EVIDENCE THAT CTP-CHOLINE-PHOSPHATE CYTIDYLYTRANSFERASE IS REGULATED AT A PRETRANSLATIONAL LEVEL IN RAT-LIVER AFTER PARTIAL-HEPATECTOMY

Regulation of CTP:choline-phosphate cytidylyltransferase activity was studied in regenerating rat liver. The formation of phosphatidylcholin e from [C-14]choline in hepatocytes isolated from regenerating liver a t 22 h after surgery was increased 1.9-fold when compared with hepatoc ytes from sham-operated animals. This effect was accompanied by a 1.4- fold increase in cytosolic cytidylyltransferase activity as well as by a 1.5-fold increase in the amount of immunoreactive cytidylyltransfer ase protein, and a 1.7-fold increase in [S-35]methionine incorporation into cytidylyltransferase protein. Northern blot analysis of cytidyly ltransferase mRNA showed two signals at 1.5 and 5.0 kb. Partial hepate ctomy caused a significant 2-3-fold increase in the 1.5-kb and 5.0-kb messengers at 12 h after surgery. During the next 10 h after partial h epatectomy cytidylyltransferase mRNA levels slightly decreased, althou gh they were still elevated in comparison with sham-operated rats 20-2 2 h after surgery. In contrast to the elevated cytidylyltransferase mR NA levels, the amount of acetyl-CoA carboxylase mRNA did not increase between 12 and 22 h after surgery, which is in line with the unchanged activity of this enzyme. In conclusion, our data demonstrate that in regenerating liver phosphatidylcholine biosynthesis and cytidylyltrans ferase activity are regulated at a pretranslational level.