Regulation of Cardiolipin Biosynthesis in H9c2 Cardiac Myoblasts by Cytidine 5′-Triphosphate

The regulation of cardiolipin biosynthesis by CTP in H9c2 cardiac myoblasts was investigated. H9c2 cells were incubated in the presence of cyclopentenylcytosine which is converted to cyclopentenylcytosine-triphosphate, a potent and specific inhibitor of CTP synthetase. Incubation of cells for 12 h with cyclopentenylcytosine reduced the cellular pool size of CTP to less than 10% of control cells but did not influence the pool size of other nucleotides. The de novo biosynthesis of phosphatidylcholine from [methyl-3H]choline, phosphatidylethanolamine from [1-3H]ethanolamine, and biosynthesis of all glycerol containing phospholipids from [U-14C]glycerol or [1,3-3H]glycerol were reduced approximately 50% after preincubation of the cells with cyclopentenylcytosine. In contrast, radioactive glycerol accumulated in phosphatidic acid, diacylglycerol, and triacylglycerol in cyclopentenylcytosine-treated cells compared with controls suggesting a re-routing of phospholipid biosynthesis away from CTP utilizing reactions toward neutral lipid synthesis. The de novo biosynthesis of all phospholipids was restored to control levels by addition of cytidine to the medium which elevated CTP levels. Cyclopentenylcytosine did not affect the in vitro enzyme activities involved in cardiolipin biosynthesis in these cells. In addition, the resynthesis of cardiolipin and most phospholipids from [1-14C]linoleic acid was not affected by cyclopentenylcytosine. Our findings indicate that the cellular CTP level may regulate cardiolipin biosynthesis in H9c2 cardiac myoblasts and support the notion that the cellular CTP level may be a universal signal/switch for all phospholipid biosynthesis in eukaryotic cells.