title: The tyrosine phosphatase SHP-1 regulates hypoxia inducible factor-1α (HIF-1α) protein levels in endothelial cells under hypoxia.
abstract: BACKGROUND
  The tyrosine phosphatase SHP-1 negatively influences endothelial function, such as VEGF signaling and reactive oxygen species (ROS) formation, and has been shown to influence angiogenesis during tissue ischemia. In ischemic tissues, hypoxia induced angiogenesis is crucial for restoring oxygen supply. However, the exact mechanism how SHP-1 affects endothelial function during ischemia or hypoxia remains unclear. We performed in vitro endothelial cell culture experiments to characterize the role of SHP-1 during hypoxia.
  
  
  RESULTS
  SHP-1 knock-down by specific antisense oligodesoxynucleotides (AS-Odn) increased cell growth as well as VEGF synthesis and secretion during 24 hours of hypoxia compared to control AS-Odn. This was prevented by HIF-1α inhibition (echinomycin and apigenin). SHP-1 knock-down as well as overexpression of a catalytically inactive SHP-1 (SHP-1 CS) further enhanced HIF-1α protein levels, whereas overexpression of a constitutively active SHP-1 (SHP-1 E74A) resulted in decreased HIF-1α levels during hypoxia, compared to wildtype SHP-1. Proteasome inhibition (MG132) returned HIF-1α levels to control or wildtype levels respectively in these cells. SHP-1 silencing did not alter HIF-1α mRNA levels. Finally, under hypoxic conditions SHP-1 knock-down enhanced intracellular endothelial reactive oxygen species (ROS) formation, as measured by oxidation of H2-DCF and DHE fluorescence.
  
  
  CONCLUSIONS
  SHP-1 decreases half-life of HIF-1α under hypoxic conditions resulting in decreased cell growth due to diminished VEGF synthesis and secretion. The regulatory effect of SHP-1 on HIF-1α stability may be mediated by inhibition of endothelial ROS formation stabilizing HIF-1α protein. These findings highlight the importance of SHP-1 in hypoxic signaling and its potential as therapeutic target in ischemic diseases.
authors: Walter Brendel Centre of Experimental Medicine, University of Munich, Munich, Germany; Department of Internal Medicine III, University of Munich, Munich, Germany.
authors: Stefan K
authors: SK
authors: Alig
authors: Walter Brendel Centre of Experimental Medicine, University of Munich, Munich, Germany.
authors: Yvonn
authors: Y
authors: Stampnik
authors: Walter Brendel Centre of Experimental Medicine, University of Munich, Munich, Germany; Department of Internal Medicine I, University of Munich, Munich, Germany.
authors: Joachim
authors: J
authors: Pircher
authors: Walter Brendel Centre of Experimental Medicine, University of Munich, Munich, Germany.
authors: Raffaela
authors: R
authors: Rotter
authors: Walter Brendel Centre of Experimental Medicine, University of Munich, Munich, Germany.
authors: Erik
authors: E
authors: Gaitzsch
authors: Department of Internal Medicine IV, University of Munich, Munich, Germany.
authors: Andrea
authors: A
authors: Ribeiro
authors: Department of Internal Medicine IV, University of Munich, Munich, Germany.
authors: Markus
authors: M
authors: Wörnle
authors: Interventional Cardiology, Starnberg Community Hospital, Starnberg, Germany.
authors: Florian
authors: F
authors: Krötz
authors: Walter Brendel Centre of Experimental Medicine, University of Munich, Munich, Germany.
authors: Hanna
authors: H
authors: Mannell
mesh_terms: D015687:Cell Hypoxia; D049109:Cell Proliferation; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000201:enzymology / Q000502:physiology*; D055785:Gene Knockdown Techniques; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6 / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017382:Reactive Oxygen Species; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C509249:PTPN6 protein, human; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6