Endothelial Tie1–mediated angiogenesis and vascular abnormalization promote tumor progression and metastasis
Silvia La Porta, Lise Roth, Mahak Singhal, Carolin Mogler, Carleen Spegg, Benjamin Schieb, Xianghu Qu, Ralf H. Adams, H. Scott Baldwin, Soniya Savant, Hellmut G. Augustin
Silvia La Porta, Lise Roth, Mahak Singhal, Carolin Mogler, Carleen Spegg, Benjamin Schieb, Xianghu Qu, Ralf H. Adams, H. Scott Baldwin, Soniya Savant, Hellmut G. Augustin
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Research Article Angiogenesis Oncology

Endothelial Tie1–mediated angiogenesis and vascular abnormalization promote tumor progression and metastasis

Abstract

The endothelial tyrosine kinase receptor Tie1 remains poorly characterized, largely owing to its orphan receptor status. Global Tie1 inactivation causes late embryonic lethality, thereby reflecting its importance during development. Tie1 also plays pivotal roles during pathologies such as atherosclerosis and tumorigenesis. In order to study the contribution of Tie1 to tumor progression and metastasis, we conditionally deleted Tie1 in endothelial cells at different stages of tumor growth and metastatic dissemination. Tie1 deletion during primary tumor growth in mice led to a decrease in microvessel density and an increase in mural cell coverage with improved vessel perfusion. Reduced angiogenesis and enhanced vascular normalization resulted in a progressive increase of intratumoral necrosis that caused a growth delay only at later stages of tumor progression. Concomitantly, surgical removal of the primary tumor decreased the number of circulating tumor cells, reduced metastasis, and prolonged overall survival. Additionally, Tie1 deletion in experimental murine metastasis models prevented extravasation of tumor cells into the lungs and reduced metastatic foci. Taken together, the data support Tie1 as a therapeutic target by defining its regulatory functions during angiogenesis and vascular abnormalization and identifying its role during metastasis.

Authors

Silvia La Porta, Lise Roth, Mahak Singhal, Carolin Mogler, Carleen Spegg, Benjamin Schieb, Xianghu Qu, Ralf H. Adams, H. Scott Baldwin, Soniya Savant, Hellmut G. Augustin

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Figure 4

Deletion of endothelial Tie1 reduces tumor cell intravasation and limits metastasis.

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Deletion of endothelial Tie1 reduces tumor cell intravasation and limits...
(A) Schematic representation of the experimental design. LLC cells were injected s.c., and tamoxifen was administrated as indicated. Tumors were surgically removed after 14 days, and mice were sacrificed 3 weeks after primary tumor resection. Shown are representative images of H&E-stained lungs from WT and Tie1iECKO mice. Arrowheads indicate metastases. Scale bar: 3 mm. (B) Number of mice that developed lung metastases (black) after primary tumor removal (n = 14). (C) Kaplan-Meier survival curve of WT and Tie1iECKO mice after primary tumor removal (n = 10 WT; n = 6 Tie1iECKO). *P < 0.05 , by Gehan-Breslow-Wilcoxon test. Mice with less than 50% endothelial Tie1 deletion were excluded from the analysis. (D) Blood was drawn from WT and Tie1iECKO tumor-bearing mice at the time of tumor removal and plated in culture dishes. The formation of tumor cell colonies was traced over time. Graph shows the number of blood samples that developed tumor cell colonies (n = 11 WT; n = 10 Tie1iECKO). (E) ECs were seeded onto gelatin-coated Transwell inserts, and PKH67-labeled LLC cells were allowed to transmigrate for 8 hours. Thereafter, the cells were counted (percentage of LLC cells transmigrated through siTie1-KD HUVECs vs. control; n = 3 independent experiments, with each experiment performed in triplicate). **P < 0.01, by 2-tailed Mann-Whitney U test. (F) Relative VE-cadherin (Cdh5) expression in isolated tumor ECs (n = 4 WT; n = 5 Tie1iECKO). *P < 0.05, by 2-tailed Mann-Whitney U test. (G) Representative confocal microscopic images of blood vessels from WT and Tie1iECKO tumors stained with VE-cadherin and DAPI. Scale bar: 100 μm. (H) Quantification of VE-cadherin mean fluorescence intensity (MFI) (n = 5). **P < 0.01, by 2-tailed Mann-Whitney U test. Error bars represent mean ± SD.