Adenovirus and the adenovirus receptor are intricately linked to airway epithelia biology, and to the development of disease. Adenoviruses were first identified from tonsils in 1953. In 1968 the Commission of Acute Respiratory Diseases of the U.S. Armed Forces found that adenovirus infection was one of the major causes of acute febrile respiratory illness in recruits. Over the past 5 decades adenovirus research has yielded impressive knowledge about the pathogenesis of viral pneumonias, vaccination, and basic aspects of molecular virology and cellular biology. However, adenovirus remains a significant civilian and military threat. The discovery of the receptor for adenovirus (Coxsackievirus and adenovirus receptor;CAR) and the recent finding that CAR plays a central role in airway epithelial cell-cell adhesion have yielded novel mechanisms for viral escape from epithelial surfaces. A major unanswered question that remains is how these pathogenic viruses initiate infection when the receptor is safely segregated on the basolateral membrane. Several protein isoforms have been described for CAR, including two transmembrane forms (CAREx7 and CAREx8). These two isoforms differ only in their C-termini, suggesting that some of their interactions, and hence localization and regulation, may differ. In polarized epithelial cells, CAREx7 resides on the basolateral surface and is thus sequestered away from potential viral interactions on the apical surface. In contrast, although CAREx8 is a less abundant isoform, our recent work reveals that CAREx8 is localized apically where it can mediate initiation of adenovirus infection from the apical surface. We hypothesize that receptor abundance and apical localization are regulated by a PDZ-based interaction with membrane-associated guanylate kinase inverted 1, isoform b (MAGI-1b).
We aim to understand the molecular basis of this interaction through PDZ domain isolation, mutation, binding and competition, ultimately in polarized airway cells. Moreover, we hypothesize that the interaction with MAGI-1b is in competition with PDZ-domain-containing proteins within the apical trafficking pathway. We will take a candidate protein approach and investigate novel interactions by immunocytochemistry and co-immunoprecipitation-Western blot analysis. Understanding the molecular mechanisms behind apical localization is clinically significant for several reasons. Currently there is no specific treatment for coxsackievirus or adenovirus infection;thus, the ability to block apical binding of the virus in the face of viral outbreaks would be a significant therapeutic advance. On the other hand, the ability to augment apical expression of the receptor would have high relevance for efficient adenoviral-mediated gene therapy. Moreover, this work will expose a team of graduate and undergraduate students to vital research at the interface of virology and medicine.
Viral-induced acute respiratory disease causes a significant amount of human illness and death each year. We have recently discovered one form of the receptor that binds both coxsackievirus and adenovirus is present on the air exposed surface of the airway epithelium. Understanding what causes this surface location and how this is regulated will provide insight into susceptibility to viral infections, and lead to strategies both for prevention of virus infection and facilitation of adenovirus-mediated gene therapy for the treatment of inherited and acquired respiratory diseases.
