Tricellulin secures the epithelial barrier at tricellular junctions by interacting with actomyosin

Abstract

The epithelial cell sheet functions as a barrier to prevent invasion of pathogens. It is necessary to eliminate intercellular gaps not only at bicellular junctions, but also at tricellular contacts, where three cells meet, to maintain epithelial barrier function. To that end, tight junctions between adjacent cells must associate as closely as possible, particularly at tricellular contacts. Tricellulin is an integral component of tricellular tight junctions (tTJs), but the molecular mechanism of its contribution to the epithelial barrier function remains unclear. In this study, we revealed that tricellulin contributes to barrier formation by regulating actomyosin organization at tricellular junctions. Furthermore, we identified α-catenin, which is thought to function only at adherens junctions, as a novel binding partner of tricellulin. α-catenin bridges tricellulin attachment to the bicellular actin cables that are anchored end-on at tricellular junctions. Thus, tricellulin mobilizes actomyosin contractility to close the lateral gap between the TJ strands of the three proximate cells that converge on tricellular junctions.

Effects of TAMP family on the tight junction strand network and barrier function in epithelial cells

“…22 In the present manuscript, we also examined the roles of C-terminal cytoplasmic tails of OCLN and TRIC, which have been implicated in the localization and function. 32,33,39,40,58,59,60 The mutant TRIC lacking the C-terminal cytoplasmic tail was localized at bicellular TJs (and lateral membranes) and restored the paracellular barrier of the Tric/Ocln-dKO cells (Figures 5B, 6, and Figure S6). This suggests that the C-terminal cytoplasmic tail of TRIC is not required to maintain the barrier function.…”

“…39 In addition, the Cterminal tail of TRIC binds to angulins and α-catenin. [40][41][42] knockin mice carrying a truncated TRIC lacking the OCEL domain exhibited a similar phenotype of TRIC-deficient mice and suffered from early onset progressive hearing loss, suggesting that this region plays a pivotal role in the inner ear cells. 43,44 Although it was reported that the C-terminal tails of both OCLN and TRIC are essential for their proper localization, 32,44 their roles in the regulation of the structure and function of TJs are not yet fully understood.…”

Closing the gap: Tricellulin/α-catenin interaction maintains epithelial integrity at vertices

“…In this issue, Cho and colleagues ( 5 ) set out to discover the molecular mechanism that maintains junctional integrity at vertebrate TCJs. Previously, partial loss of tricellulin was shown to impair tTJ organization and epithelial barrier function ( 1 ).…”

“…Previous work proposed that the organization of actomyosin at TCJs might be important for generating a tightening force for sealing tTJs ( 7 ). Using a calcium switch assay, Cho et al ( 5 ) demonstrated that during TCJ formation, actin filaments form a crisscrossing meshwork at TCJs, and myosin II localizes on overlapping antiparallel actin filaments ( Fig. 1 ).…”

“…Surprisingly, Cho et al ( 5 ) demonstrated that α-catenin interacts directly with tricellulin. The authors made a strong case for this novel interaction using a combination of pulldown assays where they narrowed the binding regions using a series of deletion mutants, a binding assay with purified recombinant proteins, and a proximity ligation assay in cells.…”