ERK-MAPK-mediated activation of CDC25 during G2 /M transition

G2/M phase transition in eukaryotic cell is driven by the maturation-promoting factor (MPF), which is composed of Cdc2 kinase and cyclin B. Activation of MPF requires protein phosphatase Cdc25-mediated dephosphorylation of Cdc2. Although Cdc25 is activated by M phase-specific phosphorylations and this process involves Cdc2 kinase- and polo-like kinase 1 (Plk1), these two kinases are insufficient to account for Cdc25 activation during G2/M transition. One of the remaining gaps in our current understanding of G2/M transition therefore is the identity of the missing kinases involved in the activation of Cdc25. To fill this gap, we used Xenopus oocytes/eggs, the model system of the G2/M transition, to identify and characterize previously unrecognized key kinases involved in Cdc25 activation. Through biochemical purification of M phase-arrested Xenopus egg extracts (MEE), we previously identified Erk-MAPK, the Xenopus ortholog of mammalian ERK2, as one of the missing kinases of Cdc25 in MEE. Here, we demonstrate that Erk-MAPK phosphorylates Cdc25 at T48, T138 and S205, increasing Cdc25\u27s phosphatase activity in vitro and that Erk-MAPK phosphorylates Cdc25 at T48 and T138 during oocyte maturation, promoting its ability to induce oocyte maturation. We further demonstrate that Erk-MAPK interacts with Cdc25 in vitro and in immature oocyte extracts, strengthening the idea that Cdc25 is a physiological substrate of Erk-MAPK. In addition, our results suggest that Erk-MAPK-mediated phosphorylation events may promote Cdc25\u27s function through regulating inter-/intra-molecular interaction of Cdc25. In a mammalian cell line A2780, we show that Erk1/2 interacts with hCdc25C in interphase cells and phosphorylates hCdc25C at T48 in mitotic cells. Moreover, inhibition of Erk activation partially inhibits T48 phosphorylation, activation of hCdc25C and mitotic induction. These findings establish an essential role of Erk-MAPK in Cdc25 activation during Xenopus oocyte maturation and suggest potential roles of the Erk-MAPK family in hCdc25C activation during somatic cell cycle