Bioengineered protein phosphatase 2A: update on need.
Ontology highlight
ABSTRACT:
SUBMITTER: Rubiolo JA
PROVIDER: S-EPMC3609624 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:RATIONALE:Voltage-gated Na+ channel ( INa) function is critical for normal cardiac excitability. However, the Na+ channel late component ( INa,L) is directly associated with potentially fatal forms of congenital and acquired human arrhythmia. CaMKII (Ca2+/calmodulin-dependent kinase II) enhances INa,L in response to increased adrenergic tone. However, the pathways that negatively regulate the CaMKII/Nav1.5 axis are unknown and essential for the design of new therapies to regulate the pathogenic INa,L. OBJECTIVE:To define phosphatase pathways that regulate INa,L in vivo. METHODS AND RESULTS:A mouse model lacking a key regulatory subunit (B56?) of the PP (protein phosphatase) 2A holoenzyme displayed aberrant action potentials after adrenergic stimulation. Unbiased computational modeling of B56? KO (knockout) mouse myocyte action potentials revealed an unexpected role of PP2A in INa,L regulation that was confirmed by direct INa,L recordings from B56? KO myocytes. Further, B56? KO myocytes display decreased sensitivity to isoproterenol-induced induction of arrhythmogenic INa,L, and reduced CaMKII-dependent phosphorylation of Nav1.5. At the molecular level, PP2A/B56? complex was found to localize and coimmunoprecipitate with the primary cardiac Nav channel, Nav1.5. CONCLUSIONS:PP2A regulates Nav1.5 activity in mouse cardiomyocytes. This regulation is critical for pathogenic Nav1.5 late current and requires PP2A-B56?. Our study supports B56? as a novel target for the treatment of arrhythmia.
| S-EPMC6395500 | biostudies-literature
Project description:Protein phosphatase 2A (PP2A) is a conserved essential enzyme that is implicated as a tumor suppressor based on its central role in phosphorylation-dependent signaling pathways. Protein phosphatase methyl esterase (PME-1) catalyzes specifically the demethylation of the C-terminal Leu309 residue of PP2A catalytic subunit (PP2Ac). It has been shown that PME-1 affects the activity of PP2A by demethylating PP2Ac, but also by directly binding to the phosphatase active site, suggesting loss of PME-1 in cells would enhance PP2A activity. However, here we show that PME-1 knockout mouse embryonic fibroblasts (MEFs) exhibit lower PP2A activity than wild type MEFs. Loss of PME-1 enhanced poly-ubiquitination of PP2Ac and shortened the half-life of PP2Ac protein resulting in reduced PP2Ac levels. Chemical inhibition of PME-1 and rescue experiments with wild type and mutated PME-1 revealed methyl-esterase activity was necessary to maintain PP2Ac protein levels. Our data demonstrate that PME-1 methyl-esterase activity protects PP2Ac from ubiquitin/proteasome degradation.
| S-EPMC4683032 | biostudies-literature
Project description:Protein phosphatase 2A (PP2A) is indispensable in development, and deficits of PP2A and deterioration of neuronal axons have been observed in several neurodegenerative disorders, but the direct link between PP2A and the neuronal axon development is still missing. Here, we show that PP2A is essential for axon development in transfected rat brain and the dissociated hippocampal neurons. Upregulation of PP2A catalytic subunit (PP2Ac) not only promotes formation and elongation of the functional axons but also rescues axon retardation induced by PP2A inhibition. PP2A can dephosphorylate collapsin response mediator protein-2 (CRMP2) that implements the axon polarization, whereas constitutive expression of phosphomimic-CRMP2 abrogates the effect of PP2A upregulation. We also demonstrate that PP2Ac is enriched in the distal axon of the hippocampal neurons. Our results reveal a mechanistic link between PP2A and axonogenesis/axonopathy, suggesting that upregulation of PP2A may be a promising therapeutic for some neurodegenerative disorders.
