Abstract 218: PI3Kγ Regulates Age-Dependent Cardiac Hypertrophy Through Kinase-Independent GSK-3-PP2A Axis

2012 ◽  
Vol 111 (suppl_1) ◽  
Author(s):  
Sathyamangla V Naga Prasad ◽  
Maradumane L Mohan ◽  
Elizabeth E Martelli ◽  
Manveen K Gupta ◽  
Neelakantan T Vasudevan
Keyword(s):  
Glycogen Synthase ◽  
Growth Factor Receptor ◽  
Methyl Transferase ◽  
Knock Out ◽  
Akt Activation ◽  
Pp2a Activity ◽  
Phosphatase 2A ◽  
Heart Size ◽  
Phosphoinositide 3 Kinase

Activation of phosphoinositide 3-kinase α (PI3Kα) by Receptor Tyrosine Kinase (RTK) or PI3Kγ by G-protein coupled receptor (GPCR) inhibits glycogen synthase kinase-3 (GSK-3) via protein kinase B (Akt). We show that in addition to promoting GSK-3 phosphorylation through Akt, PI3Kγ in parallel suppresses PP2A dependent GSK-3 dephosphorylation. This is evidenced by accelerated GSK-3 dephosphorylation in PI3Kγ knock out (PI3Kγ-KO) mice downstream of RTK-PI3Kα-Akt axis despite robust Akt activation by insulin. Confocal microscopy and immunoblotting show marked reduction of steady state GSK-3 phosphorylation in PI3Kγ-KO compared to littermate controls. Assessment of GSK-3 dephosphorylating enzyme protein phosphatase 2A (PP2A) showed significant elevation in PP2A and GSK-associated phosphatase activity in PI3Kγ-KO mice compared to controls. Mechanistically, we found that elevated PP2A activity in PI3Kγ-KO was due to PP2A methylation mediated by elevated PP2A methyl transferase (PPMT-1) activity. Consistent with the elevated anti-hypertrophic GSK-3 activity, we observed reduced heart size in PI3Kγ-KO mice at 6, 12, and 18 months compared to age matched littermate controls. To test in vivo whether PI3Kγ activity regulates cardiac GSK-3 function through PP2A, we bred transgenic mice with cardiac overexpression of inactive PI3Kγ (PI3Kγ inact ) with PI3Kγ-KO mice. Surprisingly, cardiac overexpression of PI3Kγ inact transgene in PI3Kγ-KO background completely normalized cardiac PPMT-1 activity resulting in reduced PP2A activity and increased GSK-3 phosphorylation. Expression of PI3Kγ inact transgene in PI3Kγ-KO resulted in normalization of heart size compared to PI3Kγ-KO littermates consistent with the increased GSK-3 phosphorylation and consequent inhibition of GSK-3 activity suggesting a novel kinase independent role of PI3Kγ downstream of growth factor receptor in regulating cardiac growth with age.

scholarly journals FGFR3△7–9 promotes tumor progression via the phosphorylation and destabilization of ten-eleven translocation-2 in human hepatocellular carcinoma

2020 ◽  
Vol 11 (10) ◽  
Author(s):  
Zhijian Jin ◽  
Haoran Feng ◽  
Juyong Liang ◽  
Xiaoqian Jing ◽  
Qiwu Zhao ◽  
...  
Keyword(s):  
Hepatocellular Carcinoma ◽  
Close Association ◽  
Growth Factor Receptor ◽  
Epigenetic Mechanism ◽  
Oncogenic Potential ◽  
Akt Activation ◽  
Cancer Mutation

