Role Of Protein Phosphatase 2A Research Articles

The PP2A inhibitor LB-100 mitigates lupus nephritis by suppressing tertiary lymphoid structure formation

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multi-organ involvement and autoantibody production. Patients with SLE face a substantial risk of developing lupus nephritis (LN), which imposes a substantial burden on both patients and their families. Protein phosphatase 2A (PP2A) is a widely distributed serine/threonine phosphatase that participates in regulating multiple signaling pathways. Inhibition of PP2A has been implicated in the treatment of various diseases. LB-100, a small molecule inhibitor of PP2A, has demonstrated anti-tumor therapeutic effects and high safety profile in preclinical experiments. However, the role of PP2A and its inhibitor has been insufficiently studied in LN. In this study, we assessed the potential effects of LB-100 in both MRL/lpr mice and R848-induced BALB/c mice. Our findings indicated that LB-100 administration led to reduced spleen enlargement, decreased deposition of immune complexes, ameliorated renal damage, and improved kidney function in both spontaneous and R848-induced lupus mouse models. Importantly, we observed the formation of tertiary lymphoid structures (TLSs) in the kidneys of two distinct lupus mouse models. The levels of signature genes of TLS were elevated in the kidneys of lupus mice, whereas LB-100 mitigated chemokine production and inhibited TLS formation. In addition, we confirmed that inhibition or knockdown of PP2A reduced the production of T cell-related chemokines by renal tubular epithelial cells (RTEC). In summary, our study highlighted the renal protective potential of the PP2A inhibitor LB-100 in two distinct lupus mouse models, suggesting its potential as a novel strategy for treating LN and other autoimmune diseases.

Abstract 4717: Small molecule modulation of PP2A selectively induces oncogenic cytotoxicity through chronic and irreversible integrated stress response

Abstract High-grade serous cancer (HGSC) is the most lethal gynecological malignancy and accounts for approximately 70% of all ovarian carcinomas. Despite recent advancements in drug discovery and a deeper understanding of the genetic mechanisms that drive HGSC oncogenesis, the mortality rate has remained stagnant over the past three decades, with a 5-year survival rate below 30%. Due to the prevalence of homologous recombination defects (HRD) in over 50% of HGSC tumors, the clinical management of patients harboring these genetic vulnerabilities has vastly relied on PARP inhibitors (PARPi). Nonetheless, about 80% of these patients ultimately relapse with refractory resistant and more aggressive disease, having no effective therapeutic alternatives currently available. Therefore, there is an urgent need for novel targeted therapies to be tailored towards the treatment of HGSC. Recently, we unveiled that 95% of HGSC tumors present with a widespread loss-of-heterozygosity in genes essential to form the tumor suppressor Protein Phosphatase 2A (PP2A) heterotrimer, second only to TP53. These deleterious alterations have been established to inhibit PP2A function, preventing it from counteracting oncogenic signatures that drive tumorigenesis. Our studies revealed that a Small Molecule Activator of PP2A (SMAP) synergizes with PARPi to induce synthetic lethality in HGSC cells while displaying favorable tolerability profiles in normal tissues. Mechanistically, SMAP activates distinct translational responses and stress signatures depending on the cellular context, driving selective oncogenic cytotoxicity through a chronic and irreversible integrated stress response (ISR), independent of PERK activation. In malignant contexts, SMAP-mediated activation of PP2A specifically drives the dephosphorylation of TFE3 to transcriptionally activate ATF4 and CHOP. Consequently, as cancer cells are incapable of activating adaptive homeostatic recovery mechanisms in response to SMAP, chronic ISR is induced, ultimately leading to cell death. Conversely, non-transformed cells leverage their intrinsic ISR plasticity to adapt, thereby restoring basal functions that allow cell survival under SMAP-mediated stress conditions. Collectively, our data highlights a new role of PP2A in HGSC and further underscore SMAP's selective cytotoxicity in cancer cells, independent of oncogenic genetic vulnerabilities or HRD profiles, by leveraging ISR plasticity and intrinsic adaptive homeostatic mechanisms. Thus, this class of PP2A modulators holds tremendous promise for broader therapeutic applications across diverse patient populations and tumor histological subtypes beyond HGSC, while mitigating standard-of-care therapy-associated toxicity. Citation Format: Rita A. Avelar, Riya Gupta, Grace Carvette, Felipe da Veiga Leprevost, Jose Colina, Jessica Teitel, Goutham Narla, Analisa DiFeo. Small molecule modulation of PP2A selectively induces oncogenic cytotoxicity through chronic and irreversible integrated stress response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4717.

