Fig. 4. The 15 PECAM-1 isoform localizes to cell-cell borders, similar to full-length PECAM-1. REN mesothelioma cells expressing equivalent amounts of WT, ITIM-less, 15 and K89A PECAM-1 were grown to confluence, fixed, permeabilized and then subsequently stained with fluorescently labeled antibodies against PECAM-1 and analyzed using confocal microscopy. The panels on the left show the XY views, whereas panels on the right illustrate the xz cross-sections. As described previously, WT PECAM-1 is concentrated at cell-cell junctions (A), whereas a mutant form (K89A) unable to mediate homophilic binding is distributed along the apical surface of the cells, as illustrated in the xz panels (D). Both the ITIM-less (B) and 15 PECAM-1 (C) forms localized normally at cell-cell borders, similar to WT PECAM-1.