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Emre C, Do KV, Jun B, Hjorth E, Alcalde SG, Kautzmann MAI, Gordon WC, Nilsson P, Bazan NG, Schultzberg M. Age-related changes in brain phospholipids and bioactive lipids in the APP knock-in mouse model of Alzheimer's disease. Acta Neuropathol Commun 2021; 9:116. [PMID: 34187579 PMCID: PMC8244172 DOI: 10.1186/s40478-021-01216-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2021] [Accepted: 06/08/2021] [Indexed: 12/19/2022] Open
Abstract
Sustained brain chronic inflammation in Alzheimer’s disease (AD) includes glial cell activation, an increase in cytokines and chemokines, and lipid mediators (LMs), concomitant with decreased pro-homeostatic mediators. The inflammatory response at the onset of pathology engages activation of pro-resolving, pro-homeostatic LMs followed by a gradual decrease. We used an APP knock-in (App KI) AD mouse that accumulates β-amyloid (Aβ) and presents cognitive deficits (at 2 and 6 months of age, respectively) to investigate LMs, their precursors, biosynthetic enzymes and receptors, glial activation, and inflammatory proteins in the cerebral cortex and hippocampus at 2-, 4-, 8- and 18-month-old in comparison with wild-type (WT) mice. We used LC-mass-spectrometry and MALDI molecular imaging to analyze LMs and phospholipids, and immunochemistry for proteins. Our results revealed an age-specific lipid and cytokine profile, and glial activation in the App KI mice. Despite an early onset of Aβ pathology, pro-inflammatory and pro-resolving LMs were prominently increased only in the oldest age group. Furthermore, the LM biosynthetic enzymes increased, and their receptor expression decreased in the aged App KI mice. Arachidonic acid (AA)-containing phospholipid molecular species were elevated, correlating with decreased cPLA2 activity. MALDI molecular imaging depicted differential distribution of phospholipids according to genotype in hippocampal layers. Brain histology disclosed increased microglia proliferation starting from young age in the App KI mice, while astrocyte numbers were enhanced in older ages. Our results demonstrate that the brain lipidome is modified preferentially during aging as compared to amyloid pathology in the model studied here. However, alterations in phospholipids signal early pathological changes in membrane composition.
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The Cell Cycle Checkpoint System MAST(L)-ENSA/ARPP19-PP2A is Targeted by cAMP/PKA and cGMP/PKG in Anucleate Human Platelets. Cells 2020; 9:cells9020472. [PMID: 32085646 PMCID: PMC7072724 DOI: 10.3390/cells9020472] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 02/14/2020] [Accepted: 02/14/2020] [Indexed: 12/13/2022] Open
Abstract
The cell cycle is controlled by microtubule-associated serine/threonine kinase-like (MASTL), which phosphorylates the cAMP-regulated phosphoproteins 19 (ARPP19) at S62 and 19e/α-endosulfine (ENSA) at S67and converts them into protein phosphatase 2A (PP2A) inhibitors. Based on initial proteomic data, we hypothesized that the MASTL-ENSA/ARPP19-PP2A pathway, unknown until now in platelets, is regulated and functional in these anucleate cells. We detected ENSA, ARPP19 and various PP2A subunits (including seven different PP2A B-subunits) in proteomic studies of human platelets. ENSA-S109/ARPP19–S104 were efficiently phosphorylated in platelets treated with cAMP- (iloprost) and cGMP-elevating (NO donors/riociguat) agents. ENSA-S67/ARPP19-S62 phosphorylations increased following PP2A inhibition by okadaic acid (OA) in intact and lysed platelets indicating the presence of MASTL or a related protein kinase in human platelets. These data were validated with recombinant ENSA/ARPP19 and phospho-mutants using recombinant MASTL, protein kinase A and G. Both ARPP19 phosphorylation sites S62/S104 were dephosphorylated by platelet PP2A, but only S62-phosphorylated ARPP19 acted as PP2A inhibitor. Low-dose OA treatment of platelets caused PP2A inhibition, diminished thrombin-stimulated platelet aggregation and increased phosphorylation of distinct sites of VASP, Akt, p38 and ERK1/2 MAP kinases. In summary, our data establish the entire MASTL(like)–ENSA/ARPP19–PP2A pathway in human platelets and important interactions with the PKA, MAPK and PI3K/Akt systems.
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Taleski G, Sontag E. Protein phosphatase 2A and tau: an orchestrated 'Pas de Deux'. FEBS Lett 2017; 592:1079-1095. [PMID: 29121398 DOI: 10.1002/1873-3468.12907] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 10/18/2017] [Accepted: 11/02/2017] [Indexed: 12/21/2022]
Abstract
The neuronal microtubule-associated protein tau serves a critical role in regulating axonal microtubule dynamics to support neuronal and synaptic functions. Furthermore, it contributes to glutamatergic regulation and synaptic plasticity. Emerging evidence also suggests that tau serves as a signaling scaffold. Tau function and subcellular localization are tightly regulated, in part, by the orchestrated interplay between phosphorylation and dephosphorylation events. Significantly, protein phosphatase type 2A (PP2A), encompassing the regulatory PPP2R2A (or Bα) subunit, is a major brain heterotrimeric enzyme and the primary tau Ser/Thr phosphatase in vivo. Herein, we closely examine how the intimate and compartmentalized interactions between PP2A and tau regulate tau phosphorylation and function, and play an essential role in neuronal homeostasis. We also review evidence supporting a strong link between deregulation of tau-PP2A functional interactions and the molecular underpinnings of various neurodegenerative diseases collectively called tauopathies. Lastly, we discuss the opportunities and associated challenges in more specifically targeting PP2A-tau interactions for drug development for tauopathies.
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Affiliation(s)
- Goce Taleski
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, Hunter Medical Research Institute, University of Newcastle, Callaghan, Australia
| | - Estelle Sontag
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, Hunter Medical Research Institute, University of Newcastle, Callaghan, Australia
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Yeh PA, Chang CJ. A novel function of twins, B subunit of protein phosphatase 2A, in regulating actin polymerization. PLoS One 2017; 12:e0186037. [PMID: 28977036 PMCID: PMC5627941 DOI: 10.1371/journal.pone.0186037] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 09/22/2017] [Indexed: 11/18/2022] Open
Abstract
Actin is an important component of the cytoskeleton and its polymerization is delicately regulated by several kinases and phosphatases. Heterotrimeric protein phosphatase 2A (PP2A) is a potent phosphatase that is crucial for cell proliferation, apoptosis, tumorigenesis, signal transduction, cytoskeleton arrangement, and neurodegeneration. To facilitate these varied functions, different regulators determine the different targets of PP2A. Among these regulators of PP2A, the B subunits in particular may be involved in cytoskeleton arrangement. However, little is known about the role of PP2A in actin polymerization in vivo. Using sophisticated fly genetics, we demonstrated a novel function for the fly B subunit, twins, to promote actin polymerization in varied tissue types, suggesting a broad and conserved effect. Furthermore, our genetic data suggest that twins may act upstream of the actin-polymerized-proteins, Moesin and Myosin-light-chain, and downstream of Rho to promote actin polymerization. This work opens a new avenue for exploring the biological functions of a PP2A regulator, twins, in cytoskeleton regulation.
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Affiliation(s)
- Po-An Yeh
- Institute of Molecular Biology, Academia Sinica, Nankang, Taipei, Taiwan
- Department of Bioscience Technology, Chung Yuan Christian University, Chung Li, Taiwan
- * E-mail:
| | - Ching-Jin Chang
- Graduate Institute of Biochemical Sciences, College of Life Science, National Taiwan University, Taipei, Taiwan
- Institute of Biological Chemistry, Academia Sinica, Nankang, Taipei, Taiwan
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Zhang Y, Chen Y, Sun L, Liang J, Guo Z, Xu L. Protein phosphatases 2A as well as reactive oxygen species involved in tributyltin-induced apoptosis in mouse livers. ENVIRONMENTAL TOXICOLOGY 2014; 29:234-242. [PMID: 22223438 DOI: 10.1002/tox.21751] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Accepted: 11/25/2011] [Indexed: 05/31/2023]
Abstract
Tributyltin (TBT), a highly toxic environmental contaminant, has been shown to induce caspase-3-dependent apoptosis in human amniotic cells through protein phosphatase 2A (PP2A) inhibition and consequent JNK activation. This in vivo study was undertaken to further verify the results derived from our previous in vitro study. Mice were orally dosed with 0, 10, 20, and 60 mg/kg of body weight TBT, and levels of PP2A, reactive oxygen species (ROS), mitogen-activated protein kinase (MAPK), Bax/Bcl-2, and caspase-3 were detected in the mouse livers. Apoptosis was also evaluated using the TUNEL assay. The results showed that PP2A activity was inhibited, ROS levels were elevated, and MAPKs including ERK, JNK, and p38 were activated in mouse livers treated with the highest dose of TBT. Additionally, the ratio of Bax/Bcl-2 was increased, caspase-3 was activated, and apoptosis in mouse livers could be detected in the highest dose group. Therefore, a possible signaling pathway in TBT-induced apoptosis in mouse livers involves PP2A inhibition and ROS elevation serving a pivotal function as upstream activators of MAPKs; activation of MAPKs in turn leads to an increase in the Bax/Bcl-2 ratio, ultimately leading to the activation of caspase-3. The results give a comprehensive and novel description of the mechanism of TBT-induced toxicity.
