title: Substrate-immobilized HIV-1 Tat drives VEGFR2/α(v)β(3)-integrin complex formation and polarization in endothelial cells.
abstract: OBJECTIVE
  The HIV-1 transactivating factor (Tat) possesses features typical of both cell-adhesive and angiogenic growth factor (AGF) proteins, inducing endothelial cell (EC) adhesion and proangiogenic activation. Tat was exploited to investigate the events triggered by EC adhesion to substrate-bound AGF that lead to proangiogenic activation.
  
  
  RESULTS
  Immobilized Tat induces actin cytoskeleton organization, formation of α(v)β(3) integrin(+)focal adhesion plaques, and recruitment of vascular endothelial growth factor receptor-2 (VEGFR2) in the ventral plasma membrane of adherent ECs. Also, acceptor photobleaching fluorescence resonance energy transfer demonstrated that VEGFR2/α(v)β(3) coupling occurs at the basal aspect of Tat-adherent ECs. Cell membrane fractionation showed that a limited fraction of α(v)β(3) integrin and VEGFR2 does colocalize in lipid rafts at the basal aspect of Tat-adherent ECs. VEGFR2 undergoes phosphorylation and triggers pp60src/ERK(1/2) activation. The use of lipid raft disrupting agents and second messenger inhibitors demonstrated that intact lipid rafts and the VEGFR2/pp60src/ERK(1/2) pathway are both required for cytoskeleton organization and proangiogenic activation of Tat-adherent ECs.
  
  
  CONCLUSIONS
  Substrate-immobilized Tat causes VEGFR2/α(v)β(3) complex formation and polarization at the basal aspect of adherent ECs, VEGFR2/pp60src/ERK(1/2) phosphorylation, cytoskeleton organization, and proangiogenic activation. These results provide novel insights in the AGF/tyrosine kinase receptor/integrin cross-talk.
authors.affiliation: Section of General Pathology and Immunology, Department of Biomedical Sciences and Biotechnology, University of Brescia, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Urbinati
authors.forename: Cosetta
authors.initials: C
authors.lastname: Ravelli
authors.forename: Elena
authors.initials: E
authors.lastname: Tanghetti
authors.forename: Mirella
authors.initials: M
authors.lastname: Belleri
authors.forename: Edoardo
authors.initials: E
authors.lastname: Giacopuzzi
authors.forename: Eugenio
authors.initials: E
authors.lastname: Monti
authors.forename: Marco
authors.initials: M
authors.lastname: Presta
authors.forename: Marco
authors.initials: M
authors.lastname: Rusnati
mesh_terms: D002465:Cell Movement; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism* / Q000821:virology; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism* / Q000821:virology; D022001:Focal Adhesions; D015497:HIV-1 / Q000378:metabolism*; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D015398:Signal Transduction; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism*; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*
chemical_list: D039302:Integrin alphaVbeta3; D054322:tat Gene Products, Human Immunodeficiency Virus; D040301:Vascular Endothelial Growth Factor Receptor-2