Activities of Mesoderm-Inducing Factors Secreted by Mammalian Cells in Culture

We have examined the activities of several mesoderm-inducing factors contained in the culture fluids of phorbol ester (4beta-phorbol 12-myristate 13-acetate;PMA)-stimulated human cell lines. Mesoderm induction was assayed by examining the differentiation of mesoderm tissues reacted with presumptive ectoderm of the Cynops blastula. The assay system also examined erythroid differentiation activity (EDF activity) in order to test the relationship between mesoderm induction and activin A (EDF). Of 22 human cell lines examined, six strains were positive for both mesoderm-inducing activity and EDF activity. Four strains showed only mesoderm inducing activity, and one showed only EDF activity. The remaining 11 strains showed neither activity. Therefore, most cell lines secreting mesoderm-inducing activity also possessed EDF activity. Furthermore, culture fluid of a strain (K-562) that exhibited both types of activities, was partially fractionated by DEAE-Toyopearl column chromatography and examined in the same way. The fractions that showed the highest amount of EDF activity were coincident with those displaying mesoderm-inducing activity. These results suggest that a number of PMA-stimulated mammalian cell lines have the ability to secrete mesoderm-inducing factors which are similar to activin A (EDF).