title: Cross-linking of glycosphingolipids at the plasma membrane: consequences for intracellular signaling and traffic.
abstract: Glycosphingolipids (GSLs) are predominantly found in the outer leaflet of the plasma membrane, where they play a role in important processes such as cell adhesion, migration and signaling. However, by which mechanisms GSLs regulate these processes remains elusive. In this study, we therefore took advantage of the fact that some GSLs also serve as receptors for certain protein toxins, which rely on receptor binding for internalization and intoxication. Here, we demonstrate that Shiga and cholera toxins, which both possess multivalent GSL-binding capacity, induce dissociation of the cytosolic cPLA2α-AnxA1 complex in HeLa and HMEC-1 cells. The dissociation is mediated through an increase in cytosolic calcium levels and activation of the tyrosine kinase Syk. Ricin, a protein toxin that does not cross-link surface molecules, has no effect on the same complex. Importantly, we find that antibody-mediated cross-linking of Gb3 and GM1, the GSL receptors for Shiga and cholera toxin, respectively, also induces dissociation. These data demonstrate that cross-linking of GSLs at the plasma membrane mediates the intracellular signaling events resulting in dissociation of the complex. After dissociation, cPLA2α and AnxA1 are translocated to intracellular membranes where they are known to function in regulating membrane transport processes. In conclusion, we have characterized a novel mechanism for cell surface-induced initiation of intracellular signaling and transport events.
authors.affiliation: Department of Molecular Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, 0379, Oslo, Norway. toklok@rr-research.no.|Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0316, Oslo, Norway. toklok@rr-research.no.
authors.forename: Tove Irene
authors.initials: TI
authors.lastname: Klokk
authors.affiliation: Department of Molecular Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, 0379, Oslo, Norway.|Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0316, Oslo, Norway.|Department of Biosciences, University of Oslo, 0316, Oslo, Norway.
authors.forename: Simona
authors.initials: S
authors.lastname: Kavaliauskiene
authors.affiliation: Department of Molecular Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, 0379, Oslo, Norway.|Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0316, Oslo, Norway.|Department of Biosciences, University of Oslo, 0316, Oslo, Norway.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Sandvig
mesh_terms: D017305:Annexin A1 / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002772:Cholera Toxin / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006028:Glycosphingolipids / Q000378:metabolism*; D054513:Group IV Phospholipases A2 / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D022621:Shiga Toxin / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase
chemical_list: D017305:Annexin A1; D006028:Glycosphingolipids; D047908:Intracellular Signaling Peptides and Proteins; D022621:Shiga Toxin; D002772:Cholera Toxin; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D054513:Group IV Phospholipases A2; C516389:PLA2G4A protein, human; D002118:Calcium
keywords: Annexin; Calcium; Cross-linking; Glycosphingolipids; Phosholipase A2; Syk