Abstract Overexpression of fibroblast growth factor receptor 3 (FGFR3) correlates with more severe clinical features of hepatocellular carcinoma (HCC). Our previous study has shown that FGFR3∆7–9, a novel splicing mutation of FGFR3, contributes significantly to HCC malignant character, but the epigenetic mechanism is still elusive. In this study, through mass spectrometry and co-immunoprecipitation studies, we discover a close association between FGFR3∆7–9 and the DNA demethylase Ten-Eleven Translocation-2 (TET2). Unlike other certain types of cancer, mutation of TET2 is rare in HCC. However, activation of FGFR3∆7–9 by FGF1 dramatically shortens TET2 half-life. FGFR3∆7–9, but not wild-type FGFR3, directly interacts with TET2 and phosphorylates TET2 at Y1902 site, leading to the ubiquitination and proteasome-mediated degradation of TET2. Overexpression of a phospho-deficient mutant TET2 (Y1902F) significantly reduces the oncogenic potential of FGFR3∆7–9 in vitro and in vivo. Furthermore, FGFR3∆7–9 significantly enhances HCC cell proliferation through the TET2-PTEN-AKT pathway. Specifically, TET2 offsets the elevation of p-AKT level induced by FGFR3∆7–9 through directly binding to PTEN promoter and increasing 5-hmC. Therefore, through phosphorylation and inhibition of TET2, FGFR3∆7–9 reduces PTEN expression and substantiates AKT activation to stimulate HCC proliferation. Together, this study identifies TET2 as a key regulator of the oncogenic role of FGFR3∆7–9 in HCC carcinogenesis and sheds light on new therapeutic strategies for HCC treatment.

Abstract 229: Novel Plasma Membrane Beta Adrenergic Receptor Resensitization By Protein Phosphatase 2a

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Neelakantan T Vasudevan ◽  
Anita Shukla ◽  
Sathyamangla V Naga Prasad
Keyword(s):  
Plasma Membrane ◽  
Protein Phosphatase ◽  
Adrenergic Receptor ◽  
Protein Phosphatase 2A ◽  
Metabolic Labeling ◽  
Specific Expression ◽  
Pp2a Activity ◽  
Pi3k Activity ◽  
Phosphatase 2A

Resensitization of β-adrenergic receptor (βAR) occurs by dephosphorylation of the internalized βAR by protein phosphatase 2A (PP2A) before being recycled back to plasma membrane (PM). Contrary to this classical paradigm, cardiac specific expression of inactive PI3Kγ (PI3Kγ inact ) leads to receptor resensitization at the plasma membrane as measured by adenylyl cyclase activity in mice chronically treated with the agonist. We hypothesized that PI3K activity inhibits PM receptor resensitization. Using cells stably expressing FLAG-β 1 AR alone (single) or along with PI3Kγ inact (double), we show that inhibition of PI3K activity results in novel PM receptor resensitization. Agonist activation of single stables showed significant receptor desensitization as measured by reduced cAMP generation (35.6 ± 4.6 pmol/mg protein). In contrast, double-or wortmannin (Wort, PI3K inhibitor) pre-treated single- stables showed marked generation of cAMP (87.4 ± 3.2 or 83.1 ± 5.7) showing β 1 AR resensitization. Agonist stimulation of metabolically labeled β 1 ARs pre-treated with inhibitors of internalization, sucrose and β-cyclodextrin resulted in accumulation of phosphorylated receptors at the PM, which was abolished with PI3Kγ inact suggesting dephosphorylation of β 1 ARs. Inhibition of PP2A by okadaic acid or Fostriecin resulted in complete loss of β 1 AR resensitization despite the presence of PI3Kγ inact showing that PI3K regulates PP2A activity at the β 1 AR complex. Pre-treatment of single stable cells with Wort resulted in significant increase in β 1 AR-associated phosphatase activity following dobutamine (Dob) treatment (Veh, 4131 ± 14; Dob, 3180 ± 111; Dob + Wort, 17123 ± 680 pmoles/mg protein). Consistently, similar results were obtained in vivo using single transgenic (FLAG-β 1 AR, Veh, 87 ± 12; Dob, 61.7 ± 8.3) and double transgenic (FLAG-β 1 AR and PI3Kγ inact , Veh, 93 ± 9; Dob, 118 ± 6) mice. In vivo metabolic labeling, co-immunoprecipitation and in vitro kinase assays showed that inhibitor of PP2A (I2PP2A) protein as a target of PI3K in regulating PP2A activity at the β 1 AR complex. Indeed, siRNA knock down of I2PP2A results in preservation of β 1 AR function by PM receptor resensitization demonstrating a novel role for PI3K in receptor resensitization. This research has received full or partial funding support from the American Heart Association, AHA Great Rivers Affiliate (Delaware, Kentucky, Ohio, Pennsylvania & West Virginia).

