Insulin-like growth factor I and insulin rapidly increase casein kinase II activity in BALB/c 3T3 fibroblasts

We have tested whether growth factors added to serum-deprived BALB/c 3T3 fibroblasts alter the casein kinase II activity measured in cell extracts. A rapid phosphocellulose chromatography method was developed that provides a 40-fold partial purification of casein kinase II activity assayed with the specific substrate peptide Arg-Arg-Glu-Glu-Glu-Thr-Glu-Glu-Glu. Using this technique, kinase activity is stimulated 1.6-2.5-fold when isolated from fibroblasts treated with insulin or insulin-like growth factor I (IGF-I). The activated kinase activity exhibits the specific properties of casein kinase II such as the ability to utilize [gamma-32P]GTP as phosphate donor and marked inhibition by low concentrations of heparin. Activation of casein kinase II appears specific for these hormones because epidermal growth factor and platelet-derived growth factor have no effect on the kinase activity when added to fibroblasts under conditions where they markedly stimulate [3H]thymidine incorporation into DNA. Increases of casein kinase II activity by insulin and IGF-I were detected within 1 min of their addition to cell cultures. IGF-I is more potent in stimulating casein kinase II than insulin in mouse fibroblasts. These results demonstrate that casein kinase II is a selective target for insulin and IGF-I action in BALB/c fibroblasts, consistent with the hypothesis that this kinase plays a role in cellular signaling by these hormones.