Phosphatidylinositol 3-kinase Class II {alpha}-Isoform PI3K-C2{alpha} Is Required for Transforming Growth Factor {beta}-induced Smad Signaling in Endothelial Cells [Cell Biology]

January 22nd, 2015 by Aki, S., Yoshioka, K., Okamoto, Y., Takuwa, N., Takuwa, Y.

We have recently demonstrated that PI3K class II-α isoform (PI3K-C2α), which generates phosphatidylinositol-3-phosphate and phosphatidylinositol-3,4-bisphosphates, plays crucial roles in angiogenesis, by analyzing PI3K-C2α−knockout mice. The PI3K-C2α actions are mediated at least in part through its participation in the internalization of VEGF receptor-2 and sphingosine-1-phosphate receptor S1P1 and thereby their signaling on endosomes. TGFβ, which is also an essential angiogenic factor, signals via the serine/threonine kinase receptor complex to induce phosphorylation of Smad2 and Smad3 (Smad2/3). Smad anchor for receptor activation (SARA) protein, which is localized in early endosomes through its FYVE domain, is required for Smad2/3 signaling. In the present study, we showed that PI3K-C2α knockdown nearly completely abolished TGFβ1−induced phosphorylation and nuclear translocation of Smad2/3 in vascular endothelial cells (EC). PI3K-C2α was necessary for TGFβ−induced increase in phosphatidylinositol-3,4-bisphosphates in the plasma membrane and TGFβ−receptor internalization into the SARA−containing early endosomes, but not for phosphatidylinositol-3-phosphate enrichment or localization of SARA in the early endosomes. PI3K-C2α was also required for TGFβreceptor−mediated formation of SARA-Smad2/3 complex. Dynasore, an inhibitor of dynamin which is required for the clathrin−dependent receptor endocytosis, suppressed both TGFβ receptor internalization and Smad2/3 phosphorylation. TGFβ1 stimulated Smad−dependent VEGF-A expression, VEGF receptor−mediated EC migration and capillary−like tube formation, which were all abolished by either PI3K-C2α knockdown or dynasore. Finally, TGFβ1−induced microvessel formation in Matrigel plugs was greatly attenuated in EC−specific PI3K-C2α−deleted mice. These observations indicate that PI3K-C2α plays the pivotal role in TGFβ receptor endocytosis and thereby Smad2/3 signaling, participating in angiogenic actions of TGFβ.
  • Posted in Journal of Biological Chemistry, Publications
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