Stimulation of phosphatidylcholine biosynthesis by hemicholinium-3, a potent inhibitor of choline uptake in human leukemic monocyte-like U937 cells.
The effect of hemicholinium-3 (HC-3) on choline uptake and phosphatidylcholine (PC) biosynthesis was examined in human leukemic monocyte-like U937 cells. HC-3 inhibited [3H]choline uptake in a dose- and time-dependent manner. After a 3 h treatment, HC-3 (100 microM) decreased choline uptake by as much as 80 per cent (p < 0.0001; n = 4). Reduction of incorporation of label into PC was also detected in a dose-dependent manner; the extent of inhibition, however, was always 10-20 per cent less than that observed in the total uptake. At 3 h HC-3 decreased the incorporation into PC by 65 per cent (p < 0.0001; n = 5). Kinetic studies in vivo showed that HC-3 inhibited total uptake and incorporation into PC differently, suggesting that the labelling of PC is not simply dictated by [3H]choline uptake. In separate experiments, cells were pretreated with 100 microM HC-3 for 3 h. After washing, the inhibitory effect on total uptake was no longer observed, while a 20 per cent stimulation of the incorporation into PC was obtained in these pretreated cells. In pulse-chase studies, the cells were prelabelled with [3H]choline for 30 min and chased with HC-3 for up to 3 h; the results showed a significant stimulation of incorporation into PC in a longer chase with 100 microM HC-3. After a 3 h treatment, the cytosolic CTP:cholinephosphate cytidylyltransferase (CT) was activated by 56 per cent, while choline kinase (CK) was inhibited slightly. The stimulation of CT was not simply due to the intact HC-3 molecule, and there was no redistribution of CT between cytosol and microsomes. Taken together, the results suggest that HC-3 activates PC biosynthesis apart from the inhibitory effect on choline uptake.
Chu
A J
AJ
Miami Heart Institute, Miami Beach, FL 33140.
D001692:Biological Transport; D002451:Cell Compartmentation; D002794:Choline / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D019916:Choline-Phosphate Cytidylyltransferase; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D006426:Hemicholinium 3 / Q000494:pharmacology*; D006801:Humans; D009000:Monocytes / Q000378:metabolism*; D009713:Nucleotidyltransferases / Q000378:metabolism; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D014407:Tumor Cells, Cultured
D010713:Phosphatidylcholines; D006426:Hemicholinium 3; D009713:Nucleotidyltransferases; D019916:Choline-Phosphate Cytidylyltransferase; D002794:Choline