| S-EPMC6632239 | biostudies-literature
Project description:The Wnt/?-catenin pathway causes accumulation of ?-catenin in the cytoplasm and its subsequent translocation into the nucleus to initiate the transcription of the target genes. Without Wnt stimulation, ?-catenin forms a complex with axin (axis inhibitor), adenomatous polyposis coli (APC), casein kinase 1? (CK1?), and glycogen synthase kinase 3? (GSK3?) and undergoes phosphorylation-dependent ubiquitination. Phosphatases, such as protein phosphatase 2A (PP2A), interestingly, also are components of this degradation complex; therefore, a balance must be reached between phosphorylation and dephosphorylation. How this balance is regulated is largely unknown. Here we show that a heat shock protein, HSP105, is a previously unidentified component of the ?-catenin degradation complex. HSP105 is required for Wnt signaling, since depletion of HSP105 compromises ?-catenin accumulation and target gene transcription upon Wnt stimulation. Mechanistically, HSP105 depletion disrupts the integration of PP2A into the ?-catenin degradation complex, favoring the hyperphosphorylation and degradation of ?-catenin. HSP105 is overexpressed in many types of tumors, correlating with increased nuclear ?-catenin protein levels and Wnt target gene upregulation. Furthermore, overexpression of HSP105 is a prognostic biomarker that correlates with poor overall survival in breast cancer patients as well as melanoma patients participating in the BRIM2 clinical study.
| S-EPMC4372692 | biostudies-literature
Project description:The catalytic subunit of protein phosphatase 2A (PP2Ac) is stabilized in a latent form by ?4, a regulatory protein essential for cell survival and biogenesis of all PP2A complexes. Here we report the structure of ?4 bound to the N-terminal fragment of PP2Ac. This structure suggests that ?4 binding to the full-length PP2Ac requires local unfolding near the active site, which perturbs the scaffold subunit binding site at the opposite surface via allosteric relay. These changes stabilize an inactive conformation of PP2Ac and convert oligomeric PP2A complexes to the ?4 complex upon perturbation of the active site. The PP2Ac-?4 interface is essential for cell survival and sterically hinders a PP2A ubiquitination site, important for the stability of cellular PP2Ac. Our results show that ?4 is a scavenger chaperone that binds to and stabilizes partially folded PP2Ac for stable latency, and reveal a mechanism by which ?4 regulates cell survival, and biogenesis and surveillance of PP2A holoenzymes.
| S-EPMC3644067 | biostudies-literature
Project description:Mitotic entry and progression require the activation of several mitotic kinases and the proper regulation and localization of several phosphatases. The activity and localization of each of these enzymes is tightly controlled through a series of specific activators, inhibitors and regulatory subunits. Two proteins, Ensa and Arpp-19, were recently identified as specific inhibitors of PP2A-B55 and are critical for allowing full activity of Cdk1/cyclin B and entry into mitosis. Here we show that Bod1, a protein required for proper chromosome alignment at mitosis, shares sequence similarity with Ensa and Arpp-19 and specifically inhibits the kinetochore-associated PP2A-B56 holoenzyme. PP2A-B56 regulates the stability of kinetochore-microtubule attachments by dephosphorylating several kinetochore proteins. Loss of Bod1 changes the balance of phosphorylation at kinetochores, causing defects in kinetochore function. Bod1, Ensa and Arpp-19 define a family of specific PP2A inhibitors that regulate specific PP2A holoenzymes at distinct locations and points in the cell cycle.
| S-EPMC3826647 | biostudies-literature
Project description:Protein phosphatase 2A- (PP2A-) catalyzed dephosphorylation of target substrate proteins is widespread and critical for cellular function. PP2A is predominantly found as a heterotrimeric complex of a catalytic subunit (C), a scaffolding subunit (A), and one member of 4 families of regulatory subunits (B). Substrate specificity of the holoenzyme complex is determined by the subcellular locale the complex is confined to, selective incorporation of the B subunit, interactions with endogenous inhibitory proteins, and specific intermolecular interactions between PP2A and target substrates. Here, we discuss recent studies that have advanced our understanding of the molecular determinants for PP2A substrate specificity.
