A growth-promoting factor for human myeloid leukemia cells from horse serum identified as horse serum transferrin

A growth-promoting factor for human myeloid cells was purified to apparent homogeneity from horse serum by a combination of gel filtration, blue Sepharose affinity chromatography, Mono Q anion-exchange chromatography, Mono P chromatofocusing and sodium dodecyl sulfate polyacrylamide gel electrophoresis. The growth promoter was an iron-bound, single glycopolypeptide chain with a molecular weight of 84,000, an isoelectric point of 5.4 and an amino terminal sequence of Glu-Gln-Thr-Val-Arg-Trp-Cys-Thr-Val-Ser-Asn-His-Glu-Val-Ser-Lys-. According to the results of the amino acid sequence, iron binding ability and physicochemical properties, we identified the growth-promoting factor as horse serum transferrin. It was highly active in promoting the proliferation of a human monocytic leukemia cell line, THP-1, as well as of two other human myeloid cell lines, HL-60 and K-562. It had the same activity in proliferating THP-1 cells as 5% fetal calf serum-supplemented medium. Horse serum transferrin could be substituted for human or bovine serum transferrin.