AbstractsBiology & Animal Science

Syndecans are cell surface heparan sulfate proteoglycans which are present in all tissues and cell types and have distinct temporal and spatial expression patterns. They play important roles in embryonic development of the organism and control relocation and alteration of extracellular matrix components. Syndecans regulate cell migration, adhesion and proliferation and are engaged in tissue injury, inflammation processes, pathogenesis of infectious diseases and tumor biology. This thesis summarizes the results of studies on one of the syndecan family receptors syndecan-3 (also known as N-syndecan). This proteoglycan is abundantly expressed in developing brain. Syndecan-3 acts as a signaling receptor upon binding of its ligand, heparin-binding growth associated molecule (HB-GAM; also known as pleiotrophin), which activates the cortactin c-Src signaling pathway. This leads to rapid neurite extension in neuronal cells, which makes syndecan-3 an interesting transmembrane receptor in neuronal development and regeneration. However, little is known about the signaling mechanism of syndecan-3. Here I show formation of ligand-syndecan-3 signaling complexes at the cell surface using fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET). Ligand binding leads to dimerization of syndecan-3 at the cell surface. The dimerized syndecan-3 colocalizes with actin in the filopodia of cells. Lysine 383 in the juxtamembrane (ERKE) sequence and G392 and G396 from GXXXG canonical motif are shown to be important for the ligand-induced dimerization, whereas the cytosolic domain are not required for the dimerization. In addition to acting as a signaling receptor, syndecan-3 acts as a co-receptor in epidermal growth factor receptor (EGFR) ligand binding. FRET analysis suggests that interactions of syndecan-3 and EGFR depend on a shared ligand such as heparin-binding EGF-like growth factor (HB-EGF). Furthermore, it was shown that syndecan-3 may act as a receptor for other ligands, like glial cell line-derived neurotrophic factor (GDNF). In addition, I have found a new receptor for HB-GAM glypican-2 which may be involved in regulation of HB-GAM signaling by competing with syndecan-3 for ligand binding. Syndekaanit ovat solun pinnan hepaanisulfaattiproteoglykaaneja, joita esiintyy kaikissa kudoksissa ja solutyypeissä. Syndekaaneilla on tärkeitä toimintoja alkionkehityksen aikana. Syndekaanit säätelevät solujen liikkuvuutta ja tarttumista ja niiden toiminnot liittyvät kudosvaurioon, tulehdusreaktioihin, tartuntatautien patogeneesiin ja syövän biologiaan. Tässä väitöskirjatyössä käsitellään yhden syndekaaniproteiiniperheen jäsenen, syndekaani-3 proteoglykaanin, tutkimusten tuloksia. Syndekaani-3 proteiinia ilmennetään runsaasti aivoissa kehityksen aikana. Sitoutuessaan ligandiin se välittää signaalin, joka nopeasti aikaansaa hermosolujen ulokkeiden kasvua. Osoitan tässä väitöskirjatyössä ligandin ja syndekaani-3 proteiinin muodostavan viestinvälityskompleksin solun pinnalla.…