| S-EPMC3132988 | biostudies-literature
Project description:Protein phosphatase 2A (PP2A) is a serine/threonine-selective holoenzyme composed of a catalytic, scaffolding, and regulatory subunit. In the heart, PP2A activity is requisite for cardiac excitation-contraction coupling and central in adrenergic signaling. We found that mice deficient in the PP2A regulatory subunit B56? (1 of 13 regulatory subunits) had altered PP2A signaling in the heart that was associated with changes in cardiac physiology, suggesting that the B56? regulatory subunit had an autoinhibitory role that suppressed excess PP2A activity. The increase in PP2A activity in the mice with reduced B56? expression resulted in slower heart rates and increased heart rate variability, conduction defects, and increased sensitivity of heart rate to parasympathetic agonists. Increased PP2A activity in B56?(+/-) myocytes resulted in reduced Ca(2+) waves and sparks, which was associated with decreased phosphorylation (and thus decreased activation) of the ryanodine receptor RyR2, an ion channel on intracellular membranes that is involved in Ca(2+) regulation in cardiomyocytes. In line with an autoinhibitory role for B56?, in vivo expression of B56? in the absence of altered abundance of other PP2A subunits decreased basal phosphatase activity. Consequently, in vivo expression of B56? suppressed parasympathetic regulation of heart rate and increased RyR2 phosphorylation in cardiomyocytes. These data show that an integral component of the PP2A holoenzyme has an important inhibitory role in controlling PP2A enzyme activity in the heart.
| S-EPMC4680974 | biostudies-literature
Project description:Protein phosphatase 2A (PP2A) represses many oncogenic signaling pathways and is an important tumor suppressor. PP2A comprises three distinct subunits and forms through a highly regulated biogenesis process, with the scaffolding A subunit existing as two highly related isoforms, A? and A?. PP2A's tumor-suppressive functions have been intensely studied, and PP2A inactivation has been shown to be a prerequisite for tumor formation. Interestingly, although partial loss of the A? isoform is growth promoting, complete A? loss has no transformative properties. Additionally, in cancer patients, A? is found to be inactivated in a haploinsufficient manner. Using both cellular and in vivo systems, colorectal and endometrial cancer cell lines, and biochemical and cellular assays, here we examined why the complete loss of A? does not promote tumorigenesis. CRISPR/Cas9-mediated homozygous A? deletion resulted in decreased colony formation and tumor growth across multiple cell lines. Protein expression analysis of PP2A family members revealed that the A? deletion markedly up-regulates A? protein expression by increasing A? protein stability. A? knockdown in control and A? knockout cell lines indicated that A? is necessary for cell survival in the A? knockout cells. In the setting of A? deficiency, co-immunoprecipitation analysis revealed increased binding of specific PP2A regulatory subunits to A?, and knockdown of these regulatory subunits restored colony-forming ability. Taken together, our results uncover a mechanism by which PP2A A? regulates A? protein stability and activity and suggests why homozygous loss of A? is rarely seen in cancer patients.
| S-EPMC6463732 | biostudies-literature
Project description:Background: While heart transplantation is the standard treatment for heart failure, both acute and chronic transplant rejection frequently occur. Since the modulation of protein phosphatase PP2A activity is critical for tissue and organ homeostasis under physiological and pathophysiological conditions, PP2A may also affect the ability to tolerate transplanted organs. Here we demonstrate that administration of a novel class of small molecule activators of PP2A (SMAPs) prolonged cardiac allograft survival in a mouse heterotopic heart transplantation model. Mechanistically, SMAPs effectively suppressed the inflammatory immune response while increasing Treg population in the allografts, findings corroborated by functional analysis of RNAseq data derived from Tregs of treated splenic tissue. Importantly, SMAPs further prolonged CTLA4-Ig (an immunosuppressive agent utilized in organ transplantation)-induced cardiac rejection tolerance and extended allograft survival. SMAPs also strongly mitigated cardiac allograft vasculopathy as evidenced by a marked reduction of neointimal hyperplasia and smooth muscle cell proliferation. Mechanistic studies implicate SMAPs elicited suppression of MEK/ERK pathways as a unifying mechanism for the aforementioned effects in Tregs and SMCs. These findings highlight the potential of PP2A activation in improving alloengraftment in heart transplantation and add knowledge to the phosphatase driven regulation of the immune system in the context of organ transplantation.
2023-07-20 | GSE236206 | GEO