Yi Sun

Karolinska Institutet, Solna, Stockholm, Sweden

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Publications (4)25.13 Total impact

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    ABSTRACT: Lack of robust methods for establishment and expansion of pluripotent human embryonic stem (hES) cells still hampers development of cell therapy. Laminins (LN) are a family of highly cell-type specific basement membrane proteins important for cell adhesion, differentiation, migration and phenotype stability. Here we produce and isolate a human recombinant LN-521 isoform and develop a cell culture matrix containing LN-521 and E-cadherin, which both localize to stem cell niches in vivo. This matrix allows clonal derivation, clonal survival and long-term self-renewal of hES cells under completely chemically defined and xeno-free conditions without ROCK inhibitors. Neither LN-521 nor E-cadherin alone enable clonal survival of hES cells. The LN-521/E-cadherin matrix allows hES cell line derivation from blastocyst inner cell mass and single blastomere cells without a need to destroy the embryo. This method can facilitate the generation of hES cell lines for development of different cell types for regenerative medicine purposes.
    Nature Communications 01/2014; 5:3195. DOI:10.1038/ncomms4195 · 11.47 Impact Factor
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    ABSTRACT: Laminin-332 (LN-332), which is essential for epithelial cell adhesion and migration, is up-regulated in most invasive carcinomas. Association between LN-332 and carcinoma cell integrins and stroma collagen is thought to be important for tumor growth and metastasis. Here, we show that function blocking LN-332 antibodies interfering with cellular adhesion and migration in vitro evoke apoptotic pathways. The antibodies also target epithelial tumors in vivo. Antibodies against the cell binding domain of the alpha3 chain of LN-332 inhibited tumor growth by up to 68%, and antibodies against the matrix binding domains of the beta3 and gamma2 chains significantly decreased lung metastases. The LN-332 antibodies appear to induce tumor cell anoikis and subsequent programmed cell death and reduce migration by interfering with tumor cell matrix interactions.
    International Journal of Cancer 10/2009; 125(8):1814-25. DOI:10.1002/ijc.24532 · 5.09 Impact Factor
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    ABSTRACT: MARCO is a class A scavenger receptor capable of binding both gram-negative and -positive bacteria. Using the surface plasmon resonance technique, we show here that a recombinant, soluble form of MARCO, sMARCO, binds the major gram-negative and -positive bacterial surface components, lipopolysaccharide and lipoteichoic acid. Yet, the interaction of these two polyanions with sMARCO is of much lower affinity than that of polyinosinic acid, a polyanionic inhibitor of bacterial binding to MARCO. To further elucidate the ligand-binding functions of MARCO, we performed a phage display screen with sMARCO. The screening resulted in the enrichment of only a handful of phage clones. Contrary to expectations, no polyanionic peptides, but only those with a predominantly hydrophobic nature, were enriched. One peptide, VRWGSFAAWL, was displayed on two-thirds of the phages recovered after four rounds of screening. The VRWGSFAAWL phage-sMARCO interaction had significantly slower dissociation kinetics than that between sMARCO and lipopolysaccharide or lipoteichoic acid. Further work with this phage, and the second most enriched phage, displaying the peptide RLNWAWWLSY, demonstrated that both peptides bind to the SRCR domain of MARCO, and that they probably bind to the same site. Data base searches suggested that the VRWGSFAAWL peptide represents complement component C4, but we could not convincingly confirm this suggestion. A study with chimeric scavenger receptors indicated that even minor sequence changes in the MARCO scavenger receptor cysteine-rich (SRCR) domain can have profound effects on the binding of the prototypic scavenger receptor ligand, acetylated low density lipoprotein. As shown by differential binding of glutathione S-transferase-VR-WGSFAAWL, these differences were very likely due to conformational changes. These findings led to experiments that demonstrated a crucial role of the SRCR domain for acetylated low density lipoprotein binding in MARCO. Thus, our results strengthen the notion that the SRCR domain is the major ligand-binding domain in MARCO. Furthermore, they suggest that the domain may contain multiple ligand-binding sites.
    Journal of Biological Chemistry 06/2006; 281(18):12767-75. DOI:10.1074/jbc.M513628200 · 4.57 Impact Factor
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    ABSTRACT: Nephrin is a signalling cell-cell adhesion protein of the Ig superfamily and the first identified component of the slit diaphragm that forms the critical and ultimate part of the glomerular ultrafiltration barrier. The extracellular domains of the nephrin molecules form a network of homophilic and heterophilic interactions building the structural scaffold of the slit diaphragm between the podocyte foot processes. The intracellular domain of nephrin is connected indirectly to the actin cytoskeleton, is tyrosine phosphorylated, and mediates signalling from the slit diaphragm into the podocytes. CD2AP, podocin, Fyn kinase, and phosphoinositide 3-kinase are reported intracellular interacting partners of nephrin, although the biological roles of these interactions are unclarified. To characterize the structural properties and protein-protein interactions of the nephrin intracellular domain, we produced a series of recombinant nephrin proteins. These were able to bind all previously identified ligands, although the interaction with CD2AP appeared to be of extremely low stoichiometry. Fyn phosphorylated nephrin proteins efficiently in vitro. This phosphorylation was required for the binding of phosphoinositide 3-kinase, and significantly enhanced binding of Fyn itself. A protein of 190 kDa was found to associate with the immobilized glutathione S-transferase-nephrin. Peptide mass fingerprinting and amino acid sequencing identified this protein as IQGAP1, an effector protein of small GTPases Rac1 and Cdc42 and a putative regulator of cell-cell adherens junctions. IQGAP1 is expressed in podocytes at significant levels, and could be found at the immediate vicinity of the slit diaphragm. However, further studies are needed to confirm the biological significance of this interaction and its occurrence in vivo.
    FEBS Journal 02/2005; 272(1):228-43. DOI:10.1111/j.1432-1033.2004.04408.x · 4.00 Impact Factor