized by electrophoresis and immunoblotting as a function of time in culture and phenotypic differentiation. Cytochrome P450 1A1 was not expressed in freshly harvested RTE cells. This isoenzyme was induced in rats by gavage with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or by exposure of early RTE cell cultures to TCDD, provided RA was also added to the cultures. Cytochrome P450 2B1 was observed in freshly isolated RTE cells, but not in early or late RTE cultures. In contrast, expression of NADPH-cytochrome P450 reductase was decreased in early cultures, but was increased in well-differentiated cultures. Flavin-containing monooxygenase was detected in lung tissue, but not in freshly harvested or cultured RTE cells. Glutathione S-transferase (GST) mu and pi were expressed in freshly harvested RTE cells. GST pi was expressed in early and late cultures, whereas GST mu was expressed in late cultures, but could not be found in early cultured RTE cells.(ABSTRACT TRUNCATED AT 250 WORDS)