MEK mediates the novel cross talk between TNFR2 and TGF-EGFR in enhancing vascular endothelial growth factor (VEGF) secretion from human mesenchymal stem cells.
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.
Wang
Yue
Y
Department of Surgery, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Wang
Meijing
M
Abarbanell
Aaron M
AM
Weil
Brent R
BR
Herrmann
Jeremy L
JL
Tan
Jiangning
J
Novotny
Nathan M
NM
Coffey
Arthur C
AC
Meldrum
Daniel R
DR
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*
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