scholarly journals Mitotic phosphorylation: breaking the balance of power by a tactical retreat

2007 ◽  
Vol 403 (2) ◽  
Author(s):  
Randy Y. C. Poon
Keyword(s):  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Phosphorylation Site ◽  
Alternative Mechanism ◽  
Topoisomerase Iiα ◽  
Mitotic Kinases ◽  
Biochemical Journal ◽  
Phosphatase 2A ◽  
Mitotic Phosphorylation ◽  
Constitutively Active

Profound changes in the phosphorylation state of many proteins occur during mitosis. It is well established that many of these mitotic phosphorylations are carried out by archetypal mitotic kinases that are activated only during mitosis, shifting the equilibrium of kinases and phosphatases towards phosphorylation. However, many studies have also detailed the phosphorylation of proteins at mitosis by kinases that are constitutively active throughout the cell cycle. In most cases, it is uncertain how kinases and phosphatases that appear to be constitutively active can induce phosphorylations specifically at mitosis. In this issue of the Biochemical Journal, Escargueil and Larsen provide evidence of an interesting alternative mechanism to attain specific mitotic phosphorylation. A mitosis-specific phosphorylation site in DNA topoisomerase IIα, which is recognized by the MPM-2 antibody, is phosphorylated by protein kinase CK2. The authors found that phosphorylation of this site is suppressed during interphase due to competing dephosphorylation by protein phosphatase 2A. Interestingly, protein phosphatase 2A is excluded from the nucleus during early mitosis, allowing CK2 to phosphorylate topoisomerase IIα. It is possible that similar mechanisms are used to regulate the phosphorylation of other proteins.

scholarly journals Mitosis-specific MPM-2 phosphorylation of DNA topoisomerase IIα is regulated directly by protein phosphatase 2A

2007 ◽  
Vol 403 (2) ◽  
pp. 235-242 ◽  
Author(s):  
Alexandre E. Escargueil ◽  
Annette K. Larsen
Keyword(s):  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Fine Tuning ◽  
Classical Pathway ◽  
Complete Disappearance ◽  
Topoisomerase Iiα ◽  
Mitotic Entry ◽  
Mitotic Kinase ◽  
Short Term Exposure ◽  
Phosphatase 2A

Recent results suggest a role for topoIIα (topoisomerase IIα) in the fine-tuning of mitotic entry. Mitotic entry is accompanied by the formation of specific phosphoepitopes such as MPM-2 (mitotic protein monoclonal 2) that are believed to control mitotic processes. Surprisingly, the MPM-2 kinase of topoIIα was identified as protein kinase CK2, otherwise known as a constitutive interphase kinase. This suggested the existence of alternative pathways for the creation of mitotic phosphoepitopes, different from the classical pathway where the substrate is phosphorylated by a mitotic kinase. In the present paper, we report that topoIIα is co-localized with both CK2 and PP2A (protein phosphatase 2A) during interphase. Simultaneous incubation of purified topoIIα with CK2 and PP2A had minimal influence on the total phosphorylation levels of topoIIα, but resulted in complete disappearance of the MPM-2 phosphoepitope owing to opposite sequence preferences of CK2 and PP2A. Accordingly, short-term exposure of interphase cells to okadaic acid, a selective PP2A inhibitor, was accompanied by the specific appearance of the MPM-2 phosphoepitope on topoIIα. During early mitosis, PP2A was translocated from the nucleus, while CK2 remained in the nucleus until pro-metaphase thus permitting the formation of the MPM-2 phosphoepitope. These results underline the importance of protein phosphatases as an alternative way of creating cell-cycle-specific phosphoepitopes.

