Transactivation of EGF receptor induced by angiotensin II regulates fibronectin and TGF-beta gene expression via transcriptional and post-transcriptional mechanisms.
The signaling cascade elicited by angiotensin II (Ang II) resembles that characteristic of growth factor, and recent evidence indicates transactivation of epidermal growth factor receptor (EGF-R) by G protein-coupled receptors. Here, we report the involvement of EGF-R in Ang II-induced synthesis of fibronectin and TGF-beta in cardiac fibroblasts. Ang II stimulated fibronectin mRNA levels dose-dependently with a maximal increase (approximately 5-fold) observed after 12 h of incubation. Ang II-, or calcium ionophore-induced fibronectin synthesis was completely abolished by tyrosine kinase inhibitors and intracellular Ca2+ chelating agents. Ang II-induced fibronectin mRNA was not affected by PKC inhibitors or PKC depletion, whereas specific inhibition of EGF-R function by a dominant negative EGF-R mutant and tyrphostin AG1478 abolished induction of fibronectin mRNA. We isolated the rat fibronectin gene including the 5'-flanking region and found that the AP-1 binding site present in the promoter region was responsible for the Ang II responsiveness of this gene. Gel retardation assay revealed the binding of nuclear protein to the AP-1 site, which was supershifted with anti-c-fos and anti-c-jun but not anti-ATF-2 antibodies. Conditioned medium from Ang II-treated cells contained TGF-beta bioactivity and addition of neutralizing TGF-beta antibody modestly (46%) inhibited induction of fibronectin. Ang II-induced synthesis of TGF-beta was also abolished by inhibition of EGF-R function. The effect of TGF-beta was exerted by stabilizing fibronectin mRNA without affecting the promoter activity and required de novo protein synthesis. We concluded that Ang II-induced expression of fibronectin and TGF-beta is mediated by downstream signaling of EGF-R transactivated by Ca2+-dependent tyrosine kinase, and that Ang II-induced fibronectin mRNA expression is regulated by two different mechanisms; transcriptional control by binding of c-fos/c-jun complex to the AP-1 site, and post-transcriptional control by mRNA stabilization due to autocrine and/or paracrine effects of TGF-beta. Thus, this study suggested that the action of Ang II on extracellular matrix formation should be interpreted in association with the EGF-R signaling cascade.
Matsubara
H
H
Department of Medicine II, Kansai Medical University, Moriguchi, Osaka, Japan.
Moriguchi
Y
Y
Mori
Y
Y
Masaki
H
H
Tsutsumi
Y
Y
Shibasaki
Y
Y
Uchiyama-Tanaka
Y
Y
Fujiyama
S
S
Koyama
Y
Y
Nose-Fujiyama
A
A
Iba
S
S
Tateishi
E
E
Iwasaka
T
T
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000235:genetics*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D005353:Fibronectins / Q000235:genetics*; D017930:Genes, Reporter; D006321:Heart / Q000502:physiology*; D007700:Kinetics; D009206:Myocardium / Q000166:cytology*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000235:genetics*
D004791:Enzyme Inhibitors; D005353:Fibronectins; D016212:Transforming Growth Factor beta; D000804:Angiotensin II; D066246:ErbB Receptors; D011493:Protein Kinase C