title: The proangiogenic phenotype of human tumor-derived endothelial cells depends on thrombospondin-1 downregulation via phosphatidylinositol 3-kinase/Akt pathway.
abstract: Tumor-derived endothelial cells (TEC) display increased survival and angiogenic properties in respect to normal endothelial cells. The aim of this study was to investigate the mechanism potentially involved in TEC proangiogenic phenotype. We found that thrombospondin-1 (TSP-1), a potent physiological inhibitor of angiogenesis, was significantly reduced in TEC in respect to normal endothelial cells. This reduction was confirmed by immunofluorescence in the intratumor vessels of clear cell renal carcinomas. As TEC were shown to display a basal upregulation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, we evaluated the possible regulation of TSP-1 by this pathway by using LY294002 and wortmannin, the PI3K inhibitors, and rapamycin, the mammalian target of rapamycin (mTOR) inhibitor. In addition, we developed negative dominant TEC for Akt. TSP-1 production by TEC was enhanced by the treatment with LY294002 and wortmannin and with rapamycin, suggesting a negative regulation of TSP-1 expression by the PI3K/Akt/mTOR pathway. In addition, downregulation of Akt activation in negative dominant Akt TEC enhanced TSP-1 expression and release. Administration of exogenous TSP-1 to TEC reduced their proangiogenic properties in vitro and in vivo. In parallel, blockade of TSP-1 with an anti-TSP-1 antibody in negative dominant Akt TEC restored their proangiogenic phenotype to levels similar to wild-type TEC. In conclusion, these results indicate that the upregulation of the PI3K/Akt/mTOR pathway is responsible for the inhibition of TSP-1 synthesis which is critical in determining the proangiogenic phenotype of TEC. Strategies aimed to inhibit the PI3K/Akt/mTOR pathway may restore a normal quiescent endothelial phenotype in TEC by promoting TSP-1 production.
authors.affiliation: Cattedra di Nefrologia, Dipartimento di Medicina Interna and Centro Ricerca Medicina Sperimentale (CeRMS), University of Torino, Ospedale Maggiore S. Giovanni Battista, Corso Dogliotti 14, 10126, Torino, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Bussolati
authors.forename: Barbara
authors.initials: B
authors.lastname: Assenzio
authors.forename: Maria Chiara
authors.initials: MC
authors.lastname: Deregibus
authors.forename: Giovanni
authors.initials: G
authors.lastname: Camussi
mesh_terms: D000328:Adult; D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002292:Carcinoma, Renal Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D015536:Down-Regulation; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007680:Kidney Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018613:Microscopy, Confocal; D009025:Morpholines / Q000494:pharmacology; D009389:Neovascularization, Pathologic / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D020411:Oligonucleotide Array Sequence Analysis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology; D019700:Thrombospondin 1 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D051057:Proto-Oncogene Proteins c-akt; D020123:Sirolimus; D019700:Thrombospondin 1; D000077191:Wortmannin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one