The role of protein phosphatase 2A (PP2A) in the unfolded protein response (UPR) of plants

Protein phosphatase 2A (PP2A) is a key regulator of plant growth and development, but its role in the endoplasmic reticulum (ER) stress response remains elusive. In this study, we investigated the function of PP2A under ER stress using loss-of-function mutants of ROOTS CURL of NAPHTHYLPHTHALAMIC ACID1 (RCN1), a regulatory A1 subunit isoform of Arabidopsis PP2A. RCN1 mutants (rcn1-1 and rcn1-2) exhibited reduced sensitivity to tunicamycin (TM), an inhibitor of N-linked glycosylation and inducer of unfolded protein response (UPR) gene expression, resulting in less severe effects compared to wild-type plants (Ws-2 and Col-0). TM negatively impacted PP2A activity in Col-0 plants but did not significantly affect rcn1-2 plants. Additionally, TM treatment did not influence the transcription levels of the PP2AA1(RCN1), 2, and 3 genes in Col-0 plants. Cantharidin, a PP2A inhibitor, exacerbated growth defects in rcn1 plants and alleviated TM-induced growth inhibition in Ws-2 and Col-0 plants. Furthermore, cantharidin treatment mitigated TM hypersensitivity in ire1a&b and bzip28&60 mutants. These findings suggest that PP2A activity is essential for an efficient UPR in Arabidopsis.

MoRts1, a regulatory subunit of PP2A, is required for fungal development and pathogenicity of Magnaporthe oryzae

Protein phosphatase 2 A (PP2A) is a major heterotrimeric serine/threonine protein phosphatase comprised of three subunits, including structural subunits (A), regulatory subunits (B), and catalytic subunits (C). PP2A has been widely shown to involve in a series of cell signal transduction processes such as cell metabolism, cell cycle regulation, DNA replication, gene transcription and protein translation in yeast and mammalian. However, the roles of PP2A in pathogenic fungi Magnaporthe oryzae still remain unclear. We here found that MoRts1, a gene encoding B regulatory subunit of PP2A homologous to Saccharomyces cerevisiae Rts1, showed up-regulated transcription during conidia and initially infectious stage. Subcellular localization revealed that MoRts1-eGFP was localized to the cytoplasm and septum. Targeted disruption of MoRts1 leads to a reduction of mycelial growth and sporulation, as well as the defects of hydrophobicity, melanin pigmentation and cell wall integrity (CWI). The MoRts1 mutants were less pathogenic to the host plants, compared to the Ku80 strain, and the transcriptional levels of several pathogenicity-related Rho GTPase genes, including MoCdc42, MoRho2, MoRho3, MoRho4, MoRhoX and MoRac1, were significantly decreased in the MoRts1 mutants. Besides, two splicing variants of MoRts1 with unique functions of regulating the growth and pathogenicity were identified, and the B56 domain is vital for determining the sporulation and pathogenicity of M. oryzae. Furthermore, MoRts1 was identified to interact with PP2A catalytic subunit MoPPG1 in vivo in M. oryzae. In summary, our results showed that MoRts1 is an important regulator contributing to the fungal development, and pathogenicity of M. oryzae.

The Pivotal Role of Protein Phosphatase 2A (PP2A) in Brain Tumors

Protein phosphatase 2A (PP2A) is a highly complex heterotrimeric Ser/Thr phosphatase that regulates many cellular processes. PP2A is dysregulated in several human diseases, including oncological pathology; interestingly, PP2A appears to be essential for controlling cell growth and may be involved in cancer development. The role of PP2A as a tumor suppressor has been extensively studied and reviewed. To leverage the potential clinical utility of combination PP2A inhibition and radiotherapy treatment, it is vital that novel highly specific PP2A inhibitors be developed. In this review, the existing literature on the role of PP2A in brain tumors, especially in gliomas and glioblastoma (GBM), was analyzed. Interestingly, the review focused on the role of PP2A inhibitors, focusing on CIP2A inhibition, as CIP2A participated in tumor cell growth by stimulating cell-renewal survival, cellular proliferation, evasion of senescence and inhibition of apoptosis. This review suggested CIP2A inhibition as a promising strategy in oncology target therapy.

