Protein Phosphatase-1α Regulates Centrosome Splitting through Nek2

Mi, Jun; Guo, Changyue; Brautigan, David L.; Larner, James M.

doi:10.1158/0008-5472.can-06-3071

Cited by 82 publications

(80 citation statements)

References 42 publications

(47 reference statements)

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“…On the other hand, the PP1 phosphatase counteracts the function of Nek2A by dephosphorylating both Nek2A and C-Nap1 (67,127,129). Because a diverse range of cellular functions are regulated by reversible protein phosphorylation through the actions of protein kinases and phosphatases, it is not surprising that PP1 and Nek2A regulate each other and exert opposing influences over C-Nap1 function.…”

Section: Centrosome Disjunction Via C-nap1 Phosphorylationmentioning

confidence: 99%

“…By contrast, protein phosphatase 1 " (PP1") counteracts the function of Nek2A by dephosphorylating both Nek2A and C-Nap1 (67,127,129). The reversible and tightly regulated phosphorylation and dephosphorylation of C-Nap1 through the actions of Nek2A and PP1" is therefore critical for proper spindle formation and mitotic progression (67,127).…”

Section: Nf-!b Activation By Tax Is Not Sufficient For the Transformamentioning

confidence: 99%

“…This allows centrosome splitting and formation of bipolar spindle to occur. During interphase, C-Nap1 is kept un-or under-phosphorylated by phosphor-Ser/Thr protein phosphatase 1 ", PP1$",$The unphosphorylated C-Nap1 remains attached to the centrioles and prevents centrosome disjunction (67,127,129). Importantly, PP1"$also dephosphorylates and inactivates Nek2A (129) to ensure that premature centrosome splitting is prevented.…”

Section: Nap1 Phosphorylation and Centrosomal Abnormalitiesmentioning

confidence: 99%

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HTLV-1 Tax Effects on Cellular Mitotic Regulation

Merling¹

2007

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The human T-cell leukemia virus 1 (HTLV-1) encodes the tax gene (transactivator encoded by the pX region) which is a potent activator of viral transcription and Nuclear , this cyclin-dependent kinase inhibitor may also play a role in tax-IRS.As part of the research presented in this dissertation, a collection of HTLV-1 tax point mutants were isolated that permit normal growth of S. cerevisiae. Similar to wild-type tax, many mutants (C23W, A108T, L159F, and L235F) transactivated both the HTLV long terminal repeat (LTR) and the NF-!B reporters. The V19M mutant preferentially activated NF-!B, but was attenuated in LTR activation. None of the mutants significantly elevated the levels of p21 CIP1/WAF1 and p27 KIP1 , indicating that dramatic Tax-induced surges in p21and p27 KIP1 occurs by mechanisms distinct from NF-!B and LTR activation. Importantly, the ability of these mutants to activate APC was attenuated or abrogated. These data show that Tax-induced rapid senescence is causally associated with APC activation and suggest iv that the mitotic abnormalities that are associated with premature APC activation might play an important role in cell transformation by Tax.In a parallel study, we demonstrate that Tax interacts with both centrosomal Nek2-associated protein 1 (C-Nap1), a large coiled-coil protein that maintains centrosome cohesion, and protein phosphatase 1 (PP1) and that these interactions localize to the centrosome. Furthermore, in cells expressing tax, C-Nap1 phosphorylation is greatly diminished. C-Nap1 phosphorylation status plays an important role in centrosome cycle progression; PP1-mediated dephosphorylation of C-Nap1 maintains centriolar cohesion during interphase, and never in mitosis A (NIMA)-related kinase 2 (Nek2A)-mediated phosphorylation of C-Nap1 during G2/M triggers C-Nap1 dissociation from duplicated centrosomes permitting normal centrosome disjunction. Our data suggest that Tax, through recruitment of PP1 to C-Nap1, may permit prolonged C-Nap1 dephosphorylation thereby disrupting normal centrosome disjunction leading to observed Tax-induced centrosome abnormalities and distinct microtubule organizing center (MTOC) loss.Our studies have revealed two distinct pathways through which Tax could contribute to oncogenesis. First, our Tax mutants that retained LTR and NF-!B activation properties but were impaired in APC activation were also defective in the ability to transform Rat1 fibroblasts. Therefore, premature APC activation by Tax appears to correlate with the ability of Tax to induce cellular transformation. Second, our demonstration of Tax-mediated alterations in C-Nap1 phosphorylation cycle offers an explanation for the centrosome abnormalities and mitotic apparatus defects observed in response to Tax expression.Chromosomal abnormalities resulting from such mitotic apparatus defects may be expected to contribute to the oncogenic potential of Tax.v

