Differential regulation of VEGF by TGF-beta and hypoxia in rat proximal tubular cells.
VEGF expression by proximal tubular epithelial cells may play a critical role in maintaining peritubular capillary endothelium in renal disease. Two major processes involved in renal injury include hypoxia (from vasoconstriction or vascular injury) and transforming growth factor (TGF)-beta-dependent fibrosis, both of which are known to stimulate VEGF. Because the TGF-beta/Smad pathway is activated in hypoxia, we tested the hypothesis that the induction of VEGF in hypoxia could be partially dependent on TGF-beta. Rat proximal tubular (NRK52E) cells treated with TGF-beta under normoxic conditions secreted VEGF at 24 h, and this was significantly reduced by blocking Smad activation by overexpressing the inhibitory Smad7 or by blocking p38 and ERK1/2 MAP kinase activation or protein kinase C activation with specific inhibitors. With acute hypoxia, rat proximal tubular cells also express VEGF mRNA and protein as well as TGF-beta. However, the induction of VEGF occurs before synthesis of TGF-beta and is not blocked by either a TGF-beta antagonist, by Smad7 overexpression, or by blockage of ERK1/2, whereas induction is blocked by PKC inhibition or partially blocked by a p38 inhibitor. Finally, the addition of TGF-beta with hypoxia results in significantly more VEGF expression than either stimulation alone. Thus TGF-beta and hypoxia act via additive/synergistic but distinct pathways to stimulate VEGF in proximal tubular cells, a finding that may be important in understanding how VEGF is stimulated in renal disease.
Nakagawa
Takahiko
T
Division of Nephrology, Hypertension, and Transplantation, University of Florida, Gainesville, FL 32610-0224, USA. nakagt@medicine.ufl.edu
Lan
Hui Y
HY
Zhu
Hong J
HJ
Kang
Duk-Hee
DH
Schreiner
George F
GF
Johnson
Richard J
RJ
D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D051900:Smad3 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases
D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D051900:Smad3 Protein; C497787:Smad3 protein, rat; D051906:Smad7 Protein; C497808:Smad7 protein, rat; C508962:Tgfb1 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D042461:Vascular Endothelial Growth Factor A; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases