Characterization of a thrombocytopoietic-stimulating factor from kidney cell culture medium

The chemical characteristics of a thrombocytopoietic-stimulating factor (TSF or thrombopoietin) found in serum-free kidney cell culture medium were further delineated by subjecting the TSF-rich medium to varying temperatures, different pH, and trypsin digested; the ability of TSF to bind lectins on affinity chromatography was also determined. After treatment, the TSF was assayed in immunothrombocythemic mice by its ability to increase the incorporation of 35S-sodium sulfate into newly formed platelets. TSF appeared to be relatively heat stable; incubation of TSF for 16 h at temperatures of 4, 37, and 56 degrees C showed no loss of TSF activity. However, after incubation at 85 degrees C, TSF was completely inactivated TSF in culture medium was stable of pH 1-8. Above these pH values, the potency of the TSF material decreased sharply. Digestion of TSF with trypsin completely destroyed the thrombocytopoietic-stimulating activity. For TSF purification, two different lectin-agarose derivatives were used; i.e., wheat germ agglutinin (WGA) and concanavalin A (Con A). Both lectins bound TSF, and the hormone was eluted by the sugars specific for the particular lectin. lectins, therefore, can be used to partially purify the hormone; a further 10 to 200-fold purification was achieved by these techniques. Since other workers have shown that TSF from plasma of thrombocytopenic rabbits will bind WGA and Con A, TSF from kidney cell culture medium and TSF from animal sources appear to have similar carbohydrate compositions.