Phosphorylation of Plk1 at Ser326 regulates its functions during mitotic progression

Department of Biochemistry, Cancer Center, Purdue University, West Lafayette, IN 47907, USA.
Oncogene (Impact Factor: 8.56). 09/2008; 27(52):6635-45. DOI: 10.1038/onc.2008.262
Source: PubMed

ABSTRACT Polo-like kinase 1 (Plk1), the best characterized member of the mammalian polo-like kinase family, is well regulated throughout the cell cycle at the protein expression level. Moreover, it is known that Plk1 kinase activity is also regulated at the post-translational level through phosphorylation. However, the upstream kinases of Plk1 have not been identified. Although the involvement of the p38 MAP kinase pathway in cellular responses to stress has been well documented, the role of this pathway in normal cell cycle progression is unclear. Here, we show that phosphorylated p38 and MAP kinase-activated protein kinase 2 (MK2) are colocalized with Plk1 to the spindle poles during prophase and metaphase. Specific depletion of various members of the p38 MAP kinase pathway by the use of RNA interference revealed that the pathway is required for mitotic progression under normal growth conditions. Furthermore, MK2 directly phosphorylates Ser326 of Plk1. Ectopic expression of Plk1-S326A completely blocked cells at mitosis, likely due to the defect of bipolar spindle formation and subsequent activation of the spindle checkpoint. Only Plk1-S326E, but not the Plk1-S326A, efficiently rescued the p38 or MK2-depletion-induced mitotic defects, further solidifying the requirement of S326 phosphorylation during mitotic progression.

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    • "Thus, p53 null cells are unable to downregulate PLK1 in response to chemotherapy, leading to chemoresistance [25] [26]. Indeed, PLK1 colocalizes with p38 and MK2 at the spindle during mitosis and is phosphorylated by MK2, linking their activities and suggesting pathway crosstalk [27]. We recently made the important discovery that endometrial cancer cells with inactivated p53 rely on the p38 pathway to maintain the G2/M checkpoint [28]. "
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    ABSTRACT: Serous uterine endometrial carcinomas are aggressive type II cancers with poor outcomes for which new treatment strategies are urgently needed, in particular, strategies that augment sensitivity to established chemotherapy regimens. The tumor suppressor gene TP53 is dysregulated in more than 90% of serous tumors, altering master regulators of the G2/M cell cycle checkpoint in unique and predictable ways and desensitizing cells to chemotherapy. We hypothesized that synthetic lethality can be achieved in endometrial cancer cells with mutant p53 by combining paclitaxel with agents to overcome G2/M arrest and induce mitotic catastrophe. The combination of BIBF1120, an investigational VEGFR, PDGFR, and FGFR multityrosine kinase inhibitor with established anti-angiogenic activity, with paclitaxel abrogated the G2/M checkpoint in p53-null endometrial cancer cells via modulation of G2/M checkpoint regulators followed by induction of mitotic cell death. In endometrial cancer cells harboring an oncogenic gain-of-function p53 mutation, synthetic lethality was created by combining paclitaxel with BIBF1120 and a histone deacetylase inhibitor, which serves to destabilize mutant p53. These cells were also sensitive to an inhibitor of the G2/M kinase Wee1 in combination with paclitaxel. These findings reveal that, in addition to antiangiogenic activity, the angiokinase inhibitor BIBF1120 can be used to restore sensitivity to paclitaxel and induce mitotic cell death in endometrial cancer cells with non-functional p53. These preclinical data serve as a critical platform for the creative design of future clinical trials utilizing molecularly enhanced chemotherapy to achieve synthetic lethality based on the mutational landscape.
    Obstetrics and Gynecology International 12/2013; 2013:828165. DOI:10.1155/2013/828165
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    • "Evidence is accumulating, however, that the sensor and signal transduction pathways behind G2 checkpoints do continue to function during mitosis. For example, when chromosomes are damaged during mitosis, the ATM kinase still phosphorylates histone H2AX (Rogakou et al. 1999; Mikhailov et al. 2002) and initiates the DNA damage response (Giunta et al. 2010), while in response to stress in mitosis, p38 still activates its major downstream MK2 target (Tang et al. 2008). However, during mitosis, these pathways do not have target(s) that can delay anaphase onset independent of the Mad/Bub-based mitotic checkpoint . "
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    ABSTRACT: In this review, I stress the importance of direct data and accurate terminology when formulating and communicating conclusions on how the G2/M and metaphase/anaphase transitions are regulated. I argue that entry into mitosis (i.e., the G2/M transition) is guarded by several checkpoint control pathways that lose their ability to delay or stop further cell cycle progression once the cell becomes committed to divide, which in vertebrates occurs in the late stages of chromosome condensation. After this commitment, progress through mitosis is then mediated by a single Mad/Bub-based checkpoint that delays chromatid separation, and exit from mitosis (i.e., completion of the cell cycle) in the presence of unattached kinetochores. When cells cannot satisfy the mitotic checkpoint, e.g., when in concentrations of spindle poisons that prohibit the stable attachment of all kinetochores, they are delayed in mitosis for many hours. In normal cells, the duration of this delay depends on the organism and ranges from ∼4 h in rodents to ∼22 h in humans. Recent live cell studies reveal that under this condition, many cancer cells (including HeLa and U2OS) die in mitosis by apoptosis within ∼24 h, which implies that biochemical studies on cancer cell populations harvested in mitosis after a prolonged mitotic arrest are contaminated with dead or dying cells.
    Chromosome Research 12/2010; 19(3):291-306. DOI:10.1007/s10577-010-9178-z · 2.69 Impact Factor
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    • "The Plkk potential of Map kinase has been reported by Tang and his colleagues. Phosphorylated p38 and MAP kinase-activated protein kinase 2 (MK2) are colocalized with Plk1 to the spindle poles during prophase and metaphase, and that MK2 directly phosphorylates Ser326 of Plk1 [35]. Additional experiments on MAPK1 and PKCiota as upstream activators of Plk1 will be performed in near future. "
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    ABSTRACT: Polo-like kinase-1 (Plk1) is phosphorylated on Thr210 for activation during mitosis. Here, we investigated the question of which kinase(s) is the specific upstream kinase of mitotic Plk1. Upstream kinases of Plk1 were purified from mitotic cell extracts through column chromatography procedures, and identified by mass spectrometry. Candidates for Plk1 kinase included p21-activated kinase, aurora A, and mammalian Ste20-like kinases. Immunoprecipitates of these proteins from mitotic cell extracts phosphorylated Plk1 on Thr210. Even if the activity of Aurora A was blocked with a specific inhibitor, Plk1 phosphorylation still occurred, suggesting that function of Plk1 could be controlled by these kinases for proper mitotic progression, as well as by Aurora A in very late G2 phase for the beginning of mitosis.
    FEBS letters 10/2010; 584(20):4299-305. DOI:10.1016/j.febslet.2010.09.025 · 3.34 Impact Factor
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