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Affiliation(s)
- Yali Zhang
- Department of Biochemistry and Genetics, School of medicine, Zhejiang University, 866th Yu Hang Tang Road, 310058, Hangzhou, China
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6
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Zhang Y, Liang J, Sun L, Guo Z, Xu L. Inhibition of PP2A and the consequent activation of JNK/c-Jun are involved in tributyltin-induced apoptosis in human amnionic cells. ENVIRONMENTAL TOXICOLOGY 2013; 28:390-400. [PMID: 21626652 DOI: 10.1002/tox.20730] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2011] [Revised: 04/03/2011] [Accepted: 04/04/2011] [Indexed: 05/30/2023]
Abstract
Tributyltin (TBT), a highly toxic environmental contaminant, has been shown to induce mitochondrial-dependent apoptosis in several mammalian cells. However, the upstream signal transduction pathways involved in TBT-induced apoptosis are still not fully elucidated. In this study, the protein phosphatase (PP) 2A, microtubule organization, and mitogen-activated protein kinases (MAPKs), including JNK, p38 and their downstream transcription factors, c-Jun and ATF-2, respectively, were investigated in human amnionic cells treated by TBT. Furthermore, the activation of procaspase-3 after blocking either one of these MAPK pathways was also observed. The results showed that TBT effectively induced apoptosis characterized by caspase-3 activation. In apoptotic cells, the inhibition of PP2A activity and microtubule depolymerization was detected. Additionally, JNK and p38, as well as their downstream targets, c-Jun and ATF-2, were activated. Moreover, a JNK inhibitor, but not p38 inhibitor, significantly reduced caspase-3 activation. It can be concluded that the inhibition of PP2A may (1) play as a role in the activation of JNK and c-Jun and the concomitant promotion of microtubule depolymerization and (2) lead to the activation of caspase-3 in TBT-induced apoptotic cells. The results of this study suggest a critical role of PP2A in the TBT toxicity mechanism.
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Affiliation(s)
- Yali Zhang
- Department of Biochemistry and Genetics, School of medicine, Zhejiang University, 388 Yu Hang Tang Road, 310058, Hangzhou, China
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Che X, Liu J, Huang H, Mi X, Xia Q, Li J, Zhang D, Ke Q, Gao J, Huang C. p27 suppresses cyclooxygenase-2 expression by inhibiting p38β and p38δ-mediated CREB phosphorylation upon arsenite exposure. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2083-91. [PMID: 23639288 DOI: 10.1016/j.bbamcr.2013.04.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 04/06/2013] [Accepted: 04/23/2013] [Indexed: 12/13/2022]
Abstract
p27 is a cyclin-dependent kinase (CDK) inhibitor that suppresses a cell's transition from G0 to S phase, therefore acting as a tumor suppressor. Our most recent studies demonstrate that upon arsenite exposure, p27 suppresses Hsp27 and Hsp70 expressions through the JNK2/c-Jun- and HSF-1-dependent pathways, suggesting a novel molecular mechanism underlying the tumor suppressive function of p27 in a CDK-independent manner. We found that p27-deficiency (p27-/-) resulted in the elevation of cyclooxygenase-2 (COX-2) expression at transcriptional level, whereas the introduction of p27 brought back COX-2 expression to a level similar to that of p27+/+ cells, suggesting that p27 exhibits an inhibitory effect on COX-2 expression. Further studies identified that p27 inhibition of COX-2 expression was specifically due to phosphorylation of transcription factor cAMP response element binding (CREB) phosphorylation mediated by p38β and p38δ. These results demonstrate a novel mechanism underlying tumor suppression effect of p27 and will contribute to the understanding of the overall mechanism of p27 tumor suppression in a CDK-independent manner.
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Affiliation(s)
- Xun Che
- Nelson Institute of Environmental Medicine, New York University, School of Medicine, 57 Old Forge Road, Tuxedo, NY 10987, USA
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8
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Homer CR, Kabi A, Marina-García N, Sreekumar A, Nesvizhskii AI, Nickerson KP, Chinnaiyan AM, Nuñez G, McDonald C. A dual role for receptor-interacting protein kinase 2 (RIP2) kinase activity in nucleotide-binding oligomerization domain 2 (NOD2)-dependent autophagy. J Biol Chem 2012; 287:25565-76. [PMID: 22665475 DOI: 10.1074/jbc.m111.326835] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Autophagy is triggered by the intracellular bacterial sensor NOD2 (nucleotide-binding, oligomerization domain 2) as an anti-bacterial response. Defects in autophagy have been implicated in Crohn's disease susceptibility. The molecular mechanisms of activation and regulation of this process by NOD2 are not well understood, with recent studies reporting conflicting requirements for RIP2 (receptor-interacting protein kinase 2) in autophagy induction. We examined the requirement of NOD2 signaling mediated by RIP2 for anti-bacterial autophagy induction and clearance of Salmonella typhimurium in the intestinal epithelial cell line HCT116. Our data demonstrate that NOD2 stimulates autophagy in a process dependent on RIP2 tyrosine kinase activity. Autophagy induction requires the activity of the mitogen-activated protein kinases MEKK4 and p38 but is independent of NFκB signaling. Activation of autophagy was inhibited by a PP2A phosphatase complex, which interacts with both NOD2 and RIP2. PP2A phosphatase activity inhibited NOD2-dependent autophagy but not activation of NFκB or p38. Upon stimulation of NOD2, the phosphatase activity of the PP2A complex is inhibited through tyrosine phosphorylation of the catalytic subunit in a process dependent on RIP2 activity. These findings demonstrate that RIP2 tyrosine kinase activity is not only required for NOD2-dependent autophagy but plays a dual role in this process. RIP2 both sends a positive autophagy signal through activation of p38 MAPK and relieves repression of autophagy mediated by the phosphatase PP2A.
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Affiliation(s)
- Craig R Homer
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA
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9
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Jarvis GE, Bihan D, Hamaia S, Pugh N, Ghevaert CJG, Pearce AC, Hughes CE, Watson SP, Ware J, Rudd CE, Farndale RW. A role for adhesion and degranulation-promoting adapter protein in collagen-induced platelet activation mediated via integrin α(2) β(1). J Thromb Haemost 2012; 10:268-77. [PMID: 22103309 PMCID: PMC3791415 DOI: 10.1111/j.1538-7836.2011.04567.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
BACKGROUND Collagen-induced platelet activation is a key step in the development of arterial thrombosis via its interaction with the receptors glycoprotein (GP)VI and integrin α(2) β(1) . Adhesion and degranulation-promoting adapter protein (ADAP) regulates α(IIb) β(3) in platelets and α(L) β(2) in T cells, and is phosphorylated in GPVI-deficient platelets activated by collagen. OBJECTIVES To determine whether ADAP plays a role in collagen-induced platelet activation and in the regulation and function of α(2) β(1). METHODS Using ADAP(-/-) mice and synthetic collagen peptides, we investigated the role of ADAP in platelet aggregation, adhesion, spreading, thromboxane synthesis, and tyrosine phosphorylation. RESULTS AND CONCLUSIONS Platelet aggregation and phosphorylation of phospholipase Cγ2 induced by collagen were attenuated in ADAP(-/-) platelets. However, aggregation and signaling induced by collagen-related peptide (CRP), a GPVI-selective agonist, were largely unaffected. Platelet adhesion to CRP was also unaffected by ADAP deficiency. Adhesion to the α(2) β(1) -selective ligand GFOGER and to a peptide (III-04), which supports adhesion that is dependent on both GPVI and α(2) β(1), was reduced in ADAP(-/-) platelets. An impedance-based label-free detection technique, which measures adhesion and spreading of platelets, indicated that, in the absence of ADAP, spreading on GFOGER was also reduced. This was confirmed with non-fluorescent differential-interference contrast microscopy, which revealed reduced filpodia formation in ADAP(-/-) platelets adherent to GFOGER. This indicates that ADAP plays a role in mediating platelet activation via the collagen-binding integrin α(2) β(1). In addition, we found that ADAP(-/-) mice, which are mildly thrombocytopenic, have enlarged spleens as compared with wild-type animals. This may reflect increased removal of platelets from the circulation.
