Behavior of tricellulin during destruction and formation of tight junctions under various extracellular calcium conditions.
Tricellulin is an important component of tricellular tight junctions (TJs) and is involved in the formation of tricellular contacts. However, little is known about its regulation during the assembly and disassembly of tricellular TJs. By using the well-differentiated pancreatic cancer cell line HPAC, which highly expresses tricellulin at tricellular contacts, we have investigated changes in the localization, expression and phosphorylation of tricellulin and in its TJ functions as a barrier and fence during the destruction and formation of TJs induced by changes in the extracellular calcium concentration. During both extracellular Ca(2+) depletion caused by EGTA treatment and Ca(2+) repletion after Ca(2+) starvation, the expression of tricellulin increased in whole lysates and in Triton-X-100-insoluble fractions without any change in its mRNA. The increases in immunoreactivity revealed by Western blotting were prevented by alkaline phosphatase treatment. Immunoprecipitation assays showed that tricellulin was phosphorylated on threonine residues when it increased after Ca(2+) depletion and repletion. In the early stage after Ca(2+) repletion, tricellulin was expressed not only at tricellular contacts but also in the cytoplasm and at bicellular borders. In confocal laser microscopy, tricellulin was observed at the apical-most regions and basolateral membranes of tricellular contacts after Ca(2+) repletion. Knockdown of tricellulin delayed the recovery of the barrier and fence functions after Ca(2+) repletion. Thus, the dynamic behavior of tricellulin during the destruction and formation of TJs under various extracellular calcium conditions seems to be closely associated with the barrier and fence functions of TJs.
Department of Pathology, Sapporo Medical University School of Medicine, Sapporo, Japan.
Akira
A
Takasawa
Takashi
T
Kojima
Takafumi
T
Ninomiya
Mitsuhiro
M
Tsujiwaki
Masaki
M
Murata
Satoshi
S
Tanaka
Norimasa
N
Sawada
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004533:Egtazic Acid / Q000494:pharmacology; D017097:Electric Impedance; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D062794:MARVEL Domain Containing 2 Protein / Q000378:metabolism* / Q000648:ultrastructure; D062793:Occludin / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D019108:Tight Junctions / Q000378:metabolism* / Q000648:ultrastructure
D062794:MARVEL Domain Containing 2 Protein; C516798:MARVELD2 protein, human; D062793:Occludin; D034741:RNA, Small Interfering; D004533:Egtazic Acid; D002118:Calcium