The protein phosphatase 2A holoenzyme is a key regulator of starch metabolism and bradyzoite differentiation in Toxoplasma gondii

Phenotypic switching between tachyzoite and bradyzoite is the fundamental mechanism underpinning the pathogenicity and adaptability of the protozoan parasite Toxoplasma gondii. Although accumulation of cytoplasmic starch granules is a hallmark of the quiescent bradyzoite stage, the regulatory factors and mechanisms contributing to amylopectin storage in bradyzoites are incompletely known. Here, we show that T. gondii protein phosphatase 2A (PP2A) holoenzyme is composed of a catalytic subunit PP2A-C, a scaffold subunit PP2A-A and a regulatory subunit PP2A-B. Disruption of any of these subunits increased starch accumulation and blocked the tachyzoite-to-bradyzoite differentiation. PP2A contributes to the regulation of amylopectin metabolism via dephosphorylation of calcium-dependent protein kinase 2 at S679. Phosphoproteomics identified several putative PP2A holoenzyme substrates that are involved in bradyzoite differentiation. Our findings provide novel insight into the role of PP2A as a key regulator of starch metabolism and bradyzoite differentiation in T. gondii.

Phosphoproteomic profiling of isolated murine cardiomyocytes reveals a role for protein phosphatase 2A (PP2A) regulatory subunit B55α as a regulator of β-adrenergic receptor signaling in the heart

Phosphoproteomic profiling of isolated murine cardiomyocytes reveals a role for protein phosphatase 2A (PP2A) regulatory subunit B55α as a regulator of β-adrenergic receptor signaling in the heart

Abstract B013: PP2A regulated macropinocytosis and therapeutic vulnerabilities in pancreatic cancer

Abstract Pancreatic Ductal Adenocarcinoma (PDAC) is the fourth leading cause of cancer related deaths in the US, with the lowest five-year survival rate of all cancers. Nutrients in the PDAC microenvironment are commonly depleted, with the vital amino acid glutamine among the most deficient metabolites. In an attempt to circumvent this deprivation, PDAC cells initiate KRAS dependent macropinocytosis, an actin-driven nutrient scavenging pathway. Macropinocytosis allows cells to replenish the nutrients required for proliferation and survival. As glutamine is essential for PDAC cell survival, therapeutic inhibition of macropinocytosis represents a novel strategy to suppress nutrient acquisition and drive cell death in PDAC. Protein phosphatase 2A (PP2A) is a heterotrimeric Serine/Threonine phosphatase known to inhibit downstream targets of the KRAS signaling cascade and is implicated in macropinocytosis regulation. We demonstrate that pharmacological activation of PDAC cell lines with the small molecule activator of PP2A, DT061, leads to significant accumulation of intracellular vesicles. Therefore, we hypothesize that PP2A activation results in methuosis, a non-apoptotic cell death process driven by aberrant macropinocytosis. Using high molecular weight TMR-Dextran, we confirmed that these vesicles are macropinosomes. PP2A activation prevented the colocalization of macropinosomes with lysosomes, likely limiting the nutrients supply to PDAC cells. RNA sequencing analysis showed that glutamine deprivation genes are significantly enriched with acute activation of PP2A, and the oxidative phosphorylation pathway was observed to be significantly inhibited. Further, combination of DT061 with Glutamine transport inhibitor V-9302 significantly inhibits the survival of PDAC cells. Together, these findings indicate that activation of PP2A in late stage PDAC promotes aberrant macropinocytosis and establishes a novel role of PP2A in nutrient scavenging and cell death. These pathways can be further exploited to identify potential therapeutics in PDAC. Citation Format: Garima Baral, Claire M. Pfeffer, Brittany L. Allen-Petersen, Indiraa Doraivel. PP2A regulated macropinocytosis and therapeutic vulnerabilities in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B013.

