ABSTRACT
We report the design, synthesis, and characterization of a novel type of cationic lipopeptide, gemini-like amphiphilic peptides or 'geminoids'. As an example, the SPKR peptide, inspired by biological nucleic acid binding motifs, was appended with unsaturated (oleoyl/oleyl) alkyl tails. The compound shows remarkable DNA and siRNA delivery, without lysogenic helper lipid, in a variety of cells, with a moderate cytotoxic effect. It aggregates to nanoparticles that combine with DNA to lipoplexes, which undergo a change from lamellar to the more lysogenic hexagonal packing upon lowering the pH. The versatility of the chemical approach allowed us to study peptides related to SPKR, and to establish that the Pro and at least one of the cationic (Lys, Arg) residues are essential for the biological activity.
Subject(s)
DNA/administration & dosage , Drug Carriers/chemistry , Gene Transfer Techniques , Oligopeptides/chemistry , RNA, Small Interfering/administration & dosage , Surface-Active Agents/chemistry , Amino Acids/chemistry , Animals , Cations , DNA/genetics , Green Fluorescent Proteins/genetics , HeLa Cells , Humans , Hydrogen-Ion Concentration , Lipids/chemistry , Liposomes , Models, Molecular , Nanoparticles/chemistry , Oleic Acids/chemistry , Oligopeptides/genetics , Particle Size , Plasmids , RNA, Small Interfering/genetics , Salmon , Scattering, Small Angle , Transfection , X-Ray DiffractionABSTRACT
C4b-binding protein (C4BP) is a protein acting as a complement inhibitor and a carrier protein for anticoagulant protein S. Previously, we reported that the in vivo clearance of C4BP involves CD91, and that a CD91-interactive site overlaps the heparin-binding site within C4BP alpha-chains 26. Here, we investigated the C4BP-CD91 interaction in more detail. Binding of C4BP to CD91 was unaffected by protein S, which associates with C4BP beta-chain. Second, mutagenesis of cationic residues within C4BP alpha-chains impaired CD91 binding, reducing the affinity of triple mutant C4BPalpha/R39Q-R64Q-R66Q by 20-fold (Kd= 10 nM versus 214 nM for wild-type and mutant C4BP, respectively). Accordingly, intracellular degradation of this mutant by CD91-expressing cells was reduced to levels of CD91-deficient cells. Moreover, C4BPalpha/R39Q-R64Q-R66Q displayed a 3-fold prolonged survival compared to normal C4BP in in vivo clearance experiments. Since these residues also contribute to heparin binding, we explored the role of heparin-sulfate proteoglycans (HSPG) in the endocytosis of C4BP. The absence of HSPG was associated with a near complete absence of cell binding and intracellular degradation of C4BP. Apparently, the cellular uptake of C4BP depends on both HSPG and CD91, involving interactions with positively charged residues within C4BP alpha-chain.
Subject(s)
Complement C4b-Binding Protein/metabolism , Heparan Sulfate Proteoglycans/physiology , Low Density Lipoprotein Receptor-Related Protein-1/metabolism , Amino Acid Substitution , Animals , Antigens, CD/metabolism , Binding Sites , CHO Cells , Cell Line , Complement C4b-Binding Protein/genetics , Complement C4b-Binding Protein/pharmacokinetics , Cricetinae , Cricetulus , Endocytosis/physiology , Fibroblasts/metabolism , Half-Life , Heat-Shock Proteins/metabolism , Humans , Mice , Mice, Inbred C57BL , Models, Molecular , Protein Binding , Protein S/metabolism , Receptors, LDL , Recombinant Proteins/metabolism , Surface Plasmon Resonance , Tumor Suppressor ProteinsABSTRACT
Beta2-integrin clustering on activation is a key event in leukocyte adhesion to the endothelium during the inflammatory response. In the search for molecular mechanisms leading to this clustering, we have identified low-density lipoprotein (LDL) receptor-related protein (LRP) as a new partner for beta2-integrins at the leukocyte surface. Immobilized recombinant LRP fragments served as an adhesive surface for blood-derived leukocytes and the U937 cell line. This adhesion was decreased up to 95% in the presence of antibodies against beta2-integrins, pointing to these integrins as potential partners for LRP. Using purified proteins, LRP indeed associated with the alphaMbeta2 complex and the alphaM and alphaL I-domains (K(d, app) approximately 0.5 microM). Immunoprecipitation experiments and confocal microscopy revealed that endogenously expressed LRP and alphaLbeta2 colocalized in monocytes and U937 cells. Furthermore, activation of U937 cells resulted in clustering of alphaLbeta2 and LRP to similar regions at the cell surface, indicating potential cooperation between both proteins. This was confirmed by the lack of alphaLbeta2 clustering in U937 cells treated by antisense oligonucleotides to down-regulate LRP. In addition, the absence of LRP resulted in complete abrogation of beta2-integrin-dependent adhesion to endothelial cells in a perfusion system, demonstrating the presence of a previously unrecognized link between LRP and leukocyte function.
