scholarly journals Phosphoinositide 3-kinase β regulates chromosome segregation in mitosis

2012 ◽  
Vol 23 (23) ◽  
pp. 4526-4542 ◽  
Author(s):  
Virginia Silió ◽  
Javier Redondo-Muñoz ◽  
Ana C. Carrera
Keyword(s):  
Chromosome Segregation ◽  
Genomic Stability ◽  
Pi3k Pathway ◽  
S Phase ◽  
Spindle Orientation ◽  
Aurora B ◽  
Pi3k Activity ◽  
Optimal Function ◽  
Phosphoinositide 3 Kinase ◽  
Phase Entry

Class IA phosphoinositide 3-kinases (PI3K) are enzymes composed of a p85 regulatory and a p110 catalytic subunit that control formation of 3-poly-phosphoinositides (PIP3). The PI3K pathway regulates cell survival, migration, and division, and is mutated in approximately half of human tumors. For this reason, it is important to define the function of the ubiquitous PI3K subunits, p110α and p110β. Whereas p110α is activated at G1-phase entry and promotes protein synthesis and gene expression, p110β activity peaks in S phase and regulates DNA synthesis. PI3K activity also increases at the onset of mitosis, but the isoform activated is unknown; we have examined p110α and p110β function in mitosis. p110α was activated at mitosis entry and regulated early mitotic events, such as PIP3 generation, prometaphase progression, and spindle orientation. In contrast, p110β was activated near metaphase and controlled dynein/dynactin and Aurora B activities in kinetochores, chromosome segregation, and optimal function of the spindle checkpoint. These results reveal a p110β function in preserving genomic stability during mitosis.

scholarly journals Phosphoinositide 3-Kinase Activation in Late G1 Is Required for c-Myc Stabilization and S Phase Entry

2006 ◽  
Vol 26 (23) ◽  
pp. 9116-9125 ◽  
Author(s):  
Amit Kumar ◽  
Miriam Marqués ◽  
Ana C. Carrera
Keyword(s):  
S Phase ◽  
Minichromosome Maintenance ◽  
Kinase Activation ◽  
Cell Cycle Entry ◽  
Pi3k Activity ◽  
Activity Peak ◽  
Pi3k Activation ◽  
Minichromosome Maintenance Protein ◽  
Phosphoinositide 3 Kinase ◽  
Phase Entry

ABSTRACT Phosphoinositide 3-kinase (PI3K) is one of the early-signaling molecules induced by growth factor (GF) receptor stimulation that are necessary for cell growth and cell cycle entry. PI3K activation occurs at two distinct time points during G1 phase. The first peak is observed immediately following GF addition and the second in late G1, before S phase entry. This second activity peak is essential for transition from G1 to S phase; nonetheless, the mechanism by which this peak is induced and regulates S phase entry is poorly understood. Here, we show that activation of Ras and Tyr kinases is required for late-G1 PI3K activation. Inhibition of late-G1 PI3K activity results in low c-Myc and cyclin A expression, impaired Cdk2 activity, and reduced loading of MCM2 (minichromosome maintenance protein) onto chromatin. The primary consequence of inhibiting late-G1 PI3K was c-Myc destabilization, as conditional activation of c-Myc in advanced G1 as well as expression of a stable c-Myc mutant rescued all of these defects, restoring S phase entry. These results show that Tyr kinases and Ras cooperate to induce the second PI3K activity peak in G1, which mediates initiation of DNA synthesis by inducing c-Myc stabilization.

scholarly journals Phosphoinositide 3-Kinases p110α and p110β Regulate Cell Cycle Entry, Exhibiting Distinct Activation Kinetics in G1 Phase

2008 ◽  
Vol 28 (8) ◽  
pp. 2803-2814 ◽  
Author(s):  
Miriam Marqués ◽  
Amit Kumar ◽  
Isabel Cortés ◽  
Ana Gonzalez-García ◽  
Carmen Hernández ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Tyrosine Kinases ◽  
Control Cell ◽  
Growth Factor Receptor ◽  
Maximum Activity ◽  
S Phase ◽  
Selective Action ◽  
Cell Cycle Entry ◽  
Phosphoinositide 3 Kinase ◽  
Phase Entry

