• Riikka Pietilä, Marjut Nätynki, Tuomas Tammela, Jaakko Kangas, Kristina H Pulkki, Nisha Limaye, Miikka Vikkula, Gou Young Koh, Pipsa Saharinen, Kari Alitalo, and Lauri Eklund.
• Oulu Center for Cell-Matrix Research, Biocenter Oulu and Department of Medical Biochemistry and Molecular Biology, University of Oulu, Oulu, Finland.
• J. Cell. Sci. 2012 May 1; 125 (Pt 9): 2212-23.

AbstractAngiopoietin 1 (Ang1) is an activating ligand for the endothelial receptor tyrosine kinase Tie2, whereas Ang2 acts as a context-dependent agonist or antagonist that has a destabilizing effect on the vasculature. The molecular mechanisms responsible for the versatile functions of Ang2 are poorly understood. We show here that Ang2, but not Ang1, induces Tie2 translocation to the specific cell-matrix contact sites located at the distal end of focal adhesions. The Ang2-specific Tie2 translocation was associated with distinct Tie2 activation and downstream signals which differed from those of Ang1, and led to impaired cell motility and weak cell-matrix adhesion. We demonstrate that the different oligomeric or multimeric forms of the angiopoietins induce distinct patterns of Tie2 trafficking; the lower oligomerization state of native Ang2 was crucial for the Ang2-specific Tie2 redistribution, whereas multimeric structures of Ang1 and Ang2 induced similar responses. The Ang2-specific Tie2 trafficking to cell-matrix contacts was also dependent on the cell substratum, α2β1-integrin-containing cell-matrix adhesion sites and intact microtubules. Our data indicate that the different subcellular trafficking of Tie2-Ang2 and Tie2-Ang1 complexes generates ligand-specific responses in the angiopoietin-Tie signaling pathway, including modulation of cell-matrix interactions.

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