ABSTRACT
Whereas the roles of proangiogenic factors in carcinogenesis are well established, those of endogenous angiogenesis inhibitors (EAIs) remain to be fully elaborated. We investigated the roles of three EAIs during de novo tumorigenesis to further test the angiogenic balance hypothesis, which suggests that blood vessel development in the tumor microenvironment can be governed by a net loss of negative regulators of angiogenesis in addition to the well-established principle of up-regulated angiogenesis inducers. In a mouse model of pancreatic neuroendocrine cancer, administration of endostatin, thrombospondin-1, and tumstatin peptides, as well as deletion of their genes, reveal neoplastic stage-specific effects on angiogenesis, tumor progression, and survival, correlating with endothelial expression of their receptors. Deletion of tumstatin and thrombospondin-1 in mice lacking the p53 tumor suppressor gene leads to increased incidence and reduced latency of angiogenic lymphomas associated with diminished overall survival. The results demonstrate that EAIs are part of a balance mechanism regulating tumor angiogenesis, serving as intrinsic microenvironmental barriers to tumorigenesis.
Subject(s)
Autoantigens/metabolism , Collagen Type IV/metabolism , Endostatins/metabolism , Neoplasms/metabolism , Thrombospondin 1/metabolism , Amino Acid Sequence , Animals , Autoantigens/chemistry , Autoantigens/genetics , Cell Line , Collagen Type IV/chemistry , Collagen Type IV/genetics , Disease Progression , Endostatins/chemistry , Endostatins/genetics , Female , Humans , Indoles/pharmacology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Molecular Sequence Data , Neoplasm Staging , Neoplasms/genetics , Neoplasms/prevention & control , Neovascularization, Pathologic/genetics , Neovascularization, Pathologic/metabolism , Neovascularization, Pathologic/prevention & control , Pancreatic Neoplasms/genetics , Pancreatic Neoplasms/metabolism , Pancreatic Neoplasms/prevention & control , Peptides/pharmacology , Propionates/pharmacology , Survival Analysis , Thrombospondin 1/chemistry , Thrombospondin 1/genetics , Tumor Burden/drug effects , Tumor Burden/genetics , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Protein p53/metabolism , Vascular Endothelial Growth Factor A/antagonists & inhibitors , Vascular Endothelial Growth Factor A/metabolismABSTRACT
Interleukin (IL) 22 is a type II cytokine that is produced by immune cells and acts on nonimmune cells to regulate local tissue inflammation. As a product of the recently identified T helper 17 lineage of CD4(+) effector lymphocytes, IL-22 plays a critical role in mucosal immunity as well as in dysregulated inflammation observed in autoimmune diseases. We used comprehensive mutagenesis combined with mammalian cell expression, ELISA cell-based, and structural methods to evaluate how IL-22 interacts with its cell surface receptor, IL-22R/IL-10R2, and with secreted IL-22 binding protein. This study identifies those amino acid side chains of IL-22 that are individually important for optimal binding to IL-22R, considerably expands the definition of IL-22 surface required for binding to IL-10R2, and demonstrates how IL-22 binding protein prevents IL-22R from binding to IL-22. The IL-22R and IL-10R2 binding sites are juxtaposed on adjacent IL-22 surfaces contributed mostly by helices A, D, and F and loop AB. Our results also provide a model for how IL-19, IL-20, IL-24, and IL-26 which are other IL-10-like cytokines, interact with their respective cell surface receptors.
Subject(s)
Interleukin-10 Receptor beta Subunit/chemistry , Interleukin-10 Receptor beta Subunit/metabolism , Interleukins/chemistry , Interleukins/metabolism , Receptors, Interleukin/chemistry , Receptors, Interleukin/metabolism , Amino Acid Sequence , Amino Acid Substitution , Binding Sites/genetics , Cell Line , Humans , In Vitro Techniques , Interleukin-10 Receptor beta Subunit/genetics , Interleukins/genetics , Models, Molecular , Molecular Sequence Data , Mutagenesis, Site-Directed , Protein Conformation , Protein Folding , Protein Structure, Secondary , Receptors, Interleukin/genetics , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Sequence Homology, Amino Acid , Thermodynamics , Interleukin-22ABSTRACT
Activated fibroblasts are key contributors to the fibrotic extracellular matrix accumulation during liver fibrosis. The origin of such fibroblasts is still debated, although several studies point to stellate cells as the principal source. The role of adult hepatocytes as contributors to the accumulation of fibroblasts in the fibrotic liver is yet undetermined. Here, we provide evidence that the pro-fibrotic growth factor, TGF-beta1, induces adult mouse hepatocytes to undergo phenotypic and functional changes typical of epithelial to mesenchymal transition (EMT). We perform lineage-tracing experiments using AlbCre. R26RstoplacZ double transgenic mice to demonstrate that hepatocytes which undergo EMT contribute substantially to the population of FSP1-positive fibroblasts in CCL(4)-induced liver fibrosis. Furthermore, we demonstrate that bone morphogenic protein-7 (BMP7), a member of the TGFbeta superfamily, which is known to antagonize TGFbeta signaling, significantly inhibits progression of liver fibrosis in these mice. BMP7 treatment abolishes EMT-derived fibroblasts, suggesting that the therapeutic effect of BMP7 was at least partially due to the inhibition of EMT. These results provide direct evidence for the functional involvement of adult hepatocytes in the accumulation of activated fibroblasts in the fibrotic liver. Furthermore, our findings suggest that EMT is a promising therapeutic target for the attenuation of liver fibrosis.
