title: c-Src-dependent EGF receptor transactivation contributes to ET-1-induced COX-2 expression in brain microvascular endothelial cells.
abstract: BACKGROUND
  Endothelin-1 (ET-1) is elevated and participates in the regulation of several brain inflammatory disorders. The deleterious effects of ET-1 on endothelial cells may aggravate brain inflammation mediated through the upregulation of cyclooxygenase-2 (COX-2) gene expression. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in brain microvascular endothelial cells remain unclear.
  
  
  OBJECTIVE
  The goal of this study was to examine whether ET-1-induced COX-2 expression and prostaglandin E2 (PGE2) release were mediated through a c-Src-dependent transactivation of epidermal growth factor receptor (EGFR) pathway in brain microvascular endothelial cells (bEnd.3 cells).
  
  
  METHODS
  The expression of COX-2 induced by ET-1 was evaluated by Western blotting and RT-PCR analysis. The COX-2 regulatory signaling pathways were investigated by pretreatment with pharmacological inhibitors, short hairpin RNA (shRNA) or small interfering RNA (siRNA) transfection, chromatin immunoprecipitation (ChIP), and promoter activity reporter assays. Finally, we determined the PGE2 level as a marker of functional activity of COX-2 expression.
  
  
  RESULTS
  First, the data showed that ET-1-induced COX-2 expression was mediated through a c-Src-dependent transactivation of EGFR/PI3K/Akt cascade. Next, we demonstrated that ET-1 stimulated activation (phosphorylation) of c-Src/EGFR/Akt/MAPKs (ERK1/2, p38 MAPK, and JNK1/2) and then activated the c-Jun/activator protein 1 (AP-1) via Gq/i protein-coupled ETB receptors. The activated c-Jun/AP-1 bound to its corresponding binding sites within COX-2 promoter, thereby turning on COX-2 gene transcription. Ultimately, upregulation of COX-2 by ET-1 promoted PGE2 biosynthesis and release in bEnd.3 cells.
  
  
  CONCLUSIONS
  These results demonstrate that in bEnd.3 cells, c-Src-dependent transactivation of EGFR/PI3K/Akt and MAPKs linking to c-Jun/AP-1 cascade is essential for ET-1-induced COX-2 upregulation. Understanding the mechanisms of COX-2 expression and PGE2 release regulated by ET-1/ETB system on brain microvascular endothelial cells may provide rational therapeutic interventions for brain injury and inflammatory diseases.
authors: Department of Nursing, Division of Basic Medical Sciences, Chang Gung University of Science and Technology, Tao-Yuan, Taiwan.
authors: Hsi-Lung
authors: HL
authors: Hsieh
authors: Chih-Chung
authors: CC
authors: Lin
authors: Hui-Ju
authors: HJ
authors: Chan
authors: Caleb M
authors: CM
authors: Yang
authors: Chuen-Mao
authors: CM
authors: Yang
mesh_terms: D000818:Animals; D001921:Brain / Q000098:blood supply / Q000166:cytology / Q000378:metabolism*; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000096:biosynthesis / Q000235:genetics*; D019332:Endothelin-1 / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D051379:Mice; D008833:Microcirculation / Q000502:physiology*; D015533:Transcriptional Activation / Q000502:physiology*; D015854:Up-Regulation / Q000235:genetics; D019061:src-Family Kinases / Q000502:physiology*
chemical_list: D019332:Endothelin-1; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2; D066246:ErbB Receptors; D019061:src-Family Kinases