THE ROLE OF INHIBITORY PHOSPHORYLATION OF CDC2 FOLLOWING DNA-REPLICATION BLOCK AND RADIATION-INDUCED DAMAGE IN HUMAN-CELLS

It has been suggested that the survival response of p53 defective tumo r cells to agents that inhibit DNA replication or damage DNA may be la rgely dependent on cell cycle checkpoints that regulate the onset of m itosis. In human cells, the mitosis-inducing kinase CDC2/cyclin B is i nhibited by phosphorylation of threonine-14 and tyrosine-15, but the r oles of these phosphorylations in enforcing checkpoints is not known. We have investigated the situation in a human cervical carcinoma cell line (HeLa cells) and found that low level expression of a mutant nonp hosphorylatable form of CDC2 abrogates regulation of the endogenous CD C2/cyclin B. Disruption of this pathway is toxic and renders cells hig hly sensitive to killing by DNA damage or by inhibition of DNA replica tion. These findings establish the importance of inhibitory phosphoryl ation of CDC2 in the survival mechanism used by human cells when expos ed to some of the most common forms of anticancer therapy.