title: Cis and Trans Cooperativity of E-Cadherin Mediates Adhesion in Biomimetic Lipid Droplets.
abstract: The regulation of cell-cell adhesion is important in cell motility, tissue growth, and for the mechanical integrity of tissues. Although the role of active cytoskeleton dynamics in regulating cadherin interactions is crucial in vivo, here we present a biomimetic emulsion system to characterize the passive E-cadherin-mediated adhesion between droplets. The visualization of a three-dimensional assembly of lipid droplets, functionalized with extracellular E-cadherin domains, reveals a hierarchy of homophilic interactions. First, the high interfacial tension of droplets facilitates trans cadherin-cadherin adhesion, which is strong enough to stabilize looser than random close packing configurations. Second, fluorescence enhancement shows that adding clustering agents, such as calcium or chelating ligands, favor the lateral cis adhesion of the already bound cadherin pairs over the clustering of monomer cadherin on the surface. Finally, above a threshold cadherin and calcium concentration, the cis and trans protein interactions become strong enough to trigger and promote droplet fusion. While E-cadherin is not known to participate in cellular fusion, this mechanism is general because replacing calcium with cholesterol to cluster the cadherin-carrying lipids also promotes fusion. These results suggest that passive clustering, via calcium-induced dimerization or membrane ordering, may contribute to the reinforcement of cell-cell contacts. Alternatively, a molecular switch for fusion offers a route to mixing droplet contents and controlling their size in situ.
authors.affiliation: Department of Physics and Center for Soft Matter Research, New York University, New York, New York; Institut des NanoSciences de Paris, UMR 7588, Centre National de la Recherche Scientifique-University Pierre et Marie Curie, University of Paris 6, Paris, France. Electronic address: pontani@insp.upmc.fr.
authors.forename: Lea-Laetitia
authors.initials: LL
authors.lastname: Pontani
authors.affiliation: Department of Physics and Center for Soft Matter Research, New York University, New York, New York.
authors.forename: Ivane
authors.initials: I
authors.lastname: Jorjadze
authors.affiliation: Department of Physics and Center for Soft Matter Research, New York University, New York, New York. Electronic address: jb2929@nyu.edu.
authors.forename: Jasna
authors.initials: J
authors.lastname: Brujic
mesh_terms: D000268:Adhesiveness; D015820:Cadherins / Q000737:chemistry* / Q000378:metabolism; D002118:Calcium / Q000737:chemistry; D065096:Calcium Chelating Agents / Q000737:chemistry; D002784:Cholesterol / Q000737:chemistry; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry; D066292:Lipid Droplets / Q000737:chemistry*; D011485:Protein Binding; D055503:Protein Multimerization
chemical_list: D015820:Cadherins; D065096:Calcium Chelating Agents; D008051:Lipid Bilayers; D002784:Cholesterol; D002118:Calcium