COLONY-STIMULATING FACTOR-I REGULATES CTP-PHOSPHOCHOLINE CYTIDYLYLTRANSFERASE MESSENGER-RNA LEVELS

Growth factor regulation of phosphatidylcholine (PtdCho) metabolism during the G1 stage of the cell cycle was investigated in the colony-stimulating factor 1 (CSF-1)-dependent murine macrophage cell-line BAC1.2F5. The transient removal of CSF-1 arrested the cells in G1. Incorporation of [H-3]choline into PtdCho was stimulated significantly 1 h after growth factor addition to quiescent cells. Metabolic labeling experiments pointed to CTP:phosphocholine cytidylyltransferase (CT) as the rate-controlling enzyme for PtdCho biosynthesis in BAC1.2F5 cells. The amount of CT mRNA increased 4-fold within 15 min of CSF-1 addition and remained elevated for 2 h. The rise in CT mRNA levels was accompanied by a 50% increase in total CT specific activity in cell extracts within 4 h after the addition of CSF-1. CSF-1-dependent elevation of CT mRNA content was neither attenuated nor superinduced by the inhibition of protein synthesis with cycloheximide. The rate of CT mRNA turnover decreased in the presence of CSF-1 indicating that message stabilization was a key factor in determining the levels of CT mRNA. These data point to increased CT mRNA abundance as a component in growth factor-stimulated PtdCho synthesis.