Discrimination between the activity of protein kinase CK2 holoenzyme and its catalytic subunits

The acronym CK2 denotes a highly pleiotropic Ser/Thr protein kinase whose over-expression correlates with neoplastic growth. A vexed question about the enigmatic regulation of CK2 concerns the actual existence in living cells of the catalytic (α and/or α′) and regulatory β-subunits of CK2 not assembled into the regular heterotetrameric holoenzyme. Here we take advantage of novel reagents, namely a peptide substrate and an inhibitor which discriminate between the holoenzyme and the catalytic subunits, to show that CK2 activity in CHO cells is entirely accounted for by the holoenzyme. Transfection with individual subunits moreover does not give rise to holoenzyme formation unless the catalytic and regulatory subunits are co-transfected together, arguing against the existence of free subunits in CHO cells.