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UBC Theses and Dissertations

Choline metabolism in Nb 2 rat node lymphoma cells Ko, Kerry Woon Sing


Phosphatidylcholine metabolism was investigated in Nb 2 node rat lymphoma, a cell line which is dependant on prolactin for growth in culture. Treatment of stationary cultures with prolactin stimulated the incorporation of [Me-³H] choline into phosphatidylcholine (1.7-fold after 4 h) and its aqueous precursors, mainly phosphocholine (2-fold after 4 h and 3-fold after 10 h). These effects were blocked by cycloheximide. Pulse-chase studies demonstrated that the reaction catalyzed by CTP:phosphocholine cytidylyltransferase (EC was rate-limiting for phosphatidylcholine synthesis in Nb 2 cells. The specific activity of choline kinase (EC increased 1.9-fold after 4 h of prolactin treatment, in correspondence with the increase in choline incorporation mentioned above, and this was also blocked by cycloheximide. The activities of the other enzymes of phosphatidylcholine synthesis were unchanged. These results suggested that phosphatidylcholine biosynthesis was not altered in Nb 2 cells after prolactin treatment. However, phosphatidylcholine levels increased in prolactin treated-cells (1.4-fold after 16 h). Turnover of labeled phosphatidylcholine was reduced 3.4-fold in prolactin treated cells. Calculated turnover rates for phosphatidylcholine averaged 3.2-fold lower in prolactin treated cells whereas the synthetic rates were similar in prolactin treated and stationary cells. Thus, Nb 2 cells utilize a novel mechanism, inhibition of turnover, to regulate the cellular levels of phosphatidylcholine during growth

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