Abstract B078: PP2A activation drives alternative EGFR activation in PDAC

Abstract Pancreatic ductal adenocarcinoma (PDAC) stands to become the 2nd most deadly cancer by 2030. Over 90% of PDAC patients have oncogenic KRAS mutations with the most prevalent being KRASG12D which have proven difficult to therapeutically target. Several studies have implicated EGFR signaling as critical for PDAC tumorigenesis in KRAS mutant tumors. Consistent with these findings, the first FDA-approved targeted therapeutic for PDAC was the EGFR inhibitor, Erlotinib. However, single agent use of Erlotinib has shown minimal efficacy in the clinic suggesting that this signaling is complex and needs further interrogation. Studies have shown the serine/threonine phosphatase, Protein Phosphatase 2A (PP2A), negatively regulates several downstream targets of EGFR and KRAS. Our previous studies using small molecule activators of PP2A demonstrate a heterogeneous response to PP2A activation, with some PDAC cell lines downregulating oncogenic signals and others maintaining the oncogenic signaling. Using pharmacological activation of PP2A, as well as overexpression and knockdown studies, we have identified a novel signaling cascade in which PP2A activation leads to increased expression and secretion of EGFR ligands and EGFR activation in a subset of PDAC cell lines. Given this unique feedback mechanism, we combined EGFR inhibitors with PP2A activation and found that the combination killed more cells than either agent alone. Together, our studies identify a novel role for PP2A in regulating EGFR signaling and support the combined use of EGFR inhibitors and PP2A activators to increase efficacy of both agents. Citation Format: Claire M. Pfeffer, Sydney J. Clifford, Elizabeth G. Hoffman, Gagan K. Mall, Garima Baral, Brittany L. Allen-Petersen. PP2A activation drives alternative EGFR activation in PDAC [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B078.

Targeting PP2A for cancer therapeutic modulation.

Protein phosphatases play essential roles as negative regulators of kinases and signaling cascades involved in cytoskeletal organization. Protein phosphatase 2A (PP2A) is highly conserved and is the predominant serine/threonine phosphatase in the nervous system, constituting more than 70% of all neuronal phosphatases. PP2A is involved in diverse regulatory functions, including cell cycle progression, apoptosis, and DNA repair. Although PP2A has historically been identified as a tumor suppressor, inhibition of PP2A has paradoxically demonstrated potential as a therapeutic target for various cancers. LB100, a water-soluble, small-molecule competitive inhibitor of PP2A, has shown particular promise as a chemo- and radio-sensitizing agent. Preclinical success has led to a profusion of clinical trials on LB100 adjuvant therapies, including a phase I trial in extensive-stage small-cell lung cancer, a phase I/II trial in myelodysplastic syndrome, a phase II trial in recurrent glioblastoma, and a completed phase I trial assessing the safety of LB100 and docetaxel in various relapsed solid tumors. Herein, we review the development of LB100, the role of PP2A in cancer biology, and recent advances in targeting PP2A inhibition in immunotherapy.

The role of PP2A /NLRP3 signaling pathway in ambient particulate matter 2.5 induced lung injury

Ambient particulate matter 2.5 (PM2.5) exposure has been linked to pulmonary fibrosis. However, the key signaling pathways remained unclear. In the present study, we applied a mouse model with myeloid-specific deletion of Ppp2r1a gene (encoding protein phosphatase 2 A (PP2A) A subunit) to identify the key signaling pathways involved in PM2.5-induced pulmonary fibrosis. PP2A Aα−/− homozygote mice and matched wild-type (WT) littermates were exposed to filtered air (FA), unfiltered air (UA), and concentrated PM2.5 (CA) in a real-ambient PM exposure system for 8 weeks and 16 weeks, respectively. The mice exposed to PM2.5 displayed a progressive inflammation and pulmonary fibrosis. Moreover, the expressions of NLRP3, pro-caspase-1, caspase-1, ASC and IL-1β were increased in mice lung following PM2.5 exposure, indicating PM2.5 exposure caused pulmonary inflammation by the NLRP3 pathways activation. Furthermore, the effects of PM exposure on pulmonary inflammation, pulmonary fibrosis, oxidative stress, and pulmonary function damage were significantly enhanced in PP2A−/− mice compared to WT mice, indicating the role of PP2A in the regulation of pulmonary injury induced by PM exposure. In vitro study confirmed that PP2A was involved in the PM2.5-induced inflammation response and NLRP3 inflammasome activation. Importantly, we identified PP2A regulated the activation of NLRP3 pathways by direct dephosphorylating IRE1α in response to PM2.5 exposure. Taken together, our results demonstrated that PP2A-IRE1α-NLRP3 signaling pathway played a crucial role in regulating the inflammation response, triggering the lung fibrogenesis upon PM2.5 exposure. Our findings provide new insights into regulatory role of PP2A in human diseases upon the PM exposure.

