Junctional adhesion molecule interacts with the PDZ domain-containing proteins AF-6 and ZO-1

We have identified the PDZ domain protein AF-6 as an intracellular binding partner of the junctional adhesion molecule (JAM), an integral membrane pro tein located at cell contacts. Binding of AF-6 to JAM: required the presenc e of the intact C terminus of JAM, which represents a classical type II PDZ domain-binding motif. Although JAM did not interact with the single PDZ do mains of ZO-1 or of CASK, we found that a ZO-1 fragment containing PDZ doma ins 2 and 3 bound to JAM in vitro in a PDZ domain-dependent manner. AF-6 as well as ZO-1 could be coprecipitated with JAM. from endothelial cell extra cts, demonstrating the association of the endogenously expressed molecules in vivo. Targeting of JAM to sites of cell contacts could be affected by th e loss of the PDZ domain-binding C terminus. Full-length mouse JAM co-distr ibuted with endogenous AF-6 in human Caco-2 cells at sites of cell contact independent of whether adjacent cells expressed mouse JAM as an extracellul ar binding partner. In contrast, truncated JAM lacking the PDZ domain-bindi ng C terminus did not co-distribute with endogenous AF-6, but was restricte d to cell contacts between cells expressing mouse JAM. Our results suggest that JAM can be recruited to intercellular junctions by its interaction wit h the PDZ domain-containing proteins AF-6 and possibly ZO-1.