Novel CAR Exon 8 Interactions Figure 8. The interaction between the hCAR PDZ binding domain and PICK1 depends on both the PDZ binding domain and the upstream isoform specific amino acids. The PDZ binding domain of hCAREx7 and hCAREx8 were swapped by PCR as shown in Figure 7, panel A. The localization was determined in transfected COS-7 cells. hCAREx7 (A) transfected with PICK1-GFP (B) results in co-localization at the junctions (C, yellow). hCAREx8 (D) transfected with PICK1-GFP (E) results in no co-localization at the junctions (F). hCAREx7/8 (G) transfected with PICK1-GFP (H) results some co-localization at the junctions (I, yellow). hCAREx8/7 (J) transfected with PICK1-GFP (K) results in no co-localization at the junctions (L). Confocal microscopy (60x oil immersion). doi:10.1371/journal.pone.0009909.g008 MAGI-1b interacting with hCAREx7 at the junctions between epithelial cells. It is also consistent with the unexpected apical localization of hCAREx8. If hCAREx8 were to go to the basolateral junctions, it would be predicted to interact with MAGI-1b and be degraded. Thus the only place it could exist in the cell is in an apical compartment devoid of MAGI-1b. Alternatively, there may be a specific mechanism for the apical localization of hCAREx8 that remains to be discovered. Apical localization is consistent with elevated adenovirus infection after expression of hCAREx8. Thus this isoform of hCAR would be able to interact with adenovirus on the luminal air-exposed surface and mediate the initial infection of an epithelium. It is notable that the increase of infection is similar to the extracellular domain of hCAR conjugated to a glycopho- sphatidyl-inositol (GPI) tail, which explicitly is apically localized in PLoS ONE | www.plosone.org 9 March 2010 | Volume 5 | Issue 3 | e9909