Hypoxic induction of Ctgf is directly mediated by Hif-1.
CTGF plays a significant role in the development of renal fibrosis by mediating the fibrotic effects of transforming growth factor (TGF)-beta(1) and has been shown to be hypoxia inducible in human breast cancer cells. It has been suggested that hypoxia is an important underlying cause for the development of renal fibrosis through the modulation of profibrotic genes. One of the key mediators of the cell's response to lowered oxygen environments is hypoxia-inducible-factor-1 (HIF-1), a basic helix-loop-helix transcription factor, which enables cells to adapt to hypoxia by regulating the expression of genes involved in increasing oxygen availability (VEGF, erythropoietin) and enhancing glucose uptake and metabolism (Glut-1, PGK). In this paper, we have used primary tubular epithelial cell cultures from a tetracycline-inducible-Hif-1alpha knockout murine model to further elucidate the role of Hif-1 in the hypoxic-induction of Ctgf expression. We show that hypoxia response elements present upstream of Ctgf enable direct interaction of Hif-1 transcription factor with the Ctgf promoter, resulting in increased transcription of Ctgf mRNA. Cells deficient in Hif-1alpha were incapable of inducing Ctgf mRNA in response to hypoxia, suggesting an absolute requirement of Hif-1. Furthermore, the observed Hif-1-mediated hypoxic stimulation of Ctgf expression was found to occur independently of TGF-beta(1) signaling. Our findings have important implications for a number of fibrotic disorders in which hypoxia, CTGF, and TGF-beta(1) are involved, including renal, dermal, hepatic, and pulmonary fibrosis.
Higgins
Debra F
DF
Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6144, USA.
Biju
Mangatt P
MP
Akai
Yasuhiro
Y
Wutz
Anton
A
Johnson
Randall S
RS
Haase
Volker H
VH
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015687:Cell Hypoxia; D002478:Cells, Cultured; D055513:Connective Tissue Growth Factor; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology; D005786:Gene Expression Regulation; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017874:Immediate-Early Proteins / Q000096:biosynthesis* / Q000235:genetics; D019426:Integrases / Q000235:genetics; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis* / Q000235:genetics; D007684:Kidney Tubules / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020218:Response Elements / Q000235:genetics; D015398:Signal Transduction; D051785:Smad Proteins; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors / Q000172:deficiency / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000502:physiology; D053773:Transforming Growth Factor beta1
C526317:CCN2 protein, human; C526318:CCN2 protein, mouse; D004268:DNA-Binding Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D051785:Smad Proteins; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D055513:Connective Tissue Growth Factor; D004247:DNA; C045073:Cre recombinase; D019426:Integrases