
The CEACAM1 transmembrane domain, but not the cytoplasmic domain, directs internalization of human pathogens via membrane microdomains
Author(s) -
Muenzner Petra,
Bachmann Verena,
Kuespert Katharina,
Hauck Christof R.
Publication year - 2008
Publication title -
cellular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.542
H-Index - 138
eISSN - 1462-5822
pISSN - 1462-5814
DOI - 10.1111/j.1462-5822.2007.01106.x
Subject(s) - internalization , microbiology and biotechnology , cytoplasm , biology , endocytosis , lipid raft , cell membrane , transmembrane protein , receptor , cell , biochemistry , signal transduction
Summary 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 ΔCT) promote equivalent internalization of several human pathogens. CEACAM1‐4L‐ and CEACAM1 ΔCT‐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 ΔCT, 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 ΔCT, but not CEACAM3. Similar to GPI‐anchored CEACAM6, both CEACAM1‐4L as well as CEACAM1 ΔCT 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.