Tumor Necrosis Factor Alpha Inhibits Type I Collagen Synthesis through Repressive CCAAT/Enhancer-Binding Proteins

Abstract

Extracellular matrix (ECM) formation and remodeling are critical processes for proper morphogenesis, organogenesis, and tissue repair. The proinflammatory cytokine tumor necrosis factor alpha (TNF-α) inhibits ECM accumulation by stimulating the expression of matrix proteolytic enzymes and by downregulating the deposition of structural macromolecules such as type I collagen. Stimulation of ECM degradation has been linked to prolonged activation of jun gene expression by the cytokine. Here we demonstrate that TNF-α inhibits transcription of the gene coding for the α2 chain of type I collagen [α2(I) collagen] in cultured fibroblasts by stimulating the synthesis and binding of repressive CCAAT/enhancer proteins (C/EBPs) to a previously identified TNF-α-responsive element. This conclusion was based on the concomitant identification of C/EBPβ and C/EBPδ as TNF-α-induced factors by biochemical purification and expression library screening. It was further supported by the ability of the C/EBP-specific dominant-negative (DN) protein to block TNF-α inhibition of α2(I) collagen but not TNF-α stimulation of the MMP-13 protease. The DN protein also blocked TNF-α downregulation of the gene coding for the α1 chain of type I collagen. The study therefore implicates repressive C/EBPs in the TNF-α-induced signaling pathway that controls ECM formation and remodeling.

ACKNOWLEDGMENTS

P. Greenwel and S. Tanaka made equal contributions to this work.

We thank K. Calame, P. Johnson, D. Ron, U. Schibler, and S. Shapiro for generously providing invaluable materials for this study and V. Vinson for critical review of the manuscript. We also thank K. Johnson for typing the manuscript and R. Ni and C. Else for excellent technical assistance.

This work was supported by grants AR38648 and AA12196 from the National Institutes of Health and by the Arthritis Foundation.