Abstract 3340: Small molecule mediated stabilization of PP2A modulates the homologous recombination pathway and potentiates DNA damage-induced cell death

Abstract High Grade Serous Carcinoma (HGSC) is the most lethal ovarian cancer subtype and accounts for approximately 60% of all ovarian tumors. Despite recent advances in drug development and increased understanding of genetic alterations that drive HGSC progression, mortality has not declined, highlighting the need for novel therapies. PARP inhibitors (PARPi) have become the mainstay of HGSC targeted therapy research given that these tumors are driven by a high degree of genomic instability resulting from the combination of fast DNA replication rates and numerous defects in the DNA-damage response (DDR) pathway. Nonetheless, only ~25% of these patients initially respond to treatment and a significant percentage eventually relapses with resistant disease. Here, we discovered that a Small Molecule Activator of Protein Phosphatase 2A (PP2A) (SMAP-061) induces apoptosis in both established and patient-derived HGSC cell lines as well as in genetically distinct Patient-Derived Xenograft (PDX) mouse models. Interestingly, we also uncovered that several genes that make-up the heterotrimer PP2A tumor suppressor protein are heterozygously lost in more than 95% of HGSC tumors, second only to p53. Mechanistically, we show that stabilization of PP2A protein by SMAP-061 inhibits the Homologous Recombination (HR) pathway via the direct inhibition of RAD51, ultimately leading to chronic accumulation of DNA damage and thus programmed cell death. Furthermore, we found that SMAP-061’s ability to inhibit HR potentiated the effects of PARP inhibition and resulted in synergistic cell death in both HR proficient and deficient models. These studies emphasize the potential of PP2A activators to expand the patient population that can benefit from PARPi therapies and possibly overcome PARPi resistance. In sum, our data highlights a new role of PP2A in regulating the DDR pathway in HGSC and supports the use of SMAPs in both HR proficient and deficient HGSC tumors. Citation Format: Rita A. Avelar, Amy Armstrong, Goutham Narla, Analisa DiFeo. Small molecule mediated stabilization of PP2A modulates the homologous recombination pathway and potentiates DNA damage-induced cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3340.

Protein Phosphatase 2A Improves Cardiac Functional Response to Ischemia and Sepsis.

Reversible protein phosphorylation is a posttranslational modification of regulatory proteins involved in cardiac signaling pathways. Here, we focus on the role of protein phosphatase 2A (PP2A) for cardiac gene expression and stress response using a transgenic mouse model with cardiac myocyte-specific overexpression of the catalytic subunit of PP2A (PP2A-TG). Gene and protein expression were assessed under basal conditions by gene chip analysis and Western blotting. Some cardiac genes related to the cell metabolism and to protein phosphorylation such as kinases and phosphatases were altered in PP2A-TG compared to wild type mice (WT). As cardiac stressors, a lipopolysaccharide (LPS)-induced sepsis in vivo and a global cardiac ischemia in vitro (stop-flow isolated perfused heart model) were examined. Whereas the basal cardiac function was reduced in PP2A-TG as studied by echocardiography or as studied in the isolated work-performing heart, the acute LPS- or ischemia-induced cardiac dysfunction deteriorated less in PP2A-TG compared to WT. From the data, we conclude that increased PP2A activity may influence the acute stress tolerance of cardiac myocytes.

Angiotensin Type-2 Receptors: Transducers of Natriuresis in the Renal Proximal Tubule.

