Protein kinase CK2a' is induced by serum as a delayed early gene and cooperates with Ha-ras in fibroblast transformation.

Protein kinase CK2 is an ubiquitous and pleiotropic Ser/Thr protein kinase composed of two catalytic (α and/or α′) and two noncatalytic (β) subunits forming a heterotetrameric holoenzyme involved in cell growth and differentiation. Here we report the identification, cloning, and oncogenic activity of the murine CK2α′ subunit. Serum treatment of quiescent mouse fibroblasts induces CK2α′ mRNA expression, which peaks at 4 h. The kinetics ofCK2α′ expression correlate with increased kinase activity toward a specific CK2 holoenzyme peptide substrate. The ectopic expression of CK2α′ (or CK2α) cooperates with Ha-ras in foci formation of rat primary embryo fibroblasts. Moreover, we observed that BALB/c 3T3 fibroblasts transformed with Ha-ras and CK2α′ show a faster growth rate than cells transformed with Ha-rasalone. In these cells the higher growth rate correlates with an increase in calmodulin phosphorylation, a protein substrate specifically affected by isolated CK2 catalytic subunits but not by CK2 holoenzyme, suggesting that unbalanced expression of a CK2 catalytic subunit synergizes with Ha-ras in cell transformation