Regulation of Endothelial Cell Proliferation and Vascular Assembly through Distinct mTORC2 Signaling Pathways
Shan Wang, etc
Molecular and Cellular Biology, 2015
Mammalian Target of Rapamycin (mTOR) is a serine/threonine kinase that regulates a diverse array of cellular processes including cell growth, survival, metabolism, and cytoskeleton dynamics. mTOR functions in two distinct complexes, mTORC1 and mTORC2, whose activities and substrate specificities are regulated by complex specific co-factors, including Raptor and Rictor, respectively. Little is known regarding the relative contribution of mTORC1 versus mTORC2 in vascular endothelial cells. Using mouse models of Raptor or Rictor gene targeting, we discovered that Rictor ablation inhibited VEGF-induced endothelial cell proliferation and assembly in vitro and angiogenesis in vivo, whereas loss of Raptor had only a modest effect on endothelial cells (EC). Mechanistically, loss of Rictor reduced the phosphorylation of AKT, PKCa, and NDRG1, without affecting the mTORC1 pathway. In contrast, loss of Raptor increased phosphorylation of AKT, despite inhibiting phosphorylation of S6K1, a direct target of mTORC1. Reconstitution of Rictor-null cells with Myr-AKT rescued vascular assembly in Rictor-deficient endothelial cells, whereas PKCa rescued proliferation defects. Further, tumor neovascularization in vivo were significantly decreased upon EC-specific Rictor deletion in mice. These data indicate that mTORC2 is a critical signaling node required for VEGF-mediated angiogenesis through regulation of AKT and PKCa in vascular endothelial cells.