title: Protein phosphatase 4 is phosphorylated and inactivated by Cdk in response to spindle toxins and interacts with γ-tubulin.
abstract: Many pharmaceuticals used to treat cancer target the cell cycle or mitotic spindle dynamics, such as the anti-tumor drug, paclitaxel, which stabilizes microtubules. Here we show that, in cells arrested in mitosis with the spindle toxins, nocodazole, or paclitaxel, the endogenous protein phosphatase 4 (Ppp4) complex Ppp4c-R2-R3A is phosphorylated on its regulatory (R) subunits, and its activity is inhibited. The phosphorylations are blocked by roscovitine, indicating that they may be mediated by Cdk1-cyclin B. Endogenous Ppp4c is enriched at the centrosomes in the absence and presence of paclitaxel, nocodazole, or roscovitine, and the activity of endogenous Ppp4c-R2-R3A is inhibited from G 1/S to the G 2/M phase of the cell cycle. Endogenous γ-tubulin and its associated protein, γ-tubulin complex protein 2, both of which are essential for nucleation of microtubules at centrosomes, interact with the Ppp4 complex. Recombinant γ-tubulin can be phosphorylated by Cdk1-cyclin B or Brsk1 and dephosphorylated by Ppp4c-R2-R3A in vitro. The data indicate that Ppp4c-R2-R3A regulates microtubule organization at centrosomes during cell division in response to stress signals such as spindle toxins, paclitaxel, and nocodazole, and that inhibition of the Ppp4 complex may be advantageous for treatment of some cancers.
authors: Medical Research Council Protein Phosphorylation and Ubiquitylation Unit; College of Life Sciences; University of Dundee; Dundee, Scotland, UK.
authors: Martin
authors: M
authors: Voss
authors: Kathryn
authors: K
authors: Campbell
authors: Nastja
authors: N
authors: Saranzewa
authors: David G
authors: DG
authors: Campbell
authors: C James
authors: CJ
authors: Hastie
authors: Mark W
authors: MW
authors: Peggie
authors: Cristina
authors: C
authors: Martin-Granados
authors: Alan R
authors: AR
authors: Prescott
authors: Patricia T W
authors: PT
authors: Cohen
mesh_terms: D000595:Amino Acid Sequence; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D015739:Nocodazole / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D025941:Protein Interaction Mapping; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021122:Protein Subunits / Q000378:metabolism; D008941:Spindle Apparatus / Q000187:drug effects / Q000378:metabolism*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism*
chemical_list: D047428:Protein Kinase Inhibitors; D021122:Protein Subunits; D014404:Tubulin; D016203:CDC2 Protein Kinase; D010749:Phosphoprotein Phosphatases; C080406:protein phosphatase 4; D015739:Nocodazole
keywords: Cdk1; cell cycle; centrosome; nocodazole; paclitaxel; protein phosphatase 4; γ-tubulin
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