Casein Kinase II Stabilizes the Activity of Human Topoisomerase IIα in a Phosphorylation-independent Manner

Abstract

Previous reports have indicated that topoisomerase II (topo II) co-purifies with and is a substrate for casein kinase II. We have carried out a detailed study of the effect that purified casein kinase II has on the activity of purified recombinant human topo II␣. Co-incubation of topo II␣ and casein kinase II led to an apparent activation of the topo II␣; however, in experiments in which topo II␣ was preincubated at 37°C with or without native casein kinase II prior to assaying for decatenation activity, it emerged that the kinase was exerting its "activating" function via a decrease in the rate of topo II␣ enzyme inactivation during the incubation period. This stabilization of topo II␣ by casein kinase II was ATP-independent and was observed in both mutated and truncated derivatives of topo II␣ 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 quantities of kinase were required for topo II␣ stabilization. These data indicate that casein kinase II plays a significant role in regulating human topo II␣ protein action via stabilization against thermal inactivation. DNA topo1 II is a ubiquitous and structurally conserved enzyme required for many different aspects of DNA metabolism (reviewed in Refs. 1 an 2). Studies in bacterial and lower eukaryotic species have revealed that topo II is required for cell viability due to an essential role in the segregation of newly replicated chromosomes during cell division (3-7). During replication, sister DNA molecules become knotted and catenated as a consequence of the difficulties inherent in the unwinding and copying of a double-stranded, helical nucleic acid structure (reviewed in Ref. 8). In eukaryotes, topo II catalyzes the disentanglement of sister chromatids and hence permits their faithful segregation during mitosis. Studies on yeast temperaturesensitive top2 mutants have shown that both chromosome hypercondensation and sister chromatid segregation are dependent upon functional topo II, and that in the absence of topo II chromosomes break or nondisjoin as the mitotic spindle attempts to pull apart the still interlinked DNA molecules (3-8).In mammalian cells, but not in yeasts, topo II exists as two closely related isoforms designated ␣ (170-kDa form) and ␤ (180-kDa form) (9 -13). The respective roles of the two isoforms are not known currently, although several differences in their activities/regulation have been noted. For example, the ␣ isoform is a strict proliferation marker in vitro and in vivo and is expressed at a high level in each cell cycle during the period just prior to cell division (14 -17). This isoform is tightly associated with condensed chromatin during metaphase. In contrast, topo II␤ is ubiquitously expressed in human tissues and is apparently excluded from chromosomes around the time of mitotic chromosome condensation, although it is found in the nucleoplasm during interphase (14 -18).Topo II is a phosphoprotei...

Mitotic Phosphorylation of DNA Topoisomerase II α by Protein Kinase CK2 Creates the MPM-2 Phosphoepitope on Ser-1469

“…This did not affect the catalytic activity (results not shown), in agreement with results reported by others (51,52). More surprisingly, dephosphorylation of topoisomerase II␣ by phosphatase (Fig.…”

Extracellular Signal-Regulated Kinase Activates Topoisomerase IIα through a Mechanism Independent of Phosphorylation

“…In fact, topoisomerase II␣ activity was enhanced following incubation with low concentrations of glycerol in the absence of kinase, suggesting that the activation mechanism involves topoisomerase autoactivation independent of CKII. A second study found that preincubation with CKII protected topoisomerase II␣ from thermal inactivation and that the apparent activation by CKII was actually due to stabilization against activity loss during the preincubation (43). This protective effect was specific for CKII and could be ascribed to stable interactions previously demonstrated between kinase and topoisomerase II␣ (4), suggesting a potential physiological role for kinase-topoisomerase interactions.…”

Interactions between Protein Kinase CK2 and Pin1

“…In the case of CK2 and topoisomerase II␣, there is additional complexity because our results demonstrate that both of these proteins can interact with Pin1. Furthermore, several studies have demonstrated that CK2 physically interacts with topoisomerase II in mammalian cells and in yeast, although controversy regarding the relationship of CK2 to the regulation of topoisomerase II remains (31)(32)(33)(34)(61)(62)(63). Clearly, additional studies beyond the scope of this present work will be required to fully illuminate the precise role of Pin1 in the regulation of CK2 and topoisomerase II␣.…”