Cardiovascular Research Advance Access [Accepted Manuscript] published online on June 4, 2009
Cardiovascular Research, doi:10.1093/cvr/cvp184
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Urokinase activates macrophage PON2 gene transcription via the PI3K/ROS/MEK/SREBP-2 signaling cascade mediated by the PDGFR-β
1 The Lipid Research Laboratory, Technion Faculty of Medicine, The Rappaport Family Institute for Research in the Medical Sciences, and Rambam Medical Center, Haifa, Israel
2 Department of Pharmacology, Johannes Gutenberg University, Mainz, Germany
3 Hannover Medical School, Hannover, Germany.
* Address for Correspondence: Bianca Fuhrman, D.Sc., Lipid Research Laboratory, Rambam Medical Center, Haifa, Israel, 31096, Telephone: 972-4-8295278, Fax: 972-4-8520076; E. mail: Fuhrman{at}tx.technion.ac.il
Aims: We have recently shown that urokinase plasminogen activator (uPA) increases oxidative stress, cholesterol biosynthesis and paraoxonase 2 (PON2) expression in macrophages via binding to its receptor, the uPAR. Since PON2 is regulated by both oxidative stress and cholesterol content, we hypothesized that uPA elicits a cascade of signal transduction events shared by NADPH oxidase and cholesterol biosynthesis that culminates in PON2 gene expression. Here we investigated the signaling pathway that leads to the expression of PON2 in macrophages in response to uPA.
Methods and Results: The increase in macrophage PON2 mRNA levels in response to uPA was shown to depend on PON2 gene promoter activation and mRNA transcription. LDL abolished these effects, suggesting a possible role for a transcription factor involved in cellular cholesterogenesis. Indeed, uPA upregulated PON2 expression in a sterol regulatory binding protein-2 (SREBP-2)-dependent manner, since blocking SREBP-2 maturation by 4-(2- aminoethyl)-benzenesulfonyl fluoride (AEBSF) abolished uPA-stimulation of PON2, whereas inhibition of SREBP-2 catabolism by N-acetyl-leucyl-norleucinal (ALLN), had an opposite effect. The upstream signaling mechanisms include uPA activation of extracellular signal-regulated kinases (ERK1/2), which was dependent on NADPH oxidase and phosphatidylinositol 3-kinase (PI3K) activation, and these latter effects were mediated by the tyrosine kinase activity of the platelet-derived growth factor receptor (PDGFR)-ß.
Conclusions: These findings provide a framework linking interactions among cellular signaling pathways associated with reactive oxygen species (ROS) production, macrophage cholesterol biosynthesis and cellular PON2 expression in vascular pathophysiology.
KEYWORDS Urokinase; Paraoxonase 2 (PON2); NADPH oxidase; SREBP2; PDGFβ receptor; Macrophages
Time for primary review: 25 Days