Mitosis-specific MPM-2 phosphorylation of DNA topoisomerase II alpha is regulated directly by protein phosphatase 2A

Alexandre E Escargueil , Annette K Larsen (1)

1 Cancerologie Fondamentale et Clinique des Tumeurs Solides

Recent results suggest a role for topoisomerase II alpha (topoIIalpha) in the fine-tuning of mitotic entry. Mitotic entry is accompanied by the formation of specific phosphoepitopes such as MPM-2 that are believed to control mitotic processes. Surprisingly, the MPM-2 kinase of topoIIalpha was identified as protein kinase CK2, otherwise known as a constitutive interphase kinase. This suggested the existence of alternative pathways for the creation of mitotic phosphoepitopes, different from the classical pathway where the substrate is phosphorylated by a mitotic kinase. We now report that topoIIalpha is colocalized with both CK2 and protein phosphatase 2A (PP2A) during interphase. Simultaneous incubation of purified topoIIalpha with CK2 and PP2A had minimal influence on the total phosphorylation levels of topoIIalpha, but resulted in complete disappearance of the MPM-2 phosphoepitope due to opposite sequence preferences of CK2 and PP2A. Accordingly, short-term exposure of interphase cells to okadaic acid, a selective PP2A inhibitor, was accompanied by the specific appearance of the MPM-2 phosphoepitope on topoIIalpha. During early mitosis, PP2A was translocated from the nucleus while CK2 remained in the nucleus until prometaphase thus permitting the formation of the MPM-2 phosphoepitope. These results underline the importance of protein phosphatases as an alternative way of creating cell-cycle specific phosphoepitopes.

Mots clés: Life Sciences

Alexandre E Escargueil, Annette K Larsen. Mitosis-specific MPM-2 phosphorylation of DNA topoisomerase II alpha is regulated directly by protein phosphatase 2A. Biochemical Journal, 2007, 403 (2), pp.235-242. ⟨10.1042/BJ20061460⟩. ⟨hal-00478669⟩