EXPRESSION OF XENOBIOTIC-METABOLIZING ENZYMES IN CULTURED RAT TRACHEAL EPITHELIAL-CELLS

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 mucocilary epithelium in the presence of RA and as I 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 mts by gavage with 2,3,7,8-teuachlorodibenzo-p-dioxin (TCDD) or by exposure of early RTE cell cultures to TCDD, provided RA was also added to the cultures. Cytochrome P450 observed in freshly isolated RTE cells, bur 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 hot in freshly harvested or cultured RTE cells. Glutathione s-transferases (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, bur could not be found in early cultured RTE cells. Levels of GST isoenzymes were unaffected by RA. These results parallel the expression of enzymes observed in proliferating and differentiating epithelium induced by mechanical injury in vivo. Induction of monooxygenases by polycyclic aromatic hydrocarbons results in RTE cells with metabolic activating and deactivating enzymes and constitutes a system suited for some toxicological studies.