Mechanism of the elevation in cardiolipin during HeLa cell entry into the S-phase of the human cell cycle

CL (cardiolipin) is it key phospholipid involved in ATPgeneration. Since progression through the cell cycle requires ATP we examined regulation of CL synthesis during S-phase in human cells and investigated whether CL or CL synthesis was required to support nucleotide synthesis in S-phase. HeLa cells were made (quiescent by serum depletion for 24 h. Scrum addition resulted in SUbStanlial stimulation of [methyl-H-4]thymidine incorporation into cells compared with serum-starved cells by 8 h, confirming entry into file S-phase. CL. mass Was unaltered at 8 11, but increased 2-fold by 16 It post-serum addition compared with serum-starved cells. The reason lor the increase in CL mass upon entry into S-phase was all increase in activity and expression of CL tie novo biosynthetic and remodelling enzymes and this paralleled the increase in mitochondrial mass. CL (le novo biosynthesis from I). [U-C-14]glucose was elevated, and from [ 1,3-H-3]glycerol reduced, upon serum addition to quiescent cells compared with controls and this was a result of differences in the selection of precursor pools ill the level Of uptake. Triascin C treatment inhibited CL. synthesis from I 1-C-14]oleate but did not affect [methyl-H-3]thymidine incorporation into HeLa cells upon serum addition to serum-starved cells. Barth Syndrome lymphoblasts, which exhibit reduced CL, showed similar [methyl-H-3]thymidine incorporation into cells upon serum addition to set-Urn-starved cells compared with cells from normal aged-matched controls. The results indicate that CL (le novo biosynthesis is up-regulated via elevated activity and expression of CL biosynthetic genes and this accounted for the doubling of CL seen during S-phase; however, normal de novo CL biosynthesis or CL itself is not essential to Support nucleotide synthesis during entry into S-phase of the human cell cycle.