Angiopoietin-2 differentially regulates angiogenesis through TIE2 and integrin signaling
Moritz Felcht, … , Sergij Goerdt, Hellmut G. Augustin
Moritz Felcht, … , Sergij Goerdt, Hellmut G. Augustin
Published May 15, 2012
Citation Information: J Clin Invest. 2012;122(6):1991-2005. https://doi.org/10.1172/JCI58832.
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Research Article Vascular biology

Angiopoietin-2 differentially regulates angiogenesis through TIE2 and integrin signaling

Abstract

Angiopoietin-2 (ANG-2) is a key regulator of angiogenesis that exerts context-dependent effects on ECs. ANG-2 binds the endothelial-specific receptor tyrosine kinase 2 (TIE2) and acts as a negative regulator of ANG-1/TIE2 signaling during angiogenesis, thereby controlling the responsiveness of ECs to exogenous cytokines. Recent data from tumors indicate that under certain conditions ANG-2 can also promote angiogenesis. However, the molecular mechanisms of dual ANG-2 functions are poorly understood. Here, we identify a model for the opposing roles of ANG-2 in angiogenesis. We found that angiogenesis-activated endothelium harbored a subpopulation of TIE2-negative ECs (TIE2lo). TIE2 expression was downregulated in angiogenic ECs, which abundantly expressed several integrins. ANG-2 bound to these integrins in TIE2lo ECs, subsequently inducing, in a TIE2-independent manner, phosphorylation of the integrin adaptor protein FAK, resulting in RAC1 activation, migration, and sprouting angiogenesis. Correspondingly, in vivo ANG-2 blockade interfered with integrin signaling and inhibited FAK phosphorylation and sprouting angiogenesis of TIE2lo ECs. These data establish a contextual model whereby differential TIE2 and integrin expression, binding, and activation control the role of ANG-2 in angiogenesis. The results of this study have immediate translational implications for the therapeutic exploitation of angiopoietin signaling.

Authors

Moritz Felcht, Robert Luck, Alexander Schering, Philipp Seidel, Kshitij Srivastava, Junhao Hu, Arne Bartol, Yvonne Kienast, Christiane Vettel, Elias K. Loos, Simone Kutschera, Susanne Bartels, Sila Appak, Eva Besemfelder, Dorothee Terhardt, Emmanouil Chavakis, Thomas Wieland, Christian Klein, Markus Thomas, Akiyoshi Uemura, Sergij Goerdt, Hellmut G. Augustin

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Figure 3

ANG-2 induces Rac activation and migration in TIE2lo ECs.

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ANG-2 induces Rac activation and migration in TIE2lo ECs. (A) Migratio...
(A) Migration of control transduced (sh-Ctrl) and TIE2-silenced ECs (sh-TEK) cotransduced with control adenovirus (Ad-Ctrl) or adenoviral ANG-2 (Ad-ANG-2) in an 18-hour lateral scratch wound migration assay. The white lines denote the wound closure front of migrating ECs. (B) Quantification of lateral sheet migration shown in A (n = 3). The migration-stimulating effect was most pronounced when TIE2 was silenced and ANG-2 overexpressed at the same time. *P < 0.05. (C) Single-cell migration of control transduced ECs and TIE2-silenced ECs cotransduced with control adenovirus or adenoviral ANG-2. The starting point of individual cells was recorded (top left), and the cells were allowed to migrate for 24 hours (bottom left). The overall distance (dotted line) as well as the net distance (solid line) were recorded (top right). (D) Quantification of the net distance of the single-cell tracking assay shown in C. Migration of 10 cells per experimental group was expressed as net distance compared with Ad-Ctrl (*P < 0.05; n = 4). (E) Quantification of persistence (net distance divided by overall distance) of the single-cell tracking assay show in C. Persistence of 10 cells per experimental group was analyzed and expressed as relative persistence compared to Ad-Ctrl (*P < 0.05; n = 4). (F–I) Biochemical analysis of Rac1 activation (Western blot), with quantitative assessment of 7 independent experiments (mean ± SEM; *P < 0.05) (I). Two representative Western blots are shown (G and H). TIE2 silencing was monitored by Western blotting (F).