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De Donatis A, Ranaldi F, Cirri P. Reciprocal control of cell proliferation and migration. Cell Commun Signal 2010; 8:20. [PMID: 20822514 PMCID: PMC2942889 DOI: 10.1186/1478-811x-8-20] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2010] [Accepted: 09/07/2010] [Indexed: 11/10/2022] Open
Abstract
In adult tissue the quiescent state of a single cell is maintained by the steady state conditions of its own microenvironment for what concern both cell-cell as well as cell-ECM interaction and soluble factors concentration. Physiological or pathological conditions can alter this quiescent state through an imbalance of both soluble and insoluble factors that can trigger a cellular phenotypic response. The kind of cellular response depends by many factors but one of the most important is the concentration of soluble cytokines sensed by the target cell. In addition, due to the intrinsic plasticity of many cellular types, every single cell is able, in response to the same stimulus, to rapidly switch phenotype supporting minimal changes of microenviromental cytokines concentration. Wound healing is a typical condition in which epithelial, endothelial as well as mesenchymal cells are firstly subjected to activation of their motility in order to repopulate the damaged region and then they show a strong proliferative response in order to successfully complete the wound repair process. This schema constitute the leitmotif of many other physiological or pathological conditions such as development vasculogenesis/angiogenesis as well as cancer outgrowth and metastasis.Our review focuses on the molecular mechanisms that control the starting and, eventually, the switching of cellular phenotypic outcome in response to changes in the symmetry of the extracellular environment.
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Paoli P, Sbrana F, Tiribilli B, Caselli A, Pantera B, Cirri P, De Donatis A, Formigli L, Nosi D, Manao G, Camici G, Ramponi G. Protein N-Homocysteinylation Induces the Formation of Toxic Amyloid-Like Protofibrils. J Mol Biol 2010; 400:889-907. [DOI: 10.1016/j.jmb.2010.05.039] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Revised: 05/14/2010] [Accepted: 05/16/2010] [Indexed: 10/19/2022]
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Pantera B, Bini C, Cirri P, Paoli P, Camici G, Manao G, Caselli A. PrPc activation induces neurite outgrowth and differentiation in PC12 cells: role for caveolin-1 in the signal transduction pathway. J Neurochem 2009; 110:194-207. [PMID: 19457127 DOI: 10.1111/j.1471-4159.2009.06123.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Cellular prion protein (PrP(c)) is a ubiquitous glycoprotein, whose physiological role is poorly characterized. It has been suggested that PrP(c) participates in neuritogenesis, neuroprotection, copper metabolism, and signal transduction. In this study we detailed the intracellular events induced by PrP(c) antibody-mediated cross-linking in PC12 cells. We found a Fyn-dependent activation of the Ras-Raf pathway, which leads to a rapid and transient phosphorylation of extracellular regulated kinases. In addition, this activation cascade relies on the engagement of integrins, and involves focal adhesion kinase activation. We demonstrated the tyrosine phosphorylation of caveolin-1 as a consequence of PrP(c) stimulation, and showed that phosphocaveolin-1 scaffolds and coordinates protein complexes involved in PrP(c)-dependent signaling. Moreover, we found that caveolin-1 phosphorylation, is a mechanism for recruiting the C-terminal Src kinase and inactivating Fyn, so as to terminate cell signaling. Furthermore our data support a significant role for PrP(c) as a response mediator in neuritogenesis and cell differentiation.
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De Donatis A, Comito G, Buricchi F, Vinci MC, Parenti A, Caselli A, Camici G, Manao G, Ramponi G, Cirri P. Proliferation Versus Migration in Platelet-derived Growth Factor Signaling. J Biol Chem 2008; 283:19948-56. [DOI: 10.1074/jbc.m709428200] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
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Caselli A, Taddei ML, Bini C, Paoli P, Camici G, Manao G, Cirri P, Ramponi G. Low Molecular Weight Protein Tyrosine Phosphatase and Caveolin-1: Interaction and Isoenzyme-Dependent Regulation. Biochemistry 2007; 46:6383-92. [PMID: 17469800 DOI: 10.1021/bi0620858] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are small enzymes that are ubiquitous in many organisms. They are important in biological processes such as cell proliferation, adhesion, migration, and invasiveness. LMW-PTP is expressed in mammalian cells as two isoforms (IF1 and IF2) originating through alternative splicing. We have previously shown that IF2 targets lipid rafts called caveolae and interacts with caveolin-1, their major structural protein. Caveolae are cholesterol- and sphingolipid-rich membrane microdomains that have been implicated in a variety of cellular functions, including signal transduction events. Caveolin-1 contains a scaffolding region that contributes to the binding of the protein to the plasma membrane and mediates protein omo- and etero-oligomerization. Interaction of many signaling molecules with the scaffolding domain sequesters them into caveolae and inhibits or suppresses their activities. Caveolin-interacting proteins usually have a typical sequence motif, also present in all the LMW-PTPs, which is characterized by aromatic or large hydrophobic residues in specific positions. We have examined here the interaction of the LMW-PTP isoforms with caveolin-1 and its molecular mechanism, together with the consequences for their tyrosine phosphatase activities. We found that IF1 and IF2 are both capable of interacting with defined regions of caveolin-1 and that their putative caveolin binding sequence motif is not responsible for the association. The formation of LMW-PTP/caveolin-1 complexes is accompanied by modulation of the enzyme activities, and the inhibitory effect elicited against IF1 is stronger than that against IF2. The caveolin scaffolding domain is directly involved in the observed phenomena.