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Affiliation(s)
- G E Jarvis
- School of Pharmacy, Queen's University Belfast, Belfast, UK.
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10
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Loyau S, Dumont B, Ollivier V, Boulaftali Y, Feldman L, Ajzenberg N, Jandrot-Perrus M. Platelet glycoprotein VI dimerization, an active process inducing receptor competence, is an indicator of platelet reactivity. Arterioscler Thromb Vasc Biol 2011; 32:778-85. [PMID: 22155453 DOI: 10.1161/atvbaha.111.241067] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
OBJECTIVE The immune receptor homologue glycoprotein VI (GPVI)/FcR receptor γ chain complex is primarily responsible for platelet activation by collagen. There is growing evidence that optimal binding of GPVI to collagen depends on the assembly of GPVI dimers. The valence of GPVI on resting platelets needs to be clearly established because platelet avidity for collagen would be greater if GPVI is constitutively expressed as a dimer than as a monomer. METHODS AND RESULTS Using a monoclonal antibody (9E18) that preferentially binds to GPVI dimers, we found that GPVI was maintained in a monomeric form on human resting platelets under the control of intraplatelet cAMP concentration. Activation by soluble agonists or von Willebrand factor induced a shift toward GPVI dimerization related to increased platelet adhesion to collagen. A correlation between platelet binding of 9E18 and P-selectin exposure was observed in patients experiencing coronary artery disease, and antagonists of the ADP receptor P2Y12 limited ADP-induced GPVI dimerization. CONCLUSION The rapid assembly of highly competent dimers of GPVI at sites of vascular lesion represents an important step in the sequence of events leading to platelet activation by collagen. GPVI dimers could represent a new marker to analyze platelet reactivity.
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Affiliation(s)
- Stéphane Loyau
- INSERM U698, CHU Xavier Bichat, 46 rue Henri Huchard 75877 Paris Cedex 18, France
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11
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Switzer CH, Cheng RYS, Vitek TM, Christensen DJ, Wink DA, Vitek MP. Targeting SET/I(2)PP2A oncoprotein functions as a multi-pathway strategy for cancer therapy. Oncogene 2011; 30:2504-13. [PMID: 21297667 PMCID: PMC3107340 DOI: 10.1038/onc.2010.622] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The SET oncoprotein participates in cancer progression by affecting multiple cellular processes, inhibiting the tumor suppressor protein phosphatase 2A (PP2A), and inhibiting the metastasis suppressor nm23-H1. On the basis of these multiple activities, we hypothesized that targeted inhibition of SET would have multiple discrete and measurable effects on cancer cells. Here, the effects of inhibiting SET oncoprotein function on intracellular signaling and proliferation of human cancer cell lines was investigated. We observed the effects of COG112, a novel SET interacting peptide, on PP2A activity, Akt signaling, nm23-H1 activity and cellular migration/invasion in human U87 glioblastoma and MDA-MB-231 breast adenocarcinoma cancer cell lines. We found that COG112 interacted with SET protein and inhibited the association between SET and PP2A catalytic subunit (PP2A-c) and nm23-H1. The interaction between COG112 and SET caused PP2A phosphatase and nm23-H1 exonuclease activities to increase. COG112-mediated increases in PP2A activity resulted in the inhibition of Akt signaling and cellular proliferation. Additionally, COG112 inhibited SET association with Ras-related C(3) botulinum toxin substrate 1 (Rac1), leading to decreased cellular migration and invasion. COG112 treatment releases the SET-mediated inhibition of the tumor suppressor PP2A, as well as the metastasis suppressor nm23-H1. These results establish SET as a novel molecular target and that the inhibition of SET may have beneficial effects in cancer chemotherapy.
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Affiliation(s)
- C H Switzer
- Radiation Biology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
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12
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Frasca D, Romero M, Landin AM, Diaz A, Riley RL, Blomberg BB. Protein phosphatase 2A (PP2A) is increased in old murine B cells and mediates p38 MAPK/tristetraprolin dephosphorylation and E47 mRNA instability. Mech Ageing Dev 2010; 131:306-14. [PMID: 20219523 DOI: 10.1016/j.mad.2010.02.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Revised: 02/09/2010] [Accepted: 02/20/2010] [Indexed: 11/18/2022]
Abstract
The transcription factor E47, which regulates immunoglobulin class switch in murine splenic B cells, is down-regulated in aged B cells due to reduced mRNA stability. Part of the decreased stability of E47 mRNA is mediated by tristetraprolin (TTP), a physiological regulator of mRNA stability. We have previously shown that TTP mRNA and protein expression are higher in old B cells, and the protein is less phosphorylated in old B cells, both of which lead to more binding of TTP to the 3'-UTR of E47 mRNA, thereby decreasing its stability. PP2A is a protein phosphatase that plays an important role in the regulation of a number of major signaling pathways. Herein we show that not only the amount but also the activity of PP2A is increased in old B cells. As a consequence of this higher phosphatase activity in old B cells, p38 MAPK and TTP (either directly or indirectly by PP2A) are less phosphorylated as compared with young B cells. PP2A dephosphorylation of p38 MAPK and/or TTP likely generates more binding of the hypophosphorylated TTP to the E47 mRNA, inducing its degradation. This mechanism may be at least in part responsible for the age-related decrease in class switch.
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Affiliation(s)
- Daniela Frasca
- Department of Microbiology and Immunology, University of Miami Miller School of Medicine, P.O. Box 016960 (R-138), Miami, FL 33101, USA
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13
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Aguilar JL, Kulkarni R, Randis TM, Soman S, Kikuchi A, Yin Y, Ratner AJ. Phosphatase-dependent regulation of epithelial mitogen-activated protein kinase responses to toxin-induced membrane pores. PLoS One 2009; 4:e8076. [PMID: 19956644 PMCID: PMC2778951 DOI: 10.1371/journal.pone.0008076] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Accepted: 11/06/2009] [Indexed: 11/29/2022] Open
Abstract
Diverse bacterial species produce pore-forming toxins (PFT) that can puncture eukaryotic cell membranes. Host cells respond to sublytic concentrations of PFT through conserved intracellular signaling pathways, including activation of mitogen-activated protein kinases (MAPK), which are critical to cell survival. Here we demonstrate that in respiratory epithelial cells p38 and JNK MAPK were phosphorylated within 30 min of exposure to pneumolysin, the PFT from Streptococcus pneumoniae. This activation was tightly regulated, and dephosphorylation of both MAPK occurred within 60 min following exposure. Pretreatment of epithelial cells with inhibitors of cellular phosphatases, including sodium orthovanadate, calyculin A, and okadaic acid, prolonged and intensified MAPK activation. Specific inhibition of MAPK phosphatase-1 did not affect the kinetics of MAPK activation in PFT-exposed epithelial cells, but siRNA-mediated knockdown of serine/threonine phosphatases PP1 and PP2A were potent inhibitors of MAPK dephosphorylation. These results indicate an important role for PP1 and PP2A in termination of epithelial responses to PFT and only a minor contribution of dual-specificity phosphatases, such as MAPK phosphatase-1, which are the major regulators of MAPK signals in other cell types. Epithelial regulation of MAPK signaling in response to membrane disruption involves distinct pathways and may require different strategies for therapeutic interventions.
