The specific fates of tight junction proteins in apoptotic epithelial cells.
The polarized morphology of epithelial cells depends on the establishment and maintenance of characteristic intercellular junctions. The dramatic morphological changes observed in apoptotic epithelial cells were ascribed at least in part to the specific fragmentation of components of adherens junctions and desmosomes. Little, however, is known about tight junctions during apoptosis. We have found that after induction of apoptosis in epithelial cells, tight junction proteins undergo proteolytic cleavage in a distinctive manner correlated with a disruption of tight junctions. The transmembrane protein occludin and, likewise, the cytoplasmic adaptor proteins ZO-1 and ZO-2 are fragmented by caspase cleavage. In addition, occludin is cleaved at an extracellular site by a metalloproteinase. The caspase cleavage site in occludin was mapped C-terminally to Asp(320) within the C-terminal cytoplasmic domain. Mutagenesis of this site efficiently blocked fragmentation. In the presence of caspase and/or metalloproteinase inhibitors, fragmentation of occludin, ZO-1 and ZO-2 was blocked and cellular morphology was almost fully preserved. Interestingly, two members of the claudin family of transmembrane tight junction proteins exhibited a different behavior. While the amount of claudin-2 protein was reduced similarly to occludin, ZO-1 and ZO-2, claudin-1 was either fully preserved or was even increased in apoptotic cells.
Bojarski
Christian
C
Institute of Clinical Chemistry and Pathobiochemistry, Charité - Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany.
Weiske
Jörg
J
Schöneberg
Torsten
T
Schröder
Werner
W
Mankertz
Joachim
J
Schulzke
Jörg-Dieter
JD
Florian
Peter
P
Fromm
Michael
M
Tauber
Rudolf
R
Huber
Otmar
O
D000818:Animals; D017209:Apoptosis; D001224:Aspartic Acid / Q000737:chemistry; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D053938:DNA Fragmentation; D018076:DNA, Complementary / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology / Q000473:pathology*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008856:Microscopy, Fluorescence; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D062793:Occludin; D010750:Phosphoproteins / Q000378:metabolism; D017434:Protein Structure, Tertiary; D019108:Tight Junctions / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D062826:Zonula Occludens-1 Protein; D062827:Zonula Occludens-2 Protein
D018076:DNA, Complementary; D008565:Membrane Proteins; D062793:Occludin; D010750:Phosphoproteins; D062826:Zonula Occludens-1 Protein; D062827:Zonula Occludens-2 Protein; D001224:Aspartic Acid; D020169:Caspases