Release of lysosomal phospholipase A1 and A2 into cytosol and rapid turnover of newly-formed lysophosphatidylcholine in FL cells during fusion-from-within induced by measles virus.

The subcellular distribution of the phospholipase activities and metabolism of lysophosphatidylcholine in cultured human cell line (FL cells) during "fusion-from-within" induced by measles virus were studied. During cell fusion, fairly high activities of phospholipase A1 and A2, the optimal pHs of which were acidic, appeared in the cytosol. These phospholipases were confirmed to be of lysosomal origin by the following facts: (1) the properties of these phospholipases were the same as those of lysosomal phospholipase A1 and A2; (2) a decrease in the total activity of phospholipases A1, A2 and acid phosphatase in the lysosomal fraction of the infected cells coincided with an increase in their activity in the cytosol. The release of lysosomal phospholipase A1 and A2 into the cytosol of the infected cells appeared to be related to the extent of cell fusion-from-within. Phospholipase A1 and A2 released to the cytosol hydrolyzed the cell membrane-bound phospholipids to form lysophospholipids. 1-[1-14C]Palmitoyl-GPC, incorporated into the cells from the culture medium, was rapidly converted into phosphatidylcholine, triacylglycerol and phosphatidylethanolamine in the cells during fusion-from-within, but the radioactive lysophosphatidylcholine and fatty acids were hardly detectable, indicating a rapid turnover of cellular lysophosphatidylcholine during cell fusion. The subcellular lysophospholipid acyl-hydrolase activities of the infected cells were higher than those of normal cells. Possible relation between the membrane fusion induced by measles virus and the phospholipid metabolism in the infected cells were discussed.