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Affiliation(s)
- Jorge L. Aguilar
- Department of Pediatrics, Columbia University, New York, New York, United States of America
| | - Ritwij Kulkarni
- Department of Pediatrics, Columbia University, New York, New York, United States of America
| | - Tara M. Randis
- Department of Pediatrics, Columbia University, New York, New York, United States of America
| | - Sandeep Soman
- Department of Pediatrics, Columbia University, New York, New York, United States of America
| | - Alexander Kikuchi
- Department of Pediatrics, Columbia University, New York, New York, United States of America
| | - Yuxin Yin
- Department of Radiation Oncology, Columbia University, New York, New York, United States of America
| | - Adam J. Ratner
- Department of Pediatrics, Columbia University, New York, New York, United States of America
- Department of Microbiology & Immunology, Columbia University, New York, New York, United States of America
- * E-mail:
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14
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Kaiser WJ, Holbrook LM, Tucker KL, Stanley RG, Gibbins JM. A Functional Proteomic Method for the Enrichment of Peripheral Membrane Proteins Reveals the Collagen Binding Protein Hsp47 Is Exposed on the Surface of Activated Human Platelets. J Proteome Res 2009; 8:2903-14. [DOI: 10.1021/pr900027j] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- William J. Kaiser
- Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, Hopkins Building, The University of Reading, Whiteknights, Reading, United Kingdom RG6 6UB
| | - Lisa-Marie Holbrook
- Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, Hopkins Building, The University of Reading, Whiteknights, Reading, United Kingdom RG6 6UB
| | - Katherine L. Tucker
- Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, Hopkins Building, The University of Reading, Whiteknights, Reading, United Kingdom RG6 6UB
| | - Ronald G. Stanley
- Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, Hopkins Building, The University of Reading, Whiteknights, Reading, United Kingdom RG6 6UB
| | - Jonathan M. Gibbins
- Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, Hopkins Building, The University of Reading, Whiteknights, Reading, United Kingdom RG6 6UB
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15
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Korporaal SJA, Koekman CA, Verhoef S, van der Wal DE, Bezemer M, Van Eck M, Akkerman JWN. Downregulation of platelet responsiveness upon contact with LDL by the protein-tyrosine phosphatases SHP-1 and SHP-2. Arterioscler Thromb Vasc Biol 2008; 29:372-9. [PMID: 19096001 DOI: 10.1161/atvbaha.108.173278] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The sensitivity of platelets to aggregating agents increases when low-density lipoprotein (LDL) binds to apolipoprotein E receptor 2' (apoER2'), triggering activation of p38MAPK and formation of thromboxane A2. LDL signaling is terminated by PECAM-1 through recruitment and activation of the Ser/Thr protein phosphatase PP2A, but platelets remain unresponsive to LDL when PECAM-1 activation disappears. We report a second mechanism that halts LDL signaling and in addition lowers platelet responsiveness to aggregating agents. METHODS AND RESULTS After a first stimulation with LDL, platelets remain unresponsive to LDL for 60 minutes, despite normal apoER2' activation by a second dose of LDL. A possible cause is persistent activation of the tyrosine phosphatases SHP-1 and SHP-2, which may not only block a second activation of p38MAPK, PECAM-1, and PP2A by LDL but also seem to reduce aggregation by TRAP, collagen, and ADP. CONCLUSION These findings reveal that p38MAPK phosphorylation and platelet activation by LDL are suppressed by two mechanisms: (1) short activation of PECAM-1/PP2A, and (2) prolonged activation of SHP-1 and SHP-2. Activation of SHP-1 and SHP-2 is accompanied by reduced responsiveness to aggregating agents, which--if present in vivo--would make LDL an aggregation inhibitor during prolonged contact with platelets.
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Affiliation(s)
- Suzanne J A Korporaal
- Department of Clinical Chemistry and Haematology, University Medical Center, Utrecht, The Netherlands
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16
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Maillet M, Purcell NH, Sargent MA, York AJ, Bueno OF, Molkentin JD. DUSP6 (MKP3) null mice show enhanced ERK1/2 phosphorylation at baseline and increased myocyte proliferation in the heart affecting disease susceptibility. J Biol Chem 2008; 283:31246-55. [PMID: 18753132 DOI: 10.1074/jbc.m806085200] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The strength and duration of mitogen-activated protein kinase signaling is regulated through phosphorylation and dephosphorylation by dedicated dual-specificity kinases and phosphatases, respectively. Here we investigated the physiological role that extracellular signal-regulated kinases 1/2 (ERK1/2) dephosphorylation plays in vivo through targeted disruption of the gene encoding dual-specificity phosphatase 6 (Dusp6) in the mouse. Dusp6(-/-) mice, which were viable, fertile, and otherwise overtly normal, showed an increase in basal ERK1/2 phosphorylation in the heart, spleen, kidney, brain, and fibroblasts, but no change in ERK5, p38, or c-Jun N-terminal kinases activation. However, loss of Dusp6 did not increase or prolong ERK1/2 activation after stimulation, suggesting that its function is more dedicated to basal ERK1/2 signaling tone. In-depth analysis of the physiological effect associated with increased baseline ERK1/2 signaling was performed in cultured mouse embryonic fibroblasts (MEFs) and the heart. Interestingly, mice lacking Dusp6 had larger hearts at every age examined, which was associated with greater rates of myocyte proliferation during embryonic development and in the early postnatal period, resulting in cardiac hypercellularity. This increase in myocyte content in the heart was protective against decompensation and hypertrophic cardiomyopathy following long term pressure overload and myocardial infarction injury in adult mice. Dusp6(-/-) MEFs also showed reduced apoptosis rates compared with wild-type MEFs. These results demonstrate that ERK1/2 signaling is physiologically restrained by DUSP6 in coordinating cellular development and survival characteristics, directly impacting disease-responsiveness in adulthood.
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Affiliation(s)
- Marjorie Maillet
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA
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17
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Ciuffini L, Castellani L, Salvati E, Galletti S, Falcone G, Alemà S. Delineating v-Src downstream effector pathways in transformed myoblasts. Oncogene 2007; 27:528-39. [PMID: 17637741 DOI: 10.1038/sj.onc.1210665] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In this study, we delineate the intracellular signalling pathways modulated by a conditional v-Src tyrosine kinase that lead to unrestrained proliferation and block of differentiation of primary avian myoblasts. By inhibiting Ras-MAPK kinase and phosphatidylinositol 3-kinase with different means, we find that both pathways play crucial roles in controlling v-Src-sustained growth factor and anchorage independence for proliferation. The Ras-MAPK kinase pathway also contributes to block of differentiation independently of cell proliferation since inhibition of this pathway both in proliferating and growth-arrested v-Src-transformed myoblasts induces expression of muscle-specific genes, fusion into multinucleated myotubes and assembly of specialized contractile structures. Importantly, we find that the p38 MAPK pathway is inhibited by v-Src in myoblasts and its forced activation results in growth inhibition and expression of differentiation, indicating p38 MAPK as a critical target of v-Src in growth transformation and myogenic differentiation. Furthermore, we show that downregulation of p38 MAPK activation may occur via Ras-MAPK kinase, thus highlighting a cross-regulation between the two pathways. Finally, we report that the simultaneous inhibition of MAPK kinase and calpain, combined to activation of p38 MAPK, are sufficient to reconstitute largely the differentiation potential of v-Src-transformed myoblasts.
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Affiliation(s)
- L Ciuffini
- Istituto di Biologia Cellulare, Consiglio Nazionale delle Ricerche, Monterotondo Scalo (RM), Italy
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18
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ten Klooster JP, Leeuwen IV, Scheres N, Anthony EC, Hordijk PL. Rac1-induced cell migration requires membrane recruitment of the nuclear oncogene SET. EMBO J 2007; 26:336-45. [PMID: 17245428 PMCID: PMC1783461 DOI: 10.1038/sj.emboj.7601518] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Accepted: 11/29/2006] [Indexed: 01/25/2023] Open
Abstract
The Rho GTPase Rac1 controls cell adhesion and motility. The effector loop of Rac1 mediates interactions with downstream effectors, whereas its C-terminus binds the exchange factor beta-Pix, which mediates Rac1 targeting and activation. Here, we report that Rac1, through its C-terminus, also binds the nuclear oncogene SET/I2PP2A, an inhibitor of the serine/threonine phosphatase PP2A. We found that SET translocates to the plasma membrane in cells that express active Rac1 as well as in migrating cells. Membrane targeting of SET stimulates cell migration in a Rac1-dependent manner. Conversely, reduction of SET expression inhibits Rac1-induced migration, indicating that efficient Rac1 signalling requires membrane recruitment of SET. The recruitment of the SET oncogene to the plasma membrane represents a new feature of Rac1 signalling. Our results suggest a model in which Rac1-stimulated cell motility requires both effector loop-based downstream signalling and recruitment of a signalling amplifier, that is, SET, through the hypervariable C-terminus.