scholarly journals Gαi1and Gαi3regulate macrophage polarization by forming a complex containing CD14 and Gab1

2015 ◽  
Vol 112 (15) ◽  
pp. 4731-4736 ◽  
Author(s):  
Xianjing Li ◽  
Duowei Wang ◽  
Zhen Chen ◽  
Ermei Lu ◽  
Zhuo Wang ◽  
...  
Keyword(s):  
Binding Protein ◽  
Macrophage Polarization ◽  
Growth Factor Receptor ◽  
Guanine Nucleotide Binding Protein ◽  
Akt Activation ◽  
Proteasome Pathway ◽  
Guanine Nucleotide Binding ◽  
Underlying Mechanisms

Heterotrimeric G proteins have been implicated in Toll-like receptor 4 (TLR4) signaling in macrophages and endothelial cells. However, whether guanine nucleotide-binding protein G(i) subunit alpha-1 and alpha-3 (Gαi1/3) are required for LPS responses remains unclear, and if so, the underlying mechanisms need to be studied. In this study, we demonstrated that, in response to LPS, Gαi1/3form complexes containing the pattern recognition receptor (PRR) CD14 and growth factor receptor binding 2 (Grb2)-associated binding protein (Gab1), which are required for activation of PI3K-Akt signaling. Gαi1/3deficiency decreased LPS-induced TLR4 endocytosis, which was associated with decreased phosphorylation of IFN regulatory factor 3 (IRF3). Gαi1/3knockdown in bone marrow-derived macrophage cells (Gαi1/3KD BMDMs) exhibited an M2-like phenotype with significantly suppressed production of TNF-α, IL-6, IL-12, and NO in response to LPS. The altered polarization coincided with decreased Akt activation. Further, Gαi1/3deficiency caused LPS tolerance in mice. In vitro studies revealed that, in LPS-tolerant macrophages, Gαi1/3were down-regulated partially by the proteasome pathway. Collectively, the present findings demonstrated that Gαi1/3can interact with CD14/Gab1, which modulates macrophage polarization in vitro and in vivo.

scholarly journals A tightly associated serine/threonine protein kinase regulates phosphoinositide 3-kinase activity.

1993 ◽  
Vol 13 (3) ◽  
pp. 1657-1665 ◽  
Author(s):  
C L Carpenter ◽  
K R Auger ◽  
B C Duckworth ◽  
W M Hou ◽  
B Schaffhausen ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Protein Phosphatase ◽  
Kinase Activity ◽  
Protein Phosphatase 2A ◽  
T Antigen ◽  
Serine Kinase ◽  
Phosphatase 2A ◽  
Phosphoinositide 3 Kinase

We identified a serine/threonine protein kinase that is associated with and phosphorylates phosphoinositide 3-kinase (PtdIns 3-kinase). The serine kinase phosphorylates both the 85- and 110-kDa subunits of PtdIns 3-kinase and purifies with it from rat liver and immunoprecipitates with antibodies raised to the 85-kDa subunit. Tryptic phosphopeptide maps indicate that p85 from polyomavirus middle T-transformed cells is phosphorylated in vivo at three sites phosphorylated in vitro by the associated serine kinase. The 85-kDa subunit of PtdIns 3-kinase is phosphorylated in vitro on serine at a stoichiometry of approximately 1 mol of phosphate per mol of p85. This phosphorylation results in a three- to sevenfold decrease in PtdIns 3-kinase activity. Dephosphorylation with protein phosphatase 2A reverses the inhibition. This suggests that the association of protein phosphatase 2A with middle T antigen may function to activate PtdIns 3-kinase.

