title: Regulated intramembrane proteolysis and degradation of murine epithelial cell adhesion molecule mEpCAM.
abstract: Epithelial cell adhesion molecule EpCAM is a transmembrane glycoprotein, which is highly and frequently expressed in carcinomas and (cancer-)stem cells, and which plays an important role in the regulation of stem cell pluripotency. We show here that murine EpCAM (mEpCAM) is subject to regulated intramembrane proteolysis in various cells including embryonic stem cells and teratocarcinomas. As shown with ectopically expressed EpCAM variants, cleavages occur at α-, β-, γ-, and ε-sites to generate soluble ectodomains, soluble Aβ-like-, and intracellular fragments termed mEpEX, mEp-β, and mEpICD, respectively. Proteolytic sites in the extracellular part of mEpCAM were mapped using mass spectrometry and represent cleavages at the α- and β-sites by metalloproteases and the b-secretase BACE1, respectively. Resulting C-terminal fragments (CTF) are further processed to soluble Aβ-like fragments mEp-β and cytoplasmic mEpICD variants by the g-secretase complex. Noteworthy, cytoplasmic mEpICD fragments were subject to efficient degradation in a proteasome-dependent manner. In addition the γ-secretase complex dependent cleavage of EpCAM CTF liberates different EpICDs with different stabilities towards proteasomal degradation. Generation of CTF and EpICD fragments and the degradation of hEpICD via the proteasome were similarly demonstrated for the human EpCAM ortholog. Additional EpCAM orthologs have been unequivocally identified in silico in 52 species. Sequence comparisons across species disclosed highest homology of BACE1 cleavage sites and in presenilin-dependent γ-cleavage sites, whereas strongest heterogeneity was observed in metalloprotease cleavage sites. In summary, EpCAM is a highly conserved protein present in fishes, amphibians, reptiles, birds, marsupials, and placental mammals, and is subject to shedding, γ-secretase-dependent regulated intramembrane proteolysis, and proteasome-mediated degradation.
authors.affiliation: Department of Otorhinolaryngology, Head and Neck Surgery, Ludwig-Maximilians-University, Munich, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Hachmeister
authors.forename: Karolina D
authors.initials: KD
authors.lastname: Bobowski
authors.forename: Sebastian
authors.initials: S
authors.lastname: Hogl
authors.forename: Bastian
authors.initials: B
authors.lastname: Dislich
authors.forename: Akio
authors.initials: A
authors.lastname: Fukumori
authors.forename: Carola
authors.initials: C
authors.lastname: Eggert
authors.forename: Brigitte
authors.initials: B
authors.lastname: Mack
authors.forename: Heidi
authors.initials: H
authors.lastname: Kremling
authors.forename: Sannia
authors.initials: S
authors.lastname: Sarrach
authors.forename: Fabian
authors.initials: F
authors.lastname: Coscia
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Zimmermann
authors.forename: Harald
authors.initials: H
authors.lastname: Steiner
authors.forename: Stefan F
authors.initials: SF
authors.lastname: Lichtenthaler
authors.forename: Olivier
authors.initials: O
authors.lastname: Gires
mesh_terms: D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism; D000818:Animals; D000951:Antigens, Neoplasm / Q000737:chemistry / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D017124:Conserved Sequence; D000071858:Epithelial Cell Adhesion Molecule; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D059748:Proteolysis; D014714:Vertebrates
chemical_list: D000951:Antigens, Neoplasm; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D053829:Amyloid Precursor Protein Secretases; D046988:Proteasome Endopeptidase Complex