ACTIVATION OF CASEIN KINASE-II IN ML-1 HUMAN MYELOBLASTIC-LEUKEMIA CELLS REQUIRES IGF-1 AND TRANSFERRIN

Casein kinase II (CK II), a key enzyme involved in the regulation of c ell growth, has been variously reported to be activated by diverse mit ogens, including insulin-like growth factor 1 (IGF-1) and epidermal gr owth factor (EGF). Activation of the enzyme is generally carried out i n the presence of serum, and we examined the question whether serum co mponents participate in the activation process. We demonstrated previo usly that ML-1 cells require IGF-1 plus transferrin (TF) for growth an d transforming growth factor beta or tumor necrosis factor alpha plus TF for differentiation. We now found that CK II is activated only when the cells are exposed to both IGF-1 and TF or when TF is replaced in this combination with relatively high levels of iron salts. Induction of differentiation with TGF-beta and TF did not result in CK II activa tion. These results show that CK II activation in ML-1 cells requires the application of both components of the growth signal, IGF-1 and TF, demonstrating that the growth factor alone is incapable of enhancing the activity of the enzyme.