scholarly journals Ribosomal S6 Kinase as a Mediator of Keratinocyte Growth Factor-induced Activation of Akt in Epithelial Cells

2004 ◽  
Vol 15 (7) ◽  
pp. 3106-3113 ◽  
Author(s):  
Zhong-Zong Pan ◽  
Yvan Devaux ◽  
Prabir Ray
Keyword(s):  
Growth Factor ◽  
Epithelial Cells ◽  
Keratinocyte Growth Factor ◽  
Growth Factor Receptor ◽  
Protective Effects ◽  
S6 Kinase ◽  
Akt Activation ◽  
Ribosomal S6 Kinase

The keratinocyte growth factor receptor (KGFR) is a member of the fibroblast growth factor receptor (FGFR) superfamily. The proximal signaling molecules of FGFRs are much less characterized compared with other growth factor receptors. Using the yeast two-hybrid assay, we have identified ribosomal S6 kinase (RSK) to be a protein that associates with the cytoplasmic domain of the KGFR. The RSK family of kinases controls multiple cellular processes, and our studies for the first time show association between the KGFR and RSK. Using a lung-specific inducible transgenic system we have recently demonstrated protective effects of KGF on the lung epithelium and have demonstrated KGF-induced activation of the prosurvival Akt pathway both in vivo and in vitro. Here we show that a kinase inactive RSK mutant blocks KGF-induced Akt activation and KGF-mediated inhibition of caspase 3 activation in epithelial cells subjected to oxidative stress. It was recently shown that RSK2 recruits PDK1, the kinase responsible for both Akt and RSK activation. When viewed collectively, it appears that the association between the KGFR and RSK plays an important role in KGF-induced Akt activation and consequently in the protective effects of KGF on epithelial cells.

Akt signaling in skeletal muscle: regulation by exercise and passive stretch

2003 ◽  
Vol 285 (5) ◽  
pp. E1081-E1088 ◽  
Author(s):  
Kei Sakamoto ◽  
William G. Aschenbach ◽  
Michael F. Hirshman ◽  
Laurie J. Goodyear
Keyword(s):  
Skeletal Muscle ◽  
Protein Kinase ◽  
Glycogen Synthase ◽  
Contractile Activity ◽  
Akt Signaling ◽  
Fiber Types ◽  
Akt Activation ◽  
Fast Twitch ◽  
Passive Stretch

Akt/protein kinase B is a serine/threonine kinase that has emerged as a critical signaling component for mediating numerous cellular responses. Contractile activity has recently been demonstrated to stimulate Akt signaling in skeletal muscle. Whether physiological exercise in vivo activates Akt is controversial, and the initiating factors that result in the stimulation of Akt during contractile activity are unknown. In the current study, we demonstrate that treadmill running exercise of rats using two different protocols (intermediate high or high-intensity exhaustive exercise) significantly increases Akt activity and phosphorylation in skeletal muscle composed of various fiber types. To determine if Akt activation during contractile activity is triggered by mechanical forces applied to the skeletal muscle, isolated skeletal muscles were incubated and passively stretched. Passive stretch for 10 min significantly increased Akt activity (2-fold) in the fast-twitch extensor digitorum longus (EDL) muscle. However, stretch had no effect on Akt in the slow-twitch soleus muscle, although there was a robust phosphorylation of the stress-activated protein kinase p38. Similar to contraction, stretch-induced Akt activation in the EDL was fully inhibited in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas glycogen synthase kinase-3 (GSK3) phosphorylation was only partially inhibited. Stretch did not cause dephosphorylation of glycogen synthase on GSK3-targeted sites in the absence or presence of wortmannin. We conclude that physiological exercise in vivo activates Akt in multiple skeletal muscle fiber types and that mechanical tension may be a part of the mechanism by which contraction activates Akt in fast-twitch muscles.

scholarly journals B56-Associated Protein Phosphatase 2A Is Required For Survival and Protects from Apoptosis in Drosophila melanogaster