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Cirri P, Taddei ML, Chiarugi P, Buricchi F, Caselli A, Paoli P, Giannoni E, Camici G, Manao G, Raugei G, Ramponi G. Insulin inhibits platelet-derived growth factor-induced cell proliferation. Mol Biol Cell 2004; 16:73-83. [PMID: 15525682 PMCID: PMC539153 DOI: 10.1091/mbc.e04-01-0011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Cellular behavior can be considered to be the result of a very complex spatial and temporal integration of intracellular and extracellular signals. These signals arise from serum-soluble factors as well as from cell-substrate or cell-cell interactions. The current approach in mitogenesis studies is generally to analyze the effect of a single growth factor on serum-starved cells. In this context, a metabolic hormone such as insulin is found to be a mitogenic agent in many cellular types. In the present study, we have considered the effect of insulin stimulation in platelet-derived growth factor (PDGF)-activated NIH-3T3 and C2C12 cells. Our results show that insulin is able to inhibit strongly both NIH-3T3 and C2C12 cell growth induced by PDGF, one of the most powerful mitotic agents for these cell types. This inhibitory effect of insulin is due primarily to a premature down-regulation of the PDGF receptor. Thus, when NIH-3T3 or C2C12 cells are stimulated with both PDGF and insulin, we observe a decrease in PDGF receptor phosphorylation with respect to cells treated with PDGF alone. In particular, we find that costimulation with insulin leads to a reduced production of H2O2 with respect to cell stimulation with PDGF alone. The relative low concentration of H2O2 in PDGF/insulin-costimulated cell leads to a limited down-regulation of protein tyrosine phosphatases, and, consequently, to a reduced PDGF receptor phosphorylation efficiency. The latter is very likely to be responsible for the insulin-dependent inhibition of PDGF-receptor mitogenic signaling.
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Cecchi C, Liguri G, Fiorillo C, Bogani F, Gambassi M, Giannoni E, Cirri P, Baglioni S, Ramponi G. Acylphosphatase overexpression triggers SH-SY5Y differentiation towards neuronal phenotype. Cell Mol Life Sci 2004; 61:1775-84. [PMID: 15241553 PMCID: PMC11138849 DOI: 10.1007/s00018-004-4192-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
An acylphosphatase (AcPase) overexpression study was carried out on SH-SY5Y neuroblastoma cells, using a green fluorescent fusion protein (AcP-GFP), with GFP acting as a reporter protein. The cellular proliferation rate was significantly reduced by overexpression of AcPase by a factor of ten. In contrast, clones transfected with two inactive AcPase mutants showed a growth rate comparable to control cells. This suggests that AcPase catalyzes the proliferative down-regulation. AcPase-overexpressing clones showed a physiological mortality rate as assessed by an MTT reduction test and by evaluation of necrotic markers. DNA fragmentation analysis and assays of caspase-3 and poly (ADP-ribose) polymerase (PARP)-active fragments showed no evidence of any apoptotic pattern. AcPase overexpression led to a marked increase in PARP activity as well as Bcl-2 content; these are commonly up-regulated during differentiative processes in neuronal cells. In fact, the typical differentiation marker, growth-associated-protein 43, was significantly up-regulated. Microscopic observations also showed a clear increase in the differentiative phenotype in AcPase-overexpressing cells. Our results clearly show that AcPase plays a primary causative role in neuronal differentiation.
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Chiarugi P, Cirri P. Redox regulation of protein tyrosine phosphatases during receptor tyrosine kinase signal transduction. Trends Biochem Sci 2003; 28:509-14. [PMID: 13678963 DOI: 10.1016/s0968-0004(03)00174-9] [Citation(s) in RCA: 247] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In addition to protein phosphorylation, redox-dependent post-translational modification of proteins is emerging as a key signaling system that has been conserved throughout evolution and that influences many aspects of cellular homeostasis. Both systems exemplify dynamic regulation of protein function by reversible modification, which, in turn, regulates many cellular processes such as cell proliferation, differentiation and apoptosis. In this article we focus on the interplay between phosphorylation- and redox-dependent signaling at the level of phosphotyrosine phosphatase-mediated regulation of receptor tyrosine kinases (RTKs). We propose that signal transduction by oxygen species through reversible phosphotyrosine phosphatase inhibition, represents a widespread and conserved component of the biochemical machinery that is triggered by RTKs.