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Section: Centrosome Disjunction Via C-nap1 Phosphorylationmentioning

confidence: 99%

Section: Nf-!b Activation By Tax Is Not Sufficient For the Transformamentioning

confidence: 99%

Section: Nap1 Phosphorylation and Centrosomal Abnormalitiesmentioning

confidence: 99%

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HTLV-1 Tax Effects on Cellular Mitotic Regulation

Merling¹

2007

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“…Evidence has also been accumulating that some Neks function in the DNA damage response. For example, budding yeast Kin3 is important for cell cycle arrest in response to genotoxic agents , and mammalian Nek1, Nek2, Nek10, and Nek11 are involved in checkpoints activated in response to ionizing and ultraviolet radiation, the DNA-damaging drug methyl methanesulfonate (MMS), oxidative damage-inducing hydrogen peroxide, and the DNA-alkylating agent cisplatin (Noguchi et al 2002(Noguchi et al , 2004Polci et al 2004;Mi et al 2007;Chen et al 2008;Melixetian et al 2009;Pelegrini et al 2010;Sorensen et al 2010;Fry et al 2012;Liu et al 2013). Mutations in several Nek kinase genes have also been associated with cancer (reviewed in Fry et al 2012), and knockdown of Nek2 or Nek6 in several cancer cell lines inhibits proliferation or induces apoptosis (Tsunoda et al 2009;Nassirpour et al 2010).…”

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confidence: 99%

Insights into Dynamic Mitotic Chromatin Organization Through the NIMA Kinase Suppressor SonC, a Chromatin-Associated Protein Involved in the DNA Damage Response

et al. 2014

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The nuclear pore complex proteins SonA and SonB, the orthologs of mammalian RAE1 and NUP98, respectively, were identified in Aspergillus nidulans as cold-sensitive suppressors of a temperature-sensitive allele of the essential mitotic NIMA kinase (nimA1). Subsequent analyses found that sonB1 mutants exhibit temperature-dependent DNA damage sensitivity. To understand this pathway further, we performed a genetic screen to isolate additional conditional DNA damage-sensitive suppressors of nimA1. We identified two new alleles of SonA and four intragenic nimA mutations that suppress the temperature sensitivity of the nimA1 mutant. In addition, we identified SonC, a previously unstudied binuclear zinc cluster protein involved with NIMA and the DNA damage response. Like sonA and sonB, sonC is an essential gene. SonC localizes to nuclei and partially disperses during mitosis. When the nucleolar organizer region (NOR) undergoes mitotic condensation and removal from the nucleolus, nuclear SonC and histone H1 localize in a mutually exclusive manner with H1 being removed from the NOR region and SonC being absent from the end of the chromosome beyond the NOR. This region of chromatin is adjacent to a cluster of nuclear pore complexes to which NIMA localizes last during its progression around the nuclear envelope during initiation of mitosis. The results genetically extend the NIMA regulatory system to include a protein with selective large-scale chromatin location observed during mitosis. The data suggest a model in which NIMA and SonC, its new chromatin-associated suppressor, might help to orchestrate global chromatin states during mitosis and the DNA damage response.T HE NIMA kinase is an essential conserved regulator of mitotic events in the filamentous fungus Aspergillus nidulans (Osmani et al. 1988). NIMA was first discovered through a genetic screen that defined several different temperature-sensitive alleles of NIMA that cause a Never in Mitosis phenotype (Morris 1975). Subsequent studies showed that NIMA is essential for mitotic entry but not for the activation of the Cdk1 mitotic kinase (Oakley and Morris 1983;Osmani et al. 1988Osmani et al. , 1991Morris et al. 1992;Ye et al. 1995). Not only is NIMA essential for initiating mitosis, but also its overexpression can prematurely induce mitotic events including DNA condensation in A. nidulans, fission yeast, Xenopus, and human cells (O'Connell et al. 1994;Lu and Hunter 1995), indicating the existence of conserved mitotic substrates as recently confirmed in mammalian cells (Laurell et al. 2011). NIMA is subject to complex regulation at both the mRNA and protein levels, leading to maximum activity during mitosis (Osmani et al. 1987;Pu and Osmani 1995;Ye et al. 1995Ye et al. , 1996Ye et al. , 1998.One of the key roles for NIMA at the onset of mitosis is its regulation of nuclear pore complexes. This insight came from a genetic screen aimed at identifying suppressors of the temperature-sensitive nimA1 allele. This genetic screen identified nimA1 suppressor mutation...