2002 ◽  
Vol 22 (11) ◽  
pp. 3674-3684 ◽  
Author(s):  
Xinghai Li ◽  
Anne Scuderi ◽  
Anthea Letsou ◽  
David M. Virshup
Keyword(s):  
Cell Death ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Specific Protein ◽  
S2 Cells ◽  
Regulatory Subunits ◽  
Pp2a Activity ◽  
Phosphatase 2A

ABSTRACT Protein phosphorylation and specific protein kinases can initiate signal transduction pathways leading to programmed cell death. The specific protein phosphatases regulating apoptosis have been more elusive. Using double-stranded RNA-mediated interference (RNAi), the role of protein phosphatase 2A (PP2A) in cellular signaling was investigated. Knockdown of A or C subunits individually or of combined B subunits led to concurrent loss of nontargeted PP2A subunits, suggesting that PP2A is an obligate heterotrimer in vivo. Global knockdown of PP2A activity or specific loss of redundant B56 regulatory subunits caused cell death with the morphological and biochemical changes characteristic of apoptosis in cultured S2 cells. B56:PP2A-regulated apoptosis required caspases and the upstream regulators dark, reaper, head involution defective, and dp53. In Drosophila embryos, knockdown of B56-regulated PP2A activity resulted in apoptosis and failure of gastrulation, an effect that was blocked by concurrent RNAi of the caspase Drice. B56-regulated PP2A activity appears to be required upstream of dp53 to maintain a critical proapoptotic substrate in a dephosphorylated, inactive state, thereby preventing apoptosis in Drosophila S2 cells.

scholarly journals Noncanonical regulation of insulin-mediated ERK activation by phosphoinositide 3-kinase γ

2017 ◽  
Vol 28 (22) ◽  
pp. 3112-3122 ◽  
Author(s):  
Maradumane L. Mohan ◽  
Arunachal Chatterjee ◽  
Swetha Ganapathy ◽  
Sromona Mukherjee ◽  
Sowmya Srikanthan ◽  
...  
Keyword(s):  
Cardiac Fibroblasts ◽  
Knock Out ◽  
Erk Activation ◽  
Cellular Processes ◽  
Gpcr Activation ◽  
Extracellular Signal ◽  
Phosphatase 2A ◽  
Epidermal Growth ◽  
Phosphoinositide 3 Kinase ◽  
Knock Out Mice

Classically Class IB phosphoinositide 3-kinase (PI3Kγ) plays a role in extracellular signal–regulated kinase (ERK) activation following G-protein coupled receptor (GPCR) activation. Knock-down of PI3Kγ unexpectedly resulted in loss of ERK activation to receptor tyrosine kinase agonists such as epidermal growth factor or insulin. Mouse embryonic fibroblasts (MEFs) or primary adult cardiac fibroblasts isolated from PI3Kγ knock-out mice (PI3KγKO) showed decreased insulin-stimulated ERK activation. However, expression of kinase-dead PI3Kγ resulted in rescue of insulin-stimulated ERK activation. Mechanistically, PI3Kγ sequesters protein phosphatase 2A (PP2A), disrupting ERK–PP2A interaction, as evidenced by increased ERK–PP2A interaction and associated PP2A activity in PI3KγKO MEFs, resulting in decreased ERK activation. Furthermore, β-blocker carvedilol-mediated β-arrestin-dependent ERK activation is significantly reduced in PI3KγKO MEF, suggesting accelerated dephosphorylation. Thus, instead of classically mediating the kinase arm, PI3Kγ inhibits PP2A by scaffolding and sequestering, playing a key parallel synergistic step in sustaining the function of ERK, a nodal enzyme in multiple cellular processes.

scholarly journals beta-blocker reverses inhibition of beta-2 adrenergic receptor resensitization by hypoxia

2020 ◽  
Author(s):  
Yu Sun ◽  
Manveen K. Gupta ◽  
Kate Stenson ◽  
Maradumane L. Mohan ◽  
Nicholas Wanner ◽  
...  
Keyword(s):  
Heart Failure ◽  
Protein Phosphatase ◽  
Adrenergic Receptor ◽  
Protein Phosphatase 2A ◽  
Receptor Internalization ◽  
Pp2a Activity ◽  
Phosphatase 2A ◽  
Β Blocker ◽  
Underlying Mechanisms