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Taddei ML, Chiarugi P, Cirri P, Buricchi F, Fiaschi T, Giannoni E, Talini D, Cozzi G, Formigli L, Raugei G, Ramponi G. Beta-catenin interacts with low-molecular-weight protein tyrosine phosphatase leading to cadherin-mediated cell-cell adhesion increase. Cancer Res 2002; 62:6489-99. [PMID: 12438242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
Abstract
Beta-catenin plays a dual role as a major constituent of cadherin-based adherens junctions and also as a transcriptional coactivator. In normal ephitelial cells, at adherens junction level, beta-catenin links cadherins to the actin cytoskeleton. The structure of adherens junctions is dynamically regulated by tyrosine phosphorylation. In particular, cell-cell adhesion can be negatively regulated through the tyrosine phosphorylation of beta-catenin. Furthermore, the loss of beta-catenin-cadherin association has been correlated with the transition from a benign tumor to an invasive, metastatic cancer. Low-molecular-weight protein tyrosine phosphatase (LMW-PTP) is a ubiquitous PTP implicated in the regulation of mitosis and cytoskeleton rearrangement. Here we demonstrate that the amount of free cytoplasmic beta-catenin is decreased in NIH3T3, which overexpresses active LMW-PTP, and this results in a stronger association between cadherin complexes and the actin-based cytoskeleton with respect to control cells. Confocal microscopy analysis shows that beta-catenin colocalizes with LMW-PTP at the plasma membrane. Furthermore, we provide evidence that beta-catenin is able to associate with LMW-PTP both in vitro and in vivo. Moreover, overexpression of active LMW-PTP strongly potentiates cadherin-mediated cell-cell adhesion, whereas a dominant-negative form of LMW-PTP induces the opposite phenotype, both in NIH3T3 and in MCF-7 carcinoma cells. On the basis of these results, we propose that the stability of cell-cell contacts at the adherens junction level is positively influenced by LMW-PTP expression, mainly because of the beta-catenin and LMW-PTP interaction at the plasma membrane level with consequent dephosphorylation.
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Chiarugi P, Cirri P, Taddei ML, Giannoni E, Fiaschi T, Buricchi F, Camici G, Raugei G, Ramponi G. Insight into the role of low molecular weight phosphotyrosine phosphatase (LMW-PTP) on platelet-derived growth factor receptor (PDGF-r) signaling. LMW-PTP controls PDGF-r kinase activity through TYR-857 dephosphorylation. J Biol Chem 2002; 277:37331-8. [PMID: 12149261 DOI: 10.1074/jbc.m205203200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Low molecular weight phosphotyrosine phosphatase (LMW-PTP) is an enzyme involved in platelet-derived growth factor-induced mitogenesis and cytoskeleton rearrangement. Our previous results demonstrated that LMW-PTP is able to bind and dephosphorylate activated platelet-derived growth factor receptor (PDGF-r), thus inhibiting cell proliferation. Here we revisit the role of LMW-PTP on activated PDGF-r dephosphorylation. We demonstrate that LMW-PTP preferentially acts on cell surface PDGF-r, excluding the internalized activated receptor pool. Many phosphotyrosine phosphatases act by site-selective dephosphorylation on several sites of PDGF-r, but until now, there has been no evidence of a direct involvement of a specific phosphotyrosine phosphatase in the dephosphorylation of the 857 kinase domain activation tyrosine. Here we report that LMW-PTP affects the kinase activity of the receptor through the binding and dephosphorylation of Tyr-857 and influences many of the signal outputs from the receptor. In particular, we demonstrate a down-regulation of phosphatidylinositol 3-kinase, Src homology phosphatase-2, and phospholipase C-gamma1 binding but not of MAPK activation. In addition, we report a slight action of LMW-PTP on Tyr-716, which directs MAPK activation through Grb2 binding. On the basis of these results, we propose a key role for LMW-PTP in PDGF-r down-regulation through the dephosphorylation of the activation loop Tyr-857, thus determining a general negative regulation of all downstream signals, with the exception of those elicited by internalized receptors.
