REQUIREMENT OF CASEIN-KINASE-2 FOR ENTRY INTO AND PROGRESSION THROUGHEARLY PHASES OF THE CELL-CYCLE

Requirement of protein kinase CK2 during cell cycle was examined by sp ecific perturbation of CK2 in the intact cell by antisense-oligodeoxyn ucleotides and microinjection of antibodies. When quiescent human prim ary lung fibroblasts (IMR-90) were exposed before growth stimulation t o oligodeoxynucleotides complementary to the translation start region of mRNAs encoding subunit alpha or beta, a significant inhibition of g rowth stimulation by epidermal growth factor or serum was observed. Th e inhibition was reversible and decreased or abolished with mutated an tisense-oligodeoxynucleotides. The inhibitory effect coincided with a decrease of CK2 protein (immunostaining with beta subunit antibody) at entry into and during the first several hours of the cell cycle. Inje ction of beta-specific monoclonal and polyclonal antibodies into IMR-9 0 cells caused significant inhibition of growth stimulation. The inhib ition was reversible, not observed with control antibodies, and strong ly reduced by coinjection of CK2 holoenzyme. Cytoplasmic injection inh ibited up to 50-60% and was effective at two intervals within the firs t 2 h and at 12-16 h poststimulation, i.e., at G0/G1 phase transition and at G1/S boundary, respectively. The inhibition at G0/G1 transition is paralleled by an inhibition of cytoplasmic-nuclear translocation o f beta subunit protein. Injection of beta antibodies into the nucleus inhibited growth stimulation by as much as 80-85% and was effective fo r the first 6 h poststimulation, i.e., at G0/G1 phase transition and p rogression through the adjoining early G1 phase. Nuclear as well as cy toplasmic injections performed during S phase affected neither DNA syn thesis nor cell division. The data demonstrate the requirement of a ce rtain level of functional CK2 at defined cellular locations for the en try into and the progression through the early phase of cell cycle. Th e action of nuclear CK2 appears to be a prerequisite for the early sig nal processing. The cytoplasmic CK2 appears to participate in the tran smission of mitogenic signals, including translocation into the nucleu s and, in addition, in processes late in G1 phase.