The early-immediate gene EGR-1 is induced by transforming growth factor-beta and mediates stimulation of collagen gene expression.
Transforming growth factor-beta (TGF-beta) stimulates collagen synthesis and accumulation, and aberrant TGF-beta signaling is implicated in pathological organ fibrosis. Regulation of type I procollagen gene (COL1A2) transcription by TGF-beta involves the canonical Smad signaling pathway as well as additional protein and lipid kinases, coactivators, and DNA-binding transcription factors that constitute alternate non-Smad pathways. By using Affymetrix microarrays to detect cellular genes whose expression is regulated by Smad3, we identified early growth response factor-1 (EGR-1) as a novel Smad3-inducible gene. Previous studies implicated Egr-1 in cell growth, differentiation, and survival. We found that TGF-beta induced rapid and transient accumulation of Egr-1 protein and mRNA in human skin fibroblasts. In transient transfection assays, TGF-beta stimulated the activity of the Egr-1 gene promoter, as well as that of a minimal Egr-1-responsive reporter construct. Furthermore, TGF-beta enhanced endogenous Egr-1 interaction with a consensus Egr-1-binding site element and with GC-rich DNA sequences of the human COL1A2 promoter in vitro and in vivo. Forced expression of Egr-1 by itself caused dose-dependent up-regulation of COL1A2 promoter activity and further enhanced the stimulation induced by TGF-beta. In contrast, the TGF-beta response was abrogated when the Egr-1-binding sites of the COL1A2 promoter were mutated or deleted. Furthermore, Egr-1-deficient embryonic mouse fibroblasts showed attenuated TGF-beta responses despite intact Smad activation, and forced expression of ectopic EGR-1 in these cells could restore COL1A2 stimulation in a dose-dependent manner. Taken together, these findings identify Egr-1 as a novel intracellular TGF-beta target that is necessary for maximal stimulation of collagen gene expression in fibroblasts. The results therefore implicate Egr-1 in the profibrotic responses elicited by TGF-beta and suggest that Egr-1 may play a new and important role in the pathogenesis of fibrosis.
Chen
Shu-Jen
SJ
Division of Rheumatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611.
Ning
Hongyan
H
Division of Rheumatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611.
Ishida
Wataru
W
Division of Rheumatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611.
Sodin-Semrl
Snezna
S
Division of Rheumatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611.
Takagawa
Shinsuke
S
Division of Rheumatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611.
Mori
Yasuji
Y
Division of Rheumatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611.
Varga
John
J
Division of Rheumatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611. Electronic address: j-varga@northwestern.edu.
D000818:Animals; D001483:Base Sequence; D003094:Collagen / Q000096:biosynthesis* / Q000378:metabolism; D024042:Collagen Type I; D051766:Early Growth Response Protein 1 / Q000096:biosynthesis* / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000096:biosynthesis*
D024042:Collagen Type I; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D016212:Transforming Growth Factor beta; D003094:Collagen