title: Fibroblast growth factor 2 endocytosis in endothelial cells proceed via syndecan-4-dependent activation of Rac1 and a Cdc42-dependent macropinocytic pathway.
abstract: Full activity of fibroblast growth factors (FGFs) requires their internalization in addition to the interaction with cell surface receptors. Recent studies have suggested that the transmembrane proteoglycan syndecan-4 functions as a FGF2 receptor. In this study we investigated the molecular basis of syndecan endocytosis and its role in FGF2 internalization in endothelial cells. We found that syndecan-4 uptake, induced either by treatment with FGF2 or by antibody clustering, requires the integrity of plasma membrane lipid rafts for its initiation, occurs in a non-clathrin-, non-dynamin-dependent manner and involves Rac1, which is activated by syndecan-4 clustering. FGF2 was internalized in a complex with syndecan-4 in 70 kDa dextran-containing endocytic vesicles. FGF2 and syndecan-4 but not dextran endocytosis were blocked by the dominant negative Rac1 while amiloride and the dominant-negative Cdc42 blocked internalization of dextran in addition to FGF2 and syndecan-4. Taken together, these results demonstrate that FGF2 endocytosis requires syndecan-4 clustering-dependent activation of Rac1 and the intact CDC42-dependent macropinocytic pathway.
authors.affiliation: Angiogenesis Research Center, Department of Medicine, Dartmouth Medical School, One Medical Center Drive, Lebanon, NH 03756, USA.
authors.forename: Eugene
authors.initials: E
authors.lastname: Tkachenko
authors.forename: Esther
authors.initials: E
authors.lastname: Lutgens
authors.forename: Radu-Virgil
authors.initials: RV
authors.lastname: Stan
authors.forename: Michael
authors.initials: M
authors.lastname: Simons
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D003911:Dextrans / Q000378:metabolism; D004705:Endocytosis; D004730:Endothelium, Vascular / Q000378:metabolism*; D004789:Enzyme Activation; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism / Q000502:physiology*; D005456:Fluorescent Dyes / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006133:Growth Substances / Q000378:metabolism; D006497:Heparan Sulfate / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism; D008856:Microscopy, Fluorescence; D005810:Multigene Family; D010873:Pinocytosis; D011485:Protein Binding; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D053671:Syndecan-4; D053667:Syndecans; D013997:Time Factors; D014162:Transfection; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism / Q000502:physiology*
chemical_list: D002784:Cholesterol; D018076:DNA, Complementary; D003911:Dextrans; D016222:Fibroblast Growth Factor 2; D005456:Fluorescent Dyes; D020558:GTP Phosphohydrolases; D006133:Growth Substances; D006497:Heparan Sulfate; D008562:Membrane Glycoproteins; D011509:Proteoglycans; D011993:Recombinant Fusion Proteins; D053671:Syndecan-4; D053667:Syndecans; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; C508307:Sdc4 protein, rat