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Affiliation(s)
- Jean Paul ten Klooster
- Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Plesmanlaan, Amsterdam, The Netherlands
| | - Ingrid v Leeuwen
- Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Plesmanlaan, Amsterdam, The Netherlands
| | - Nina Scheres
- Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Plesmanlaan, Amsterdam, The Netherlands
| | - Eloise C Anthony
- Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Plesmanlaan, Amsterdam, The Netherlands
| | - Peter L Hordijk
- Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Plesmanlaan, Amsterdam, The Netherlands
- Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Plesmanlaan, 1066 CX, Amsterdam, The Netherlands. Tel.: +31 20 512 3263; Fax: +31 20 512 3474; E-mail:
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19
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Vahebi S, Ota A, Li M, Warren CM, de Tombe PP, Wang Y, Solaro RJ. p38-MAPK induced dephosphorylation of alpha-tropomyosin is associated with depression of myocardial sarcomeric tension and ATPase activity. Circ Res 2007; 100:408-15. [PMID: 17234967 DOI: 10.1161/01.res.0000258116.60404.ad] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Our objective in work presented here was to understand the mechanisms by which activated p38alpha MAPK depresses myocardial contractility. To test the hypothesis that activation of p38 MAPK directly influences sarcomeric function, we used transgenic mouse models with hearts in which p38 MAPK was constitutively turned on by an upstream activator (MKK6bE). These hearts demonstrated a significant depression in ejection fraction after induction of the transgene. We also studied hearts of mice expressing a dominant negative p38alpha MAPK. Simultaneous determination of tension and ATPase activity of detergent-skinned fiber bundles from left ventricular papillary muscle demonstrated a significant inhibition of both maximum tension and ATPase activity in the transgenic-MKK6bE hearts. Fibers from hearts expressing dominant negative p38alpha MAPK demonstrated no significant change in tension or ATPase activity. There were no significant changes in phosphorylation level of troponin-T3 and troponin-T4, or myosin light chain 2. However, compared with controls, there was a significant depression in levels of phosphorylation of alpha-tropomyosin and troponin I in fiber bundles from transgenic-MKK6bE hearts, but not from dominant negative p38alpha MAPK hearts. Our experiments also showed that p38alpha MAPK colocalizes with alpha-actinin at the Z-disc and complexes with protein phosphatases (PP2alpha, PP2beta). These data are the first to indicate that chronic activation of p38alpha MAPK directly depresses sarcomeric function in association with decreased phosphorylation of alpha-tropomyosin.
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Affiliation(s)
- Susan Vahebi
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612-7342, USA
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20
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Boudreau RTM, Conrad DM, Hoskin DW. Apoptosis induced by protein phosphatase 2A (PP2A) inhibition in T leukemia cells is negatively regulated by PP2A-associated p38 mitogen-activated protein kinase. Cell Signal 2007; 19:139-51. [PMID: 16844342 DOI: 10.1016/j.cellsig.2006.05.030] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2006] [Revised: 05/29/2006] [Accepted: 05/31/2006] [Indexed: 01/21/2023]
Abstract
Serine/threonine phosphatase regulation of phosphorylation-mediated intracellular signaling controls a number of important processes in mammalian cells. In this study, we show that constitutively active protein phosphatase 2A (PP2A), which is a serine/threonine phosphatase, is essential for T leukemia cell survival. Jurkat and CCRF-CEM T leukemia cells treated with the PP2A-selective inhibitor okadaic acid (OA) showed a dose- and time-dependent induction of apoptosis, as indicated by loss of mitochondrial transmembrane potential (delta psi(m)), cleavage-induced activation of caspase-3, -8, and -9, and DNA fragmentation. In addition, caspase-8 or caspase-9 inhibition with z-IETD-fmk or z-LEHD-fmk, respectively, largely prevented OA-induced apoptosis. Although OA treatment did not affect constitutive Bcl-2 expression, overexpression of Bcl-2 prevented both OA-induced DNA fragmentation and dissipation of delta psi(m). Furthermore, inhibition of caspase-3, -8, or -9 partially protected against OA-induced loss of delta psi(m). In addition, caspase-9 and caspase-3 inhibition largely prevented procaspase-3 and procaspase-8 cleavage, respectively, while caspase-8 inhibition partially interfered with procaspase-9 cleavage in OA-treated T leukemia cells. Thus, PP2A inhibition triggered the intrinsic pathway of apoptosis, which was enhanced by a mitochondrial feedback amplification loop. PP2A has also been implicated in the regulation of p38 mitogen-activated protein kinase (MAPK). Co-immunoprecipitation analysis revealed a physical association between the catalytic subunit of PP2A and p38 MAPK in T leukemia cells. Moreover, OA treatment caused p38 MAPK to be phosphorylated in a dose- and time-dependent fashion, indicating that PP2A prevented p38 MAPK activation. Although p38 MAPK activation usually promotes apoptosis, pharmacologic inhibition of p38 MAPK exacerbated OA-induced DNA fragmentation and loss of delta psi(m) in T leukemia cells, suggesting that, in this instance, the p38 MAPK signaling pathway promoted cell survival. Collectively, these findings indicate that PP2A and p38 MAPK have coordinate effects on signaling pathways that regulate the survival of T leukemia cells.
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Affiliation(s)
- Robert T M Boudreau
- Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Sir Charles Tupper Medical Building, 5850 University Ave., Halifax, Nova Scotia, Canada B3H 1X5
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21
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Moscardó A, Vallés J, Piñón M, Aznar J, Martínez-Sales V, Santos MT. Regulation of cytosolic PlA2 activity by PP1/PP2A serine/threonine phosphatases in human platelets. Platelets 2006; 17:405-15. [PMID: 16973502 DOI: 10.1080/09537100600757869] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Platelet thromboxane A2 (TXA2) synthesis is an important pathway of platelet reactivity. We report that in thrombin-stimulated platelets, PP1/PP2A serine/threonine phosphatases regulate phospholipase A2 (cPLA2) activity, which is required for TXA2 synthesis. Two mechanisms are involved: (a) constitutively active PP1/PP2A regulate cPLA2 phosphorylation, and (b) PP1/PP2A activity mediates agonist-induced increase in cytosolic Ca2+ ([Ca2+]i). Inhibition of PP1/PP2A with okadaic acid (OA) induces cPLA2 phosphorylation but reduces Ca2+ responses: release from intracellular stores and influx through the plasma membrane, particularly that mediated by store-mediated Ca2+ entry (SMCE). A significant correlation (r = 0.64) exists between OA-regulated [Ca2+]i and TXA2 synthesis. Okadaic acid-induced decrease in SMCE and the associated TXA2 synthesis are mediated by a reduction in protein-tyrosine phosphorylation. This reduction is not due to inhibition of tyrosine kinases but rather to an OA-mediated increase in tyrosine phosphatases. This is the first study to report that PP1/PP2A phosphatases are involved in the regulation of the two key elements in eicosanoid synthesis, [Ca2+]i and cPLA2 phosphorylation. Moreover, PP1/PP2A regulation of [Ca2+]i and tyrosine phosphorylation may be important for other calcium-dependent processes and/or signal transduction mechanisms in platelets.
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22
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Korporaal SJA, Akkerman JWN. Platelet activation by low density lipoprotein and high density lipoprotein. PATHOPHYSIOLOGY OF HAEMOSTASIS AND THROMBOSIS 2006; 35:270-80. [PMID: 16877876 DOI: 10.1159/000093220] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cardiovascular disease is the main cause of death and disability in the Western society. Lipoproteins are important in the development of cardiovascular disease since they change the properties of different cells involved in atherosclerosis and thrombosis. The interaction of platelets with lipoproteins has been under intense investigation. Particularly the initiation of platelet signaling pathways by low density lipoprotein (LDL) has been studied thoroughly, since platelets of hypercholesterolemic patients, whose plasma contains elevated LDL levels due to absent or defective LDL receptors, show hyperaggregability in vitro and enhanced activity in vivo. These observations suggest that LDL enhances platelet responsiveness. Several signaling pathways induced by LDL have been revealed in vitro, such as signaling via p38 mitogen-activated protein kinase and p125 focal adhesion kinase. High density lipoprotein (HDL) consists of two subtypes, HDL(2) and HDL(3), which have opposing effects on platelet activation. This review provides a summary of the activation of signaling pathways after platelet-LDL and platelet-HDL interaction, with special emphasis on their role in the development of thrombosis and atherosclerosis.
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Affiliation(s)
- Suzanne J A Korporaal
- Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center Utrecht and The Institute for Biomembranes, University of Utrecht, The Netherlands.
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23
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Zuluaga S, Alvarez-Barrientos A, Gutiérrez-Uzquiza A, Benito M, Nebreda AR, Porras A. Negative regulation of Akt activity by p38alpha MAP kinase in cardiomyocytes involves membrane localization of PP2A through interaction with caveolin-1. Cell Signal 2006; 19:62-74. [PMID: 16844343 DOI: 10.1016/j.cellsig.2006.05.032] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2006] [Accepted: 05/11/2006] [Indexed: 01/07/2023]
Abstract
Cardiomyocyte-derived cell lines deficient in p38alpha are more resistant to apoptosis owing to lower expression of the pro-apoptotic proteins Bax and Fas and upregulation of the ERK survival pathway. Here, we show that increased Akt activity also contributes to the enhanced survival of p38alpha-deficient cardiomyocytes. We found that the serine/threonine phosphatase PP2A can be targeted to caveolae through interaction with caveolin-1 in a p38alpha-dependent manner. In agreement with this, PP2A activity associated with caveolin-1 was higher in wild type than in p38alpha-deficient cells. Akt was also present in caveolae and incubation of wild-type cells with the PP2A inhibitor okadaic acid increases the levels of Akt activity. Thus, p38alpha-induced re-localization of PP2A to caveolae can lead to dephosphorylation and inhibition of Akt, which in turn would contribute to the decreased survival observed in wild type cells. However, cell detachment impairs the formation of the PP2A/caveolin-1 complex and, as a consequence, phospho-Akt levels and survival are no longer regulated by p38alpha in detached wild type cardiomyocytes. Our results suggest that p38alpha can negatively modulate Akt activity, independently of PI3K, by regulating the interaction between caveolin-1 and PP2A through a mechanism dependent on cell attachment.
