Lecithin biosynthesis in a clonal line of lung adenoma cells with type II alveolar cell properties

The content and synthesis of certain phospholipids associated with lung surfactant has been investigated in a clonal line of epithelial cells derived from mouse lung adenoma. These cells, designated LA-4, possess osmiophilic intracytoplasmic lamellar inclusion bodies similar in appearance to lamellar bodies observed in normal type 2 alveolar epithelial cells (Stoner et al., 1975).Lecithin was the most abundant phospholipid in the LA-4 cells, comprising more than 50% of all phospholipid. LA-4 cells had significantly higher contents of total lecithin than in vivo adenoma and normal lung, but a lower proportion (27–29%) of the total lecithin in disaturated form than normal lung (36%). In addition, LA-4 cells had a significantly higher proportion of total lecithin in disaturated form than a clonal line of mouse lung fibroblasts (14%). The content of phosphatidylglycerol in LA-4 cells was significantly lower than in normal lung.Radiolabeled precursor studies showed that palmitic acid was rapidly incorporated into disaturated lecithin of LA-4 adenoma cells and to a greater extent than glycerol, suggesting that the saturation pathways forming disaturated lecithins are active. Studies with radiolabeled choline and methionine suggest that LA-4 cells synthesize total and disaturated lecithins de novo principally through the choline incorporation pathway, with a minor contribution by the three-step methylation of phosphatidyl-ethanolamine.The present results indicate that the phospholipid metabolism of lung adenoma cells is preserved when cultured in vitro. Urethan-induced transformation of type 2 alveolar cells appears to result in a diminished capacity of the cells to synthesize phosphatidylglycerol and disaturated phosphatidylcholine.