Altered lipid raft composition and defective cell death signal transduction in glycosylphosphatidylinositol anchor-deficient PIG-A mutant cells.

Summary Paroxysmal nocturnal haemoglobinuria (PNH) is a clonal disorder of haematopoietic stem cells caused by somatic PIGA mutations, resulting in a deficiency in glycosylphosphatidylinositol-anchored proteins (GPI-AP). Because GPI-AP associate with lipid rafts (LR), lack of GPI-AP on PNH cells may result in alterations in LR-dependent signalling. Conversely, PNH cells are a suitable model for investigating LR biology. LR from paired, wild-type GPI(+), and mutant GPI(−) cell lines (K562 and TF1) were isolated and analysed; GPI(−) LR contained important anti-apoptotic proteins, not found in LR from GPI(+) cells. When methyl-β-cyclodextrin (MβCD) was utilized to probe for functional differences between normal and GPI(−) LR, increased levels of phospho-p38 mitogen-activated protein kinase (MAPK), and phospho-p65 nuclear factor NF-κB were found in control and GPI(−) cells respectively. Subsequent experiments addressing the inhibition of phosphoinositide-3-kinase (PI3K) suggest that the PI3K/AKT pathway may be responsible for the resistance of K562 GPI(−)cells to negative effects of MβCD. In addition, transduction of tumour necrosis factor-α (TNF-α) signals in a LR-dependent fashion increased induction of p38 MAPK in GPI(+) and increased pro-survival NF-κB levels in K562 GPI(−) cells. Therefore, we suggest that the altered LR-dependent signalling in PNH-like cells may induce different responses to pro-inflammatory cytokines from those observed in cells with intact GPI-AP.