Spliceform specific Coxsackie‐adenovirus receptor interactions

Abstract

The Coxsackievirus and Adenovirus Receptor (CAR) is both a homotypic cell adhesion molecule and a viral receptor. The murine gene for CAR, Cxadr, consists of 8 alternatively spliced exons terminating in either exon 7 (CAREx7) or exon 8 (CAREx8). Both splice forms contain a C‐terminal PDZ binding domain and differ only in the last 26 (Exon 7, ‐GSIV) or 13 (Exon 8, ‐ITVV) amino acids. The gene encoding human CAR, Cxadr, was previously described as 7 alternatively spliced exons. We hypothesized that a human CAREx8 isoform exists, has similar virus receptor characteristics to CAREx7, but differs in other biological aspects. Human CAREx8 was cloned from primary human airway epithelia, inserted into an expression vector and evaluated for localization, adenovirus gene transfer and PDZ‐interaction. CAREx7 and CAREx8 showed similar localization and adenovirus infection in non‐polarized cells. In polarized cells, CAREx7 localized exclusively to the basolateral membrane. In contrast, CAREx8 showed apical localization and mediated apical adenovirus infection. Moreover, whereas co‐expression of CAREx7 with the PDZ‐domain containing protein MAGI‐1b altered the localization of MAGI‐1b from diffusely cytoplasmic to cell junctions, co‐expression of CAREx8 with MAGI‐1b resulted in the loss of CAREx8. This loss required both the PDZ interaction and the upstream 9 amino acids. In conclusion, human CAR is an 8 exon alternatively spliced protein yielding isoforms with distinct localization and interactions. Furthermore, CAREx8 may be responsible for respiratory viral infection. (NIH)