title: The CEACAM1 transmembrane domain, but not the cytoplasmic domain, directs internalization of human pathogens via membrane microdomains.
abstract: Several bacterial pathogens exploit carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) to promote attachment and uptake into eukaryotic host cells. The widely expressed isoform CEACAM1 is involved in cell-cell adhesion, regulation of cell proliferation, insulin homeostasis, and neo-angiogenesis, processes that depend on the cytoplasmic domain of CEACAM1. By analysing the molecular requirements for CEACAM1-mediated internalization of bacteria, we surprisingly find that the CEACAM1 cytoplasmic domain is completely obsolete for bacterial uptake. Accordingly, CEACAM1-4L as well as a CEACAM1 mutant with a complete deletion of the cytoplasmic domain (CEACAM1 DeltaCT) promote equivalent internalization of several human pathogens. CEACAM1-4L- and CEACAM1 DeltaCT-mediated uptake proceeds in the presence of inhibitors of actin microfilament dynamics, which is in contrast to CEACAM3-mediated internalization. Bacteria-engaged CEACAM1-4L and CEACAM1 DeltaCT, but not CEACAM3, localize to a gangliosid GM1- and GPI-anchored protein-containing portion of the plasma membrane. In addition, interference with cholesterol-rich membrane microdomains severely blocks bacterial uptake via CEACAM1-4L and CEACAM1 DeltaCT, but not CEACAM3. Similar to GPI-anchored CEACAM6, both CEACAM1-4L as well as CEACAM1 DeltaCT partition into a low-density, Triton-insoluble membrane fraction upon receptor clustering, whereas CEACAM3 is not detected in this fraction. Bacterial uptake by truncated CEACAM1 or chimeric CEACAM1/CEACAM3 molecules reveals that the transmembrane domain of CEACAM1 is responsible for its association with membrane microdomains. Together, these data argue for a functional role of lipid rafts in CEACAM1-mediated endocytosis that is promoted by the transmembrane domain of the receptor and that might be relevant for CEACAM1 function in physiologic settings.
authors: Lehrstuhl für Zellbiologie, Universität Konstanz, Postfach X908, D-78457 Konstanz, Germany.
authors: Petra
authors: P
authors: Muenzner
authors: Verena
authors: V
authors: Bachmann
authors: Katharina
authors: K
authors: Kuespert
authors: Christof R
authors: CR
authors: Hauck
mesh_terms: D000199:Actins / Q000378:metabolism; D015703:Antigens, CD / Q000737:chemistry / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D009344:Neisseria gonorrhoeae / Q000502:physiology*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D014443:Tyrosine / Q000378:metabolism
chemical_list: D000199:Actins; D015703:Antigens, CD; C069847:CD66 antigens; D015815:Cell Adhesion Molecules; D014443:Tyrosine; D002784:Cholesterol