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Chiarugi P, Cirri P, Taddei ML, Talini D, Doria L, Fiaschi T, Buricchi F, Giannoni E, Camici G, Raugei G, Ramponi G. New perspectives in PDGF receptor downregulation: the main role of phosphotyrosine phosphatases. J Cell Sci 2002; 115:2219-32. [PMID: 11973362 DOI: 10.1242/jcs.115.10.2219] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Uncontrolled activation of receptor tyrosine kinases (RTKs) is implicated in the proliferation of cancerous cells, and deficiencies in RTKs results in pathological conditions such as developmental abnormalities and immunodeficiencies. Tight regulation of RTK cascades is therefore critical for eliciting an appropriate type and level of response to external stimuli. The aim of this work is to compare different RTK downregulation mechanisms, such as ligandinduced internalisation, ubiquitin-mediated proteolysis and dephosphorylation by protein phosphotyrosine phosphatase (PTPs). We choose platelet-derived growth factor receptor (PDGF-r) in NIH3T3 cells as a model of RTK. Our data suggest that PDGF-r internalisation could be mainly considered as a positive signaling system, as it is involved in MAPK activation rather than a downregulation of the mitotic signal. Inhibition of receptor ubiquitination does not result in regulation of PDGF-r tyrosine phosphorylation and does not lead to variation of intracellular signalling pathways. The overall PDGF-r protein degradation upon PDGF stimulation does not exceed 30-40% of the total receptor; thus the receptor remains functionally active for further stimulation. On the contrary, PTP-dependent dephosphorylation of the activated receptors appears to play a crucial role. In fact, inhibition of PTP upon PDGF stimulation results in upregulation of receptor phosphorylation level, of PI3K recruitment and activation and of cell cycle rate. On the contrary, PTP-dependent dephosphorylation does not affect the endosomic pool of activated receptor. Furthermore, we demonstrate that PDGF-r downregulation by means of PTP dephosphorylation is important for both short term (2 hours) and long-lasting (up to 8 hours) PDGF-r activation. Herein we propose a revisited model of PDGF-r downregulation in which PTPs dephosphorylation retains a major role, conferring on receptor internalisation a signal transduction function.
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Chiarugi P, Taddei ML, Cirri P, Talini D, Buricchi F, Camici G, Manao G, Raugei G, Ramponi G. Low molecular weight protein-tyrosine phosphatase controls the rate and the strength of NIH-3T3 cells adhesion through its phosphorylation on tyrosine 131 or 132. J Biol Chem 2000; 275:37619-27. [PMID: 10980198 DOI: 10.1074/jbc.m006375200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low molecular weight protein-tyrosine phosphatase (LMW-PTP) is an enzyme involved in platelet-derived growth factor (PDGF)-induced mitogenesis and cytoskeleton rearrangement. Our previous results demonstrated that LMW-PTP is able to bind and dephosphorylate activated PDGF receptor, thus inhibiting cell proliferation. Recently we have shown that LMW-PTP is specifically phosphorylated by c-Src in a cytoskeleton-associated fraction in response to PDGF, and this phosphorylation increases LMW-PTP activity about 20-fold. LMW-PTP strongly influences cell adhesion, spreading, and chemotaxis induced by PDGF stimulation, by regulating the phosphorylation level of p190Rho-GAP, a protein that is able to regulate Rho activity and hence cytoskeleton rearrangement. In the present study we investigate the physiological role of the two LMW-PTP tyrosine phosphorylation sites, using LMW-PTP mutants on tyrosine 131 or 132. We demonstrate that each tyrosine residue is involved in specific LMW-PTP functions. Both of them are phosphorylated during PDGF signaling. Phosphorylation on tyrosine 131 influences mitogenesis, dephosphorylating activated PDGF-R and cytoskeleton rearrangement, acting on p190RhoGAP. Phosphorylation on tyrosine 132 leads to an increase in the strength of cell substrate adhesion, down-regulating matrix metalloproteases expression, through the inhibition of Grb2/MAPK pathway. In conclusion, LMW-PTP tyrosine phosphorylation on both Tyr(131) or Tyr(132) cooperate to determine a faster and stronger adhesion to extracellular matrix, although these two events may diverge in timing and relative amount.
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Giannoni E, Cirri P, Paoli P, Fiaschi T, Camici G, Manao G, Raugei G, Ramponi G. Acylphosphatase is a strong apoptosis inducer in HeLa cell line. MOLECULAR CELL BIOLOGY RESEARCH COMMUNICATIONS : MCBRC 2000; 3:264-70. [PMID: 10964749 DOI: 10.1006/mcbr.2000.0228] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Acylphosphatase (AcP) is a low-molecular-weight protein widely distributed in many vertebrate tissues with a yet unknown physiologic function. To study the in vivo behavior of AcP, HeLa cells were transiently transfected with a vector expressing the AcP/EGFP fusion protein. Analysis of the transfected cells showed a high level of cellular death in cells expressing the AcP/EGFP fusion protein with respect to control cells expressing EGFP alone. Flow cytometry and time lapse analysis of AcP/EGFP transfected cells evidenced a typical pattern of apoptosis. Surprisingly, cells transfected with a mutated form of AcP, with negligible in vitro acylphosphatase activity, undergo apoptosis as well as cells transfected with wild-type protein, suggesting that the physiologic role of AcP could be not related to this catalytic activity.
