Abstract
Vascular remodeling in host tissues surrounding growing tumors is implicated in the successful development of tumor neovasculature. Cooperation between vascular endothelial growth factor (VEGF) and angiopoietins (Angs) is considered to be critical in this context. However, the mechanisms regulating the coordinated expression of these molecules remain, to date, elusive. In this study, we used a murine ovarian cancer angiogenesis model induced by overexpression of VEGF, as well as 52 human ovarian cancer specimens and 36 established cancer cell lines to characterize the expression and regulation of Ang-2 in the context of tumor angiogenesis. Using a combination of immunohistochemistry, laser capture microdissection and real-time quantitative reverse transcription-PCR, we showed that tumor-derived VEGF significantly up-regulated the expression of Ang-2 in host stroma endothelial cells, resulting in markedly increased Ang-2/Tie-2 mRNA copy number ratio in vivo. In vitro experiments showed that VEGF directly up-regulated Ang-2, which is mediated via VEGF receptor-2/flk-1/KDR pathway, in cultured endothelial cells through transcriptional activation rather than the enhanced mRNA stability. In human ovarian cancer, Ang-2 was primarily expressed in stroma endothelial cells and detectable in tumor cells of only 12% tumor specimens; however, it was not detected in the majority of established ovarian cancer cell lines. In addition, a significant correlation was observed between VEGF and Ang-2 mRNA expression (P < 0.01) but not between VEGF and Ang-1 or Tie-2 in human ovarian cancer specimens. In the mouse ovarian cancer model, up-regulation of Ang-2 in host stroma endothelial cells was significantly associated with pericyte loss and instability of the host vasculature surrounding the tumor. Our study suggests a novel mechanism by which tumor-derived VEGF interacts with Angs/Tie-2 system in host stroma endothelial cells and induces in a paracrine manner the remodeling of host vasculature to support angiogenesis during tumor growth.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Angiogenesis Inducing Agents / biosynthesis*
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Angiogenesis Inducing Agents / genetics
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Angiopoietin-1
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Angiopoietin-2
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Animals
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Carcinoma / blood supply
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Carcinoma / metabolism
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Carcinoma / pathology
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Carcinoma / physiopathology*
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Cell Line, Transformed / drug effects
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Cell Line, Transformed / metabolism
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Dactinomycin / pharmacology
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Endothelial Growth Factors / pharmacology
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Endothelial Growth Factors / physiology*
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Endothelium, Vascular / drug effects*
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Endothelium, Vascular / metabolism
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Female
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Gene Expression Regulation, Neoplastic*
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Genes, Reporter
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Humans
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Intercellular Signaling Peptides and Proteins / pharmacology
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Intercellular Signaling Peptides and Proteins / physiology*
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Lymphokines / pharmacology
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Lymphokines / physiology*
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Membrane Glycoproteins / biosynthesis
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Membrane Glycoproteins / genetics
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Mice
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Mice, Inbred C57BL
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Models, Biological
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Neoplasm Proteins / biosynthesis
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Neoplasm Proteins / genetics
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Neoplasm Proteins / pharmacology
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Neoplasm Proteins / physiology*
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Neovascularization, Pathologic / physiopathology*
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Nucleic Acid Synthesis Inhibitors / pharmacology
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Ovarian Neoplasms / blood supply
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Ovarian Neoplasms / metabolism
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Ovarian Neoplasms / pathology
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Ovarian Neoplasms / physiopathology*
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Paracrine Communication*
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Pericytes / pathology
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RNA, Messenger / biosynthesis
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RNA, Neoplasm / biosynthesis
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Receptor Protein-Tyrosine Kinases / biosynthesis
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Receptor Protein-Tyrosine Kinases / genetics
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Receptor, TIE-2
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Recombinant Fusion Proteins / biosynthesis
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Recombinant Fusion Proteins / physiology
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Stromal Cells / drug effects
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Stromal Cells / metabolism
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Vascular Endothelial Growth Factor A
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Vascular Endothelial Growth Factors
Substances
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ANGPT1 protein, human
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Angiogenesis Inducing Agents
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Angiopoietin-1
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Angiopoietin-2
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Angpt1 protein, mouse
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Endothelial Growth Factors
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Intercellular Signaling Peptides and Proteins
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Lymphokines
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Membrane Glycoproteins
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Neoplasm Proteins
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Nucleic Acid Synthesis Inhibitors
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RNA, Messenger
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RNA, Neoplasm
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Recombinant Fusion Proteins
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Vascular Endothelial Growth Factor A
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Vascular Endothelial Growth Factors
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Dactinomycin
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Receptor Protein-Tyrosine Kinases
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Receptor, TIE-2