Abstract
Activated macrophages are critical cellular participants in inflammatory disease states. Transforming growth factor (TGF)-β1 is a growth factor with pleiotropic effects including inhibition of immune cell activation. Although the pathway of gene activation by TGF-β1 via Smad proteins has recently been elucidated, suppression of gene expression by TGF-β1 remains poorly understood. We found that of Smad1-Smad7, Smad3 alone was able to inhibit expression of markers of macrophage activation (inducible nitric-oxide synthase and matrix metalloproteinase-12) following lipopolysaccharide treatment in gene reporter assays. Transient and constitutive overexpression of a dominant negative Smad3 opposed the inhibitory effect of TGF-β1. Domain swapping experiments suggest that both the Smad MH-1 and MH-2 domains are required for inhibition. Mutation of a critical amino acid residue required for DNA binding in the MH-1 of Smad3 (R74A) resulted in the loss of inhibition. Transient overexpression of p300, an interactor of the Smad MH-2 domain, partially alleviated the inhibition by TGF-β1/Smad3, suggesting that inhibition of gene expression may be due to increased competition for limiting amounts of this coactivator. Our results have implications for the understanding of gene suppression by TGF-β1 and for the regulation of activated macrophages by TGF-β1.
Original language | English (US) |
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Pages (from-to) | 36653-36658 |
Number of pages | 6 |
Journal | Journal of Biological Chemistry |
Volume | 275 |
Issue number | 47 |
DOIs | |
State | Published - Nov 24 2000 |
Externally published | Yes |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology