Abstract
Apoptotic extrusion of cells from epithelial cell layers is of central importance for epithelial homeostasis. As a prerequisite cell–cell contacts between apoptotic cells and their neighbors have to be dissociated. Tricellular tight junctions (tTJs) represent specialized structures that seal polarized epithelial cells at sites where three cells meet and are characterized by the specific expression of tricellulin and angulins. Here, we specifically addressed the fate of tricellulin in apoptotic cells. Methods: Apoptosis was induced by staurosporine or camptothecin in MDCKII and RT-112 cells. The fate of tricellulin was analyzed by Western blotting and immunofluorescence microscopy. Caspase activity was inhibited by Z-VAD-FMK or Z-DEVD-FMK. Results: Induction of apoptosis induces the degradation of tricellulin with time. Aspartate residues 487 and 441 were identified as caspase cleavage-sites in the C-terminal coiled-coil domain of human tricellulin. Fragmentation of tricellulin was inhibited in the presence of caspase inhibitors or when Asp487 or Asp441 were mutated to asparagine. Deletion of the tricellulin C-terminal amino acids prevented binding to lipolysis-stimulated lipoprotein receptor (LSR)/angulin-1 and thus should impair specific localization of tricellulin to tTJs. Conclusions: Tricellulin is a substrate of caspases and its cleavage in consequence contributes to the dissolution of tTJs during apoptosis.
Highlights
Tight junctions (TJs) represent the most apical cell–cell contacts in polarized epithelial cell layers
Claudins and occludin form the apical sealing belt between two opposing cells where they are arranged in a network of TJ strands that restricts and regulates paracellular flux depending on the specific claudin composition
The images are representatives of at least three independent experiments. These results indicate that caspase-mediated cleavage of tricellulin liberates it from angulin and ThetsheusrefrsoumlttsTJisn. dHiocwaetevetrh, tahtiscdaosepsansoet-emxceluddieattheadt LcSleRa/avnagguelino-1f ittrsieclfeilslutalrignetleidbedruartinegsaipt ofprotomsis.angulin and fromThteTreJfso.reH, wowe neevxet ra,ntahlyizseddotheesfnatoetoef xLcSlRu/adneguthlina-t1LaSftRer/ainndguuctliionn-o1f iatpsoeplftoissistainrgMeDteCdKIdI ucerlilns.g apoptosis
Summary
Tight junctions (TJs) represent the most apical cell–cell contacts in polarized epithelial cell layers. The situation is different at tricellular contacts where apical TJs strands of three neighboring cells meet and are assumed to represent weak points for the paracellular TJ network [5] At these tricellular tight junctions, bicellular TJs converge, and TJ strands turn basally and form the so-called central sealing element [6]. These tricellular TJs (tTJs) differ from bicellular TJs (bTJs) by a specific set of proteins including tricellulin [7] and one of the three angulins [8]. A similar effect was obtained in RT-112 cells (bladder carcinoma) (Figure 1E) showing that the observed effect is not restricted to MDCKII cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
