Abstract
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.
Highlights
We havetestedthe effects osferum-stimulated Lorillon et al, 1988)
CK-I1 previously has been linked to cell growth by a number of observations coupling CK-I1 activity tothe modification of enzymes andproteins involved in protein synthesis, RNA metabolism, and DNA synthesis.The potential importance of CK-I1 in cell growth is indicated by higher CK-I1 activity in some transformed cells than in normal cells (Prowald et al, 1984; Rose et al, 1981), enhanced activity during mouse embryogenesis (Schneider et al, 1987),activation in response to insulin and epidermal growth factor (Klarlund & Czech, 1988; Sommercorn et al, 1987), andacentral role in the transition between prophase and metaphase during meiotic cell division of full grown Xenopus laevis ooyctes
The datapresented in this report demonstrate that CK-I1 activity is subject to cellular regulation and that changes in its activity are coupled to cell growth
Summary
Anisomycin Treatment-An aliquot (0.01 ml) of the protein synthesis inhibitor, anisomycin (Pfizerl (Lewis & Mathews, 1980),from a 20 mM stock solution in absolute ethanol was added 30 min prior to the time of serum supplementation to serum-deprived WI-38 cells in 2 ml of medium, to a final concentration of 100 p ~ A.n equal volume of absolute ethanol without anisomycin was added to control three peaks was sensitive to both heparin inhibition (Ki of 20 nM) and spermine activation (K,,of 1mM). The sensitivity of the protein kinase activity to heparin and spermine is similar to thatreported for CK-I1 (Hathaway & Traugh, 1982),leading us to conclude that the oscillations illustrated in Fig. 1 plates. Reflect changes in CK-I1 activity and not in another cellular protein kinase.
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