The glycolipid glycosylphosphatidylinositol anchor (GPI-A) plays an important role in lipid raft formation which is required for proper expression on the cell surface of two inhibitors of the complement cascade CD55 and CD59. membrane lipid rafts respond weakly to SDF-1 stimulation and show defective adhesion to fibronectin. Similar data were obtained with the GPI-A? Jurkat cell line. Moreover we also report that chimeric mice transplanted with CD55?/??CD59?/? BM cells but with proper GPI-A expression do not expand over time in transplanted hosts. On the basis of these findings we propose that a defect in lipid raft formation in PNH-mutated HSPCs makes these cells more mobile so that they expand and out-compete normal HSPCs from their BM niches over Cobicistat (GS-9350) time. 0.8 respectively). Since we found that CD34+?FLAER? cells (Fig.?(Fig.1B) 1 like FLAER? BMMNCs (data not shown) have defective 5-min. and 15-min. adhesion to both fibronectin- Cobicistat (GS-9350) and SDF-1-coated plates and while adhesion to SDF-1 is CXCR4-dependent and adhesion to fibronectin is mostly VLA-4-dependent we investigated by confocal analysis whether both receptors are incorporated into lipid rafts in patient BM-purified CD34+?FLAER? cells. Lipid raft formation was analysed in Cobicistat (GS-9350) the presence of cationic peptide LL-37 which promotes lipid raft formation on the surface of hematopoietic cells 20 21 We found that CD34+?FLAER? cells have a defect in lipid raft formation compared with normal CD34+?FLAER+ cells and neither CXCR4 nor VLA-4 are detected in lipid rafts (Fig.?(Fig.2A2A and ?andB).B). At the same time we observed a defect in actin polymerization in CD34+?FLAER? cells compared with healthy CD34+?FLAER+ cells (Fig.?(Fig.2C2C). Figure 2 Defective adhesiveness and lipid raft formation in BM-derived CD34+?FLAER? cells (A and B). Representative images of CD34+?FLAER+ (normal) and CD34+?FLAER? (PNH) cells sorted from BM stimulated by LL-37 (2.5?μg/ml) … GPI-A? Jurkat cells show defective spontaneous and SDF-1-stimulated adhesion to fibronectin as well as defective SDF-1 signalling and they do not incorporate CXCR4 and VLA-4 into lipid rafts Next we performed similar experiments with GPI-A-deficient and GPI-A-expressing Jurkat human lymphocytic T-cell lines 13. GPA-I-A?/? Jurkat cells demonstrated a lack of FLAER binding (Fig.?(Fig.3A) 3 and by employing adhesion assays we observed that these cells show defective spontaneous 5 and 15?min. adhesion to fibronectin (Fig.?(Fig.3B 3 left panel) which also remained defective after pre-treatment of cells with SDF-1 (0-100?ng/ml Fig.?Fig.3B 3 right panel). FLAER? Jurkat cells like normal BM-purified CD34+?FLAER? cells did not incorporate CXCR4 and VLA-4 into membrane lipid rafts (Fig.?(Fig.3C).3C). Finally GPI-A? Jurkat cells demonstrated a decrease in phosphorylation of p42/44 MAPK in response to SDF-1 (Fig.?(Fig.3D3D). Figure 3 Defective SDF-1 responsiveness of GPI-A-deficient human Jurkat PF4 cells. (A). Binding of FLAER to GPI-A-deficient and normal Jurkat cells. One representative staining out of three is shown. (B). Jurkat GPI-A-deficient cells show defective spontaneous (left … Murine BM-derived CD55?/??CD59?/? cells that properly express GPI-A show normal adhesion and chemotaxis Cobicistat (GS-9350) in response to SDF-1 and do not outcompete wild-type BM cells after transplantation into normal recipients Human PNH cells which lack GPI-A and therefore do not express the complement inhibitors CD55 and CD59 on their cell surface expand over time in BM. To dissect the potential involvement of the absence of CD55 and CD59 in this expansion we isolated BM from CD55?/? CD59?/? mice 19 and tested these cells in adhesion and chemotaxis assays. Murine Sca-1+?CD55?/??CD59?/? cells displayed normal adhesion to fibronectin-coated plates with or without SDF-1 pre-incubation (Fig.?(Fig.4A 4 left and right panels respectively) and showed normal chemotaxis in response to an SDF-1 gradient in a Transwell assay compared with BM cells isolated from normal littermates (Fig.?(Fig.4B4B). Cobicistat (GS-9350) Figure 4 BM cells from CD55?/??CD59?/? mice have normal adhesion and chemotaxis and do not expand in transplanted wild-type control animals (A). BM Sca-1+ cells from CD55?/??CD59?/? Cobicistat (GS-9350) … On the basis of the observation that PNH-affected cells expand in patient BM over time we transplanted BM cells from CD55?/? CD59?/? mice and normal WT BM cells CD55+/+?CD59+/+ mixed in different ratios (1:9 1 1 3 and 9:1) into normal WT mice. Six months after transplantation we analysed the percentage of chimerism in PB BM and spleen of recipient mice and did not observe significant changes in the ratio of transplanted mutant to.