NUCLEAR PHOSPHATIDYLINOSITOLS DECREASE DURING S-PHASE OF THE CELL-CYCLE IN HELA-CELLS

In the current study we have measured phosphatidylinositols during the cell cycle. HeLa cells were labeled with [H-3]myoinositol to a steady state, synchronized to the G1/S boundary, and the levels of phosphati dylinositol (PtdIns) lipids were measured at various times after relea se from the block. The levels of total cellular PtdIns, PtdIns(4)P, an d PtdIns(4,5)P-2 relative to total cellular phospholipid did not vary throughout the cell cycle. We then isolated nuclei from synchronized c ells using a non detergent method and found that the levels of nuclear PtdIns lipids decreased by over 50% at 2 and 4 h after release from t he G1/S boundary (S-phase of the cell cycle) and returned to the origi nal levels by 9 h. Separation of individual inositol containing nuclea r lipids showed that PtdIns decreased by 50% while levels of PtdIns(4) P and PtdIns(4,B)P-2 decreased by 66%. Levels of the cytoplasmic PtdIn s lipids remained constant throughout this period, This experiment ind icates that there is specific nuclear PtdIns turnover that is activate d during DNA synthesis.