Perturbation of membrane microdomains reduces mitogenic signaling and increases susceptibility to apoptosis after T cell receptor stimulation

Acid sphingomyelinase-deficient (asmase(-/-)) mice generated by gene target ing abundantly store sphingomyelin in the reticuloendothelial system of liv er, spleen, bone marrow, and in brain. Liver cells of asmase(-/-) mice accu mulate sphingomyelin and glycosphingolipids in purified lipid bilayers of m icrosomes, Golgi, and the plasma membrane, but cholesterol is depleted in t he plasma membrane. Detergent-insoluble glycolipid-enriched membrane microd omains (GEM) can be isolated from hepatocytes, embryonic fibroblasts, and s plenocytes of wild-type, but not of (-/-) mice, by sucrose gradient density centrifugation. asmase Lck and other Src-family kinases are reduced in iso pycnic fractions of asmase(-/-) splenocytes compared to GEM-containing frac tions of wild-type cells. The proliferation of (-/-) T lymphocytes is reduc ed, whereas their asmase susceptibility to Pas-induced apoptosis is increas ed after T cell receptor (TCR) stimulation. TNF receptor I signaling remain s unimpaired. The perturbation of GEM impairs tyrosine phosphorylation and, consequently, mitogenic signaling of the TCR, Reduced MARK activity-depend ent FLICE-like inhibitory protein (FLIP) expression in asmase(-/-) T lympho cytes increases their sensitivity towards Fas-mediated apoptosis.