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The Protein Phosphatase 2A regulatory subunit Twins stabilizes Plk4 to induce centriole amplification.

Brownlee CW, Klebba JE, Buster DW, Rogers GC - J. Cell Biol. (2011)

Bottom Line: However, Plk4 activity is required during mitosis for proper centriole duplication, but the mechanism stabilizing mitotic Plk4 is unknown.However, untimely Tws expression stabilizes Plk4 inappropriately, inducing centriole amplification.We demonstrate that ST actually mimics Tws function in stabilizing Plk4 and inducing centriole amplification.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cellular and Molecular Medicine, Arizona Cancer Center, University of Arizona, Tucson, AZ 85724, USA.

ABSTRACT
Centriole duplication is a tightly regulated process that must occur only once per cell cycle; otherwise, supernumerary centrioles can induce aneuploidy and tumorigenesis. Plk4 (Polo-like kinase 4) activity initiates centriole duplication and is regulated by ubiquitin-mediated proteolysis. Throughout interphase, Plk4 autophosphorylation triggers its degradation, thus preventing centriole amplification. However, Plk4 activity is required during mitosis for proper centriole duplication, but the mechanism stabilizing mitotic Plk4 is unknown. In this paper, we show that PP2A (Protein Phosphatase 2A(Twins)) counteracts Plk4 autophosphorylation, thus stabilizing Plk4 and promoting centriole duplication. Like Plk4, the protein level of PP2A's regulatory subunit, Twins (Tws), peaks during mitosis and is required for centriole duplication. However, untimely Tws expression stabilizes Plk4 inappropriately, inducing centriole amplification. Paradoxically, expression of tumor-promoting simian virus 40 small tumor antigen (ST), a reported PP2A inhibitor, promotes centrosome amplification by an unknown mechanism. We demonstrate that ST actually mimics Tws function in stabilizing Plk4 and inducing centriole amplification.

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Related in: MedlinePlus

Model depicting the regulation of Plk4 activity by a counteracting autophosphorylation/dephosphorylation mechanism. (A) Plk4 is expressed throughout interphase, but continuous Plk4 autophosphorylation of its DRE triggers its own proteasome-mediated degradation by inducing SCFSlimb binding and ubiquitination. As a result, centriole amplification is blocked. Plk4 stabilization can be achieved by PP2A activity, which dephosphorylates Plk4. However, this does not normally occur because its required regulatory subunit, Tws, is present at insufficient levels. (B) During mitosis, Tws protein levels rise, thus activating a PP2ATws complex, which counteracts Plk4 autophosphorylation. Plk4 is stabilized and modifies centrioles, making them competent to duplicate during the next S phase. Upon mitotic exit, Tws levels decrease, and PP2A is unable to maintain Plk4 stability. (C) This same mechanism is exploited by tumor-promoting SV40 ST. ST binds PP2A and functionally mimics Tws, counteracting Plk4 autophosphorylation. Plk4 is inappropriately stabilized during interphase, localizes to centrioles, and thus, promotes centriole amplification. CPB, cryptic polo box; PB, polo box.
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fig6: Model depicting the regulation of Plk4 activity by a counteracting autophosphorylation/dephosphorylation mechanism. (A) Plk4 is expressed throughout interphase, but continuous Plk4 autophosphorylation of its DRE triggers its own proteasome-mediated degradation by inducing SCFSlimb binding and ubiquitination. As a result, centriole amplification is blocked. Plk4 stabilization can be achieved by PP2A activity, which dephosphorylates Plk4. However, this does not normally occur because its required regulatory subunit, Tws, is present at insufficient levels. (B) During mitosis, Tws protein levels rise, thus activating a PP2ATws complex, which counteracts Plk4 autophosphorylation. Plk4 is stabilized and modifies centrioles, making them competent to duplicate during the next S phase. Upon mitotic exit, Tws levels decrease, and PP2A is unable to maintain Plk4 stability. (C) This same mechanism is exploited by tumor-promoting SV40 ST. ST binds PP2A and functionally mimics Tws, counteracting Plk4 autophosphorylation. Plk4 is inappropriately stabilized during interphase, localizes to centrioles, and thus, promotes centriole amplification. CPB, cryptic polo box; PB, polo box.

Mentions: Recent studies have increased our understanding of Plk4 inactivation considerably. Plk4 protein is maintained at near-undetectable levels for the majority of the cell cycle by ubiquitin-mediated proteolysis (Fig. 6 A; Fode et al., 1996; Rogers et al., 2009). The ubiquitin ligase SCFSlimb is responsible for Plk4 degradation and recognizes an extensively phosphorylated degron situated immediately downstream of the KD. Slimb is appropriately positioned on centrioles throughout the cell cycle to promote rapid Plk4 destruction, but centrioles are not required for its activity (Rogers et al., 2009). In any case, Plk4 degradation is critical in blocking all pathways of centriole amplification. Unlike other Polo kinase members, Plk4 is a homodimer capable of autophosphorylating its DRE in trans to promote Slimb binding (Leung et al., 2002; Guderian et al., 2010). Our findings demonstrate that autoregulation is a conserved feature of Plk4. Moreover, our RNAi screen of the fly kinome suggests that no other kinase is required for Plk4 degradation. The continuous and efficient degradation of Plk4 indicates that Plk4 is immediately active when expressed and that control of Plk4’s protein level is key to regulating its activity.