Angiotensin II (Ang II) type-2 receptors (AT2R) are expressed in the adult kidney, prominently in renal proximal tubule cells (RPTCs), and play an important role in opposing renal sodium (Na+) retention induced by Ang II stimulation of Ang II type-1 receptor (AT1R). Natriuresis induced by AT1R blockade is due at least in part to AT2R activation and whole body deletion of AT2Rs reduces the natriuretic response to increased blood pressure (BP). The major endogenous AT2R agonist mediating the natriuretic response is Ang III, the Ang II heptapeptide metabolite generated by aminopeptidase A, and the principal nephron site mediating inhibition of Na+ reabsorption by the AT2R is the renal proximal tubule (RPT). AT2Rs induce natriuresis via a bradykinin, nitric oxide and cyclic GMP (cGMP) signaling cascade. Recent studies demonstrated a key role for protein phosphatase 2A (PP2A) in the AT2R-mediated natriuretic response upstream of cGMP. By inducing natriuresis, AT2Rs lower BP in the Ang II-infusion model of hypertension. PP2A activation and the natriuretic response to AT2R stimulation are defective in spontaneously hypertensive rats, a model of primary hypertension in humans. AT2R agonists are candidates for proximal tubule natriuretic agents in Na+ and fluid retention disorders.

Protein Phosphatase 2A Deficiency in Macrophages Increases Foam Cell Formation and Accelerates Atherosclerotic Lesion Development.

Protein phosphatase 2A (PP2A), a crucial serine/threonine phosphatase, has recently been reported to play an important role in cardiovascular disease. Previous studies have hinted that PP2A is involved in atherosclerosis formation, but the associated mechanisms remain poorly understood. In this study, we investigate the role of PP2A in the pathogenesis of atherosclerosis. In human atherosclerotic coronary arteries, we found that the expression and activity of PP2A decreased significantly when compared to non-atherosclerotic arteries. Additional experiments demonstrated that pharmacological inhibition of PP2A aggravated atherosclerosis of ApoE−/− mice. Considering the central role of macrophages in atherosclerosis, mice with conditional knockout of the PP2A-Cα subunit in myeloid cells were produced to investigate the function of PP2A in macrophages. Results showed that PP2A deficiency in myeloid cells aggravated atherosclerotic lesions in mice. in vitro experiments indicated that PP2A-deficient macrophages had an enhanced ability of lipid uptake and foam cell formation. Mechanistically, the deficiency of the PP2A in macrophages led to an increase in the phosphorylation level of p38, which contributed to the elevated expression of scavenger receptor CD36, a key factor involved in lipoprotein uptake. Our data suggest that PP2A participates in the pathophysiological process of atherosclerosis. The decrease of PP2A expression and activity in macrophages is a crucial determinant for foam cell formation and the initiation of atherosclerosis. Our study may provide a potential novel approach for the treatment of atherosclerosis.

PP2A and Its Inhibitors in Helper T-Cell Differentiation and Autoimmunity.

Protein phosphatase 2A (PP2A) is a highly complex heterotrimeric Ser/Thr phosphatase that regulates many cellular processes. The role of PP2A as a tumor suppressor has been extensively studied and reviewed. However, emerging evidence suggests PP2A constrains inflammatory responses and is important in autoimmune and neuroinflammatory diseases. Here, we reviewed the existing literature on the role of PP2A in T-cell differentiation and autoimmunity. We have also discussed the modulation of PP2A activity by endogenous inhibitors and its small-molecule activators as potential therapeutic approaches against autoimmunity.

Liver PP2A-Cα Protects From Parenteral Nutrition-associated Hepatic Steatosis

Background & AimsParenteral nutrition (PN) is a lifesaving therapy for patients with intestinal failure. Hepatic steatosis is a potentially fatal complication of long-term PN, but the involved pathological mechanisms are incompletely unclarified. Herein, we identify the role of protein phosphatase 2A (PP2A) in the pathogenesis of parenteral nutrition-associated hepatic steatosis (PNAHS).MethodsProteomic/phosphoproteomic analyses of liver samples from patients with PNAHS were applied to identify the mechanism of PNAHS. Total parenteral nutrition (TPN) mice model, in vivo, and in vitro experiments were used to assess the effect of PP2A-Cα on liver fatty acid metabolism.ResultsReduced expression of PP2A-Cα (catalytic subunit) enhanced activation of serine/threonine kinase Akt2 and decreased activation of adenosine monophosphate-activated protein kinase (AMPK) were associated with hepatic steatosis in patients with PNAHS. Mice given PN for 14 days developed hepatic steatosis, down-regulation of PP2A-Cα, activation of Akt2, and inhibition of AMPK. Hepatocyte-specific deletion of PP2A-Cα in mice given PN exacerbated Akt2 activation, AMPK inhibition, and hepatic steatosis through an effect on fatty acid degradation, whereas hepatocyte-specific PP2A-Cα overexpression significantly ameliorated hepatic steatosis accompanied with Akt2 suppression and AMPK activation. Additionally, pharmacological activation of Akt2 in mice overexpressing PP2A-Cα led to the aggravation of hepatic steatosis.ConclusionsOur findings demonstrate that hepatic PP2A-Cα serves as a protective factor of PNAHS due to ameliorating hepatic steatosis and improving liver function. Our study provides a strong rationale that PP2A-Cα may be involved in the pathogenesis of PNAHS.

