Angiogenesis occurs when new blood vessels sprout from the existing vasculature and mature into an organized and functional circulatory system. Physiological angiogenesis is stringently regulated and occurs transiently. Numerous disease states, including chronic inflammation and cancer, induce pathological angiogenesis, which disrupts the stable vascular network by altering both positive and negative angiogenic regulators. The chemokine stromal-cell derived factor-1 (SDF-1α, also called CXCL12) and its receptor CXCR4 promote endothelial cell (EC) migration and tube formation. PI3K is a key downstream regulator of CXCR4-mediated chemotaxis and mammalian target of rapamycin (mTOR) is at the center of PI3K-mediated signal transduction. mTOR exists in two complexes: mTOR complex 1 (mTORC1) and 2 (mTORC2). Receptor induced mTORC1 signal transduction has been widely studied. In contrast, the signaling upstream of mTORC2 remains elusive. We hypothesized that the SDF-1 α/CXCR4/mTOR signaling axis contributes to the molecular mechanism of tumor angiogenesis. This study illustrates that SDF-1α activates a distinct molecular signaling cascade in EC that involves CXCR4, G protein, PI3K and mTORC2, but not mTORC1. CXCR4 inhibition blocks sprouting in a 3D in vitro angiogenesis model, and specific inhibition of each of the mTOR complexes reveals that sprouting angiogenesis requires mTORC2 signal transduction. In a mouse model, tumor angiogenesis is significantly reduced only when mTORC2 is targeted. An analysis of targets downstream of mTORC2 indicates that 6-phosphofructo-2-kinase (PFKFB3), which is a key regulator of glycolytic flux and sprouting angiogenesis, is reduced in vivo when mTORC2 is targeted and tumor angiogenesis is inhibited. This study provides evidence that mTORC2 is an important regulator of angiogenesis that is downstream of GPCR signaling and upstream of metabolic regulation. In addition, these data present a potential link between mTORC2, metabolism and angiogenesis.
Citation Format: Mary E. Ziegler, Michaela M.S. Hatch, Christopher C.W. Hughes. mTORC2 mediates SDF-1α/CXCL12-induced angiogenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5228. doi:10.1158/1538-7445.AM2015-5228