Protein Phosphatase 2A Inactivates Bcl2’s Antiapoptotic Function by Dephosphorylation and Up-Regulation of Bcl2-p53 Binding.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1436-1436
Author(s):  
Xingming Deng ◽  
Fengqin Gao ◽  
Tammy Flagg ◽  
W. Stratford May
Keyword(s):  
Cell Death ◽  
Cell Survival ◽  
Okadaic Acid ◽  
Protein Phosphatase ◽  
Apoptotic Cell ◽  
Protein Phosphatase 2A ◽  
Survival Function ◽  
Phosphorylation Site ◽  
Apoptotic Cell Death ◽  
Phosphatase 2A

Abstract DNA damage-induced p53/Bcl2 interaction at the outer mitochondrial membranes results in a Bcl2 conformational change and loss of its antiapoptotic function. Our data now indicate that either treatment of cells with the protein phosphatase 2A (PP2A) inhibitor, okadaic acid (10 nM), or specific disruption of PP2A activity by the expression of SV40 small tumor antigen enhances Bcl2 phosphorylation and suppresses the cisplatin-stimulated Bcl2-p53 interaction in association with prolonged cell survival. By contrast, C2-ceramide, a potent PP2A activator, reduces Bcl2 phosphorylation and increases Bcl2-p53 binding and promotes apoptotic cell death, suggesting that PP2A may function as a physiological regulator of Bcl2 by, at least in part, affecting its association with p53. Overexpression of the PP2A catalytic subunit (PP2A/C) suppresses Bcl2 phosphorylation in association with increased p53-Bcl2 binding and apoptotic cell death. By contrast, specific depletion of PP2A/C by RNA interference enhances Bcl2 phosphorylation, suppresses p53-Bcl2 interaction and prolongs cell survival. Purified PP2A can directly enhance the formation of the p53-Bcl2 complex in vitro in an okadaic acid-sensitive manner, supporting a direct mechanism. Importantly, PP2A directly interacts with Bcl2 at its BH4 domain which may function as the PP2A ‘docking site’ to potentially ‘bridge’ PP2A to the flexible loop domain which contains the physiological serine 70 phosphorylation site. Thus, PP2A may provide a double whammy to Bcl2’s survival function by both dephosphorylating and enhancing p53-Bcl2 binding. Therapeutically stimulating Bcl2 dephosphorylation and/or increasing Bcl2/p53 binding by activating PP2A may represent an efficient and novel antineoplastic approach.

scholarly journals Protein phosphatase 2A inactivates Bcl2's antiapoptotic function by dephosphorylation and up-regulation of Bcl2-p53 binding

Blood ◽  
2009 ◽  
Vol 113 (2) ◽  
pp. 422-428 ◽  
Author(s):  
Xingming Deng ◽  
Fengqin Gao ◽  
W. Stratford May
Keyword(s):  
Conformational Change ◽  
Protein Phosphatase ◽  
Apoptotic Cell ◽  
Protein Phosphatase 2A ◽  
Survival Function ◽  
Phosphorylation Site ◽  
Hematologic Malignancies ◽  
T Antigen ◽  
Phosphatase 2A

Abstract Bcl2 is associated with chemoresistance and poor prognosis in patients with various hematologic malignancies. DNA damage-induced p53/Bcl2 interaction at the outer mitochondrial membrane results in a Bcl2 conformational change with loss of its antiapoptotic activity in interleukin-3–dependent myeloid H7 cells. Here we find that specific disruption of protein phosphatase 2A (PP2A) activity by either expression of small t antigen or depletion of PP2A/C by RNA interference enhances Bcl2 phosphorylation and suppresses cisplatin-stimulated p53/Bcl2 binding in association with prolonged cell survival. By contrast, treatment of cells with C2-ceramide (a potent PP2A activator) or expression of the PP2A catalytic subunit (PP2A/C) inhibits Bcl2 phosphorylation, leading to increased p53/Bcl2 binding and apoptotic cell death. Mechanistically, PP2A-mediated dephosphorylation of Bcl2 in vitro promotes its direct interaction with p53 as well as a conformational change in Bcl2. PP2A directly interacts with the BH4 domain of Bcl2 as a docking site to potentially “bridge” PP2A to Bcl2's flexible loop domain containing the target serine 70 phosphorylation site. Thus, PP2A may provide a dual inhibitory effect on Bcl2's survival function by both dephosphorylating Bcl2 and enhancing p53-Bcl2 binding. Activating PP2A to dephosphorylate Bcl2 and/or increase Bcl2/p53 binding may represent an efficient and novel approach for treatment of hematologic malignancies.

