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Inorganic polyphosphate elicits pro-inflammatory responses through activation of the mammalian target of rapamycin complexes 1 and 2 in vascular endothelial cells.

ABSTRACT: Inorganic polyphosphate (polyP) elicits pro-inflammatory signaling responses in endothelial cells through interaction with two receptors, RAGE and P2Y1 . It is known that polyP activates mTOR signaling in breast cancer cells.The objective of this study is to understand the mechanism of the polyP-mediated signaling pathway in endothelial cells and to determine whether polyP exerts its pro-inflammatory effect through activation of mTOR.mTOR activation by polyP or platelet releasates in cellular and animal models was monitored in the absence and presence of pharmacological inhibitors and/or siRNA knockdown of specific signaling molecules.PolyP effectively induced phosphorylation of mTOR complex 1 (mTORC1) substrate, p70S6K, in endothelial cells by an AKT-dependent but ERK-independent mechanism. The siRNA knockdown of both RAGE and P2Y1 or specific inhibitors of the PI3K/PLC/PKC/Ca(2+) signaling axis inhibited polyP-mediated p70S6K phosphorylation. Moreover, either rapamycin or siRNA knockdown of raptor (mTORC1-specific component) abrogated polyP-mediated phosphorylation of p70S6K. By contrast, the siRNA knockdown of rictor (mTOR complex 2-specific component) but not raptor eliminated the barrier-disruptive effect of polyP. Specific NF-?B inhibitors abrogated polyP-mediated phosphorylation of p70S6K and rapamycin suppressed polyP-induced activation of NF-?B. Finally, specific inhibitors of the mTOR signaling network eliminated polyP-mediated vascular leakage and leukocyte recruitment in animal models.PolyP, through interaction with RAGE and P2Y1 , activates both the mTORC1 and mTORC2 signaling network. Both the pro-inflammatory and mTOR signaling functions of polyP are linked.

SUBMITTER: Hassanian SM

PROVIDER: S-EPMC4424178 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Inorganic polyphosphate elicits pro-inflammatory responses through activation of the mammalian target of rapamycin complexes 1 and 2 in vascular endothelial cells.

Hassanian S M SM Dinarvand P P Smith S A SA Rezaie A R AR

Journal of thrombosis and haemostasis : JTH 20150413 5

<h4>Background</h4>Inorganic polyphosphate (polyP) elicits pro-inflammatory signaling responses in endothelial cells through interaction with two receptors, RAGE and P2Y1 . It is known that polyP activates mTOR signaling in breast cancer cells.<h4>Objectives</h4>The objective of this study is to understand the mechanism of the polyP-mediated signaling pathway in endothelial cells and to determine whether polyP exerts its pro-inflammatory effect through activation of mTOR.<h4>Methods</h4>mTOR act ...[more]

PMID: 25776944

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Project description:Polycystic liver disease may complicate autosomal dominant polycystic kidney disease (ADPKD), a disease caused by mutations in polycystins, which are proteins that regulate signaling, morphogenesis, and differentiation in epithelial cells. The cystic biliary epithelium [liver cystic epithelium (LCE)] secretes vascular endothelial growth factor (VEGF), which promotes liver cyst growth via autocrine and paracrine mechanisms. The expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor 1 receptor (IGF1R), and phosphorylated mammalian target of rapamycin (p-mTOR) and the protein kinase A (PKA)-dependent phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) are also up-regulated in LCE. We have hypothesized that mammalian target of rapamycin (mTOR) represents a common pathway for the regulation of hypoxia-inducible factor 1 alpha (HIF1alpha)-dependent VEGF secretion by IGF1 and ERK1/2. Conditional polycystin-2-knockout (Pkd2KO) mice were used for in vivo studies and to isolate cystic cholangiocytes [liver cystic epithelial cells (LCECs)]. The expression of p-mTOR, VEGF, cleaved caspase 3 (CC3), proliferating cell nuclear antigen (PCNA), IGF1, IGF1R, phosphorylated extracellular signal-regulated kinase, p-P70S6K, HIF1alpha, and VEGF in LCE, LCECs, and wild-type cholangiocytes was studied with immunohistochemistry, western blotting, or enzyme-linked immunosorbent assays. The cystic area was measured by computer-assisted morphometry of pancytokeratin-stained sections. Cell proliferation in vitro was studied with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and bromodeoxyuridine assays. The treatment of Pkd2KO mice with the mTOR inhibitor rapamycin significantly reduced the liver cyst area, liver/body weight ratio, pericystic microvascular density, and PCNA expression while increasing expression of CC3. Rapamycin inhibited IGF1-stimulated HIF1alpha accumulation and VEGF secretion in LCECs. IGF1-stimulated LCEC proliferation was inhibited by rapamycin and SU5416 (a vascular endothelial growth factor receptor 2 inhibitor). Phosphorylation of the mTOR-dependent kinase P70S6K was significantly reduced by PKA inhibitor 14-22 amide and by the mitogen signal-regulated kinase inhibitor U1026.These data demonstrate that PKA-dependent up-regulation of mTOR has a central role in the proliferative, antiapoptotic, and pro-angiogenic effects of IGF1 and VEGF in polycystin-2-defective mice. This study also highlights a mechanistic link between PKA, ERK, mTOR, and HIF1alpha-mediated VEGF secretion and provides a proof of concept for the potential use of mTOR inhibitors in ADPKD and conditions with aberrant cholangiocyte proliferation.

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Inorganic polyphosphate elicits pro-inflammatory responses through activation of the mammalian target of rapamycin complexes 1 and 2 in vascular endothelial cells.

Publications

Inorganic polyphosphate elicits pro-inflammatory responses through activation of the mammalian target of rapamycin complexes 1 and 2 in vascular endothelial cells.

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