Effects of erythropoietin on uridine metabolism in cell cultures of fetal calf liver

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Abstract
The effect of sheep plasma erythropoietin preparations on the incorporation of [5-3H]uridine into erythroid cells has been studied using cells of fetal calf liver cultured in serum-free medium. The cells were incubated for 20 h with the hormone, followed by a 1-h incubation with [3H]uridine. Erythropoietin caused a 2.5-fold increase in the incorporation of uridine into cold trichloroacetic-acid-insoluble cell extracts and a 70% increase in the incorporation of uridine into the cold acid-soluble cell extracts. The phosphorylated metabolites of labeled uridine present in the cold acid-soluble fraction were analyzed by anion-exchange high performance liquid chromatography (HPLC). Erythropoietin increased the amounts of labeled UDP and UTP per cell. However, the specific activity of UTP and the labeled amounts of UDP-glucose in erythropoietin-treated cells were not significantly different from those in control cell cultures. After chromatography of the crude erythropoietin preparations on reversed-phase and gel-permeation HPLC, there was a perfect coincidence of the fractions stimulating uridine incorporation into acid-soluble and acid-insoluble cell extracts. The protein fractions from crude erythropoetin which stimulated uridine incorporation after purification by reversed-phased HPLC were also able to stimulate globin chain synthesis in fetal calf liver cells. These experiments suggest that the multiple effects on uridine metabolism described above are due to erythropoietin, rather than other proteins contaminating the crude hormone preparations.

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