title: PAR-1 activation rescues astrocytes through the PI3K/Akt signaling pathway from chemically induced apoptosis that is exacerbated by gene silencing of β-arrestin 1.
abstract: Protease-activated receptors (PARs) are seven transmembrane-domains G-protein-coupled receptors with four members: PAR-1, PAR-2, PAR-3, and PAR-4. The scaffold proteins β-arrestin 1 and β-arrestin 2 have been shown mediating responses to various receptor agonists, including PAR-1 and PAR-2. The aim of this study was to investigate whether the signaling adaptor β-arrestin 1 is (i) associated with apoptosis of astrocytes and (ii) involved in thrombin-induced PAR-1-mediated cytoprotection. Here, we found firstly that staurosporine-induced apoptosis, detected as cleavage of caspase 3 is more than 3-times higher in β-arrestin 1-lacking astrocytes than in control cells. This indicates that β-arrestin 1 is important to protect astrocytes from apoptosis. Secondly, PAR-1 activation by thrombin protects non-silenced and β-arrestin 1-deficient astrocytes from staurosporine-induced chemical toxicity. Furthermore, application of thrombin rescues β-arrestin 1-lacking astrocytes from apoptosis by enhanced Akt (Ser 473) phosphorylation. Rescue from cell death was measured by quantification of the cleavage of caspase 3. Thus, we conclude that the thrombin-activated PI3K/Akt signaling cascades play pivotal roles in survival of β-arrestin 1-deficient astrocytes. Our most striking novel finding is that β-arrestin 1 inhibits long-term thrombin-stimulated phosphorylation of Akt (Ser 473). This has been demonstrated by enhanced Akt (Ser 473) phosphorylation in astrocytes with knockdown of β-arrestin 1. Blockade of the PI3K/Akt signaling pathway by LY294002 abrogates the protection caused by thrombin treatment. In addition, we also found that thrombin-induced phosphorylation of Akt (Ser 473) is increased by transactivation of the EGF and PDGF receptors in β-arrestin 1-silenced astrocytes.
authors.affiliation: Institut für Neurobiochemie, Otto-von-Guericke-Universität Magdeburg, Medizinische Fakultät, Leipziger Straße 44, 39120 Magdeburg, Germany.
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Zhu
authors.affiliation: Institut für Neurobiochemie, Otto-von-Guericke-Universität Magdeburg, Medizinische Fakultät, Leipziger Straße 44, 39120 Magdeburg, Germany. Electronic address: georg.reiser@med.ovgu.de.
authors.forename: Georg
authors.initials: G
authors.lastname: Reiser
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D019390:Arrestins / Q000235:genetics*; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D044463:Receptor, PAR-1 / Q000378:metabolism*; D015398:Signal Transduction; D013917:Thrombin / Q000494:pharmacology; D000071559:beta-Arrestin 1; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
chemical_list: C000605256:Arrb1 protein, rat; C000605257:Arrb2 protein, rat; D019390:Arrestins; D044463:Receptor, PAR-1; D000071559:beta-Arrestin 1; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D013917:Thrombin; D053148:Caspase 3
keywords: Astrocytes; Cell death; Neuroprotection; PAR-1; PI3K/Akt pathway; Thrombin