Following homozygosity mapping in a single kindred, we identified nonsense and missense mutations in MYO5B, encoding type Vb myosin motor protein, in individuals with microvillus inclusion disease (MVID). MVID is characterized by lack of microvilli on the surface of enterocytes and occurrence of intracellular vacuolar structures containing microvilli. In addition, mislocalization of transferrin receptor in MVID enterocytes suggests that MYO5B deficiency causes defective trafficking of apical and basolateral proteins in MVID.

In an analysis of a large cohort of subjects with IBD, we found a significant association between symptoms of depression or anxiety and clinical recurrence. Patients with IBD should therefore be screened for clinically relevant levels of depression and anxiety and referred to psychologists or psychiatrists for further evaluation and treatment.

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The establishment of tight junctions (TJ) between columnar epithelial cells defines the functional barrier, which enteroinvasive pathogens have to overcome. Salmonella enterica serovar Typhimurium (S. typhimurium) directly invades intestinal epithelial cells but it is not well understood how the pathogen is able to overcome the intestinal barrier and gains access to the circulation. Therefore, we sought to determine whether infection with S. typhimurium could regulate the molecular composition of the TJ and, if so, whether these modifications would influence bacterial translocation and polymorphonuclear leukocyte (PMN) movement across model intestinal epithelium. We found that infection of a model intestinal epithelium with S. typhimurium over 2 h resulted in an approximately 80% loss of transepithelial electrical resistance. Western blot analysis of epithelial cell lysates demonstrated that S. typhimurium regulated the distribution of the TJ complex proteins claudin-1, zonula occludens (ZO)-2, and E-cadherin in Triton X-100-soluble and insoluble fractions. In addition, S. typhimurium was specifically able to dephosphorylate occludin and degrade ZO-1. This TJ alteration in the epithelial monolayer resulted in 10-fold increase in bacterial translocation and a 75% increase in N-formylmethionin-leucyl-phenyalanine-induced PMN transepithelial migration. Our data demonstrate that infection with S. typhimurium is associated with the rapid targeting of the tight junctional complex and loss of barrier function. This results in enhanced bacterial translocation and initiation of PMN migration across the intestinal barrier. Therefore, the ability to regulate the molecular composition of TJs facilitates the pathogenicity of S. typhimurium by aiding its uptake and distribution within the host.

SummaryShigella spp. are a group of Gram-negative enteric bacilli that cause acute dysentery in humans. We demonstrate that Shigella flexneri has evolved the ability to regulate functional components of tight junctions after interaction at the apical and basolateral pole of model intestinal epithelia. In the regulation of tight junctional protein assemblies, S. flexneri can engage serotype-specific mechanisms, which targets not only expression, but also cellular distribution and membrane association of components of tight junctions. Distinct mechanisms resulting in the regulation of tight junction-associated proteins are initiated after either apical or basolateral interactions. S. flexneri serotype 2a has the ability to remove claudin-1 from Triton X-insoluble protein fractions upon apical exposure to T-84 cell monolayers. S. flexneri serotype 2a and 5, but not the non-invasive Escherichia coli strain F-18, share the ability to regulate expression of ZO-1, ZO-2, E-cadherin and to dephosphorylate occludin. The disruption of tight junctions is dependent on direct interaction of living Shigella with intestinal epithelial cells and is supported by heat-stable secreted bacterial products. Intestinal epithelial cells have the ability to compensate in part for S. flexneri induced regulation of tight junction-associated proteins. IntroductionShigella flexneri causes bacillary dysentery and is the major aetiological agent of the endemic form of this disease, which frequently affects young children in developing areas of the world Tight junction regulation by Shigella flexneri 369 (P < 0.01, compared with the buffer control). The reduction in TER occurred more rapidly with the non-invasive S. flexneri than with the wild type (Fig. 1A). Similarly, basolateral exposure with either of the strains of S. flexneri resulted in a progressive decrease of the TER. Ninety minutes after S. flexneri exposure, the TER decreased to 40 ± 19% and 23 ± 5% of basal levels when either non-invasive or wild-type S. flexneri were added, respectively ( Fig. 1A; P < 0.01, compared with the buffer control). The viability of T-84 cell monolayers as determined by Trypan blue exclusion was comparable after exposure to buffer alone, non-invasive or wild-type S. flexneri (data not shown). Furthermore, we examined the levels of lactose dehydrogenase (LDH), released from the cells undergoing the cell death pathway, in the medium. The LDH levels were not significantly different 2 h after stimulation with buffer (HBSS+) alone, wild-type S. flexneri, and non-invasive S. flexneri (67.0 ± 1.0 U ml -1 , 100.0 ± 0.7 U ml -1 and 66.6 ± 2.1 U ml -1 respectively). In contrast, the LDH level observed in 1% Triton X-treated cells (266.0 ± 1.4 U ml -1 ) was significantly higher than those in cells treated with buffer or S. flexneri. Thus, the decrease in TER, which followed shortly after S. flexneri infection, was not due to cell death.Next, we carried out confocal microscopy of T-84 cell monolayers after apical exposure to wild-type and noninvasive S. flexneri. Ba...

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