Rac1-mediated mitochondrial H2O2 generation regulates MMP-9 gene expression in macrophages via inhibition of SP-1 and AP-1.
Aberrant matrix deposition is a hallmark of pulmonary fibrosis and is characterized by an imbalance between matrix deposition and degradation. We have previously shown that mice harboring a conditional deletion of the GTP-binding protein, Rac1, in macrophages are protected from asbestos-induced pulmonary fibrosis. To investigate the contribution of aberrant matrix degradation, we addressed the role of Rac1 in regulating expression of macrophage-specific MMP-9 (matrix metalloproteinase-9). We found that MMP-9 gene transcription was significantly greater in Rac1 null macrophages. Deletion and mutational analysis of the MMP-9 promoter revealed that both SP-1 and AP-1 are essential for MMP-9 transcription. Overexpression of constitutive active Rac1 (V12) revealed that H(2)O(2) was derived from the mitochondria. Rac1-induced H(2)O(2) generation down-regulated MMP-9 gene transcription, whereas catalase overexpression in WT cells enhanced MMP-9 expression. SP-1 interacted directly with both c-Jun and c-Fos, and H(2)O(2) decreased this binding, suggesting that SP-1 and AP-1 function cooperatively to regulate MMP-9 transcription. Rac1-mediated H(2)O(2) inhibited the ERK MAPK, which was essential for activation of SP-1 and AP-1. ERK activation and MMP-9 expression were recovered by overexpressing catalase or transfecting siRNA for the mitochondrial iron-sulfur protein, Rieske. These observations were recapitulated in vivo. MMP-9 mRNA was higher in alveolar macrophages isolated from Rac1 null mice and wild type mice given catalase. Rac1 regulates MMP-9 transcription via mitochondrial H(2)O(2) generation, providing a potential mechanism by which Rac1 null mice fail to develop pulmonary fibrosis.
Murthy
Shubha
S
Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
Ryan
Alan
A
He
Chao
C
Mallampalli
Rama K
RK
Carter
A Brent
AB
D000818:Animals; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006861:Hydrogen Peroxide / Q000737:chemistry*; D020935:MAP Kinase Signaling System; D008264:Macrophages / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D011658:Pulmonary Fibrosis / Q000378:metabolism; D015398:Signal Transduction; D016329:Sp1 Transcription Factor / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
C107953:RAC1 protein, human; D016329:Sp1 Transcription Factor; D018808:Transcription Factor AP-1; D006861:Hydrogen Peroxide; D048049:Extracellular Signal-Regulated MAP Kinases; D020780:Matrix Metalloproteinase 9; D020830:rac1 GTP-Binding Protein