re susceptible to CE-induced inflammation, Scopoletin site permeability increase, and apoptosis mediated by both E-cadherin and FAK in vivo and in vitro compared with WT mice. Furthermore, the induction PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19762596 of HO-1 following CE exposure confers epithelial protection. CE at the concentrations of 50 ppm markedly upregulates HO-1 protein expression and demonstrates a stronger expression level at higher concentrations of CE. HO-1 protects against oxidative stress induced by H2O2 in retinal epithelial cells, demonstrating its antioxidant role. The antiapoptotic action of HO-1 may be mediated by both biliverdin and CO because both these heme degradation products are catalyzed by HO-1 and reverses the antiapoptotic action of HO-1 in endothelial cells. These data suggest that HO-1 and/or its reaction product, CO, are necessary and effective inducible antioxidants and anti-apoptotic molecules that can protect against CE-induced cell injury and apoptosis. However, the upstream signaling pathways that induce HO-1 expression remain unclear. In the present study, exposure to CE results in a concentration dependent increase in the level of ROS and upregulation of HO-1 expression. Oxidative stress has been implicated in the induction of HO-1 by Nrf2, a HO-1 inducing gene and H2O2 can directly induce HO-1 expression in neurons, epithelial cells and endothelial cells. Therefore, ROS may be involved in the induction of HO-1 in CE exposed epithelial cells. On the other hand, Akt/PI3K inhibitor significantly inhibits Nrf2 activation and subsequent HO-1 expression in retinal epithelial cells, indicating that activation of Akt/PI3K signaling is required for HO-1 expression. This study also demonstrated that the increase in permeability of the bronchial epithelial monolayer was paralleled by the delocalization of ZO-1, down-regulation of ZO-1, ZO-2, occludin, E-cadherin, FAK and disruption and internalization of F-actin. The morphological changes occurred before activation of the caspase-3 dependent apoptosis, suggesting that the induction of apoptosis attributes to the changes in intracellular junctions and their cytoskeletal filaments. Once initiated, the activated caspase-3 could further reversely degrade the junction proteins and consequently, increased epithelial permeability. This possibility is supported by evidence that caspase inhibitors reverse Giardia-induced increase of epithelial permeability and ZO-1 redistribution. The effects of CE on the cell-cell and cell-matrix interactions of human epithelial cells have not been clarified but a number of proteins, such as FAK, are involved in the formation and regulation of cell-cell and cell-matrix contacts, which modulate cell survival and apoptosis. We examined the effect of CE on the activation of FAK and showed that FAK is efficiently cleaved by CE exposure in epithelial cell lines and primary mice cells. Activation of caspase-3 is the central mechanism in CE-induced apoptosis, which is subsequently followed by the cleavage of their substrates. Considering the involvement of ROS PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19763404 in apoptosis induced by CE, the inhibitory effect of CE on FAK suggests that FAK is a key substrate protein that is the target of ROS-mediated caspase-3 activation. The normal function of E-cadherin is critical for the maintenance of adherens junctions and the stability of cell membrane. Disruption of E-cadherin down-regulates anti-apoptotic protein, Bcl-2 and caspase-3 inhibitor blocks the cleavage of E-cadherin. Therefore, cleavage of E-cadheri