AbstractIschemia/hypoxia is major underlying cause for heart failure and stroke. Although beta-adrenergic receptor (βAR) is phosphorylated in response to hypoxia, less is known about the underlying mechanisms. Hypoxia results in robust GRK2-mediated β2AR phosphorylation but does not cause receptor internalization. However, hypoxia leads to significant endosomal-β2AR phosphorylation accompanied by inhibition of β2AR-associated protein phosphatase 2A (PP2A) activity impairing resensitization. Phosphoinositide 3-kinase γ (PI3Kγ) impedes resensitization by phosphorylating endogenous inhibitor of protein phosphatase 2A, I2PP2A that inhibits PP2A activity. Hypoxia increased PI3Kγ activity leading to significant phosphorylation of I2PP2A resulting in inhibition of PP2A and consequently resensitization. Surprisingly, β-blocker abrogated hypoxia-mediated β2AR phosphorylation instead of phosphorylation in normoxia. Subjecting mice to hypoxia leads to significant cardiac dysfunction and β2AR phosphorylation showing conservation of non-canonical hypoxia-mediated pathway in vivo. These findings provide mechanistic insights on hypoxia-mediated βAR dysfunction which is rescued by β-blocker and will have significant implications in heart failure and stroke.

Protein Phosphatase 2A Affects the Symptoms of Depressive Rats by Regulating Extracellular Signal-regulated Kinases/Glycogen Synthase Kinase 3β Signaling Pathway

2019 ◽  
Vol 9 (5) ◽  
pp. 592-598
Author(s):  
Guangshan Zheng ◽  
Zhenzhen Chen ◽  
Longjian Huang ◽  
Jianmin Huang ◽  
Yan Li ◽  
...  
Keyword(s):  
Protein Phosphatase ◽  
Common Mental Disorders ◽  
Glycogen Synthase ◽  
Protein Phosphatase 2A ◽  
Antidepressant Drugs ◽  
Morris Water Maze Test ◽  
Model Group ◽  
Expression Levels ◽  
Pp2a Activity ◽  
Phosphatase 2A

As one of the world's more common mental disorders, the incidence of depression has increased yearly, seriously affecting the lives and health of many people. Protein phosphatase 2A (PP2A) is a protein that is enriched in the brain tissue, is the major serine/threonine phosphatase in the central nervous system, and plays a very important role in many aspects of cellular function. To explore the role of PP2A in the pathogenesis of depression in our study, we constructed the depressive disorder model, which involves the exposure of Sprague Dawley rats to chronic unpredictable stress (CUS). The rats with depression were then treated with different concentrations (low, moderate, high) of okadaic acid (OA), and the optimal OA concentration (OOA) for the follow-up study was selected based on PP2A activity. The results showed that the use of higher OA concentrations corresponded with stronger inhibition of PP2A activity. Moreover, the behavioral test performed on the depression model rats showed that OOA group exhibited significant improvements in weight, as well as in their results in the sucrose preference test, open-field test, and Morris water maze test compared to the model group (P < 0.05). Moreover, when compared with the model group, the amounts of NE and 5-HT increased significantly (P < 0.05), and the expression levels of TH, ERK1, AKT1, as well as the phosphorylation of TH, ERK1, AKT1, and GSK-3β, were observed to be increased in the OOA group (P < 0.05). Furthermore, the content of CORT decreased significantly (P < 0.05), and the expression levels of GSK-3β were decreased in the OOA group (P < 0.05). Thus, the potential mechanism of how OA ameliorates depression in model rats may be through the inhibition of PP2A activity, the increase in phosphorylation levels of AKT and GSK-3β, and through the PP2A/AKT/GSK-3β signal pathway; these components may serve as important intracellular targets for antidepressant drugs.

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