Roles of Rho/Rock Signaling Pathway in Silica-induced Epithelial-mesenchymal Transition in Human Bronchial Epithelial Cells

Objective To investigate the roles of Rho/Rock signaling pathway in silica-induced Epithelial-mesenchymal transition （EMT） in human bronchial epithelial cells （BEC） in vitro. Methods Human BEC were incubated with silica with various concentrations for indicated times. Cell viability was assayed by MTT test. Morphologic Changes were observed by microscope. Mesenchymal marker a-smooth muscle actin （a-SMA）, vimentin （Vim）, and epithelial marker E-cadherin （E-cad） were analyzed by Western Blot. The pull-down assay was used to measure Rho activity. In the prevention experiments, the specific inhibitor for Rho effector ROCK （Y27632） was used to inhibit the activity of Rho. Results Human BEC stimulated with silica were converted from a ＂cobblestone＂ epithelial structure into an elongated fibroblast-like shape structure. Incubation of human BEC with silica induced de novo expression of a-SMA and Vim, and loss of E-cad. Also, silica treatment resulted in Rho activation in human BEC. Y27632 up-regulated the E-cad expression but attenuated a-SMA and Vim expression in silica-stimulated cells. Conclusion The activation of Rho/ROCK signaling pathways is most likely involved in Silica-induced EMT in human bronchial epithelial cells.

Transcriptional Factor Snail Mediates Epithelial-Mesenchymal Transition in Human Bronchial Epithelial Cells Induced by Silica

Epithelial-mesenchymal transition （EMT） plays an important role in fibrotic diseases. We have previously showed that silica induces EMT in human bronchial epithelial cells （BECs）; however, the underlying mechanism of silica-induced EMT is poorly understood. In the present study, we investigated the role of Snail in silica-induced EMT in human BECs in vitro. Human BECs were treated with silica at various concentrations and incubation times. Then MTr assay, western blot, electrophoretic mobility shift assay （EMSA）, and small interfering RNA （siRNA） transfection were performed. We found that silica increased the expression and DNA binding activity of Snail in human BECs. SNAI silica-induced expression siRNA upregulated the siRNA inhibited the of Snail. Moreover, SNAI expression of epithelial marker E-cadherin, but attenuated the expression of mesenchymal marker a-smooth muscle actin and vimentin in silica-stimulated cells. These results suggest that Snail mediates the silica-induced EMT in human BECs.

Role of Endoplasmic Reticulum Stress in Silica-induced Apoptosis in RAW264.7 Cells＊

Objective We investigated the role of endoplasmic reticulum stress （ERS） in silica-induced apoptosis in alveolar macrophages in vitro. Methods RAW264.7 cells were incubated with 200 μm/mL silica for different time periods. Cell viability was assayed by the MTT assay. Cell apoptosis was evaluated by DAPI staining, flow cytometry analysis, and Western blot analysis of caspase-3. Morphological changes in the endoplasmic reticulum were observed by transmission electron microscopy. The expression of ERS markers binding protein （BiP） and CCAAT-enhancer-binding protein homologous protein （CHOP） was examined by Western blotting and real-time PCR. As an inhibitor of ERS, 4-phenylbutyric acid （4-PBA） was used in the experiments. Results Silica exposure induced nuclear condensation and caspase-3 expression in RAW264.7 cells. The number of apoptotic cells increased after silica exposure in a time-dependent manner. Silica treatment induced expansion of the endoplasmic reticulum. In addition, the expression of BiP and CHOP increased in silica-stimulated cells. Furthermore, 4-PBA treatment inhibited silica-induced endoplasmic reticulum expansion and the expression of BiP and CHOP. Moreover, 4-PBA treatment attenuated nuclear condensation, reduced apoptotic cells, and downregulated caspase-3 expression in silica-stimulated cells. Conclusion Silica-induced ERS is involved in the apoptosis of alveolar macrophages