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Taddei ML, Chiarugi P, Cirri P, Talini D, Camici G, Manao G, Raugei G, Ramponi G. LMW-PTP exerts a differential regulation on PDGF- and insulin-mediated signaling. Biochem Biophys Res Commun 2000; 270:564-9. [PMID: 10753664 DOI: 10.1006/bbrc.2000.2456] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Low-molecular-weight protein tyrosine phosphatase (LMW-PTP) is able to specifically bind and dephosphorylate activated PDGF and insulin receptors, modulating the onset of mitogenic process. LMW-PTP is present in two distinct intracellular locations. While the cytosolic LMW-PTP pool interacts directly with activated insulin or PDGF receptors, the cytoskeleton-associated LMW-PTP is tyrosine phosphorylated upon PDGF stimulation and is involved in cytoskeleton rearrangement acting on p190Rho-GAP. We investigated the differential role of LMW-PTP in PDGF- or insulin-induced mitogenesis and cytoskeleton rearrangement. Dominant negative LMW-PTP influences both PDGF- and insulin-induced mitogenesis with a different extent and it induces a decrease in cellular adhesion and chemotaxis after PDGF but not insulin treatment. PDGF but not insulin stimulation leads to tyrosine phosphorylation of LMW-PTP. We propose that the differential effect of LMW-PTP on PDGF and insulin signaling is mainly due to the fact that during insulin signaling LMW-PTP does not become phosphorylated and thus does not act on its cytoskeleton-associated substrate/s.
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Chiarugi P, Cirri P, Taddei L, Giannoni E, Camici G, Manao G, Raugei G, Ramponi G. The low M(r) protein-tyrosine phosphatase is involved in Rho-mediated cytoskeleton rearrangement after integrin and platelet-derived growth factor stimulation. J Biol Chem 2000; 275:4640-6. [PMID: 10671492 DOI: 10.1074/jbc.275.7.4640] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low molecular weight protein-tyrosine phosphatase (LMW-PTP) is an enzyme that is involved in the early events of platelet-derived growth factor (PDGF) receptor signal transduction. In fact, LMW-PTP is able to specifically bind and dephosphorylate activated PDGF receptor, thus modulating PDGF-induced mitogenesis. In particular, LMW-PTP is involved in pathways that regulate the transcription of the immediately early genes myc and fos in response to growth factor stimulation. Recently, we have found that LMW-PTP exists constitutively in cytosolic and cytoskeleton-associated localization and that, after PDGF stimulation, c-Src is able to bind and phosphorylate LMW-PTP only in the cytoskeleton-associated fraction. As a consequence of its phosphorylation, LMW-PTP increases its catalytic activity about 20-fold. In this study, our interest was to investigate the role of LMW-PTP phosphorylation in cellular response to PDGF stimulation. To address this issue, we have transfected in NIH-3T3 cells a mutant form of LMW-PTP in which the c-Src phosphorylation sites (Tyr(131) and Tyr(132)) were mutated to alanine. We have established that LMW-PTP phosphorylation by c-Src after PDGF treatment strongly influences both cell adhesion and migration. In addition, we have discovered a new LMW-PTP substrate localized in the cytoskeleton that becomes tyrosine-phosphorylated after PDGF treatment: p190Rho-GAP. Hence, LMW-PTP plays multiple roles in PDGF receptor-mediated mitogenesis, since it can bind and dephosphorylate PDGF receptor, and, at the same time, the cytoskeleton-associated LMW-PTP, through the regulation of the p190Rho-GAP phosphorylation state, controls the cytoskeleton rearrangement in response to PDGF stimulation.
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Taddei L, Chiarugi P, Brogelli L, Cirri P, Magnelli L, Raugei G, Ziche M, Granger HJ, Chiarugi V, Ramponi G. Inhibitory effect of full-length human endostatin on in vitro angiogenesis. Biochem Biophys Res Commun 1999; 263:340-5. [PMID: 10491294 DOI: 10.1006/bbrc.1999.1342] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Endostatin, a C-terminal product of collagen XVIII, is a very powerful angiogenesis inhibitor. In vivo experiments in mice indicate that endostatin dramatically reduces tumor mass without causing the onset of any resistance to the treatment. Recently, a 12-aa shorter human endostatin has been purified from plasma, but is ineffective in in vitro angiogenesis assays. Here we report that the full-length human recombinant endostatin has a potent inhibitory activity in in vitro angiogenesis assays. Two powerful angiogenic factors were used to stimulate endothelial cells: FGF-2 and VEGF-165. Endostatin prevented cell growth both in the basal condition and after stimulation with FGF-2 or VEGF-165. Migration of microvascular endothelial cells toward FGF-2 or VEGF-165 was impaired, both when cells were pretreated with the inhibitor and when endostatin was added together with the growth factors. Furthermore, experiments of inhibition of proliferation performed on nonmicroendothelial cells showed that endostatin was ineffective. This study indicates that human endostatin is a potent angiogenesis inhibitor and suggests its use in human anticancer therapy.
