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The integrity, or barrier function, of the intestinal epithelium is of paramount importance in -maintaining good health. This is largely imparted by a single layer of epithelial cells linked by the transmembrane tight junction protein complex near their apical surface. Disruption of epithelial permeability via the tight junctions can contribute to disease progression. The cytokine IFNγ is involved in many inflammatory processes and has been shown to dramatically increase permeability via changes at the tight junction in experimental models. One of its key effectors is the transcription factor, -IRF-1. In our studies of the role of IRF-1 in barrier function using the human T84 intestinal epithelial cell monolayer model, we have found that induction of IRF-1 alone is insufficient to change permeability and that if IRF-1 is involved in mediating the permeability effects of IFNγ, then other factors must also be required.

Abstract: Coeliac disease is a chronic enteropathy caused by the ingestion of wheat gliadin and other cereal prolamines derived from rye and barley. In the present work, we investigated the mechanisms underlying altered barrier function properties exerted by gliadin-derived peptides in human Caco-2 intestinal epithelial cells. We demonstrate that gliadin alters barrier function almost immediately by decreasing transepithelial resistance and increasing permeability to small molecules (4kDa). Gliadin caused a reorganisation of actin filaments and altered expression of the tight junction proteins occludin, claudin-3 and claudin-4, the TJ-associated protein ZO-1 and the adherens junction protein E-cadherin. [Copyright &y& Elsevier]

Flightless I (Flii), a highly conserved member of the gelsolin family of actin-remodelling proteins associates with actin structures and is involved in cellular motility and adhesion. Our previous studies have shown that Flii is an important negative regulator of wound repair. Here, we show that Flii affects hemidesmosome formation and integrin-mediated keratinocyte adhesion and migration. Impaired hemidesmosome formation and sparse arrangements of keratin cytoskeleton tonofilaments and actin cytoskeleton anchoring fibrils were observed in FliiTg/+ and FliiTg/Tg mice with their skin being significantly more fragile than Flii+/− and WT mice. Flii+/− primary keratinocytes showed increased adhesion on laminin and collagen I than WT and FliiTg/Tg primary keratinocytes. Decreased expression of CD151 and laminin-binding integrins α3, β1, α6 and β4 were observed in Flii overexpressing wounds, which could contribute to the impaired wound re-epithelialization observed in these mice. Flii interacts with proteins directly linked to the cytoplasmic domain of integrin receptors suggesting that it may be a mechanical link between ligand-bound integrin receptors and the actin cytoskeleton driving adhesion-signaling pathways. Therefore Flii may regulate wound repair through its effect on hemidesmosome formation and integrin-mediated cellular adhesion and migration.Journal of Investigative Dermatology (2009) 129, 2031–2045; doi:10.1038/jid.2008.461; published online 12 February 2009 [ABSTRACT FROM AUTHOR]

Abstract: The epithelial tight junction forms a barrier to paracellular solute movement. In this study we show that the heterotrimeric G-protein Gα13 regulates the epithelial tight junction barrier. We generated MDCKII kidney epithelial cell lines in which the expression of an active Gα13 mutant (Gα13Q226L) could be induced. We demonstrated that Gα13Q226L expression increased paracellular permeability and caused the disruption and redistribution of proteins comprising the tight junction and the adherens junction away from sites of cell contact and the appearance of basal stress fibers. The effects on the junctional proteins and the actin cytoskeleton were abrogated by the Rho kinase inhibitor Y27632 but not by the Src kinase inhibitor PP2. The Gα13 mediated increase in permeability was also Src kinase independent but was partly dependent on Rho kinase signalling. Our data establish a link between Gα13, Rho kinase signaling and epithelial barrier function and not only demonstrate that Gα13 regulates epithelial apical junction properties but that it does so via signaling pathways that are distinct from the closely related protein Gα12. [Copyright &y& Elsevier]