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Regulated intramembrane proteolysis and degradation of murine epithelial cell adhesion molecule mEpCAM

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Item Type:Article
Title:Regulated intramembrane proteolysis and degradation of murine epithelial cell adhesion molecule mEpCAM
Creators Name:Hachmeister, M. and Bobowski, K.D. and Hogl, S. and Dislich, B. and Fukumori, A. and Eggert, C. and Mack, B. and Kremling, H. and Sarrach, S. and Coscia, F. and Zimmermann, W. and Steiner, H. and Lichtenthaler, S.F. and Gires, O.
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.
Keywords:Amino Acid Sequence, Amyloid Precursor Protein Secretases, Cell Adhesion Molecules, Cell Line, Cell Membrane, Conserved Sequence, Epithelial Cell Adhesion Molecule, Molecular Sequence Data, Neoplasm Antigens, Proteasome Endopeptidase Complex, Protein Interaction Domains and Motifs, Proteolysis, Vertebrates, Animals, Mice
Source:PLoS ONE
Publisher:Public Library of Science
Page Range:e71836
Date:29 August 2013
Official Publication:https://doi.org/10.1371/journal.pone.0071836
PubMed:View item in PubMed

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