Increased Phosphatidylcholine Synthesis Research Articles

Effect of 1,25-dihydroxyvitamin D3 on phospholipid metabolism in chick duodenal mucosal cell. Relationship to its mechanism of action.

Pretreatment of the D-deficient chick with 1,25-dihydroxyvitamin D3 increases de novo synthesis of phosphatidylcholine by a stimulation of CDP-choline: sn-1,2-diacylglycerol choline-phosphotransferase reaction. The time course of change in the incorporation of [3H]choline and [14C]ethanolamine into the brush border lipid fraction after 1,25-dihydroxyvitamin D3 treatment correlates closely with the time course of change in calcium uptake into the brush border membrane vesicles. Prior treatment with cycloheximide does not block this increase in phosphatidylcholine synthesis. In addition, 1,25-dihydroxyvitamin D3 administration increases the incorporation of [3H]arachidonic acid into the phosphatidylcholine fraction of the brush border to a great extent but does not increase the incorporation of [3H]palmitic acid into the phosphatidylcholine fraction. The incorporation of these 3H labeled fatty acids into diacylglycerol is not changed by 1,25-dihydroxyvitamin D3. These data indicate that 1,25-dihydroxyvitamin D3 enhances the synthesis of phosphatidylcholine independent of new protein synthesis, and also increases the incorporation of unsaturated fatty acids into phosphatidylcholine. From these results we suggest that changes in phospholipid metabolism in the enterocyte are the mechanisms by which 1,25-dihydroxyvitamin D3 acts to enhance calcium entry across the brush border membrane.

Effect of mengovirus replication on choline metabolism and membrane formation in novikoff hepatoma cells.

Infection of Novikoff rat hepatoma cells (subline NlSL-67) with mengovirus resulted in a two- to threefold increase in the rate of choline incorporation into membrane phosphatidylcholine at about 3 hr after infection, without affecting the rate of transport of choline into the cell or its phosphorylation. The time course of virus-stimulated phosphatidylcholine synthesis was compared with the time courses of other virus-induced processes during a single cycle of replication. The formation of viral ribonucleic acid (RNA) polymerase and of viral RNA commenced about 1 hr earlier than the virus-stimulated choline incorporation. Further, isopycnic centrifugation of cytoplasmic extracts indicated that the excess of phosphatidylcholine synthesized by infected cells is not located in the membrane structures associated with the viral RNA replication complex, but with structures of a lower density (1.08 to 1.14 g/cc). These membrane structures probably represent the smooth vesicles which accumulate in the cytoplasm of infected cells during the period of increased phosphatidylcholine synthesis between 3 and 5 hr after infection. They are formed with both newly synthesized phosphatidylcholine and phosphatidylcholine present prior to infection. However, concomitant protein synthesis is not required for the stimulated synthesis of membranes; the effect was not inhibited by treating the cells with inhibitors of protein synthesis at 3 hr after infection, although virus production was inhibited about 90% and virus-induced cell degeneration was markedly reduced and delayed. Production of mature virus began normally at about the same time as the stimulation of phosphatidylcholine synthesis. Treatment of infected cells with puromycin at 2 hr, on the other hand, completely inhibited the stimulation of phosphatidylcholine synthesis.