The Functional Interaction of the β2 Integrin Lymphocyte Function-Associated Antigen-1 with Junctional Adhesion Molecule-A Is Mediated by the I Domain

Abstract

Binding of the β2 integrin LFA-1 (αLβ2) to junctional adhesion molecule-A (JAM-A) has been shown to enhance leukocyte adhesion and transendothelial migration. This is mediated by the membrane-proximal Ig-like domain 2 of JAM-A; however, the location of the JAM-A binding site in LFA-1 has not been identified. We have deleted the I domain in the αL subunit of LFA-1 and expressed this αL mutant in αl-deficient Jurkat J-β2.7 cells to demonstrate that the I domain of LFA-1 is crucial for their adhesion to immobilized JAM-A. This was substantiated by blocking the stimulated adhesion of wild-type Jurkat T cells or monocytic Mono Mac 6 cells to JAM-A using the I domain-directed mAb TS1/22 or the small molecule antagonist BIRT 377, which stabilizes the low-affinity conformation of the I domain. The immobilized LFA-1 I domain locked in the open high-affinity conformation was sufficient to support binding of transfected Chinese hamster ovary cells expressing JAM-A. Solid-phase binding assays confirmed a direct interaction of recombinant JAM-A with the immobilized locked-open I domain. These data provide the first evidence that the I domain of LFA-1 contains a functional binding site for JAM-A.

Cis-Dimerization Mediates Function of Junctional Adhesion Molecule A

“…Possibilities include direct interactions of ␤1 integrins with JAM-associated scaffolding proteins; activation of signaling molecules that affect ␤1 integrin turnover, such as the small GTPase Rap1; or sequestration of negative regulators of ␤1 integrin stability by scaffolding complexes. In other studies, JAM-A has been reported to physically interact with ␣v␤3 (Naik and Naik, 2006) and ␤2 integrin (Fraemohs et al, 2004) and to regulate migration of endothelial cells (Fraemohs et al, 2004;Naik and Naik, 2006); however, we have been unable to detect a direct association between JAM-A and ␤1 integrin in coimmunoprecipitation experiments. These observations suggest that JAM-A mediates decreased ␤1 integrin protein levels through an indirect mechanism(s).…”

“…This scaffolding complex might interact with ␤1 integrin via yet unidentified partners leading to stabilization of ␤1 integrin at the plasma membrane. In other studies, JAM-A has been reported to physically interact with ␣v␤3 (Naik and Naik, 2006) and ␤2 integrin (Fraemohs et al, 2004) and regulate migration of endothelial cells (Fraemohs et al, 2004;Naik and Naik, 2006); however, we have been unable to detect a direct association between JAM-A and ␤1 integrin in coimmunoprecipitation experiments. Therefore, it is most E. A.…”

IL-18 Is Involved in Eosinophil-Mediated Tumoricidal Activity against a Colon Carcinoma Cell Line by Upregulating LFA-1 and ICAM-1

“…We showed previously that the b 2 integrin LFA-1 played a crucial role in the cytolytic effect of eosinophils on Colo-205 cells (9). The interaction between LFA-1 and its ligands, ICAMs 1-3 and JAM-A, was shown to enhance leukocyte cell-cell binding (42,43). In the basal state, Colo-205 cells express ICAM-1 and JAM-A.…”

β2 Integrin–Mediated Crawling on Endothelial ICAM-1 and ICAM-2 Is a Prerequisite for Transcellular Neutrophil Diapedesis across the Inflamed Blood–Brain Barrier

“…Besides mediating homophilic interactions with JAM-A on leukocytes, endothelial JAM-A can also engage in heterophilic interactions with LFA-1 (71). Endothelial JAM-A has been shown to mediate the migration of myeloid cells across a number of vascular beds in vitro and in vivo (summarized in Ref.…”