Submitted on March 14, 2007
Accepted on June 26, 2007
TGF-
1 Stimulates Human AT1 Receptor Expression in Lung Fibroblasts by Cross-Talk Between the Smad, p38 MAPK, JNK and PI3K Signaling Pathways
Mickey M. Martin1, Jessica A. Buckenberger1, Jinmai Jiang2, Geraldine E. Malana1, Daren L Knoell3, David S. Feldman4, and Terry S Elton1*
1 Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio, United States
2 Pharmacology, The Ohio State University, COLUMBUS, Ohio, United States
3 Pharmacy, The Ohio State University, Columbus, Ohio, United States
4 Cardiology, The Ohio State University, COLUMBUS, Ohio, United States
* To whom correspondence should be addressed. E-mail: terry.elton{at}osumc.edu.
Both angiotensin II (Ang II) and transforming growth factor-
1 (TGF-1) are thought to be involved in mediating pulmonary fibrosis. Interactions between the renin-angiotensin system (RAS) and TGF-1 have been well documented with most studies describing the effect of Ang II on TGF-1 expression. However, recent gene expression profiling experiments demonstrated that the angiotensin II type 1 receptor (AT1R) gene was a novel TGF-1 target in human adult lung fibroblasts. In this report, we show that TGF-1 augments human AT1R (hAT1R) steady state mRNA and protein levels in a dose- and time-dependent manner in primary human fetal pulmonary fibroblasts (hPFBs). Nuclear run-on experiments demonstrate that TGF-1 transcriptionally activates the hAT1R gene and does not influence hAT1R mRNA stability. Pharmacological inhibitors and specific siRNA knockdown experiments demonstrate that the TGF-1 type 1 receptor (TRI/ALK5), Smad2/3, and Smad4 are essential for TGF-1-stimulated hAT1R expression. Additionally, pharmacological inhibitor and siRNA experiments also demonstrated that p38MAPK, JNK and PI3K signaling pathways are also involved in the TGF-1-stimulated increase in hAT1R density. Taken together, our results suggest an important role for cross-talk between Smad, p38MAPK, JNK and PI3K pathways in mediating the augmented expression of hAT1R following TGF-1 treatment in hPFBs. This study supports the hypothesis that a self-potentiating loop exists between the RAS and the TGF-1 signaling pathways and suggests that Ang II and TGF-1 may cooperate in the pathogenesis of pulmonary fibrosis. The synergy between these systems may require that both pathways be simultaneously inhibited in order to treat fibrotic lung disease.