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Affiliation(s)
- Susana Zuluaga
- Departamento de Bioquímica y Biología Molecular II, Facultad de Farmacia, UCM, Ciudad Universitaria, 28040 Madrid, Spain
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24
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Thirone ACP, JeBailey L, Bilan PJ, Klip A. Opposite effect of JAK2 on insulin-dependent activation of mitogen-activated protein kinases and Akt in muscle cells: possible target to ameliorate insulin resistance. Diabetes 2006; 55:942-51. [PMID: 16567515 DOI: 10.2337/diabetes.55.04.06.db05-1265] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Many cytokines increase their receptor affinity for Janus kinases (JAKs). Activated JAK binds to signal transducers and activators of transcription, insulin receptor substrates (IRSs), and Shc. Intriguingly, insulin acting through its own receptor kinase also activates JAK2. However, the impact of such activation on insulin action remains unknown. To determine the contribution of JAK2 to insulin signaling, we transfected L6 myotubes with siRNA against JAK2 (siJAK2), reducing JAK2 protein expression by 75%. Insulin-dependent phosphorylation of IRS1/2 and Shc was not affected by siJAK2, but insulin-induced phosphorylation of the mitogen-activated protein kinases (MAPKs) extracellular signal-related kinase, p38, and Jun NH2-terminal kinase and their respective upstream kinases MKK1/2, MKK3/6, and MKK4/7 was significantly lowered when JAK2 was depleted, correlating with a significant drop in insulin-mediated cell proliferation. These effects were reproduced by the JAK2 inhibitor AG490. Conversely, insulin-stimulated Akt phosphorylation, glucose uptake, and GLUT4 translocation were not affected by siJAK2. Interestingly, in two insulin-resistant states, siJAK2 led to partial restoration of Akt phosphorylation and glucose uptake stimulation but not of the MAPK pathway. These results suggest that JAK2 may depress the Akt to glucose uptake signaling axis selectively in insulin-resistant states. Inhibition of JAK2 may be a useful strategy to relieve insulin resistance of metabolic outcomes.
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Affiliation(s)
- Ana C P Thirone
- The Hospital for Sick Children, 555 University Ave., Toronto, Ontario, Canada M5G 1X8
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25
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Adams DG, Coffee RL, Zhang H, Pelech S, Strack S, Wadzinski BE. Positive regulation of Raf1-MEK1/2-ERK1/2 signaling by protein serine/threonine phosphatase 2A holoenzymes. J Biol Chem 2005; 280:42644-54. [PMID: 16239230 DOI: 10.1074/jbc.m502464200] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein serine/threonine phosphatase 2A (PP2A) regulates a wide variety of cellular signal transduction pathways. The predominant form of PP2A in cells is a heterotrimeric holoenzyme consisting of a scaffolding (A) subunit, a regulatory (B) subunit, and a catalytic (C) subunit. Although PP2A is known to regulate Raf1-MEK1/2-ERK1/2 signaling at multiple steps in this pathway, the specific PP2A holoenzymes involved remain unclear. To address this question, we established tetracycline-inducible human embryonic kidney 293 cell lines for overexpression of FLAG-tagged Balpha/delta regulatory subunits by approximately 3-fold or knock-down of Balpha by greater than 70% compared with endogenous levels. The expression of functional epitope-tagged B subunits was confirmed by the detection of A and C subunits as well as phosphatase activity in FLAG immune complexes from extracts of cells overexpressing the FLAG-Balpha/delta subunit. Western analysis of the cell extracts using phosphospecific antibodies for MEK1/2 and ERK1/2 demonstrated that activation of these kinases in response to epidermal growth factor was markedly diminished in Balpha knock-down cells but elevated in Balpha- and Bdelta-overexpressing cells as compared with control cells. In parallel with the activation of MEK1/2 and ERK1/2, the inhibitory phosphorylation site of Raf1 (Ser-259) was dephosphorylated in cells overexpressing Balpha or Bdelta. Pharmacological inhibitor studies as well as reporter assays for ERK-dependent activation of the transcription factor Elk1 revealed that the PP2A holoenzymes ABalphaC and ABdeltaC act downstream of Ras and upstream of MEK1 to promote activation of this MAPK signaling cascade. Furthermore both PP2A holoenzymes were found to associate with Raf1 and catalyze dephosphorylation of inhibitory phospho-Ser-259. Together these findings indicate that PP2A ABalphaC and ABdeltaC holoenzymes function as positive regulators of Raf1-MEK1/2-ERK1/2 signaling by targeting Raf1.
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Affiliation(s)
- Deanna G Adams
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA
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Keen JC, Zhou Q, Park BH, Pettit C, Mack KM, Blair B, Brenner K, Davidson NE. Protein phosphatase 2A regulates estrogen receptor alpha (ER) expression through modulation of ER mRNA stability. J Biol Chem 2005; 280:29519-24. [PMID: 15965230 DOI: 10.1074/jbc.m505317200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein phosphatase 2A (PP2A) is a ubiquitously expressed member of the serine-threonine phosphatase family that is involved in regulation of many cellular processes including transcription, translation, cellular metabolism, and apoptosis. Because of a correlation between PP2A and estrogen receptor alpha (ER) expression in several human breast cancer cell lines, the effect of PP2A on regulation of ER expression in the human breast cancer cell line MCF-7 was studied. Inhibition of PP2A using the pharmacologic inhibitor okadaic acid at 250 nm for 16 h resulted in a 60% reduction in PP2A activity in MCF-7 cells concurrent with a 75% reduction in ER mRNA and protein expression. Similar results were obtained with a small interfering RNA probe that specifically inhibited PP2A expression. ER promoter studies showed that regulation of ER through the PP2A pathway did not occur through transcriptional activation. Rather, PP2A mediated ER expression through modulation of ER mRNA stability through degradation of ER mRNA, reversible with concomitant treatment with the proteasomal inhibitor MG 132. These data suggest a novel pathway controlling ER expression resulting from the activation of PP2A, potentially providing a novel therapeutic target.
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Affiliation(s)
- Judith C Keen
- Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, Maryland 21231, USA
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Goral J, Kovacs EJ. In vivo ethanol exposure down-regulates TLR2-, TLR4-, and TLR9-mediated macrophage inflammatory response by limiting p38 and ERK1/2 activation. THE JOURNAL OF IMMUNOLOGY 2005; 174:456-63. [PMID: 15611271 DOI: 10.4049/jimmunol.174.1.456] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Ethanol is known to increase susceptibility to infections, in part, by suppressing macrophage function. Through TLRs, macrophages recognize pathogens and initiate inflammatory responses. In this study, we investigated the effect of acute ethanol exposure on murine macrophage activation mediated via TLR2, TLR4, and TLR9. Specifically, the study focused on the proinflammatory cytokines IL-6 and TNF-alpha and activation of p38 and ERK1/2 MAPKs after a single in vivo exposure to physiologically relevant level of ethanol followed by ex vivo stimulation with specific TLR ligands. Acute ethanol treatment inhibited IL-6 and TNF-alpha synthesis and impaired p38 and ERK1/2 activation induced by TLR2, TLR4, and TLR9 ligands. We also addressed the question of whether ethanol treatment modified activities of serine/threonine-specific, tyrosine-specific phosphatases, and MAPK phosphatase type 1. Inhibitors of three families of protein phosphatases did not restore ethanol-impaired proinflammatory cytokine production nor p38 and ERK1/2 activation. However, inhibitors of serine/threonine protein phosphatase type 1 and type 2A significantly increased IL-6 and TNF-alpha levels, and prolonged activation of p38 and ERK1/2 when triggered by TLR4 and TLR9 ligands. In contrast, with TLR2 ligand stimulation, TNF-alpha production was reduced, whereas IL-6 levels, and p38 and ERK1/2 activation were not affected. In conclusion, acute ethanol exposure impaired macrophage responsiveness to multiple TLR agonists by inhibiting IL-6 and TNF-alpha production. Mechanism responsible for ethanol-induced suppression involved inhibition of p38 and ERK1/2 activation. Furthermore, different TLR ligands stimulated IL-6 and TNF-alpha production via signaling pathways, which showed unique characteristics.
