The cell-cell adhesion molecule EpCAM interacts directly with the tight junction protein claudin-7.
We recently described that in the metastasizing rat pancreatic carcinoma line BSp73ASML the cell-cell adhesion molecule EpCAM, CD44 variant isoforms and the tetraspanins D6.1A and CD9 form a complex that is located in glycolipid-enriched membrane microdomains. This complex contains, in addition, an undefined 20 kDa protein. As such complex formation influenced cell-cell adhesion and apoptosis resistance, it became of interest to identify the 20 kDa polypeptide. This 20 kDa protein, which co-precipitated with EpCAM in BSp73ASML lysates, was identified as the tight junction protein claudin-7. Correspondingly, an association between EpCAM and claudin-7 was noted in rat and human tumors and in non-transformed tissues of the gastrointestinal tract. Co-localization of the two molecules was most pronounced at basolateral membranes, but was also observed in tight junctions. Evidence for direct protein-protein interactions between EpCAM and claudin-7 was obtained by co-immunoprecipitation after treatment of tumor cells with a membrane-permeable chemical cross-linker. The complex, which is located in glycolipid-enriched membrane microdomains, is not disrupted by partial cholesterol depletion, but claudin-7 phosphorylation is restricted to the localization in glycolipid-enriched membrane microdomains. This is the first report on an association between EpCAM and claudins in both non-transformed tissues and metastasizing tumor cell lines.
Ladwein
Markus
M
Department of Tumor Progression and Tumor Defense, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
Pape
Ulrich-Frank
UF
Schmidt
Dirk-Steffen
DS
Schnölzer
Martina
M
Fiedler
Sabine
S
Langbein
Lutz
L
Franke
Werner W
WW
Moldenhauer
Gerhard
G
Zöller
Margot
M
D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D002448:Cell Adhesion / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D045744:Cell Line, Tumor; D057167:Claudins; D004386:Duodenum / Q000378:metabolism / Q000648:ultrastructure; D000071858:Epithelial Cell Adhesion Molecule; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism*; D008854:Microscopy, Electron; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D051381:Rats; D019108:Tight Junctions / Q000502:physiology*
D000951:Antigens, Neoplasm; C112697:CD44v6 antigen; C473255:CLDN7 protein, human; D015815:Cell Adhesion Molecules; D057167:Claudins; C499379:EPCAM protein, human; D000071858:Epithelial Cell Adhesion Molecule; D006023:Glycoproteins; D018960:Hyaluronan Receptors; D008565:Membrane Proteins