ABSTRACT Phosphoinositide 3-kinase (PI3K) is an early signaling molecule that regulates cell growth and cell cycle entry. PI3K is activated immediately after growth factor receptor stimulation (at the G0/G1 transition) and again in late G1. The two ubiquitous PI3K isoforms (p110α and p110β) are essential during embryonic development and are thought to control cell division. Nonetheless, it is presently unknown at which point each is activated during the cell cycle and whether or not they both control S-phase entry. We found that p110α was activated first in G0/G1, followed by a minor p110β activity peak. In late G1, p110α activation preceded that of p110β, which showed the maximum activity at this time. p110β activation required Ras activity, whereas p110α was first activated by tyrosine kinases and then further induced by active Ras. Interference with p110α and -β activity diminished the activation of downstream effectors with different kinetics, with a selective action of p110α in blocking early G1 events. We show that inhibition of either p110α or p110β reduced cell cycle entry. These results reveal that PI3Kα and -β present distinct activation requirements and kinetics in G1 phase, with a selective action of PI3Kα at the G0/G1 phase transition. Nevertheless, PI3Kα and -β both regulate S-phase entry.

scholarly journals Chk1 Phosphorylates Cdh1 to Promote SCFβTRCP-Dependent Degradation of Cdh1 During S-Phase

2019 ◽  
Author(s):  
Debjani Pal ◽  
Adrian E. Torres ◽  
Abbey L. Messina ◽  
Andrew Dickson ◽  
Kuntal De ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Feedback Loop ◽  
Cellular Proliferation ◽  
Genomic Stability ◽  
Cyclin A ◽  
S Phase ◽  
Anaphase Promoting Complex ◽  
Replication Machinery ◽  
Key Factor ◽  
Phase Entry

ABSTRACTThe interplay of the Anaphase-Promoting Complex/Cyclosome (APC/C) and Skp1-Cul1-F-box (SCF) E3 ubiquitin ligases is necessary for controlling cell cycle transitions and checkpoint responses, which are critical for maintaining genomic stability. Yet, the mechanisms underlying the coordinated activity of these enzymes are not completely understood. Recently, Cyclin A- and Plk1- mediated phosphorylation of Cdh1 was demonstrated to trigger its ubiquitination by SCFβTRCP at the G1/S transition. However, Cyclin A-Cdk and Plk1 activities peak in G2 so it is unclear why Cdh1 is targeted at G1/S but not in G2. Here, we show that phosphorylation of Cdh1 by Chk1 contributes to its recognition by SCFβTRCP, promotes efficient S-phase entry, and is important for cellular proliferation. Conversely, Chk1 activity in G2 inhibits Cdh1 accumulation. Overall, these data suggest a model whereby the rise and fall of Chk1 activity is a key factor in the feedback loop between APC/CCdh1 and the replication machinery that enhances the G1/S and S/G2 transitions, respectively.

scholarly journals CDK1-mediated phosphorylation at H2B serine 6 is required for mitotic chromosome segregation

2019 ◽  
Vol 218 (4) ◽  
pp. 1164-1181 ◽  
Author(s):  
Markus Seibert ◽  
Marcus Krüger ◽  
Nikolaus A. Watson ◽  
Onur Sen ◽  
John R. Daum ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Chromosomal Instability ◽  
Mitotic Chromosome ◽  
Chromatin Modification ◽  
Genomic Stability ◽  
Cyclin B1 ◽  
Aurora B ◽  
Chromatin Binding ◽  
Histone H2b ◽  
Chromosome Separation

Faithful mitotic chromosome segregation is required for the maintenance of genomic stability. We discovered the phosphorylation of histone H2B at serine 6 (H2B S6ph) as a new chromatin modification site and found that this modification occurs during the early mitotic phases at inner centromeres and pericentromeric heterochromatin. This modification is directly mediated by cyclin B1–associated CDK1, and indirectly by Aurora B, and is antagonized by PP1-mediated dephosphorylation. H2B S6ph impairs chromatin binding of the histone chaperone SET (I2PP2A), which is important for mitotic fidelity. Injection of phosphorylation-specific H2B S6 antibodies in mitotic cells caused anaphase defects with impaired chromosome segregation and incomplete cytokinesis. As H2B S6ph is important for faithful chromosome separation, this modification may contribute to the prevention chromosomal instability and aneuploidy which frequently occur in cancer cells.

scholarly journals The SCFSlimb ubiquitin ligase regulates Plk4/Sak levels to block centriole reduplication

2009 ◽  
Vol 184 (2) ◽  
pp. 225-239 ◽  
Author(s):  
Gregory C. Rogers ◽  
Nasser M. Rusan ◽  
David M. Roberts ◽  
Mark Peifer ◽  
Stephen L. Rogers
Keyword(s):  
Cell Cycle ◽  
Chromosome Segregation ◽  
Ubiquitin Ligase ◽  
E3 Ubiquitin Ligase ◽  
Genomic Stability ◽  
Ubiquitin Ligases ◽  
S Phase ◽  
Proteolytic Degradation ◽  
Centriole Duplication ◽  
F Box Protein

