Protein Phosphatases 1 and 2A Maintain Endothelial Cells in a Resting State, Limiting the Motility that is Needed for the Morphogenic Process of Angiogenesis

Gabel, Steven; Benefield, Janet; Meisinger, Jeremy; Petruzzelli, Guy J.; Young, Matthew R.

doi:10.1016/s0194-5998(99)70238-x

Cited by 25 publications

(32 citation statements)

References 19 publications

(46 reference statements)

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“…Whereas a role for PP2A in the regulation of cell motility has been suggested by pharmacological approaches using okadaic acid in transformed cells (90) and cancer cell lines (38,40,91,92), the investigations reported here demonstrate that intracellular PP2A activity can be manipulated in keratinocytes by a novel, receptor-mediated mechanism with resultant effects on the migratory ability of the cells. Our findings open up the possibility of exploring the use of ␤ 2 -adrenergic agonists as pharmaceutical agents to inhibit cell migration.…”

Section: Discussionmentioning

confidence: 50%

PP2A Activation by β2-Adrenergic Receptor Agonists

Pullar

Chen

Isseroff

2003

Journal of Biological Chemistry

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Understanding the mechanisms that regulate cell migration is important for devising novel therapies to control metastasis or enhance wound healing. Previously, we demonstrated that ␤ 2 -adrenergic receptor (␤ 2 -AR) activation in keratinocytes inhibited their migration by decreasing the phosphorylation of a critical promigratory signaling component, the extracellular signal-related kinase (ERK). Here we demonstrate that ␤ 2 -ARinduced inhibition of migration is mediated by the activation of the serine/threonine phosphatase PP2A. Pretreating human keratinocytes with the PP2A inhibitor, okadaic acid, prevented the ␤ 2 -AR-induced inhibition of migration, either as isolated cells or as a confluent sheet of cells repairing an in vitro "wound" and also prevented the ␤ 2 -AR-induced reduction in ERK phosphorylation. Similar results were obtained with human corneal epithelial cells. In keratinocytes, immunoprecipitation studies revealed that ␤ 2 -AR activation resulted in the rapid association of ␤ 2 -AR with PP2A as well as a 37% increase in association of PP2A with ERK2. Finally, ␤ 2 -AR activation resulted in a rapid and transient 2-fold increase in PP2A activity. Thus, we provide the first evidence that ␤ 2 -AR activation in keratinocytes modulates migration via a novel pathway utilizing PP2A to alter the promigratory signaling cascade. Exploiting this pathway may result in novel therapeutic approaches for control of epithelial cell migration.When skin is wounded, keratinocytes within the epidermis must migrate from the wound edges to re-epithelialize the wound surface (1). One of the best characterized mediators of keratinocyte migration is the epidermal growth factor receptor (EGFR) 1 (2-4). The mitogen-activated protein (MAP) kinases, extracellular signal-related kinase 1 (ERK1) and ERK2, are activated upon EGF binding to its cognate receptor (reviewed in Ref. 5). They are activated by phosphorylation on both conserved threonine and tyrosine residues and inactivated upon dephosphorylation by dual specificity phosphatases, tyrosine phosphatases, and serine/threonine-specific phosphatases (5-9). The activation of ERK is tightly controlled. The MAP kinase pathway is usually only transiently activated, and its constitutive activation is sufficient to cause the oncogenic transformation of some cell types (10). Inhibiting ERK phosphorylation and activation prevents growth factor-induced keratinocyte migration (11), demonstrating the pivotal role of ERK in the keratinocyte promigratory signaling pathways (11-13).In addition to the EGFR, keratinocytes also express high levels of the G-protein-coupled receptor, the ␤ 2 -adrenergic receptor, (␤ 2 -AR) (14, 15), whose functional role in the epidermis has not yet been elucidated. Keratinocytes do not express the ␤ 1 -AR (16). Earlier studies have investigated the role of ␤-ARs in epithelial wound healing and migration, but the results have been paradoxical. ␤-Antagonists have been reported to either delay (17, 18) or enhance (19) corneal epithelial wound healing, and ␤-agon...

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Section: Discussionmentioning

confidence: 50%

PP2A Activation by β2-Adrenergic Receptor Agonists

Pullar

Chen

Isseroff

2003

Journal of Biological Chemistry

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“…33 We had also shown increased migration by endothelial cells whose PP-2A is diminished in response to tumor-derived angiogenic factors or whose PP-2A activity is inhibited pharmacologically. 34,25 In identifying the mechanisms by which the decline in PP-2A stimulates tumor migration, our studies showed paxillin serine hyperphosphorylation and tyrosine dephosphorylation, and dissolution of the FAK/Src/paxillin complexes that are important in stabilizing cellular adhesions. Accompanying this dissolution of FAK/Src/paxillin complexes was a reduction in phosphorylation of the inhibitory Y527 residue of Src, suggesting increased Src activity.…”

Section: Discussionmentioning

confidence: 96%

Protein phosphatase‐2A restricts migration of Lewis lung carcinoma cells by modulating the phosphorylation of focal adhesion proteins

