Oleic acid stimulates rapid translocation of cholinephosphate cytidylyltransferase in type II cells

Activity of cholinephosphate cytidylyltransferase, the rate-limiting enzyme in phosphatidylcholine synthesis, increases rapidly in the lung after birth predominantly due to an increase in membrane-associated activity. Although there is strong evidence that enzyme translocation is a major regulatory mechanism in other cells, this mechanism has not been conclusively demonstrated in intact alveolar type II cells. In this study, we show that oleic acid stimulates rapid translocation of cytidylyltransferase activity and protein from cytosol to microsomes in both primary cultured fetal and adult type II cells and MLE12 cells, a cell line derived from murine distal respiratory epithelial cells. Shifts in subcellular distribution occurred within 5 min of exposure to 200 microM oleic acid. The magnitude of the increases in microsomal enzyme activity and immunoreactive protein levels was several-fold greater in d21 fetal cells than adult type II cells. Oleic acid-induced translocation was confirmed in in vitro translocation experiments. After incubating MLE12 cell postmitochondrial supernatants at 37 degrees C with oleic acid and separation of enzyme isoforms on glycerol density gradients, enzyme activity was decreased in gradient fractions corresponding to both cytosolic isoforms and microsomal activity increased 7.9-fold compared to the distribution of enzyme activity in postmitochondrial supernatants incubated at 4 degrees C without oleic acid. The increase in microsomal activity was associated with an increased incorporation of [14C]oleic acid in the membrane free fatty acid fraction. Developmental changes in type II cell membrane lipid composition may induce the rapid translocation/activation of cytidylyltransferase in the lung after birth.