scholarly journals Cytokine Activation of p38 Mitogen-Activated Protein Kinase and Apoptosis Is Opposed by alpha-4 Targeting of Protein Phosphatase 2A for Site-Specific Dephosphorylation of MEK3

2007 ◽  
Vol 27 (12) ◽  
pp. 4217-4227 ◽  
Author(s):  
Todd D. Prickett ◽  
David L. Brautigan
Keyword(s):  
Protein Kinase ◽  
P38 Mapk ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Phosphorylation Site ◽  
Mitogen Activated Protein Kinase ◽  
Mapk Activation ◽  
Tnf Α ◽  
Mitogen Activated Protein ◽  
Phosphatase 2A

ABSTRACT alpha-4 is an essential gene and is a dominant antiapoptotic factor in various tissues that is a regulatory subunit for type 2A protein phosphatases. A multiplexed phosphorylation site screen revealed that knockdown of alpha-4 by small interfering RNA (siRNA) increased p38 mitogen-activated protein kinase (MAPK) and c-Jun phosphorylation without changes in JNK or ERK. FLAG-alpha-4 coprecipitated hemagglutinin-MEK3 plus endogenous protein phosphatase 2A (PP2A) and selectively enhanced dephosphorylation of Thr193, but not Ser189, in the activation loop of MEK3. Overexpression of alpha-4 suppressed p38 MAPK activation in response to tumor necrosis factor alpha (TNF-α). The alpha-4 dominant-negative domain (DND) (residues 220 to 340) associated with MEK3, but not PP2A, and its overexpression sensitized cells to activation of p38 MAPK by TNF-α and interleukin-1β, but not by ansiomycin or sorbitol. The response was diminished by nocodazole or by siRNA knockdown of the Opitz syndrome protein Mid1 that binds alpha-4 to microtubules. Interference by alpha-4 DND or alpha-4 siRNA increased caspase 3/7 activation in response to TNF-α. Growth of transformed cells in soft agar was enhanced by alpha-4 and suppressed by alpha-4 DND. The results show that alpha-4 targets PP2A activity to MEK3 to suppress p38 MAPK activation by cytokines, thereby inhibiting apoptosis and anoikis.

scholarly journals Reduction of protein phosphatase 2A (PP2A) complexity reveals cellular functions and dephosphorylation motifs of the PP2A/B′δ holoenzyme

2020 ◽  
Vol 295 (17) ◽  
pp. 5654-5668 ◽  
Author(s):  
Chian Ju Jong ◽  
Ronald A. Merrill ◽  
Emily M. Wilkerson ◽  
Laura E. Herring ◽  
Lee M. Graves ◽  
...  
Keyword(s):  
Substrate Specificity ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Second Messengers ◽  
Phosphorylation Site ◽  
Regulatory Subunit ◽  
Regulatory Subunits ◽  
Endogenous Expression ◽  
Phosphatase 2A ◽  
B Subunits

Protein phosphatase 2A (PP2A) is a large enzyme family responsible for most cellular Ser/Thr dephosphorylation events. PP2A substrate specificity, localization, and regulation by second messengers rely on more than a dozen regulatory subunits (including B/R2, B′/R5, and B″/R3), which form the PP2A heterotrimeric holoenzyme by associating with a dimer comprising scaffolding (A) and catalytic (C) subunits. Because of partial redundancy and high endogenous expression of PP2A holoenzymes, traditional approaches of overexpressing, knocking down, or knocking out PP2A regulatory subunits have yielded only limited insights into their biological roles and substrates. To this end, here we sought to reduce the complexity of cellular PP2A holoenzymes. We used tetracycline-inducible expression of pairs of scaffolding and regulatory subunits with complementary charge-reversal substitutions in their interaction interfaces. For each of the three regulatory subunit families, we engineered A/B charge–swap variants that could bind to one another, but not to endogenous A and B subunits. Because endogenous Aα was targeted by a co-induced shRNA, endogenous B subunits were rapidly degraded, resulting in expression of predominantly a single PP2A heterotrimer composed of the A/B charge–swap pair and the endogenous catalytic subunit. Using B′δ/PPP2R5D, we show that PP2A complexity reduction, but not PP2A overexpression, reveals a role of this holoenzyme in suppression of extracellular signal–regulated kinase signaling and protein kinase A substrate dephosphorylation. When combined with global phosphoproteomics, the PP2A/B′δ reduction approach identified consensus dephosphorylation motifs in its substrates and suggested that residues surrounding the phosphorylation site play roles in PP2A substrate specificity.

