A recent study (Nusrat, A., Chen, J. A., Foley, C. S., Liang, T. W., Tom, J., Cromwell, M., Quan, C., and Mrsny, R. J. (2000) J. Biol. Chem. 275, 29816 -29822) suggested that phosphatidylinositol 3-kinase (PI 3-kinase) may interact with occludin; however, there exists no evidence of direct interaction of PI 3-kinase with the tight junctions. Activation of PI 3-kinase by oxidative stress and its role in disruption of tight junctions was examined in Caco-2 cell monolayer. The oxidative stress-induced decrease in electrical resistance, increase in inulin permeability, and redistribution of occludin and ZO-1 were reduced by a PI 3-kinase inhibitor, LY294002. Oxidative stress-induced tyrosine phosphorylation and dissociation from the actin cytoskeleton of occludin and ZO-1 were reduced by LY294002. The regulatory subunit of PI 3-kinase, p85, and the PI 3-kinase activity were co-immunoprecipitated with occludin, which were rapidly increased by oxidative stress. Oxidative stress resulted in increased translocation of p85 from the intracellular compartment into the intercellular junctions. Pair-wise glutathione S-transferase pull-down assay showed that glutathione S-transferase-occludin (C-terminal tail) binds to recombinant p85. This study shows that oxidative stress increases the association of PI 3-kinase with the occludin, and that PI 3-kinase activity is involved in oxidative stress-induced disruption of tight junction.

We have studied the role of nuclear factor of activated T-cells (NFAT) transcription factors in the induction of vascular smooth muscle cell (VSMC) growth by platelet-derived growth factor-BB (PDGF-BB) and thrombin, the receptor tyrosine kinase (RTK) and G-protein-coupled receptor (GPCR) agonists, respectively. NFATc1 but not NFATc2 or NFATc3 was translocated from the cytoplasm to the nucleus upon treatment of VSMCs with PDGF-BB or thrombin. Translocation of NFATc1 was followed by an increase in NFAT-DNA binding activity and NFAT-dependent reporter gene expression. Cyclosporin A (CsA), a potent and specific inhibitor of calcineurin, a calcium/calmodulin-dependent serine phosphatase involved in the dephosphorylation and activation of NFATs, blocked NFAT-DNA binding activity and NFAT-dependent reporter gene expression induced by PDGF-BB and thrombin. CsA also completely inhibited PDGF-BB- and thrombin-induced VSMC growth, as measured by DNA synthesis and cell number. In addition, forced expression of the NFAT-competing peptide VIVIT for calcineurin binding significantly attenuated the DNA synthesis induced by PDGF-BB and thrombin in VSMCs. Together, these findings for the first time demonstrate a role for NFATs in RTK and GPCR agonist-induced growth in VSMCs.

Probiotics are beneficial bacteria present in various dietary components and many of these colonize in the human and animal intestine. In the gut probiotics help the host by assisting in maintenance of normal mucosal homeostasis. Probiotics not only help maintain normal function of the gut mucosa, but also protect mucosa from injurious factors such as toxins, allergens and pathogens. The beneficial effect of probiotics is mediated by multiple mechanisms, including cytoprotection, cell proliferation, cell migration, resistance to apoptosis, synthesis of proteins and gene expression. One of the important cytoprotective effects of probiotics in the intestinal mucosa is to strengthen the epithelial tight junctions and preservation of mucosal barrier function. Probiotics not only enhance barrier function by inducing synthesis and assembly of tight junction proteins, but also preventing disruption of tight junctions by injurious factors. Bioactive factors released by probiotics trigger activation of various cell signaling pathways that lead to strengthening of tight junctions and the barrier function. This article reviews and summarizes the current understanding of various probiotics that are involved in the protection of gut barrier function, highlights the cellular and molecular mechanisms involved in the protective effect and addresses the clinical implications of probiotic supplementation.

Computer games provide a good environment for learning. Players learn to play the game without being taught didactically as the learning process takes place naturally in the virtual world. Learning is no longer a process of knowledge transfer from the expert to the novice. Learners need to construct the knowledge themselves by interacting with the environment. It is beneficial to study the theory underpinning computer games: how players learn and respond in the game environment. In this paper, the theories of learning, i.e. behavioural learning theory, cognitive learning theory and motivation theory, are elucidated in the context of computer game. Psychology provides a way to apprehend the learning that occurs naturally in games and also helps in developing an environment in which the player can learn a particular domain of knowledge extrinsically. By studying the psychology and its relatedness to computer games, we can know the players more comprehensively, thus predict their responses. The understanding of psychology offers a framework to developing an educational game that promotes learning while maintaining high motivation of the player. This paper also attempts to shed some light on how players learn in computer games based on the theory, thus infers better techniques in supporting game-based learning.

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