Restricting centriole duplication to once per cell cycle is critical for chromosome segregation and genomic stability, but the mechanisms underlying this block to reduplication are unclear. Genetic analyses have suggested an involvement for Skp/Cullin/F box (SCF)-class ubiquitin ligases in this process. In this study, we describe a mechanism to prevent centriole reduplication in Drosophila melanogaster whereby the SCF E3 ubiquitin ligase in complex with the F-box protein Slimb mediates proteolytic degradation of the centrosomal regulatory kinase Plk4. We identified SCFSlimb as a regulator of centriole duplication via an RNA interference (RNAi) screen of Cullin-based ubiquitin ligases. We found that Plk4 binds to Slimb and is an SCFSlimb target. Both Slimb and Plk4 localize to centrioles, with Plk4 levels highest at mitosis and absent during S phase. Using a Plk4 Slimb-binding mutant and Slimb RNAi, we show that Slimb regulates Plk4 localization to centrioles during interphase, thus regulating centriole number and ensuring the block to centriole reduplication.

scholarly journals Mitotic control of kinetochore-associated dynein and spindle orientation by human Spindly

2009 ◽  
Vol 185 (5) ◽  
pp. 859-874 ◽  
Author(s):  
Ying Wai Chan ◽  
Luca L. Fava ◽  
Andreas Uldschmid ◽  
Michael H.A. Schmitz ◽  
Daniel W. Gerlich ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Critical Role ◽  
Spindle Orientation ◽  
Aurora B ◽  
C Elegans ◽  
Spindle Rotation ◽  
Mitotic Control ◽  
New Protein

Mitotic spindle formation and chromosome segregation depend critically on kinetochore–microtubule (KT–MT) interactions. A new protein, termed Spindly in Drosophila and SPDL-1 in C. elegans, was recently shown to regulate KT localization of dynein, but depletion phenotypes revealed striking differences, suggesting evolutionarily diverse roles of mitotic dynein. By characterizing the function of Spindly in human cells, we identify specific functions for KT dynein. We show that localization of human Spindly (hSpindly) to KTs is controlled by the Rod/Zw10/Zwilch (RZZ) complex and Aurora B. hSpindly depletion results in reduced inter-KT tension, unstable KT fibers, an extensive prometaphase delay, and severe chromosome misalignment. Moreover, depletion of hSpindly induces a striking spindle rotation, which can be rescued by co-depletion of dynein. However, in contrast to Drosophila, hSpindly depletion does not abolish the removal of MAD2 and ZW10 from KTs. Collectively, our data reveal hSpindly-mediated dynein functions and highlight a critical role of KT dynein in spindle orientation.

scholarly journals Regulated targeting of protein phosphatase 1 to the outer kinetochore by KNL1 opposes Aurora B kinase

2010 ◽  
Vol 188 (6) ◽  
pp. 809-820 ◽  
Author(s):  
Dan Liu ◽  
Mathijs Vleugel ◽  
Chelsea B. Backer ◽  
Tetsuya Hori ◽  
Tatsuo Fukagawa ◽  
...  
Keyword(s):  
Chromosome Segregation ◽  
Protein Phosphatase ◽  
Genomic Stability ◽  
Feedback Mechanism ◽  
Protein Phosphatase 1 ◽  
Aurora B ◽  
Aurora B Kinase ◽  
Conserved Motif ◽  
Spindle Microtubules ◽  
Positive Feedback Mechanism

Regulated interactions between kinetochores and spindle microtubules are essential to maintain genomic stability during chromosome segregation. The Aurora B kinase phosphorylates kinetochore substrates to destabilize kinetochore–microtubule interactions and eliminate incorrect attachments. These substrates must be dephosphorylated to stabilize correct attachments, but how opposing kinase and phosphatase activities are coordinated at the kinetochore is unknown. Here, we demonstrate that a conserved motif in the kinetochore protein KNL1 directly interacts with and targets protein phosphatase 1 (PP1) to the outer kinetochore. PP1 recruitment by KNL1 is required to dephosphorylate Aurora B substrates at kinetochores and stabilize microtubule attachments. PP1 levels at kinetochores are regulated and inversely proportional to local Aurora B activity. Indeed, we demonstrate that phosphorylation of KNL1 by Aurora B disrupts the KNL1–PP1 interaction. In total, our results support a positive feedback mechanism by which Aurora B activity at kinetochores not only targets substrates directly, but also prevents localization of the opposing phosphatase.

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