Smad-independent transforming growth factor-beta regulation of early growth response-1 and sustained expression in fibrosis: implications for scleroderma.
Transforming growth factor-beta (TGF-beta) plays a key role in scleroderma pathogenesis. The transcription factor early growth response-1 (Egr-1) mediates the stimulation of collagen transcription elicited by TGF-beta and is necessary for the development of pulmonary fibrosis in mice. Here, we report that TGF-beta causes a time- and dose-dependent increase in Egr-1 protein and mRNA levels and enhanced transcription of the Egr-1 gene via serum response elements in normal fibroblasts. The ability of TGF-beta to stimulate Egr-1 was preserved in Smad3-null mice and in explanted Smad3-null fibroblasts. The response was blocked by a specific mitogen-activated protein kinase kinase 1 (MEK1) inhibitor but not by an ALK5 kinase inhibitor. Furthermore, MEK1 was phosphorylated by TGF-beta, which was sufficient to drive Egr-1 transactivation. Stimulation by TGF-beta enhanced the transcriptional activity of Elk-1 via the MEK-extracellular signal-regulated kinase 1/2 pathway. Bleomycin-induced scleroderma in the mouse was accompanied by increased Egr-1 accumulation in lesional fibroblasts. Furthermore, biopsies of lesional skin and lung from patients with scleroderma showed increased Egr-1 levels, which were highest in early diffuse disease. Moreover, both Egr-1 mRNA and protein were elevated in explanted scleroderma skin fibroblasts in vitro. Together, these findings define a Smad-independent TGF-beta signal transduction mechanism that underlies the stimulation of Egr-1, demonstrate for the first time sustained Egr-1 up-regulation in fibrotic lesions and suggests that Egr-1 has a role in the induction and progression of fibrosis.
Bhattacharyya
Swati
S
Division of Rheumatology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
Chen
Shu-Jen
SJ
Wu
Minghua
M
Warner-Blankenship
Matthew
M
Ning
Hongyan
H
Lakos
Gabriella
G
Mori
Yasuji
Y
Chang
Eric
E
Nihijima
Chihiro
C
Takehara
Kazuhiro
K
Feghali-Bostwick
Carol
C
Varga
John
J
D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001761:Bleomycin; D051766:Early Growth Response Protein 1 / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology; D005355:Fibrosis; D006801:Humans; D008168:Lung / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D041681:NIH 3T3 Cells; D011401:Promoter Regions, Genetic / Q000235:genetics; D012595:Scleroderma, Systemic / Q000201:enzymology / Q000235:genetics* / Q000473:pathology*; D012867:Skin / Q000378:metabolism / Q000473:pathology; D051900:Smad3 Protein / Q000378:metabolism; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D050807:ets-Domain Protein Elk-1 / Q000235:genetics / Q000378:metabolism
D051766:Early Growth Response Protein 1; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D050807:ets-Domain Protein Elk-1; D001761:Bleomycin; D020928:Mitogen-Activated Protein Kinases
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