title: MEK mediates the novel cross talk between TNFR2 and TGF-EGFR in enhancing vascular endothelial growth factor (VEGF) secretion from human mesenchymal stem cells.
abstract: BACKGROUND
  Bone marrow mesenchymal stem cells (MSCs) may mediate their beneficial effects by paracrine mechanisms. Recently, we reported that tumor necrosis factor-alpha (TNF-alpha) increased the release of vascular endothelial growth factor (VEGF) from human MSCs and augmented transforming growth factor-alpha (TGF-alpha)-stimulated VEGF secretion. However, it is unknown whether TNF-alpha stimulates VEGF production via TNF receptor 1 (TNFR1) or 2 (TNFR2) and the mechanism by which TNF-alpha augments TGF-alpha (a ligand of epidermal growth factor receptor, EGFR) stimulated VEGF production. We hypothesized that the ablation of TNFR2 would decrease TNF-alpha-stimulated and/or TGF-alpha- stimulated VEGF production via MEK-dependent mechanisms.
  
  
  METHODS
  MSCs transfected with TNFR1, TNFR2, or GAPDH siRNA were stimulated with TNF-alpha and/or TGF-alpha for 24 h. VEGF levels in the supernatant were determined by enzyme-linked immunosorbent assay (ELISA). A Western blot analysis was performed to measure the activation of MEK and ERK and the expression of TNFR1 and TNFR2.
  
  
  RESULTS
  TNF-alpha or TGF-alpha increased VEGF secretion in cells transfected with GAPDH or TNFR1 siRNA. The combination of TNF-alpha and TGF-alpha increased VEGF production. TNF-alpha and/or TGF-alpha stimulation increased phospho-MEK and phospho-ERK in cells transfected with TNFR1 siRNA. Conversely, the effects of TNF-alpha and/or TGF-alpha on MSC VEGF production were significantly decreased, and MEK/ERK activation was negated in cells transfected TNFR2 siRNA.
  
  
  CONCLUSIONS
  TNFR2 plays a vital role in the effects of TNF-alpha and TGF-alpha on MSC VEGF production. The activation of MEK was implicated in this novel cross talk between TNFR2 and TGF-alpha-EGFR in regulating the production of VEGF in human MSCs.
authors.affiliation: Department of Surgery, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wang
authors.forename: Meijing
authors.initials: M
authors.lastname: Wang
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Abarbanell
authors.forename: Brent R
authors.initials: BR
authors.lastname: Weil
authors.forename: Jeremy L
authors.initials: JL
authors.lastname: Herrmann
authors.forename: Jiangning
authors.initials: J
authors.lastname: Tan
authors.forename: Nathan M
authors.initials: NM
authors.lastname: Novotny
authors.forename: Arthur C
authors.initials: AC
authors.lastname: Coffey
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Meldrum
mesh_terms: D002478:Cells, Cultured; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D034741:RNA, Small Interfering; D020239:Receptor Cross-Talk; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000235:genetics / Q000378:metabolism; D047889:Receptors, Tumor Necrosis Factor, Type II / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016211:Transforming Growth Factor alpha / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
chemical_list: D034741:RNA, Small Interfering; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D016211:Transforming Growth Factor alpha; D042461:Vascular Endothelial Growth Factor A; D020929:Mitogen-Activated Protein Kinase Kinases