Tricellulin forms a barrier to macromolecules in tricellular tight junctions without affecting ion permeability.
Tricellulin is a tight junction protein localized in tricellular tight junctions (tTJs), the meeting points of three cells, but also in bicellular tight junctions (bTJs). To investigate its specific barrier functions in bTJs and tTJs, TRIC-a was expressed in low-level tricellulin-expressing cells, and MDCK II, either in all TJs or only in tTJs. When expressed in all TJs, tricellulin increased paracellular electrical resistance and decreased permeability to ions and larger solutes, which are associated with enhanced ultrastructural integrity of bTJs toward enhanced strand linearity. In tTJs in contrast, ultrastructure was unchanged and tricellulin minimized permeability to macromolecules but not to ions. This paradox is explained by properties of the tTJ central tube which is wide enough for passage of macromolecules, but too rare to contribute significantly to ion permeability. In conclusion, at low tricellulin expression the tTJ central tube forms a pathway for macromolecules. At higher expression, tricellulin forms a barrier in tTJs effective only for macromolecules and in bTJs for solutes of all sizes.
Krug
Susanne M
SM
Institute of Clinical Physiology, Charité, Freie Universität, Berlin, Germany.
Amasheh
Salah
S
Richter
Jan F
JF
Milatz
Susanne
S
Günzel
Dorothee
D
Westphal
Julie K
JK
Huber
Otmar
O
Schulzke
Jörg D
JD
Fromm
Michael
M
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000502:physiology*; D062445:Claudin-1; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D007477:Ions / Q000378:metabolism*; D062794:MARVEL Domain Containing 2 Protein; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D062793:Occludin; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D019108:Tight Junctions / Q000378:metabolism* / Q000648:ultrastructure
C568108:CLDN1 protein, human; D062445:Claudin-1; D007477:Ions; D062794:MARVEL Domain Containing 2 Protein; C516798:MARVELD2 protein, human; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; D020033:Protein Isoforms; D034741:RNA, Small Interfering