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Review
. 2023 Jan 2;12(1):187.
doi: 10.3390/cells12010187.

Multiple Roles of PLK1 in Mitosis and Meiosis

Jaroslav Kalous  1 , Daria Aleshkina  1
Affiliations
Review

Multiple Roles of PLK1 in Mitosis and Meiosis

Jaroslav Kalous et al. Cells. .

Abstract

Cells are equipped with a diverse network of signaling and regulatory proteins that function as cell cycle regulators and checkpoint proteins to ensure the proper progression of cell division. A key regulator of cell division is polo-like kinase 1 (PLK1), a member of the serine/threonine kinase family that plays an important role in regulating the mitotic and meiotic cell cycle. The phosphorylation of specific substrates mediated by PLK1 controls nuclear envelope breakdown (NEBD), centrosome maturation, proper spindle assembly, chromosome segregation, and cytokinesis. In mammalian oogenesis, PLK1 is essential for resuming meiosis before ovulation and for establishing the meiotic spindle. Among other potential roles, PLK1 regulates the localized translation of spindle-enriched mRNAs by phosphorylating and thereby inhibiting the translational repressor 4E-BP1, a downstream target of the mTOR (mammalian target of rapamycin) pathway. In this review, we summarize the functions of PLK1 in mitosis, meiosis, and cytokinesis and focus on the role of PLK1 in regulating mRNA translation. However, knowledge of the role of PLK1 in the regulation of meiosis remains limited.

Keywords: PLK1; mRNA translation; meiosis; mitosis; oocytes; polo-like kinase 1; spindle.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Scheme of polo-like kinase 1 (Plk1) mRNA translation. (A) Cytoplasmic polyadenylation element-binding protein 1 (CPEB1) represses the translation of CPE-containing mRNAs with short poly(A) tails, including Plk1 mRNA. Phosphorylated CPEB1 promotes the binding of the cleavage and polyadenylation specificity factor (CPSF) complex to the hexanucleotide sequence (AAUAAA). (B) In mouse oocytes, CPSF recruits poly(A) polymerase α (PAPα), which promotes polyadenylation.
Figure 2
Figure 2
Polo-like kinase 1 (PLK1) and maturation-promoting factor (MPF) activity and the level of early mitotic inhibitor 1 (EMI1) and early mitotic inhibitor 2 (EMI2) during meiotic maturation and oocyte-to-embryo transition. During the first meiotic arrest at the germinal vesicle (GV) stage, PLK1 activity is at very low levels. PLK1 activity starts to increase before nucleus envelope breakdown (NEBD), the inhibition of the anaphase-promoting complex (APC/C) by EMI1 leads to the accumulation of cyclin B, and the activity of the MPF increases. During NEBD, chromosome compaction and nuclear envelope breakdown occur, PLK1 activity rises, MPF activity increases, and EMI1 undergoes destruction immediately after NEBD. At metaphase I (MI), the first metaphase plate is formed, and the first polar body is extruded; PLK1 activity is maintained, MPF reaches maximum activity but is reduced by cyclin B’s destruction by APC/C, and the first polar body is extruded. EMI2 starts to be expressed prior to metaphase II (MII). The second metaphase plate is formed at the MII stage, and meiosis is halted in the second meiotic arrest. PLK1 activity is maintained after the first polar body extrusion, MPF activity is restored to the MI levels, and the oocyte awaits fertilization [49]. In the zygote, after fertilization, EMI2 is degraded and the second polar body is extruded, and both male and female pronuclei are formed. PLK1 activity decreases slowly until the pronucleus stage and is again upregulated after NEBD during the first mitotic division. MPF activity is downregulated by APC/C and restored before the first mitotic division [50]. At the 2-cell embryonic stage, the first mitotic division is completed, PLK1 activity is downregulated, and MPF activity is restored during the subsequent mitotic division.
Figure 3
Figure 3
Role of PLK1 in the initiation of translation. (A) Activation of polo-like kinase 1 (PLK1) requires phosphorylation of conserved threonine residue (Thr 210) by aurora kinase A (AURKA). Later PLK1 phosphorylates the mammalian target of rapamycin complex 1 (mTORC1), which plays a major role in the phosphorylation and inactivation of eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1) and in the initiation of cap-dependent translation. Moreover, PLK1 also regulates the phosphorylation of the 4E-BP1 at the Ser111 residue located on the spindle, enabling the local translation of spindle-associated proteins. Phosphorylated mTORC1 activates p70S6 kinase (p70S6K), resulting in ribosome biogenesis and translation elongation. (B) Scheme of cap-dependent translational initiation after poly(A) elongation. MTORC1 hyperphosphorylates 4E-BP1, which results in the dissociation of 4E-BP1 from the cap-binding subunit eIF4E. Released eIF4E together with the RNA helicase eIF4A and large adaptor protein eIF4G form the eIF4F complex, which binds to the m7G cap of mRNA. Poly(A)-binding protein (PABP) binds to the elongated poly(A) tail and eIF4G, forming an mRNA loop and stabilizing the cap. EIF4B interacts with and promotes eIF4A activity and interacts with the eIF3A subunit of the 43S preinitiation complex. After 5′ UTR scanning and AUG recognition, the complex recruits a 60S ribosomal subunit and starts protein synthesis.
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Grants and funding

This work was supported by the grant CZ.02.1.01/0.0/0.0/15_003/0000460 from the Operational Programme Research, Development, and Education, by Institutional Research Concept RVO67985904, by GAUK 389321 for D. A. and by GACR (22-27301S).

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