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Bucciantini M, Chiarugi P, Cirri P, Taddei L, Stefani M, Raugei G, Nordlund P, Ramponi G. The low Mr phosphotyrosine protein phosphatase behaves differently when phosphorylated at Tyr131 or Tyr132 by Src kinase. FEBS Lett 1999; 456:73-8. [PMID: 10452533 DOI: 10.1016/s0014-5793(99)00828-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The low molecular weight phosphotyrosine protein phosphatase (LMW-PTP) is phosphorylated by Src and Src-related kinases both in vitro and in vivo; in Jurkat cells, and in NIH-3T3 cells, it becomes tyrosine-phosphorylated upon stimulation by PDGF. In this study we show that pp60Src phosphorylates in vitro the enzyme at two tyrosine residues, Tyr131 and Tyr132, previously indicated as the main phosphorylation sites of the enzyme, whereas phosphorylation by the PDGF-R kinase is much less effective and not specific. The effects of LMW-PTP phosphorylation at each tyrosine residue were investigated by using Tyr131 and Tyr132 mutants. We found that the phosphorylation at either residue has differing effects on the enzyme behaviour: Tyr131 phosphorylation is followed by a strong (about 25-fold) increase of the enzyme specific activity, whereas phosphorylation at Tyr132 leads to Grb2 recruitment. These differing effects are discussed on the light of the enzyme structure.
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Cirri P, Chiarugi P, Taddei L, Raugei G, Camici G, Manao G, Ramponi G. Low molecular weight protein-tyrosine phosphatase tyrosine phosphorylation by c-Src during platelet-derived growth factor-induced mitogenesis correlates with its subcellular targeting. J Biol Chem 1998; 273:32522-7. [PMID: 9829986 DOI: 10.1074/jbc.273.49.32522] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low molecular weight phosphotyrosine phosphatase (LMW-PTP) is an enzyme that is involved in the early events of platelet-derived growth factor (PDGF) receptor signal transduction. Our previous results have shown that LMW-PTP is able to specifically bind and dephosphorylate activated PDGF receptor, thus modulating PDGF-induced mitogenesis. In particular LMW-PTP is involved in pathways that regulate the transcription of the immediately early genes myc and fos in response to growth factor stimulation. In this study we have established that, in nontransformed NIH3T3 cells, LMW-PTP exists constitutively in cytosolic and cytoskeleton-associated localization and that, after PDGF stimulation, c-Src is able to bind and to phosphorylate LMW-PTP only in the cytoskeleton-associated fraction. As a consequence of its tyrosine phosphorylation, LMW-PTP significantly increases its catalytic activity. After PDGF stimulation these two LMW-PTP pools act on distinct substrates, contributing in different manners to the PDGF receptor signaling. The cytoplasmic LMW-PTP fraction exerts its well known action on activated PDGF receptor. On the other hand we have now demonstrated that the cytoskeleton-associated LMW-PTP acts specifically on a few not yet identified proteins that become tyrosine-phosphorylated in response to the PDGF receptor activation. Finally, these two LMW-PTP pools markedly differ in the timing of the processes in which they are involved. The cytoplasmic LMW-PTP pool exerts its action within a few minutes from PDGF receptor activation (short term action), while tyrosine phosphorylation of cytoskeleton-associated LMW-PTP lasts for more than 40 min (long term action). In conclusion LMW-PTP is a striking example of an enzyme that exerts different functions and undergoes different regulation in consequence of its subcellular localization.
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Magherini F, Giannoni E, Raugei G, Cirri P, Paoli P, Modesti A, Camici G, Ramponi G. Cloning of murine low molecular weight phosphotyrosine protein phosphatase cDNA: identification of a new isoform. FEBS Lett 1998; 437:263-6. [PMID: 9824304 DOI: 10.1016/s0014-5793(98)01241-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The low molecular weight phosphotyrosine protein phosphatase (LMW-PTP) is a 18 kDa cytosolic enzyme, involved in the negative regulation of cell proliferation. In different mammalian species LMW-PTPs are expressed in two molecular forms produced from a single primary transcript through an alternative splicing mechanism. In this paper we report the cloning, expression and characterization of mouse isoforms of LMW-PTPs (called m-IF1 and m-IF2), very similar to the corresponding rat and human isoenzymes. Moreover we have identified a third cDNA encoding a protein (m-IF2P) that presents three substitutions compared to m-IF2. This new isoform is still active on pNPP, although to a lower extent: this reduction is mainly due to the leucine to proline substitution in position 13, within the catalytic loop. The mRNA expression level of this isoform is comparable to those of m-IF1 and m-IF2. It is likely that a gene duplication process followed by mutations has generated this new gene.
