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Abstract:
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The Coxsackievirus and adenovirus receptor (CAR) is important for the binding and entry of adenoviruses into the cells of human lungs. This receptor has two transmembrane isoforms, CAREx7 and CAREx8. CAREx8 localizes to the apical surface of polarized human airway epithelial cells where it is accessible for viral infection, while CAREx7 localizes to the inaccessible basolateral surface. Co-expression of CAREx8 with a PDZ-domain containing protein named MAGI-1 (membrane associated guanylate kinase with inverted domain structure-1) results in the loss of CAREx8. This results in decreased viral receptor availability and decreased adenoviral infection. We have recently discovered that CAREx8 interacts with two different domains of MAGI-1, PDZ domain 1 and 3 (PDZ1, PDZ3). Co-expression of CAREx8 with PDZ3 decreases CAREx8 cell surface protein levels and hence, availability for viral infection, while PDZ1 protects CAREx8 from MAGI-1 mediated loss and sustains viral infection. Endoplasmic reticulum associated degradation (ERAD) is a pathway to degrade newly synthesized proteins. When protein chaperones in the endoplasmic reticulum (ER) detect a misfolded or mutated protein, the deformed protein is transported out of the ER and polyubiquinated for targeted destruction by the proteasome. I hypothesize that MAGI-1, and more specifically the PDZ3 domain of MAGI-1, causes newly synthesized CAREx8 to be identified as abnormal and shuttled into the ERAD pathway for destruction. Adenovirus entry, and thus apical CAREx8 expression, will be evaluated via beta galactosidase assay. I have shown that treating CHO or MDCK cells with an ERAD inhibitor, Eeyarestatin, can increase the apical adenovirus infection. This suggests that inhibiting the ERAD pathway allows more CAREx8 to be available for apical infection. Given these data, ERAD is a likely pathway for CAREx8 degradation. Potentially, ERAD inhibitors could be used to increase adenoviral infection for gene therapy. |
