Katherine Excoffon (Advisor), David Goldstein (Committee Member), Julian Gomez-Cambronero (Committee Member), Robert Putnam (Committee Member), Dawn Wooley (Committee Member)
Doctor of Philosophy (PhD)
The airway epithelium poses a formidable barrier for the entry of pathogenic viruses due to the formation of tight junctions between adjacent epithelial cells. The coxsackievirus and adenovirus receptor (CAR), a member of the Ig superfamily of cell junction adhesion proteins, is the primary receptor for adenovirus entry and infection. As a result of alternative splicing, two transmembrane isoforms of CAR are generated. While the seven-exon isoform of CAR (CAREX7) is hidden on the basolateral surface of polarized epithelia, the eight-exon isoform of CAR (CAREX8) localizes within the sub-apical region and at the air-exposed apical surface. Apical localization of CAREX8 makes it accessible to invading adenovirus entering the lumen of the airway and able to facilitate viral entry into the epithelium. Previous studies have shown that Interleukin-8 (IL-8), a proinflammatory cytokine and a neutrophil chemoattractant, increases the susceptibility of the airway epithelium to adenoviral infection. I hypothesized that the apical CAREX8 protein expression level and localization are responsible for the susceptibility of a polarized epithelium to viral infection. Moreover, I hypothesized that CAREX8expression is tightly regulated by mediators of IL-8 signaling and the endogenous function CAREX8is to tether neutrophils at the apical surface of the polarized epithelium. Finally, I hypothesized that adenovirus has co-opted CAREX8 and neutrophil transmigration to enhance infection of the polarized epithelium. Consistent with these hypotheses, I demonstrate that IL-8 increases the expression and the apical localization of CAREX8 in polarized airway epithelial cells. In addition, IL-8 differentially activates AKT/S6K and inactivates GSK3ß to augment the protein synthesis of CAREX8. Increased CAREX8 is able to mediate increased neutrophil binding at the apical surface of the epithelium that is completely abolished by competition with CAR-binding adenovirus fiber-knob. Finally, I also demonstrate that neutrophils adhering to the epithelial apical surface are able to promote adenoviral infection. Taken together, these data suggest that adenovirus has evolved to co-opt the host innate-immune response to the inflammation caused by molecules within inhaled droplets, pre-existing inflammation, or even adenovirus itself, in order to gain entry into the polarized epithelium by inducing the increased expression of endogenous apically localized CAREX8.
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