CASEIN KINASE-II STABILIZES THE ACTIVITY OF HUMAN TOPOISOMERASE II-ALPHA IN A PHOSPHORYLATION-INDEPENDENT MANNER

Previous reports have indicated that topoisomerase II (topo II) co-pur ifies with and is a substrate for casein kinase II. We have carried ou t a detailed study of the effect that purified casein kinase II has on the activity of purified recombinant human topo II alpha. Co-incubati on of topo II alpha and casein kinase II led to an apparent activation of the topo II alpha; however, in experiments in which topo II alpha was preincubated at 37 degrees C with or without native casein kinase II prior to assaying for decatenation activity, it emerged that the ki nase was exerting its ''activating'' function via a decrease in the ra te of topo II alpha enzyme inactivation during the incubation period. This stabilization of topo II alpha by casein kinase II was ATP-indepe ndent and was observed in both mutated and truncated derivatives of to po II alpha lacking the major casein kinase II phospho-acceptor sites, indicating the lack of a requirement for phosphorylation. Consistent with a nonenzymatic role for casein kinase II, stoichiometric quantiti es of kinase were required for topo II alpha stabilization. These data indicate that casein kinase II plays a significant role in regulating human topo II alpha protein action via stabilization against thermal inactivation.