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“…These were originally identified as heat-stable and trypsin-sensitive proteins (11), and they now are recognized as regulatory/targeting subunits (1,(12)(13)(14). The best known of these inhibitor proteins are Inh1 (inhibitor-1) (15,16), its neuronal homologue DARPP-32 (17), and Inh2 (inhibitor-2) (12).…”

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confidence: 99%

Protein Phosphatase-1 Inhibitor-3 Is an in Vivo Target of Caspase-3 and Participates in the Apoptotic Response

Huang

Lee

2008

Journal of Biological Chemistry

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Inh3 (inhibitor-3) is a potent inhibitor of protein phosphatase-1 that selectively associates with PP1␥1 and PP1␣ but not the PP1␤ isoform. We demonstrate that Inh3 is a novel substrate for caspase-3 and is degraded in vivo during apoptosis induced by actinomycin D. Inh3 was not degraded in apoptotic MCF-7 cells, which lack caspase-3. These experiments establish that Inh3 is a novel physiological substrate of caspase-3. Electroporation of the caspase-3-resistant Inh3-D49A mutant into HL-60 cells resulted in a significant attenuation of apoptosis induced by actinomycin D. These results show that Inh3 degradation contributes to the apoptotic process. Immunofluorescence based examination of the subcellular localizations of Inh3 and PP1␥1 revealed a major relocalization of the cellular pool of PP1␥1 from the nucleolus to the nucleus and then to the cytoplasm during actinomycin D-induced apoptosis. A similar redistribution of PP1␣ from the nucleus to the cytoplasm occurred. These results are consistent with an unexpected discovery that significant fractions of the cellular pools of PP1␥1 and PP1␣ are associated with Inh3 in HL-60 cells. Thus, Inh3 is a major factor in the cellular economy of PP1␥1 and PP1␣ subunits. The unscheduled relocalization of this large a pool of PP1 subunits and their release from a potent inhibitor could deregulate a diverse range of essential cellular processes and signaling pathways. We discuss the significance of these findings in relation to working hypotheses whereby Inh3 destruction could contribute to the apoptotic process.Serine/threonine protein phosphatase-1 activity is involved in the regulation of a remarkably diverse range of cellular functions (1-3). Protein phosphatase-1 activity is provided by as many as 100 enzyme forms in which the catalytic subunit, PP1 2 , is associated with one or more different subunits (1). These noncatalytic subunits function as targeting proteins, which serve to specify the substrates that are acted on by PP1. The PP1 catalytic subunit is a 37-kDa protein and is ubiquitously expressed in mammalian cells as three closely related isoforms, PP1␣, PP1␤/␦, and PP1␥1 (4). The structural basis for the interaction of PP1 with a large number of partners is due to a hydrophobic pocket, distal to the active site, that recognizes a sequence motif of the type RVXF (5-7). Spatial restriction by the targeting subunits is the primary mechanism for the endowment of specificity to the PP1 catalytic subunit, which by itself is relatively nonspecific (8). Each PP1-targeting subunit complex can be considered to be a Ser/Thr phosphatase with its own specificity (1, 6). Gene deletion of PP1-binding proteins in yeast has been shown to generate specific phenotypes associated with loss of dephosphorylation of specific PP1 substrates (9, 10). A corollary of the targeting hypothesis is that no free active PP1 is present in the cell, since this could lead to unregulated and nonspecific dephosphorylation of phospho-Ser/Thr-containing proteins.There are also potent inhibitors of t...

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Protein Phosphatase-1α Regulates Centrosome Splitting through Nek2

Cited by 82 publications

References 42 publications

HTLV-1 Tax Effects on Cellular Mitotic Regulation

HTLV-1 Tax Effects on Cellular Mitotic Regulation

Insights into Dynamic Mitotic Chromatin Organization Through the NIMA Kinase Suppressor SonC, a Chromatin-Associated Protein Involved in the DNA Damage Response

Protein Phosphatase-1 Inhibitor-3 Is an in Vivo Target of Caspase-3 and Participates in the Apoptotic Response

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