Growth factor(s) produced by a human leukemic cell line growing in a protein-free chemically defined medium

To examine whether human leukemic cells produce growth factor(s), a protein-free culture line of human erythroleukemic cells (K-562T1) has been established. This unique cell line has been continuously propagated in protein-free Ham's F-10 medium without any supplement for 5 yr. Growth-promoting activity was determined by measuring [3H]thymidine incorporation into DNA in serum-deprived chick embryo fibroblasts. The conditioned medium of K-562T1 contained the growth-promoting activity against chick embryo fibroblasts, mouse 3T3-L1 cells, and K-562 human leukemic cells. This leukemia-derived growth-promoting activity was heat and acid stable and trypsin sensitive. The activity was destroyed by dithiothreitol. Size exclusion chromatography revealed three peaks of activity, with apparent molecular weights of 13,500, 6,300, and 2,400, respectively.