Abstract
The catalytic activity of topoisomerase II is stimulated approximately 2-3-fold following phosphorylation by either casein kinase II or protein kinase C. A previous study [Corbett, A. H., DeVore, R. F., & Osheroff, N. (1992) J. Biol. Chem. 267, 20513-20518] demonstrated that casein kinase II regulates the activity of topoisomerase II by specifically enhancing the ability of the enzyme to hydrolyze its ATP cofactor. To determine whether other protein kinases use a similar mechanism to activate the enzyme, the effects of protein kinase C mediated phosphorylation on the individual steps of the topoisomerase II catalytic cycle were assessed. Modification stimulated rates of enzyme-mediated ATP hydrolysis approximately 2.7-fold, but had no effect on any reaction that preceded this step, including enzyme.DNA binding, pre- or poststrand passage DNA cleavage/religation, or the double-stranded DNA strand passage event. Furthermore, the activation of ATP hydrolysis was reversed following treatment of phosphorylated topoisomerase II with alkaline phosphatase. As determined by partial proteolytic mapping, the site(s) of protein kinase C modification was (were) localized to the 350 amino acid C-terminal regulatory domain of topoisomerase II within approximately 50 amino acids of the site(s) phosphorylated by casein kinase II. Finally, while protein kinase C and casein kinase II were able to modify the enzyme simultaneously, rates of ATP hydrolysis for doubly-modified topoisomerase II were comparable to those observed for the enzyme following phosphorylation by either individual kinase.(ABSTRACT TRUNCATED AT 250 WORDS)
