Cdc25C phosphorylation on serine 191 by Plk3 promotes its nuclear translocation

Abstract

Mitosis in human cells is initiated at the end of G2 by activation of the Cdc2/cyclin B complex. Activation occurs by dephosphorylation of the inhibitory residues, threonine 14 (T14) and tyrosine 15 (Y15), on Cdc2 by the Cdc25C phosphatase. Entry into mitosis is regulated by the subcellular relocalization of Cdc2/cyclin B, which is rapidly imported into the nucleus at the end of G2. Here, we show that polo-like kinase 3 (Plk3) is able to phosphorylate Cdc25C primarily on S191, and to a lesser extent on S198 in vitro, both of which are within a nuclear exclusion motif. Following transfection, the S191D Cdc25C mutant leads to an enhanced accumulation of Cdc25C in the nucleus, while the S191A mutant facilitated the Cdc25C nuclear exclusion. Furthermore, translocation of Cdc25C to the nucleus was accompanied by a decrease in Cdc2 phosphorylation on Y15. Plk3-WT overexpression led to a sharp increase in Cdc25C nuclear accumulation, while Plk3-KD overexpression failed to do so. The effect of Plk3 overexpression on Cdc25C was reversed by coexpression of a Plk3 siRNA. These results support a role for the polo kinases in coordinating the translocation and perhaps the timing of both Cdc25C and its target Cdc2/cyclin B to the nucleus upon entry into mitosis.

Getting in and out of mitosis with Polo-like kinase-1

“…Indeed, whereas Plk1 was shown to mediate nuclear translocation of Cdc25C, Plk3 phosphorylates Cdc25C on Ser216, a site known to be involved in nuclear exclusion (Ouyang et al, 1999;ToyoshimaMorimoto et al, 2002). The exact mechanism by which Plk3 regulates the G2/M transition in general and Cdc25C in particular is unclear however, as a recent report showed that Cdc25C translocates to the nucleus after (direct) phosphorylation by Plk3 (Bahassi el et al, 2004).…”

Plk1 Regulates Activation of the Anaphase Promoting Complex by Phosphorylating and Triggering SCFβTrCP-dependent Destruction of the APC Inhibitor Emi1

“…Thus, it could be that the requirement for Polo-like kinases in triggering Emi1 destruction and APC activation includes both Plk1 and Plk3 or that in the absence of Plk1, Plk3 can substitute for Plk1. Some precedent exists for overlapping roles of Plk1 and Plk3 because both kinases can phosphorylate Cdc25C (Bahassi el et al, 2004). Furthermore, it is possible that mitotically phosphorylated APC is somewhat less susceptible to Emi1 inhibition.…”

Human Plk4 phosphorylates Cdc25C

“…13 Quite interestingly, S191 and S198, residues found in the nuclear export signal of Cdc25C, are phosphorylated by Plk1 and Plk3 and lead to the nuclear accumulation of the protein. 11,12 Our observation that Plk4 phosphorylates Cdc25C suggests that Plk4, like Plk1 and 3, is involved in the entry into mitosis. Although the synthesis and destruction of regulatory proteins such as cyclins is important for cell cycle regulation, localization of these proteins to the right place at the right time is a fundamental step in ensuring proper cell cycle controls.…”

“…7,10 Furthermore, Plk1 and Plk3 have both been shown to phosphorylate Cdc25C phosphatase thus resulting in its localization to the nucleus. 11,12 Nuclear localization and activation of this protein are necessary in order for mitosis to occur. 13 Interestingly, Plk4 is primarily found to localize to centrosomes, a site which Cdc25C is also localized prior to its movement into the nucleus upon mitotic entry.…”