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Chiarugi P, Cirri P, Marra F, Raugei G, Fiaschi T, Camici G, Manao G, Romanelli RG, Ramponi G. The Src and signal transducers and activators of transcription pathways as specific targets for low molecular weight phosphotyrosine-protein phosphatase in platelet-derived growth factor signaling. J Biol Chem 1998; 273:6776-85. [PMID: 9506979 DOI: 10.1074/jbc.273.12.6776] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low molecular weight phosphotyrosine-protein phosphatase (LMW-PTP) is a cytosolic phosphotyrosine-protein phosphatase specifically interacting with the activated platelet-derived growth factor (PDGF) receptor through its active site. Overexpression of the LMW-PTP results in modulation of PDGF-dependent mitogenesis. In this study we investigated the effects of this tyrosine phosphatase on the signaling pathways relevant for PDGF-dependent DNA synthesis. NIH 3T3 cells were stably transfected with active or dominant negative LMW-PTP. The effects of LMW-PTP were essentially restricted to the G1 phase of the cell cycle. Upon stimulation with PDGF, cells transfected with the dominant negative LMW-PTP showed an increased activation of Src, whereas the active LMW-PTP induced a reduced activation of this proto-oncogene. We observe that c-Src binding to PDGF receptor upon stimulation is prevented by overexpression of LMW-PTP. These effects were associated with parallel changes in myc expression. Moreover, wild-type and dominant negative LMW-PTP differentially regulated STAT1 and STAT3 activation and tyrosine phosphorylation, whereas they did not modify extracellular signal-regulated kinase activity. However, these modifications were associated with changes in fos expression despite the lack of any effect on extracellular signal-regulated kinase activation. Other independent pathways involved in PDGF-induced mitogenesis, such as phosphatidylinositol 3-kinase and phospholipase C-gamma1, were not affected by LMW-PTP. These data indicate that this phosphatase selectively interferes with the Src and the STATs pathways in PDGF downstream signaling. The resulting changes in myc and fos proto-oncogene expression are likely to mediate the modifications observed in the G1 phase of the cell cycle.
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Brunati AM, Pinna LA, Bergantino E, Ruzzene M, Cirri P, Ramponi G, Donella-Deana A. Src homology-2 domains protect phosphotyrosyl residues against enzymatic dephosphorylation. Biochem Biophys Res Commun 1998; 243:700-5. [PMID: 9500984 DOI: 10.1006/bbrc.1998.8153] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The SH2 domain of c-Fgr (class 1A) has been expressed in E. coli as GST fusion protein and tested for its ability to prevent the dephosphorylation of a variety of phosphotyrosyl (poly)peptides by three distinct protein tyrosine phosphatases (TC-PTPase, YOP, and Low Mr PTPase). Dephosphorylation of HS1 protein and of a derived phosphopeptide, HS1 (388-402), exhibiting the motif selected by class 1A SH2 domains is inhibited in a dose dependent manner with full inhibition promoted by a 2- to 3-molar excess of GST/SH2 domain irrespective of either the nature or the amount of phosphatase used. The IC50 values for inhibition of these and other phosphotyrosyl substrates roughly correlates with their expected affinity for class 1A SH2 domain. Inhibition is partially reversed by the addition of D-myo-inositol 1,4,5-triphosphate, which competes for the binding to the SH2 domains. Our data on one side show that additional mechanism(s) besides mere competition must assist PTPases to dissociate SH2-PTyr complexes and on the other suggest a role for SH2 domains in protecting phosphotyrosyl residues from premature dephosphorylation.
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Paoli P, Fiaschi T, Cirri P, Camici G, Manao G, Cappugi G, Raugei G, Moneti G, Ramponi G. Mechanism of acylphosphatase inactivation by Woodward's reagent K. Biochem J 1997; 328 ( Pt 3):855-61. [PMID: 9396731 PMCID: PMC1218997 DOI: 10.1042/bj3280855] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The organ common-type (CT) isoenzyme of acylphosphatase is inactivated by Woodward's reagent K (WRK) (N-ethyl-5-phenylisoxazolium-3'-sulphonate) at pH6.0. The inactivation reaction follows apparent pseudo first-order kinetics. The dependence of the reciprocal of the pseudo first-order kinetic constant (kobs) on the reciprocal WRK concentration reveals saturation kinetics, suggesting that the WRK forms a reversible complex with the enzyme before causing inactivation. Competitive inhibitors, such as inorganic phosphate and ATP, protect the enzyme from WRK inactivation, suggesting that this reagent acts at or near to the enzyme active site. The reagent-enzyme adduct, which elicits a strong absorption band with lambdamax at 346 nm, was separated from unreacted enzyme by reverse phase HPLC and the modified protein was cleaved with endoproteinase Glu-C to produce fragments. The HPLC fractionation gave two reagent-labelled peptides (peak 1 and peak 2) that were analysed by ion-spray MS and sequenced. The former is VFFRKHTQAE (residues 20-29 of human CT acylphosphatase) and the latter IFGKVQGVFFRKHTQAE (residues 13-29). MS demonstrated that both peptides are WRK adducts. A fragment ion with m/z of 1171, which is present in the mass spectrum of peak 1, has been identified as a WRK adduct of the peptide fragment 20-26. The lambdamax at 346 nm of WRK adduct suggests that the modified residue is His-25. Five recombinant enzymes mutated in residues included in the 20-29 polypeptide stretch have been produced. Analysis of their reactivities with WRK demonstrates that His-25 is the molecular target of the reagent as its modification causes the inactivation of the enzyme. Since both His-25-->Gln and His-25-->Phe mutants maintain high catalytic activity, we suggest that the observed enzyme inactivation is caused by the reagent (covalently bound to His-25), which shields the active site.
