JAM2 interacts with alpha4beta1. Facilitation by JAM3.

Abstract We have previously reported that junctional adhesion molecule 2 (JAM2) adheres to T cells through heterotypic interactions with JAM3. An examination of the cation dependence of JAM2 adhesion to HSB cells revealed a Mn2+-enhanced binding component indicative of integrin involvement. Using neutralizing integrin antibodies, we have defined an interaction between JAM2 and α4β1 in T cells. The interaction is readily amenable to drug intervention as demonstrated by the ability of TBC 772, an α4-specific inhibitor, to attenuate the Mn2+-enhanced component. Intriguingly, the engagement of α4β1 by JAM2 is only enabled following prior adhesion of JAM2 with JAM3 and is not detectable in cells where JAM3 expression is absent. Supporting this observation, we show that neutralizing JAM3 serum and soluble JAM3 ectodomain inhibit not only JAM2 binding to JAM3 but also prevent JAM2/α4β1 interactions in T cells. We further define the first Ig-like fold of JAM2 as being competent in binding both JAM3 and α4β1counter-receptors. Mutagenesis of the only acidic residue in the C-D loop of this Ig fold, namely Asp-82, has no bearing on α4β1 interactions, and thus JAM2 deviates somewhat from the mechanism used by other immunoglobulin superfamily cell adhesion molecules to engage integrin.