Tricellulin forms homomeric and heteromeric tight junctional complexes

Abstract

Sealing of the paracellular cleft by tight junctions is of central importance for epithelia and endothelia to function as efficient barriers between the extracellular space and the inner milieu. Occludin and claudins represent the major tight junction components involved in establishing this barrier function. A special situation emerges at sites where three cells join together. Tricellulin, a recently identified tetraspan protein concentrated at tricellular contacts, was reported to organize tricellular as well as bicellular tight junctions. Here we show that in MDCK cells, the tricellulin C-terminus is important for the basolateral translocation of tricellulin, whereas the N-terminal domain appears to be involved in directing tricellulin to tricellular contacts. In this respect, identification of homomeric tricellulin-tricellulin and of heteromeric tricellulin-occludin complexes extends a previously published model and suggests that tricellulin and occludin are transported together to the edges of elongating bicellular junctions and get separated when tricellular contacts are formed.

In tight junctions, claudins regulate the interactions between occludin, tricellulin and marvelD3, which, inversely, modulate claudin oligomerization

“…1F (values relative to the positive control Cld5-CFP/Cld5-YFP). In contrast, strong colocalization and FRET within intracellular compartments (YFPTric/CFP-Occl: FRET efficiency 3.8160.75%) suggests an intracellular interaction between Occl and Tric in HEK cells probably during transport to the cell surface as discussed earlier (Westphal et al, 2010).…”

“…2A). In HEK-293 cells, Tric was located at bicellular contacts in contrast to the tricellular localization in epithelial cell lines endogenously expressing Tric (Westphal et al, 2010). When Tric was expressed alone in the HEK-293 cells no contact enrichment was detectable at bicellular contacts (enrichment factor: 0.7860.19, n551).…”

“…On the other hand, they also found complexes between Md3 and Occl or Tric. In another study, it was shown with transfected HEK-293 cell lysates by coimmunoprecipitation (Westphal et al, 2010) that Occl and Tric physically form a complex. Experiments with deletion mutants of Tric used in the latter study suggested that this interaction may occur during the transport of Occl and Tric to the cell membrane.…”

“…Due to the homology of the marvel domain of the TAMPs and the great variation in the length of their cytosolic tails a heterophilic interaction between the transmembrane domains of all three members has been assumed (Blasig et al, 2011;Westphal et al, 2010). As a matter of fact, Md3 is interacting with both Occl and Tric, at bicellular cell-cell contacts within one plasma membrane (cis-interaction).…”

“…Tric reveals extended Nand C-terminal cytoplasmic domains, with the C-terminal tail exhibiting homology to the Occl C-terminus (Ikenouchi et al, 2005). It has been shown that the C-terminus is important for the basolateral translocation of Tric (Westphal et al, 2010) and its binding to the lipolysis-stimulated lipoprotein receptor (LSR). LSR builds a landmark for tricellular TJs (Masuda et al, 2011).…”