Homeostatic modulation of cell surface KDR and Flt1 expression and expression of the vascular endothelial cell growth factor (VEGF) receptor mRNAs by VEGF.
Vascular endothelial cell growth factor (VEGF) is a potent angiogenic factor expressed during embryonic development, during wound healing, and in pathologies dependent on neovascularization, including cancer. Regulation of the receptor tyrosine kinases, KDR and Flt-1, to which VEGF binds on endothelial cells is incompletely understood. Chronic incubation with tumor-conditioned medium or VEGF diminished (125)I-VEGF binding to human umbilical vein endothelial cells, incorporation of (125)I-VEGF into covalent complexes with KDR and Flt1, and immunoreactive KDR in cell lysates. Receptor down-regulation desensitized VEGF activation of mitogen-activated protein kinase (extracellular signal-regulated kinases 1 and 2) and p38 mitogen-activated protein kinase. Preincubation with VEGF or tumor-conditioned medium down-regulated cell surface receptor expression but up-regulated KDR and Flt-1 mRNAs, an effect abrogated by a neutralizing VEGF antibody. Removal of VEGF from the medium led to recovery of (125)I-VEGF binding and resensitization of human umbilical vein endothelial cells. Recovery of receptor expression was inhibited by cycloheximide, indicating that augmented VEGF receptor mRNAs, and not receptor recycling from a cytoplasmic pool, restored responsiveness. As the VEGF receptors promote endothelial cell survival, proliferation, and other events necessary for angiogenesis, the noncoordinate regulation of VEGF receptor proteins and mRNAs suggests that human umbilical vein endothelial cells are protected against inappropriate or prolonged loss of VEGF receptors by a homeostatic mechanism important to endothelial cell function.
Wang
D
D
Surgical Oncology Laboratory, Department of Surgery, University of California at San Francisco, San Francisco, California 94143-0790, USA.
Donner
D B
DB
Warren
R S
RS
D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D016228:Endothelial Growth Factors / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007457:Iodine Radioisotopes; D008222:Lymphokines / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D017978:Receptors, Growth Factor / Q000235:genetics / Q000378:metabolism*; D040262:Receptors, Vascular Endothelial Growth Factor; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A; D040281:Vascular Endothelial Growth Factor Receptor-1; D042442:Vascular Endothelial Growth Factors
D017077:Culture Media, Conditioned; D016228:Endothelial Growth Factors; D007457:Iodine Radioisotopes; D008222:Lymphokines; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D017978:Receptors, Growth Factor; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor; D040281:Vascular Endothelial Growth Factor Receptor-1; D020928:Mitogen-Activated Protein Kinases