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Cirri P, Chiarugi P, Marra F, Raugei G, Camici G, Manao G, Ramponi G. c-Src activates both STAT1 and STAT3 in PDGF-stimulated NIH3T3 cells. Biochem Biophys Res Commun 1997; 239:493-7. [PMID: 9344858 DOI: 10.1006/bbrc.1997.7493] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Treatment of cells with PDGF and EGF specifically induces STAT1 and STAT3, which became phosphorylated on tyrosine residues to form homo and heterodimers: in these configurations they translocate into the nucleus where they act as transcription activators. However little is known about the activation of STATs in growth factor receptor signal transduction. Recently it has been shown that v-Src modulates the tyrosine phosphorylation of STAT3 but not of STAT1. Here we report that the cellular Src tyrosine kinase is involved in the activation of both STAT1 and STAT3 in PDGF stimulated NIH3T3 cells. Both tyrosine phosphorylation and DNA binding activity of STAT1 and STAT3 are up-regulated in c-Src overexpressing cells, while we observe the opposite phenomenon in cells overexpressing the dominant negative Src. Furthermore, our results show that STAT1 co-immunoprecipitates with c-Src, suggesting that the activation of STATs by Src occurs via a direct interaction. Taken together, these data suggest that c-Src is involved in activation of both STAT1 and 3 in PDGF signal transduction.
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Paoli P, Cirri P, Camici L, Manao G, Cappugi G, Moneti G, Pieraccini G, Camici G, Ramponi G. Common-type acylphosphatase: steady-state kinetics and leaving-group dependence. Biochem J 1997; 327 ( Pt 1):177-84. [PMID: 9355750 PMCID: PMC1218778 DOI: 10.1042/bj3270177] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A number of acyl phosphates differing in the structure of the acyl moiety (as well as in the leaving-group pKa of the acids produced in hydrolysis) have been synthesized. The Km and Vmax values for the bovine common-type acylphosphatase isoenzyme have been measured at 25 degrees C and pH 5.3. The values of kcat differ widely in relation to the different structures of the tested acyl phosphates: linear relationships between log kcat and the leaving group pKa, as well as between log kcat/Km and the leaving-group pKa, were observed. On the other hand, the Km values of the different substrates are very close to each other, suggesting that the phosphate moiety of the substrate is the main chemical group interacting with the enzyme active site in the formation of the enzyme-substrate Michaelis complex. The enzyme does not catalyse transphosphorylation between substrate and concentrated nucleophilic acceptors (glycerol and methanol); nor does it catalyse H218O-inorganic phosphate oxygen exchange. It seems that no phosphoenzyme intermediate is formed in the catalytic pathway. Furthermore, during the enzymic hydrolysis of benzoyl phosphate in the presence of 18O-labelled water, only inorganic phosphate (and not benzoate) incorporates 18O, suggesting that no acyl enzyme is formed transiently. all these findings, as well as the strong dependence of kcat upon the leaving group pK1, suggest that neither a nucleophilic enzyme group nor general acid catalysis are involved in the catalytic pathway. The enzyme is competitively inhibited by Pi, but it is not inhibited by the carboxylate ions produced during substrate hydrolysis, suggesting that the last step of the catalytic process is the release of Pi. The activation energy values for the catalysed and spontaneous hydrolysis of benzoyl phosphate have been determined.
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Chiarugi P, Cirri P, Marra F, Raugei G, Camici G, Manao G, Ramponi G. LMW-PTP is a negative regulator of insulin-mediated mitotic and metabolic signalling. Biochem Biophys Res Commun 1997; 238:676-82. [PMID: 9299573 DOI: 10.1006/bbrc.1997.7355] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To understand the physiological role of low Mr weight phosphotyrosine protein phosphatase (LMW-PTP) in insulin mediated signaling, we established clonal cell lines overexpressing the dominant negative (C12S mutant) LMW-PTP (dnLMW-PTP) from NIH3T3 murine fibroblasts expressing insulin receptor. Upon insulin stimulation we observe an association between the dnLMW-PTP and the beta-subunit of the insulin receptor. This association is dependent on the tyrosine phosphorylation of the insulin receptor since it is not observed in unstimulated cells. Furthermore, in vitro binding experiments between dnLMW-PTP and the insulin receptor reveal that the interaction is mediated by the LMW-PTP catalytic site, as indicated by competition with orthovanadate. DnLMW-PTP overexpression influences both the mitogenic and the metabolic bioeffects of insulin. In particular, in cells overexpressing dnLMW-PTP we observe an increase in the glycogenosynthesis rate and in mitosis as indicated by glucose incorporation into glycogen and thymidine incorporation into DNA, respectively. Moreover, we studied the insulin mediated signal transduction pathways starting from insulin receptor, such as the Src kinase, the p21Ras/ERK, and the PI3K routes. Our findings are consistent with a specific regulation of mitogenesis by LMW-PTP through a pathway involving c-Src kinase but independent by both PI3K and ERK. These data strongly suggest that LMW-PTP acts as a negative regulator of both mitogenetic and metabolic insulin signalling.
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