Young

Liu

Meisinger

2002

Intl Journal of Cancer

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The process of metastasis requires migration of tumor cells from the primary tumor into the vasculature and the target tissue. 1 Studies with a variety of tumor types have shown that metastatic tumor cells are more highly motile than are nonmetastatic cells. [2][3][4][5] Cellular migration is influenced by the degree of adhesiveness to a substratum, signaling through integrins, and active turnover of focal adhesions. 6,7 There is, however, a fine balance between adherence/detachment and motility. A strong shift toward focal adhesion formation results in strong adherence with little migration, whereas excessive loss of adherence results in the inability to navigate across the substratum. Interactions with a substratum leads to the formation and stabilization of focal adhesions, where the actin skeleton converges with integrins and an interconnection of protein complexes. 6,8 Among the focal adhesion proteins that mediates communication through integrins during interaction with the substratum is the cytosolic tyrosine kinase FAK. 6,9 When FAK activity is reduced, cellular adhesiveness is diminished 10. During motility, the levels of membrane-associated FAK decline. 11 In adherent cells, FAK is complexed with Src within stable focal adhesions. 6 The tyrosine kinase Src (pp60c-Src) is a prototype of a family of tyrosine kinases that also includes Fyn, Lyn, Yes. Src Y527 residue (Y530 in humans) regulates Src activity. 7,12 When phosphorylated, Y527 inactivates Src by undergoing a conformational change and binding with the Src SH2 domain. FAK complexing with Src is important in Src activation and stabilization of focal adhesions, Src activation can also increase turnover of focal adhesions and increase motility. [13][14][15] An in vivo role of FAK or Src in cancer invasion has been suggested by their increased levels in malignancies. 16 Key in the formation of stable adhesions is association of FAK and Src with paxillin. Paxillin is a 68 kDa adaptor protein that binds a multitude of structural and signaling molecules within focal adhesions. The ability of paxillin to facilitate interaction between molecules of the focal adhesions is regulated by its level of serine and tyrosine phosphorylation. 17 Focal adhesion formation and cellular adhesion are accompanied by tyrosine phosphorylation of paxillin, 18,19 whereas the breakdown of focal adhesions and loss of adherence are accompanied by tyrosine dephosphorylation of paxillin. 20,21 Blocking tyrosine phosphorylation of paxillin results in failure to form organized stress fibers and focal adhesions, and defective cellular adherence. 22 In contrast, serine phosphorylation of paxillin has been associated with redistribution of paxillin from the tyrosine-phosphorylated focal adhesions and increased cell scattering. 23 Our studies with a murine Lewis lung carcinoma model have shown regulation of cell migration by the serine/threonine protein phosphatase PP-2A. 3,24 More highly motile and metastatic tumor cells have diminished PP-2A activity. Inhibition of PP-2A activity wit...

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“…Similarly, endostatin has been reported to activate the serine/threonine phosphatase PP2A, and this, in turn, perturbs the phosphorylation of endothelial nitric-oxide synthase that is essential for endothelial cell migration and survival (31). Moreover, pharmacological inhibition of protein phosphatase activity has been reported to stimulate the motility of endothelial cells and nonmetastatic tumor cells (32,33). Recently, DEP1/CD148, a membrane-associated tyrosine phosphatase that is up-regulated by confluence and is located at intercellular junctions, has been reported to play a crucial role in developmental vascular organization through the regulation of endothelial proliferation and endothelium-pericyte interactions (34).…”

Section: Discussionmentioning

confidence: 99%

A Truncated Kringle Domain of Human Apolipoprotein(a) Inhibits the Activation of Extracellular Signal-regulated Kinase 1 and 2 through a Tyrosine Phosphatase-dependent Pathway

Ahn¹,

Kim

Yu³

et al. 2004

Journal of Biological Chemistry

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Most proangiogenic factors exert their biological effects primarily by activating extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3-K)/Akt signaling pathways. These pathways appear to play a critical role in endothelial cell migration, because selective inhibition of either ERK or PI3-K/Akt signaling almost completely prevented endothelial cell migration. Recently, we demonstrated that a truncated kringle domain of human apolipoprotein(a), termed rhLK68, inhibits endothelial cell migration in vitro. However, its mechanism of action was not well defined. In this study, we determined the effects of rhLK68 on ERK1/2 and PI3-K/Akt signaling pathways to explore the molecular mechanism of rhLK68-mediated inhibition of endothelial cell migration. Treatment with rhLK68 inhibited ERK1/2 phosphorylation but did not influence Akt activation. Interestingly, an inhibitor of protein-tyrosine phosphatase, sodium orthovanadate, dose-dependently reversed both rhLK68-induced dephosphorylation of ERK1/2 and decreased migration of endothelial cells, whereas rhLK68 showed no significant effects on MEKs phosphorylation. In conclusion, these results indicate that inhibition of endothelial cell migration by rhLK68 may be achieved by interfering with ERK1/2 activation via a protein-tyrosine phosphatase-dependent pathway.

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Protein Phosphatases 1 and 2A Maintain Endothelial Cells in a Resting State, Limiting the Motility that is Needed for the Morphogenic Process of Angiogenesis

Cited by 25 publications

References 19 publications

PP2A Activation by β2-Adrenergic Receptor Agonists

PP2A Activation by β2-Adrenergic Receptor Agonists

Protein phosphatase‐2A restricts migration of Lewis lung carcinoma cells by modulating the phosphorylation of focal adhesion proteins

A Truncated Kringle Domain of Human Apolipoprotein(a) Inhibits the Activation of Extracellular Signal-regulated Kinase 1 and 2 through a Tyrosine Phosphatase-dependent Pathway

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