Sialyl Lewis X modification of the epidermal growth factor receptor regulates receptor function during airway epithelial wound repair

BACKGROUND

Epidermal growth factor receptor (EGFR) is a major regulator of airway epithelial cell (AEC) functions such as migration, proliferation and differentiation, which play an essential role in epithelial repair. EGFR is a glycoprotein with 12 potential N-glycosylation sites in its extracellular domain. Glycosylation of EGFR has been shown to modulate its function. Previously, our laboratory demonstrated an important role of the carbohydrate structure sialyl Lewis x (sLe(x)) in airway epithelial repair.

OBJECTIVE

To examine whether an sLe(x) decoration of EGFR can modulate receptor function during AEC repair.

METHODS

Primary normal human bronchial epithelial (NHBE) cells were cultured in vitro. Co-localization of sLe(x) and EGFR was examined using confocal microscopy. Expressions of RNA and protein were analysed using RT-PCR and Western blotting. The final step in the synthesis of sLe(x) was catalysed by a specific alpha-1,3-fucosyltransferase (FucT-IV). To evaluate the role of sLe(x) in EGFR activation, a knockdown of the FucT-IV gene with small interfering RNA (siRNA) and an inhibitory anti-sLe(x) antibody (KM-93) was used.

RESULTS

We demonstrated a co-localization of sLe(x) with EGFR on NHBE cells using confocal microscopy. Using a blocking antibody for sLe(x) after a mechanical injury, we observed a reduction in EGFR phosphorylation and epithelial repair following injury. FucT-IV demonstrates a temporal expression coordinate with epithelial repair. Down-regulation of FucT-IV expression in NHBE by specific siRNA suppressed sLe(x) expression. The use of FucT-IV siRNA significantly reduced phosphorylation of EGFR and prevented epithelial repair. An immunohistochemical analysis of human normal and asthmatic airways showed a significant reduction in sLe(x) and tyrosine-phosphorylated EGFR (pY(845)-EGFR) in the epithelium of asthmatic subjects compared with that of normal subjects.

CONCLUSION

The present data demonstrate that sLe(x), in association with EGFR, in NHBE is coordinate with repair. This glycosylation is important in modulating EGFR activity to affect the repair of normal primary AEC.

Inhibition of glycogen synthase kinase 3beta suppresses coxsackievirus-induced cytopathic effect and apoptosis via stabilization of beta-catenin

Coxsackievirus B3 (CVB3), a common human pathogen for viral myocarditis, induces a direct cytopathic effect (CPE) and apoptosis on infected cells. To elucidate the mechanisms that contribute to these processes, we studied the role of glycogen synthase kinase 3beta (GSK3beta). GSK3beta activity was significantly increased after CVB3 infection and addition of tyrosine kinase inhibitors blocked CVB3-triggered GSK3beta activation. Inhibition of caspase activity had no inhibitory effect on CVB3-induced CPE; however, blockage of GSK3beta activation attenuated both CVB3-induced CPE and apoptosis. We further showed that CVB3 infection resulted in reduced beta-catenin protein expression, and GSK3beta inhibition led to the accumulation and nuclear translocation of beta-catenin. Finally, we found that CVB3-induced CPE and apoptosis were significantly reduced in cells stably overexpressing beta-catenin. Taken together, our results demonstrate that CVB3 infection stimulates GSK3beta activity via a tyrosine kinase-dependent mechanism, which contributes to CVB3-induced CPE and apoptosis through dysregulation of beta-catenin.