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.

Metastasis Suppressor Tetraspanin CD82/KAI1 Regulates Ubiquitylation of Epidermal Growth Factor Receptor

“…The timing of EGFR co-localization with EEA1-containing endosomes was delayed, which could be due to the altered ubiquitylation and subsequent endocytosis of the receptors associated with HSPG in TERM. Syndecans are known to mediate endocytosis of heparin-binding ligands and proteins (e.g., FGF2 or eosinophil cationic protein) by macropinocytosis (42,43). This pathway is slow and involves formation of uncoated vesicles that eventually fuse with sorting endosomes.…”

Motoneurons Secrete Angiogenin to Induce RNA Cleavage in Astroglia

“…Syndecan 4 is also expressed by endothelial cells wherein it regulates multiple aspects of angiogenesis including ligand endocytosis (e.g., FGF-2 and VEGF) and stimulates endothelial migration and tubularization (Tkachenko et al, 2004(Tkachenko et al, , 2006Nunes et al, 2008). This raises the possibility that motoneuron-derived angiogenin may stimulate endothelial cells to induce neovascularization.…”

“…Although these receptors lack catalytic activity, syndecan 4 is unique in being capable of binding phosphatidylinositol (4,5)-P2, therefore independently initiating signaling via Rac1, protein kinase C␣, PI3K, Cdc42, mTORC2, and Akt (Ilan et al, 1998;Simons and Horowitz, 2001;Tkachenko et al, 2004;Partovian et al, 2008). Previous reports have also demonstrated that the uptake of angiogenic molecules such as bFGF, which requires astroglia to mediate neuroprotection in vitro, is mediated via syndecan 4, the in vivo expression of which appears to be restricted to glial lineages (Knusel et al, 1990;Engele and Bohn, 1991;Hou et al, 1997;Hsueh and Sheng, 1999;Tkachenko et al, 2004). We therefore investigated whether angiogenin endocytosis was mediated by syndecan 4.…”

Syndecan-4 proteoliposomes enhance fibroblast growth factor-2 (FGF-2)–induced proliferation, migration, and neovascularization of ischemic muscle

“…Syndecan-4 is recruited to focal adhesions (7), has both phosphatidylinositol 4,5-bisphosphate and PSD-95/ Discs-large/ZO-1 homology domain binding regions and has been implicated in the activation of protein kinase C (8). Syndecan-4 is a powerful regulator of FGF-2 signaling and can modulate growth factor response in multiple cell types (9)(10)(11). In addition, syndecan-4 is capable of signaling in response to FGF independently of FGF receptor interactions (12).…”