Serum-stimulated cell growth causes oscillations in casein kinase II activity

We have tested the effects of serum-stimulated growth of quiescent WI38 human lung fibroblasts on cellular casein kinase II (CK-II) activity. Using the casein kinase II synthetic substrate RRREEETEEE we find a transient 6-fold elevation in CK-II activity in cell homogenates within 30 min following serum stimulation. Additional cycles of CK-II activation and inactivation are seen at 12 and 24 h after stimulation. The oscillations in CK-II activity are largely independent of de novo protein synthesis, and, thus, are likely to reflect cycles of post-translational activation and inhibition of the cellular kinase pool. In contrast to the activity profile of CK-II, we find that cyclic AMP-dependent protein kinase is rapidly inhibited upon serum-stimulation of WI38 cells. These results demonstrate that CK-II activity is subject to unique cellular regulation during proliferation and are consistent with the postulate that CK-II plays an important role in cell growth.