title: How do angiopoietins Tie in with vascular endothelial growth factors?
abstract: OBJECTIVE
  The endothelial cells of the blood and lymphatic vessels are involved in common human diseases. Excess blood and lymphatic vessel growth enhances tumor progression and metastasis, whereas insufficient growth leads to tissue ischemia and lymphedema. Lymphatic and blood vascular endothelial cells are regulated by two endothelial specific receptor tyrosine kinase systems, the vascular endothelial growth factor (VEGF) receptors (VEGFRs) and the Tie receptors, activated by the VEGF and angiopoietin ligands, respectively. Blocking of the VEGF-VEGFR-2 pathway has provided the first antiangiogenic strategy for cancer therapy and here we discuss the other pathways where progress is made for drug development, in particular the angiopoietin (Ang)-Tie receptor pathway.
  
  
  RESULTS
  VEGF-activated VEGFR-2 is the major transducer of angiogenic signals, but recent results show that the lymphangiogenic VEGFR-3 induces angiogenic sprouting as well. VEGF-B, a member of the VEGF family with low angiogenic activity, has been found to be involved in the regulation of energy metabolism in the heart. Recent reports have implicated Ang2 in tumor angiogenesis and revealed that Tie2 utilizes a unique signaling mechanism at endothelial cell-cell junctions.
  
  
  CONCLUSIONS
  The VEGF-VEGFR and Ang-Tie systems regulate different aspects of blood and lymphatic vessel growth. Thus, targeting both systems may be beneficial in maximizing the efficacy of anti/pro-angiogenic therapies.
authors.affiliation: Molecular and Cancer Biology Program, Biomedicum Helsinki, University of Helsinki, Finland.
authors.forename: Pipsa
authors.initials: P
authors.lastname: Saharinen
authors.forename: Maija
authors.initials: M
authors.lastname: Bry
authors.forename: Kari
authors.initials: K
authors.lastname: Alitalo
mesh_terms: D042682:Angiopoietins / Q000378:metabolism*; D000818:Animals; D006801:Humans; D042601:Lymphatic Vessels / Q000502:physiology*; D042764:Receptors, TIE / Q000378:metabolism*; D015398:Signal Transduction; D042442:Vascular Endothelial Growth Factors / Q000378:metabolism*
chemical_list: D042682:Angiopoietins; D042442:Vascular Endothelial Growth Factors; D042764:Receptors, TIE