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J Biol Chem. 2014 Sep 12;289(37):25486-96. doi: 10.1074/jbc.M114.578609. Epub 2014 Jul 28.

Src-mediated post-translational regulation of endoglin stability and function is critical for angiogenesis.

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From the Division of Pharmacology, College of Pharmacy, and.
the Department of Molecular Cell Biology, Leiden University Medical Center, Leiden University, 2333 Leiden, the Netherlands.
the Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, and.
From the Division of Pharmacology, College of Pharmacy, and Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio 43210,


Endoglin is a transforming growth factor β (TGF-β) co-receptor essential for angiogenesis and tumor vascularization. Endoglin modulates the crucial balance between pro- and anti-angiogenic signaling by activin receptor-like kinase (ALK) 1, 5, and TGF-β type II (TβRII) receptors. Despite its established role in physiology and disease, the mechanism of endoglin down-regulation remains unknown. Here we report that the conserved juxtamembrane cytoplasmic tyrosine motif ((612)YIY(614)) is a critical determinant of angiogenesis. Src directly phosphorylates this motif to induce endoglin internalization and degradation via the lysosome. We identified epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF) as Src-activators that induce endoglin turnover following (612)YIY(614) phosphorylation. Interestingly, Src phosphorylation of endoglin-(612)YIY(614) was also an important process for receptor down-regulation by TRACON105 (TRC105), an endoglin-targeting antibody currently in clinical trials. The regulation of (612)YIY(614) phosphorylation was critical for angiogenesis, as both the phosphomimetic and unphosphorylatable mutants impaired endothelial functions including proliferation, migration, and capillary tube formation. Collectively, these findings establish Src and pro-angiogenic mitogens as critical mediators of endoglin stability and function.


Angiogenesis; Endothelial Cell; Transforming Growth Factor Beta (TGF-β); Tyrosine-Protein Kinase (Tyrosine Kinase); Vascular Biology

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