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Affiliation(s)
- Joanna Goral
- Department of Cell Biology, Neurobiology and Anatomy, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 20153, USA
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Boudreau RTM, Hoskin DW, Lin TJ. Phosphatase inhibition potentiates IL-6 production by mast cells in response to FcepsilonRI-mediated activation: involvement of p38 MAPK. J Leukoc Biol 2004; 76:1075-81. [PMID: 15316034 DOI: 10.1189/jlb.1003498] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Mast cells are crucial effector cells in the immune response through mediator secretion and release of cytokines. A coordinated balance between protein kinases and phosphatases plays an essential role in the regulation of mast cell mediator secretion. We have previously shown that treatment of mast cells with okadaic acid (OA), a protein phosphatase 2A (PP2A) inhibitor, results in a dose-dependent increase in interleukin (IL)-6 production. We show here for the first time a synergism between OA and immunoglobulin E (IgE)-mediated IL-6 secretion by murine bone marrow-derived mast cells (BMMC). Selective p38 mitogen-activated protein kinase (p38 MAPK) inhibition reduces OA and IgE-mediated IL-6 production. Regulation of p38 MAPK by PP2A was demonstrated, as OA treatment caused a dose-dependent increase in p38 MAPK phosphorylation. Antigen-mediated activation of murine mast cells also resulted in an increase in p38 MAPK phosphorylation, which was potentiated by cotreatment of the cells with OA. Lastly, in two mast cell lines (human mast cell-1 5C6 and murine MC/9) and primary-cultured murine BMMC, we show by coimmunoprecipitation an interaction between p38 MAPK and PP2A. These data support a role for PP2A through interaction with p38 MAPK in the regulation of IgE-dependent mast cell activation.
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Affiliation(s)
- Robert T M Boudreau
- Department of Microbiology, Dalhousie University, Halifax, Nova Scotia, Canada
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Nika K, Hyunh H, Williams S, Paul S, Bottini N, Taskén K, Lombroso PJ, Mustelin T. Haematopoietic protein tyrosine phosphatase (HePTP) phosphorylation by cAMP-dependent protein kinase in T-cells: dynamics and subcellular location. Biochem J 2004; 378:335-42. [PMID: 14613483 PMCID: PMC1223964 DOI: 10.1042/bj20031244] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2003] [Revised: 11/06/2003] [Accepted: 11/13/2003] [Indexed: 11/17/2022]
Abstract
The HePTP (haematopoietic protein tyrosine phosphatase) is a negative regulator of the ERK2 (extracellular signal-regulated protein kinase 2) and p38 MAP kinases (mitogen-activated protein kinases) in T-cells. This inhibitory function requires a physical association of HePTP through an N-terminal KIM (kinase-interaction motif) with ERK and p38. We previously reported that PKA (cAMP-dependent protein kinase) phosphorylates Ser-23 within the KIM of HePTP, resulting in dissociation of HePTP from ERK2. Here we follow the phosphorylation of this site in intact T-cells. We find that HePTP is phosphorylated at Ser-23 in resting T-cells and that this phosphorylation increases upon treatment of the cells with agents that elevate intracellular cAMP, such as prostaglandin E2. HePTP phosphorylation occurred at discrete regions at the cell surface. Phosphorylation was reduced by inhibitors of PKA and increased by inhibitors of protein phosphatases PP1 and PP2A, but not by inhibitors of calcineurin. In vitro, PP1 efficiently dephosphorylated HePTP at Ser-23, while PP2A was much less efficient. Activation of PP1 by treatment of the cells with ceramide suppressed Ser-23 phosphorylation, as did transfection of the catalytic subunit of PP1. Phosphorylation at Ser-23 is also increased in a transient manner upon T-cell antigen receptor ligation. In contrast, treatment of cells with phorbol ester had no effect on HePTP phosphorylation at Ser-23. We conclude from these results that HePTP is under continuous control by PKA and a serine-specific phosphatase, probably PP1, in T-cells and that this basal phosphorylation at Ser-23 can rapidly change in response to external stimuli. This, in turn, will affect the ability of HePTP to inhibit the ERK and p38 MAP kinases.
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Affiliation(s)
- Konstantina Nika
- Program of Signal Transduction, Cancer Research Center, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA
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Coffey MJ, Jarvis GE, Gibbins JM, Coles B, Barrett NE, Wylie ORE, O'Donnell VB. Platelet 12-lipoxygenase activation via glycoprotein VI: involvement of multiple signaling pathways in agonist control of H(P)ETE synthesis. Circ Res 2004; 94:1598-605. [PMID: 15142951 DOI: 10.1161/01.res.0000132281.78948.65] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Lipoxygenases (LOX) contribute to vascular disease and inflammation through generation of bioactive lipids, including 12-hydro(pero)xyeicosatetraenoic acid (12-H(P)ETE). The physiological mechanisms that acutely control LOX product generation in mammalian cells are uncharacterized. Human platelets that contain a 12-LOX isoform (p12-LOX) were used to define pathways that activate H(P)ETE synthesis in the vasculature. Collagen and collagen-related peptide (CRP) (1 to 10 microg/mL) acutely induced platelet 12-H(P)ETE synthesis. This implicated the collagen receptor glycoprotein VI (GPVI), which signals via the immunoreceptor-based activatory motif (ITAM)-containing FcRgamma chain. Conversely, thrombin only activated at high concentrations (> 0.2 U/mL), whereas U46619 and ADP alone were ineffective. Collagen or CRP-stimulated 12-H(P)ETE generation was inhibited by staurosporine, PP2, wortmannin, BAPTA/AM, EGTA, and L-655238, implicating src-tyrosine kinases, PI3-kinase, Ca2+ mobilization, and p12-LOX translocation. In contrast, protein kinase C (PKC) inhibition potentiated 12-H(P)ETE generation. Finally, activation of the immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing platelet endothelial cell adhesion molecule (PECAM-1) inhibited p12-LOX product generation. This study characterizes a receptor-dependent pathway for 12-H(P)ETE synthesis via the collagen receptor GPVI, which is negatively regulated by PECAM-1 and PKC, and demonstrates a novel link between immune receptor signaling and lipid mediator generation in the vasculature.
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MESH Headings
- 12-Hydroxy-5,8,10,14-eicosatetraenoic Acid/biosynthesis
- 12-Hydroxy-5,8,10,14-eicosatetraenoic Acid/blood
- 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology
- Adenosine Diphosphate/pharmacology
- Amino Acid Motifs
- Arachidonate 12-Lipoxygenase/blood
- Arachidonate 12-Lipoxygenase/metabolism
- Arachidonic Acid/pharmacology
- Blood Platelets/drug effects
- Blood Platelets/enzymology
- Calcimycin/pharmacology
- Calcium Signaling/drug effects
- Carrier Proteins/pharmacology
- Collagen/pharmacology
- Cyclooxygenase 1
- Egtazic Acid/analogs & derivatives
- Egtazic Acid/pharmacology
- Enzyme Activation/drug effects
- Enzyme Inhibitors/pharmacology
- Humans
- Inflammation/immunology
- Isoenzymes/physiology
- Leukotrienes/biosynthesis
- Leukotrienes/blood
- Leukotrienes/metabolism
- Membrane Proteins
- Peptides/pharmacology
- Phosphorylation/drug effects
- Platelet Activation/drug effects
- Platelet Endothelial Cell Adhesion Molecule-1/physiology
- Platelet Membrane Glycoproteins/physiology
- Prostaglandin-Endoperoxide Synthases/physiology
- Protein Kinase C/antagonists & inhibitors
- Protein Kinase C/physiology
- Protein Processing, Post-Translational/drug effects
- Protein Transport/drug effects
- Quinolines/pharmacology
- Receptors, IgG/physiology
- Thrombin/pharmacology
- p38 Mitogen-Activated Protein Kinases/antagonists & inhibitors
- p38 Mitogen-Activated Protein Kinases/physiology
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Affiliation(s)
- Marcus J Coffey
- Department of Medical Biochemistry and Immunology, University of Wales College of Medicine, Heath Park, Cardiff, UK.