The Protein Phosphatase 2A regulatory subunit Twins stabilizes Plk4 to induce centriole amplification.

Brownlee CW, Klebba JE, Buster DW, Rogers GC - J. Cell Biol. (2011)

Model depicting the regulation of Plk4 activity by a counteracting autophosphorylation/dephosphorylation mechanism. (A) Plk4 is expressed throughout interphase, but continuous Plk4 autophosphorylation of its DRE triggers its own proteasome-mediated degradation by inducing SCFSlimb binding and ubiquitination. As a result, centriole amplification is blocked. Plk4 stabilization can be achieved by PP2A activity, which dephosphorylates Plk4. However, this does not normally occur because its required regulatory subunit, Tws, is present at insufficient levels. (B) During mitosis, Tws protein levels rise, thus activating a PP2ATws complex, which counteracts Plk4 autophosphorylation. Plk4 is stabilized and modifies centrioles, making them competent to duplicate during the next S phase. Upon mitotic exit, Tws levels decrease, and PP2A is unable to maintain Plk4 stability. (C) This same mechanism is exploited by tumor-promoting SV40 ST. ST binds PP2A and functionally mimics Tws, counteracting Plk4 autophosphorylation. Plk4 is inappropriately stabilized during interphase, localizes to centrioles, and thus, promotes centriole amplification. CPB, cryptic polo box; PB, polo box.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3198173&req=5

fig6: Model depicting the regulation of Plk4 activity by a counteracting autophosphorylation/dephosphorylation mechanism. (A) Plk4 is expressed throughout interphase, but continuous Plk4 autophosphorylation of its DRE triggers its own proteasome-mediated degradation by inducing SCFSlimb binding and ubiquitination. As a result, centriole amplification is blocked. Plk4 stabilization can be achieved by PP2A activity, which dephosphorylates Plk4. However, this does not normally occur because its required regulatory subunit, Tws, is present at insufficient levels. (B) During mitosis, Tws protein levels rise, thus activating a PP2ATws complex, which counteracts Plk4 autophosphorylation. Plk4 is stabilized and modifies centrioles, making them competent to duplicate during the next S phase. Upon mitotic exit, Tws levels decrease, and PP2A is unable to maintain Plk4 stability. (C) This same mechanism is exploited by tumor-promoting SV40 ST. ST binds PP2A and functionally mimics Tws, counteracting Plk4 autophosphorylation. Plk4 is inappropriately stabilized during interphase, localizes to centrioles, and thus, promotes centriole amplification. CPB, cryptic polo box; PB, polo box.
Mentions: Recent studies have increased our understanding of Plk4 inactivation considerably. Plk4 protein is maintained at near-undetectable levels for the majority of the cell cycle by ubiquitin-mediated proteolysis (Fig. 6 A; Fode et al., 1996; Rogers et al., 2009). The ubiquitin ligase SCFSlimb is responsible for Plk4 degradation and recognizes an extensively phosphorylated degron situated immediately downstream of the KD. Slimb is appropriately positioned on centrioles throughout the cell cycle to promote rapid Plk4 destruction, but centrioles are not required for its activity (Rogers et al., 2009). In any case, Plk4 degradation is critical in blocking all pathways of centriole amplification. Unlike other Polo kinase members, Plk4 is a homodimer capable of autophosphorylating its DRE in trans to promote Slimb binding (Leung et al., 2002; Guderian et al., 2010). Our findings demonstrate that autoregulation is a conserved feature of Plk4. Moreover, our RNAi screen of the fly kinome suggests that no other kinase is required for Plk4 degradation. The continuous and efficient degradation of Plk4 indicates that Plk4 is immediately active when expressed and that control of Plk4’s protein level is key to regulating its activity.

Bottom Line: However, Plk4 activity is required during mitosis for proper centriole duplication, but the mechanism stabilizing mitotic Plk4 is unknown.However, untimely Tws expression stabilizes Plk4 inappropriately, inducing centriole amplification.We demonstrate that ST actually mimics Tws function in stabilizing Plk4 and inducing centriole amplification.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Cellular and Molecular Medicine, Arizona Cancer Center, University of Arizona, Tucson, AZ 85724, USA.

ABSTRACT
Centriole duplication is a tightly regulated process that must occur only once per cell cycle; otherwise, supernumerary centrioles can induce aneuploidy and tumorigenesis. Plk4 (Polo-like kinase 4) activity initiates centriole duplication and is regulated by ubiquitin-mediated proteolysis. Throughout interphase, Plk4 autophosphorylation triggers its degradation, thus preventing centriole amplification. However, Plk4 activity is required during mitosis for proper centriole duplication, but the mechanism stabilizing mitotic Plk4 is unknown. In this paper, we show that PP2A (Protein Phosphatase 2A(Twins)) counteracts Plk4 autophosphorylation, thus stabilizing Plk4 and promoting centriole duplication. Like Plk4, the protein level of PP2A's regulatory subunit, Twins (Tws), peaks during mitosis and is required for centriole duplication. However, untimely Tws expression stabilizes Plk4 inappropriately, inducing centriole amplification. Paradoxically, expression of tumor-promoting simian virus 40 small tumor antigen (ST), a reported PP2A inhibitor, promotes centrosome amplification by an unknown mechanism. We demonstrate that ST actually mimics Tws function in stabilizing Plk4 and inducing centriole amplification.

Show MeSH
Related in: MedlinePlus