Fibroblast growth factor 2 endocytosis in endothelial cells proceed via syndecan-4-dependent activation of Rac1 and a Cdc42-dependent macropinocytic pathway.
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.
Tkachenko
Eugene
E
Angiogenesis Research Center, Department of Medicine, Dartmouth Medical School, One Medical Center Drive, Lebanon, NH 03756, USA.
Lutgens
Esther
E
Stan
Radu-Virgil
RV
Simons
Michael
M
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*
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