scholarly journals Activation of hepatic acetyl-CoA carboxylase by glutamate and Mg2+ is mediated by protein phosphatase-2A

1996 ◽  
Vol 316 (1) ◽  
pp. 217-224 ◽  
Author(s):  
Vinciane GAUSSIN ◽  
Louis HUE ◽  
Willy STALMANS ◽  
Mathieu BOLLEN
Keyword(s):  
Phosphatase Activity ◽  
Protein Phosphatase ◽  
Muscle Protein ◽  
Protein Phosphatase 2A ◽  
Phosphorylation Site ◽  
Dicarboxylic Acids ◽  
Acetyl Coa Carboxylase ◽  
Acetyl Coa ◽  
Phosphatase 2A ◽  
A Subunit

The activation of hepatic acetyl-CoA carboxylase by Na+-co-transported amino acids such as glutamine has been attributed mainly to the stimulation of its dephosphorylation by accumulating dicarboxylic acids, e.g. glutamate. We report here on a hepatic species of protein phosphatase-2A that activates acetyl-CoA carboxylase in the presence of physiological concentrations of glutamate or Mg2+ and, under these conditions, accounts for virtually all the hepatic acetyl-CoA carboxylase phosphatase activity. Glutamate also stimulated the dephosphorylation of a synthetic pentadecapeptide encompassing the Ser-79 phosphorylation site of rat acetyl-CoA carboxylase, but did not affect the dephosphorylation of other substrates such as phosphorylase. Conversely, protamine, which stimulated the dephosphorylation of phosphorylase, inhibited the activation of acetyl-CoA carboxylase. A comparison with various species of muscle protein phosphatase-2A showed that the stimulatory effects of glutamate and Mg2+ on the acetyl-CoA carboxylase phosphatase activity are largely mediated by the regulatory A subunit. Glutamate and Mg2+ emerge from our study as novel regulators of protein phosphatase-2A when acting on acetyl-CoA carboxylase.

scholarly journals AKT Regulates Mitotic Progression of Mammalian Cells by Phosphorylating MASTL, Leading to Protein Phosphatase 2A Inactivation

2020 ◽  
Vol 40 (10) ◽  
Author(s):  
Irfana Reshi ◽  
Misbah Un Nisa ◽  
Umer Farooq ◽  
Syed Qaaifah Gillani ◽  
Sameer Ahmed Bhat ◽  
...  
Keyword(s):  
Protein Phosphatase ◽  
Mammalian Cells ◽  
Protein Phosphatase 2A ◽  
Critical Role ◽  
Mitotic Progression ◽  
Serine Threonine Kinase ◽  
Threonine Kinase ◽  
Mitotic Kinases ◽  
Colorectal Cell ◽  
Phosphatase 2A

ABSTRACT Microtubule-associated serine/threonine kinase like (MASTL), also known as Greatwall (Gwl) kinase, has an important role in the regulation of mitosis. By inhibiting protein phosphatase 2A (PP2A), it plays a crucial role in activating one of the most important mitotic kinases, known as cyclin-dependent kinase 1 (CDK1). MASTL has been seen to be upregulated in various types of cancers and is also involved in tumor recurrence. It is activated by CDK1 through phosphorylations in the activation/T-loop, but the complete mechanism of its activation is still unclear. Here, we report that AKT phosphorylates MASTL at residue T299, which plays a critical role in its activation. Our results suggest that AKT increases CDK1-mediated phosphorylation and hence the activity of MASTL, which, in turn, promotes mitotic progression through PP2A inhibition. We also show that the oncogenic potential of AKT is augmented by MASTL activation, since AKT-mediated proliferation in colorectal cell lines can be attenuated by inhibiting and/or silencing MASTL. In brief, we report that AKT plays an important role in the progression of mitosis in mammalian cells and that it does so through the phosphorylation and activation of MASTL.

Sign in / Sign up

Export Citation Format

Share Document