Adopting a Phosphoproteomics Approach to Investigate a Role for Protein Phosphatase 2A (PP2A) Regulatory Subunit B55α in Cardiac β-Adrenergic Receptor Signalling

Protein kinases are recognised as integral regulators of phosphorylation within beta-adrenergic receptor (β-AR) signalling pathways in the heart. In contrast, the role of protein phosphatases and dephosphorylation in β-AR pathways is less well defined. In vitro evidence suggests that protein phosphatase 2A (PP2A) regulatory subunit B55α may modulate gene transcription as a key downstream effector of β-AR signalling in cardiomyocytes. The goal of this study was to determine how loss of PP2A-B55α impacts β-AR signalling in cardiomyocytes.

Cellular Protein Phosphatase 2A Regulates Cell Survival Mechanisms in Influenza A Virus Infection.

Influenza A viruses (IAVs) are respiratory pathogens that are able to hijack multiple cellular mechanisms to drive their replication. Consequently, several viral and cellular proteins undergo posttranslational modifications such as dynamic phosphorylation/dephosphorylation. In eukaryotic cells, dephosphorylation is mainly catalyzed by protein phosphatase 2A (PP2A). While the function of kinases in IAV infection is quite well studied, only little is known about the role of PP2A in IAV replication. Here, we show, by using knockdown and inhibition approaches of the catalytic subunit PP2Ac, that this phosphatase is important for efficient replication of several IAV subtypes. This could neither be attributed to alterations in the antiviral immune response nor to changes in transcription or translation of viral genes. Interestingly, decreased PP2Ac levels resulted in a significantly reduced cell viability after IAV infection. Comprehensive kinase activity profiling identified an enrichment of process networks related to apoptosis and indicated a synergistic action of hyper-activated PI3K/Akt, MAPK/JAK-STAT and NF-kB signaling pathways, collectively resulting in increased cell death. Taken together, while IAV seems to effectively tap leftover PP2A activity to ensure efficient viral replication, reduced PP2Ac levels fail to orchestrate cell survival mechanisms to protect infected cells from early cell death.

Allosteric activation of PP2A inhibits experimental abdominal aortic aneurysm

Although extremely important, the molecular mechanisms that govern aortic aneurysm (AA) formation and progression are still poorly understood. This deficit represents a critical roadblock toward the development of effective pharmaceutical therapies for the treatment of AA. While dysregulation of protein phosphatase 2A (PP2A) is thought to play a role in cardiovascular disease, its role in aortic aneurysm is unknown. The objective of the present study is to test the hypothesis that PP2A regulates abdominal aortic aneurysm (AAA) progression in a murine model. In an angiotensin II-induced AAA murine model, the PP2A inhibitor, LB-100, markedly accelerated AAA progression as demonstrated by increased abdominal aortic dilation and mortality. AAA progression was associated with elevated inflammation and extracellular matrix fragmentation, concomitant with increases in both metalloproteinase activity and reactive oxygen species production. Conversely, administration of a novel class of small molecule activators of PP2A (SMAPs) resulted in an antithetical effect. SMAPs effectively reduced AAA incidence along with the corresponding pathologies that were increased with LB-100 treatment. Mechanistically, modulation of PP2A activities in vivo functioned in part via alteration of the ERK1/2 and NFκB signaling pathways, known regulators of AAA progression. These studies, for the first time, demonstrate a role of PP2A in AAA etiology and demonstrate that PP2A activation may represent a novel strategy for the treatment of abdominal aortic aneurysms.