A deazaadenosine-insensitive methylation of phosphatidylethanolamine is involved in lipoprotein secretion

We have examined the effect of inhibitors of methylation of phosphatidylethanolamine on lipoprotein secretion from cultured rat hepatocytes. The incorporation of [1-3H]ethanolamine into phosphatidylcholine of hepatocytes and secreted lipoproteins was inhibited by greater than 90% by the methylation inhibitors 3-deazaadenosine and Neplanocin. In addition, these compounds strongly inhibited the incorporation of [3-3H]serine into the choline moiety of phosphatidylcholine of the hepatocytes, but had no effect on incorporation of [3-3H]serine into secreted phosphatidylcholine. The results suggest that a pool of phosphatidylcholine targeted for lipoprotein secretion originates from phosphatidylethanolamine made from serine and this methylation reaction has the unique property of being insensitive to 3-deazaadenosine.