Human junction adhesion molecule regulates tight junction resealing in epithelia

Epithelial cells form a highly selective barrier and line many organs. The epithelial barrier is maintained by closely apposed cell-cell contacts cont aining tight junctions, the regulation of which is incompletely understood. Here we report the cloning, tissue localization and evidence for a role in epithelial barrier regulation of an immunoglobulin superfamily member that likely represents the human homolog of murine Junction adhesion molecule ( JAM). Analysis of the primary structure of human JAM, cloned from T84 epith elial cells, predicts a transmembrane protein with an extracellular domain that contains two IgV loops. Monoclonal antibodies generated against the pu tative extracellular domain were reactive with a 35-39 kDa protein from bot h T84 epithelial cells and human neutrophils. By immunofluorescence, JAM mA bs labeled epithelial cells from intestine, lung, and kidney, prominently i n the region of tight junctions (co-localization with occludin) and also al ong lateral cell membranes below the tight junctions. Flow cytometric studi es confirmed predominant JAM expression ill epithelial cells but also revea led expression on endothelial and hematopoietic cells of ail lineages, Func tional studies demonstrated that JAM specific mAbs markedly inhibited trans epithelial resistance recovery of T84 monolayers after disruption of interc ellular junctions (including tight junctions) by transient calcium depletio n. Morphologic analysis revealed that, after disassembly of cell-cell junct ions, anti-JAM inhibition of barrier function recovery correlated with a lo ss of both occludin and JAM, but not ZO-1, in reassembling tight junction s tructure. Reassembly of the major adherens junction component E-cadherin wa s not affected by JAM specific mAbs. Our findings suggest that JAM plays an important role in the regulation of tight junction assembly in epithelia. Furthermore, these JAM-mediated effects may occur by either direct, or indi rect interactions with occludin.