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Balasubramanian A, Ganju RK, Groopman JE. Hepatitis C virus and HIV envelope proteins collaboratively mediate interleukin-8 secretion through activation of p38 MAP kinase and SHP2 in hepatocytes. J Biol Chem 2003; 278:35755-66. [PMID: 12824191 DOI: 10.1074/jbc.m302889200] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hepatitis C virus (HCV) infects approximately 40% of human immunodeficiency virus (HIV) patients, and the resulting hepatic dysfunction that occurs is the primary cause of death in patients with co-infection. We hypothesized that hepatocytes exposed to HCV and HIV proteins might be susceptible to injury via an "innocent bystander" mechanism. To assess this, we studied the effects of envelope proteins, E2 of HCV and gp120 of HIV, in model HepG2 cells. Upon co-stimulation with HCV-E2 and HIV-gp120, we observed a potent proinflammatory response with the induction of IL-8. Furthermore, our studies revealed that HCV-E2 and HIV-gp120 act collaboratively to trigger a specific set of downstream signaling pathways that include activation of p38 mitogen-activated protein (MAP) kinase and the tyrosine phosphatase, SHP2. Both specific inhibitors of p38 MAP kinase and sodium vanadate, a potent protein-tyrosine phosphatase inhibitor, blocked IL-8 production in a dose-dependent manner. The role of p38 MAP kinase and SHP2 was further defined by transiently overexpressing dominant negative mutants of these proteins into HepG2 cells. These studies revealed that overexpression of an inactive p38 MAP kinase or SHP2 mutant partially abrogated HCV-E2- and HIV-gp120-induced IL-8 production. Further studies revealed that IL-8 induction was not mediated through activation of the NF-kappa B pathway. However, HCV-E2 plus HIV-gp120 was shown to increase the DNA binding activity of AP-1. These results emphasize that expression of the proinflammatory chemokine IL-8, induced by HCV-E2 and HIV-gp120, may be mediated through p38 MAP kinase and SHP2 in an NF-kappa B-independent manner, albeit through AP-1-driven processes.
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Affiliation(s)
- Anuradha Balasubramanian
- Division of Experimental Medicine, Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, Boston, Massachusetts 02115, USA
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Relou IAM, Gorter G, Ferreira IA, van Rijn HJM, Akkerman JWN. Platelet endothelial cell adhesion molecule-1 (PECAM-1) inhibits low density lipoprotein-induced signaling in platelets. J Biol Chem 2003; 278:32638-44. [PMID: 12775720 DOI: 10.1074/jbc.m212675200] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
At physiological concentrations, low density lipoprotein (LDL) increases the sensitivity of platelets to aggregation- and secretion-inducing agents without acting as an independent activator of platelet functions. LDL sensitizes platelets by inducing a transient activation of p38MAPK, a Ser/Thr kinase that is activated by the simultaneous phosphorylation of Thr180 and Tyr182 and is an upstream regulator of cytosolic phospholipase A2 (cPLA2). A similar transient phosphorylation of p38MAPK is induced by a peptide mimicking amino acids 3359-3369 in apoB100 called the B-site. Here we report that the transient nature of p38MAPK activation is caused by platelet endothelial cell adhesion molecule 1 (PECAM-1), a receptor with an immunoreceptor tyrosine-based inhibitory motif. PECAM-1 activation by cross-linking induces tyrosine phosphorylation of PECAM-1 and a fall in phosphorylated p38MAPK and cPLA2. Interestingly, LDL and the B-site peptide also induce tyrosine phosphorylation of PECAM-1, and studies with immunoprecipitates indicate the involvement of c-Src. Inhibition of the Ser/Thr phosphatases PP1/PP2A (okadaic acid) makes the transient p38MAPK activation by LDL and the B-site peptide persistent. Inhibition of Tyr-phosphatases (vanadate) increases Tyr-phosphorylated PECAM-1 and blocks the activation of p38MAPK. Together, these findings suggest that, following a first phase in which LDL, through its B-site, phosphorylates and thereby activates p38MAPK, a second phase is initiated in which LDL activates PECAM-1 and induces dephosphorylation of p38MAPK via activation of the Ser/Thr phosphatases PP1/PP2A.
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Affiliation(s)
- Ingrid A M Relou
- Laboratory for Thrombosis and Haemostasis, Department of Haematology, University Medical Center Utrecht and the Institute for Biomembranes, University of Utrecht, 3508 GA Utrecht, The Netherlands
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Joutsi-Korhonen L, Smethurst PA, Rankin A, Gray E, IJsseldijk M, Onley CM, Watkins NA, Williamson LM, Goodall AH, de Groot PG, Farndale RW, Ouwehand WH. The low-frequency allele of the platelet collagen signaling receptor glycoprotein VI is associated with reduced functional responses and expression. Blood 2003; 101:4372-9. [PMID: 12560230 DOI: 10.1182/blood-2002-08-2591] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Interaction of platelets with collagen under conditions of blood flow is a multi-step process with tethering via glycoprotein IbIXV (GPIbIXV) over von Willebrand factor, adhesion by direct interaction with the integrin GPIaIIa, and signaling via GPVI. GPVI can be specifically agonized by cross-linked collagen-related peptide (CRP-XL), which results in a signaling cascade very similar to that evoked by native collagen. The GPVI gene has 2 common alleles that differ by 3 replacements in the glycosylated stem and 2 in the cytoplasmic domain. We used CRP-XL to elucidate the variation in responses observed in platelet function in different individuals. We observed a 3-fold difference in the response to CRP-XL in platelet aggregation when comparing platelets from 10 high-frequency allele homozygotes with 8 low-frequency ones (2-way analysis of variance [ANOVA], P <.0001). The difference in functional responses was reflected in fibrinogen binding and in downstream signaling events as measured by tyrosine phosphorylation, the expression of P-selectin, and the binding of annexin V and the generation of thrombin on the platelet surface (2-way ANOVA, P <.001). Platelets homozygous for the low-frequency allele tended to be less able to form a thrombus on a collagen surface in flowing whole blood or in the platelet function analyzer-100 (t test, P =.065 and P =.061, respectively). The functional difference was correlated to a difference in total and membrane-expressed GPVI measured by monoclonal and polyclonal antibodies. This study demonstrates for the first time that platelet function may be altered by allelic differences in GPVI.
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Liu Y, Cheng J, Li K, Yang Q, Lu YY, Wang L, Wang JJ. Gene expression profile of HepG2 cell transfected with hepatitis C virus coreprotein-binding protein6 gene. Shijie Huaren Xiaohua Zazhi 2003; 11:394-398. [DOI: 10.11569/wcjd.v11.i4.394] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM To screen and clone genes of hepatic protein interacting with hepatitis C virus (HCV) core protein and analyze the gene expression profiles of HepG2 cell transfected with HCV coreprotein-binding protein6 (HCBP6) gene.
METHODS Using yeast two-hybrid system3, bait plasmid of HCV coreprotein was constructed and genes encoding HCV coreprotein-binding protein were screened and identified. One gene named HCBP6 was identified. Humanfull-length encoding gene of HCBP6 and its amino acid sequences were identified by bioinformatics method, and there combined expression plasmidpc DNA3. 1(-)-HCBP6 was constructed. mRNA from HepG2 cell stransfected with pcDNA3. 1(-)-HCBP6 and the empty vector were detected with cDNA microarray, respectively.
RESULTS Human HCBP6 cDNA sequence was identified. The coding sequence for human HCBP6 consists of 456 nt and its protein consists of 152 aa. Twenty of 1152 gene sobtained from gene expression profile analysis differed from those in GenBank, in which 13 genes were up-regulated and 7 genes were down-regulated in HepG2 cells transfected with HCBP6 plasmid. These genes differentially regulated by HCBP6 protein included human genes encoding proteins involved in signal transduction, cell proliferation, differentiation, and growth regulation.
CONCLUSION The bioinformatics combined yeast two hybrid technique is a powerful method for screening and analysis of genes of hepatic protein interacting with HCV coreprotein. The findings obtained by cDNA microarray technique provided significant data for preliminary understanding of the biologica lfunction of new gene, and also provided some clues for furthe rclarifying the molecular biological processes of hepatocytes in interaction between HCV core protein and HCBP6.
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Affiliation(s)
- Yan Liu
- Gene Therapy Research Center, Institute of Infectious Diseases, The 302 Hospital of PLA, Beijing 100039, China
| | - Jun Cheng
- Gene Therapy Research Center, Institute of Infectious Diseases, The 302 Hospital of PLA, Beijing 100039, China
| | - Ke Li
- Gene Therapy Research Center, Institute of Infectious Diseases, The 302 Hospital of PLA, Beijing 100039, China
| | - Qian Yang
- Gene Therapy Research Center, Institute of Infectious Diseases, The 302 Hospital of PLA, Beijing 100039, China
| | - Yin-Ying Lu
- Gene Therapy Research Center, Institute of Infectious Diseases, The 302 Hospital of PLA, Beijing 100039, China
| | - Lin Wang
- Gene Therapy Research Center, Institute of Infectious Diseases, The 302 Hospital of PLA, Beijing 100039, China
| | - Jian-Jun Wang
- Gene Therapy Research Center, Institute of Infectious Diseases, The 302 Hospital of PLA, Beijing 100039, China
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