Phospholipid turnover during cell-cycle traverse in synchronous Chinese-hamster ovary cells. Mitogenesis without phosphoinositide breakdown.
The turnover of phospholipids was investigated in quiescent serum-starved Chinese-hamster ovary (CHO-K1) cells stimulated to progress through the cell cycle by the addition of dialysed bovine serum. A variety of radiolabelling techniques were employed to study the rapid effects of serum on phospholipids and later events during G1 and S phases of the cell cycle. Pulse-labelling studies using [32P]Pi revealed that there was a stimulation of the synthesis rate of all phospholipids investigated during the initial few hours after serum addition. The greatest stimulation (20-fold) was observed in phosphatidylcholine, and the smallest in the polyphosphoinositides (PPIs). Mock stimulation with serum-free medium caused a similar increase in PPI turnover, but little or no effect on turnover of other phospholipids. This effect could be accounted for by a stimulation of the turnover of cellular ATP pools increasing [32P]ATP specific radioactivity. Late G1 and S phases were associated with a decrease in the rate of synthesis of all phospholipids. Phosphatidic acid was the only phospholipid whose labelling fell below that in mock-stimulated cells during the period of the cell cycle. Stimulation of serum-starved cells that had been prelabelled with myo-[2-3H]inositol caused no change in the amounts of inositol trisphosphate, but both serum-stimulated and mock-stimulated cells exhibited similar small decreases in both inositol bisphosphate and inositol monophosphate, of approx. 30% after 30 s. When cells were serum-stimulated in the presence of 10 mM-Li+, there was no increase in the size of the total inositol phosphate pool. We conclude that mitogenic stimulation and cell-cycle traverse cause profound and complex effects on phospholipid turnover in CHO-K1 cells, but there is no evidence for a role of inositol lipid turnover in the proliferative response to serum in this cell line.
Tones
M A
MA
Department of Biochemistry, University of Nottingham Medical School, Queen's Medical Centre, U.K.
Sharif
N A
NA
Hawthorne
J N
JN
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001769:Blood; D002453:Cell Cycle; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D007295:Inositol Phosphates / Q000378:metabolism; D008938:Mitosis; D010053:Ovary; D010716:Phosphatidylinositols / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*
D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; D000255:Adenosine Triphosphate